Effecient delivery requires fast beam cycling – dark current in tube can cause unwanted radiation during movement.
A third system (BodyFIX, Medical Intelligence) has been evaluated by Fuss et al. (2004). It consists of a base plate with variable sizes of a vacuum cushions and a clear plastic foil covering the patient’s body. The cushion is modeled using an additional vacuum between the patient’s front and a plastic foil. An arch-like attachment can be afﬁxed to the base plate providing CT-, MR-, and PET-visible ﬁducials.
Radiolabelled Thymidine based markers are based on the principle that they can be used to detect proliferation of cells as onlu actively divinding cells take up thymidine.The use of these markers can thus allow the oncologist to obtain a rough idea of the proliferation markers. The use of cell proliferation markers namely amino acids provides us with the advantage that the inflammatory cells take up less of the substance and so it is possible to image the tumor bearing tissues seperately. Hypoxia markers are substances that contain a nitroimidazole entity which is reduced and subsequently the entire molecule is taken up by the concerned cell. It acts as a hypoxia marker in such circumstances. Among all the hypoxic cell markers the Cu-ASTM i s the best as: The images are produced within 10 min of contrast injection. Images have high contrast with moderate doses. The substance is taken up by cells with active mitochondria and thus it is possible to distinguish alive cells from necrotic ones. Apoptosis markers are based on certain molecules that avidly bind to domains of membrane lipids that are exposed on apoptotic cells, Annexin V is an example of such a molecule and it binds to the membrane bound phosphatidyl serine which is exposed on the outer leaflet of cell membrane on cell death.
The registration metrics used are of two broad types: Geometry based metrics : This metric type finds the difference between two images based on several points or surface of a structure(s) in question Intensity based metrics : This type of metric attempts to evaluate the difference in the two images by using numerical grey scale differences. The geometry based metrics are limited by the ability to precisely determine the location of identical points or delineate the surface of the organ in question in two image sets. This is allright in certain structures like the brain. However the different levels of imaging contrast provided by different studies makes the use of this process difficult in practice in other areas The intensity based metrics on the other hand determine the differnce in the intensity distribution of voxels and calculate the degree of transformations required. Various types of intensity based metrices exist: Sum of squared differences Cross correlation metric Mutual information metric The mutual information technique is most commonly used to estimate the differnce in the intensity of voxel values. The technique's strength lies in the fact that it can overcome differences due to areas of different contrasts in the two images and in addition it can overcome the problem due to missing data.
This diagram illustrates the three senarios faced by the oncologist in choosing a PTV Senario A : Here the OAR are far away and the PTV can be derived by simple addition of the internal margin and setup margin. Also note that the IM is constant and definable. Here the TCP is highest but if there are critical OARs nearby they can be seriuosly damaged. Senario B : Here the IM is not well defined and hence the PTV margins are not simple addition of the IM and SM. This is a typical senario in areas where the target volume has significant interfraction and intrafraction movement. The PTV margins are derived mainly from clinical experience. Senario C : This includes a series of senarios where the OARs are closer and closer to the gross tumor (as represented by the inward pointed arrow\\. Alsot the IM varies with time. Due to closeness of the margin, a single margin is defined to include the SM and IM depending on the distance to the OAR. Note that in all these senarios the margin doesnot impinge upon the GTV – if id did the treatment aim would be palliation instead of cure.
Organs can be classified into 4 broad types based on the arrangement of the FSUs: Serial : Where the FSUs are arranged in serial and damage to one can result in the total impairment of function of the organ. Example: Spinal cord Parallel : Here the FSU are arranged in parallel so that damage to a certain proportion of the FSUs are required befor e functional deterioration becomes apparent. Example Parotid Gland, Lung and Kidney Serial in parallel : These organs have serially arranged FSU so that damage to a single FSU can impair the function significantly but damage to a certain proportion is still required before the damage becomes apparent. Example: Heart. Combination of serial and parallel organs : Here the damage to the serial component can result in the stoppage of function of the organ concerned. Example is the nephron The concept of the organization of the FSUs has lead to a new classification of organs for purposes of calculation of the equivalent dose. Organs are now classified into 3 categories: Critical Element(CE) : Example Spinal Cord Critical Volume (CV) : Example Lung Graded Response (GR) : Example oral mucosa
BEV Display : The observer’s viewing point is at the source of radiation looking out along the axis of the radiation beam. Allows planner to visualize target volumes and critcal organ volumes facilitating planning of the aperture. REV Display : The planner can simulate any arbitrary viewing location within the treatment room. Allows planner to appreciate the composite beam arrangement and geometry Digitally Composite Radiograph is a type of DRR that allows different ranges of CT numbers that relate to a certain tissue type to be selectively suppressed or enhanced in the image. Analogous to a transmission radiograph through a virtual patient where certain tissue types have been removed , leaving only the organs of interest to be displayed. Allow better visualization of the organ of interest
Spatial dose distribution in the 3 dimensional volume is first defined. Defination of dose coverage for the PTV(s) Defination of sparing for the organ at risk Establishment of a hierarchy of targets and organs at risk Beam intensity distribution required to achieve this dose distribution goal would be calculated. Photon Fluence required to deliver this intensity distribution is then generated.
Normally optimization as done today is a repetative process which requires plan generation, calculatio, evaluation and repeat iteration by changing the priorities or penalties. As such the process of designing priorities and penalties is not intuitive and optimization solution will not arrive at the biologically optimal solution in all cases. Multicriteria optimization is a process where a set of inverse plans are generated with variety of dose solutions. These solutions form a continuum from one extreme of the dose spectrum to the other. These plans together form a set of pareto optimal solutions and one solution among them is the pareto optimal. The pareto optimal is that solution where an improvement in one criteria will not occur without a deterioration in the other. The planner then has to choose the pareto optimal instead of choosing the criteria or the penalty. A software allows an interactive visualization of the possible solutions and based on the EUD concept one can determine the TCP and NTCP that is acceptable. For this the sliders in the triangular area are moved back and forth for each organ so that the solution for that TCP and NTCP is taken from the database and presented to the individual.
Langen, K. M., & Jones, D. T. (2001). Organ motion and its management. International journal of radiation oncology, biology, physics, 50(1), 265-78.
Room mounted OBI systems are present in two modern day systems: Cyberknife (Accuray) BrainLAB (Exectrac system) RTRT system installed at the Hokkoido university The advantages of the room mounted OBI are: Advantageous for real time tracking of implanted radiological markers High degree of mechanical precision As the intensifiers or the As-Si panels are far away from the treatment head so image is not deteriorated by the simultaneous scatter from the MV beam. In addition the mechanical precision is very high as the parts are not moving The disadvantages of the room mounted OBI are: Small field of view Poor imaging effeciency – so high doses of radiation have to be used unconventional imaging angles are another downside The gantry mounted systems have the advantages that: They have a large field of view Can image tumors from conventional angles Cone beam CT scans can be obtained Direct tumor tracking like in lung is also possible Gantry mounted systems are available commercially by Varian as well as Elekta IRIS (Intgrated Radiotherapy Imaging System) developed at Japan uses two orthogonally mounted gantry based OBI system and can potentially give more accurate tumor localization
During the simulation process the CT scans are acquired with the tracking system in situ so that the motion can be recorded. The system can acquire the CT scan in two modes: In one mode the scans are acquired in only the specified phase of respiration – a single set of CT scans is acquired (prospective trigerring). In the other mode CT images are continously acquired at all phases of the respiratory cycle for each position and subsequntly the images are correlated with the respiratory cycle phase to generate imaging data for each phase (retrospective triggering - 4-D CT) The treatment process is analogous with the beam being turned on at the particular phase of treatment only. The limitations of the system include: The patient should be cooperative and hold breath regularly in a taught pattern The patient should be taught regarding the process The imaging and treatment are time consuming Treatment time is increased by 10 -15 min The period of gating can be choosen according to: Phase of respiration : usually the end expiration is more reproducible Amplitude of respiration: The beam turns on at predetermined degrees of excursion of the chest.
This is an example of a 4 D CT scan acquired for a patient with implanted hepatic markers. The first CT scan represents the image of the patient in a normal helical CT. Note that due to the nature of respiratory motion the implanted fiducial appears twice in the normal image. The motion artifacts are present in the CT image and the outline of the abdominal skin is also jagged because of the motion. These defects are absent in the 3D CT data sets as they were taken for the same respiratory phase.
Various image matching algorithms are available. All of them work on the principle of creation of deformation vector maps from the 4 D CT data and then image is manipulated for voxel matching. Each algorithm has a similiarty metric or end point which is to be acheived e.g. matching contour of a designated organ and an interpolation method. Various methods in development have errors ranging from 1 -3 mm and are not foolproof yet.
Maximum experience with this modality is in the William Beaumont Hospital mDIBH technique has the advantage of moving the lung away from the treatment fields 2 sets of CT scans are taken – one free breathing for setup and the other with ABC for treatment Patients are setup according to coordinates provided by the setup CT The ABC apparatus is used to deliver the treatment synchronized to the mDIBH phase. Segments of fields for IMRT are subdivided to coincide with the breath hold sessions Mean Setup variation of 2.5 mm in sueproinferior direction Mean setup variation of 1.6 mm in the transverse direction Treatment time usually 15 min Other studies: Hepatic Tumors (University of Michigan) Setup error reduced with mean error of 6.7 mm to 3.5 mm in superoinferior direction Reduced margins allowed increase in tumor dose by 5 Gy In Lung tumors movements in lung tumors can be as low as 2 mm
The treatment to an imaged tumor position can only be delivered after a certain period of time in which the image is processed. The time for image processing and the signal processing for MLC / machine movement is unavoidable. Thus actual real time Adaptive radiotherapy is not possible.
The 5-year and 7 year bRFS rate for 2991 localized prostate cancer patients: Radical Prostatectomy : 81% , 76% EBRT <72, 51%, 48% EBRT ≥72, 81% , 81% Permanent Implant: 83%, 75% (Kupelian, P. A., Potters, L., Khuntia, D., Ciezki, J. P., Reddy, C. A., Reuther, A. M., et al. (2004). Radical prostatectomy, external beam radiotherapy <72 Gy, external beam radiotherapy >=72 Gy, permanent seed implantation, or combined seeds/external beam radiotherapy for stage T1-T2 prostate cancer. International Journal of Radiation Oncology*Biology*Physics, 58(1), 25-33.)
The use of 3DCRT, particularly with only 3–4 beam angles, can reduce toxicity but has limited potential for dose escalation beyond the current standard in node (+) patients. IMRT is of minimal value in node (-) cases, but is beneficial in node (+) cases or those with target volumes close to the esophagus. In node positive (+) cases, however, IMRT reduced the lung V20 and mean dose by 15% and lung NTCP by 30% compared to 3DCRT. When meeting all normal tissue constraints in node (+) patients, IMRT can deliver RT doses 25–30% greater than 3DCRT and 130–140% greater than ENI. While the possibility of dose escalation is severely limited with ENI, the potential for pulmonary and esophageal toxicity is clearly increased.
In Brain Tumors especially high grade leisons IMRT is being evaluated as a method to deliver hypofractionated radiation to the gross tumor volume without excessive neurotoxicity. However the approach is not validated yet. Small series have also looked at IMRT in situations like clival chordomas, optic nerve gliomas and pituitary tumors.
In Carcinoma Cervix IMRT can be used in the following senarios: As a replacement for 4 field box technique to deliver WPRT As a replacement for conventional RT for EFRT As an alternative to Brachytherapy when ICBT is not possible. Along with brachytherapy for boosting the pelvic nodes as an alternative to parametrial EBRT boost or Interstital brachytherapy As a method to reduce bone marrow radiation dose to ensure better chemotolerance for concomitant Chemoradiation.
The IMRT plans improved the dose conformality around the PTV and pelvic lymph nodes, keeping Dmax within the PTV. Particularly helpful for inguinal lymph nodes coverage with a >25% improvement. IMRT plans greatly improved tissue sparing for critical normal structures including the bladder, femoral heads and bowel. Mean bladder dose decreased 59–65%, femoral head dose by 3–22%, and bowel dose by 27–38%. The low dose to bone marrow was similar for the different plans. PTV coverage and tissue sparing appeared to be equivalent between standard and integrated boost plans.
LINAC based stereotactic radiotherapy offers several advantages which include: Treatemnt of wide range of leisons possible Treatment can be given for extracranial target The machine can be used for IMRT/IMAT etc On board imaging including stereoscopic Xrays and On board KC CT scanners are intergrated. RPM system based motion gating possible. Patient postion can be maintained with non invasive frame based systems Both MLC based and circular collimator based aperture designing possible. Output is higher so the entire treatment is completed quickly Collimators used in radiosurgery are of two types: Conical Collimators: Used in the NOVALIS BrainLAB system Circular Collimators Used in the Trilogy system Collimators come in diameters of 1 -35 mm – However use is cumbersome MicorMLCs circimvent the problem of a fixed collimator opening by allowing a dynamic field shaping.
It consists of a robotic system with 6 MV LINAC. The robotic arms are computer controlled and have
Applicators used for IGBRT should be such that the applicator doesnot produce an artifact on the cross sectional imaging technique being used. For this purpose special CT/MRI Compatible apllicators should be used. The applicators are usually made up of a titanium alloy which has other advantages like: Corrosion resistance High tensile stength Easy to clean Precisely machined to minimize tissue trauma Long service life Capable of repeated use The principle disadvantage of using Titanium in these applicators is the cost. Now a days carbon fibre based brachytherapy applicators are also available.
Patient is first placed in lithotomy position and 150 cc of contrast is introduced into the bladder. The urethra may be delineated with air filled gel which gives good contrast on USG A B mode USG is taken from the base of the prostate to the apex and the prostate is contoured at 5 mm intervals. The dose distribution is planned and needles are inserted using the template. Indications for prostate brachythearpy are : Patients should have a life expectancy of at least five years. The disease should be localised within the prostate capsule, ie stage T1 and T2. GS < 7 ; PSA < 10 ng/mL (if treated with implant only) IPSS score < 15 There should be no evidence of metastases in bones or pelvic lymph nodes. The prostate volume should be less than 50 – 60 cm³ in order to avoid interference with the pubic arch. Patients with T2 tumors with GS > 7 and PSA > 20 are best served with a boost implant
Beaulieu L, Aubin S, Tascherean R, et al. Dosimetric impact of the variation of the prostate volume and shape between pretreatment planning and treatment procedure. Int J Radiat Oncol Biol Phys. 2002;53(1):215â€“221.
Goes by the name of AXXENT Uses a 30 - 50 KV Miniature Xray tube which is actively water cooled The Xray tube is attached to a High Voltage Cable and the assembly is flexible and retractable like a HDR source assembly. Output 10 cGy at 1 cm in water. Air Kerma Rates are comparable to 10 Ci Ir 192 HDR Source Source is 2 mm in diameter Has a different anisotropy profile than HDR Sources Radiobiology is still under investigation – preclinical trials in animals have indicated need for a further dose rate correction.
New Techniques inRadiation therapy Moderator: Dr S C Sharma Department of Radiotherapy PGIMER Chandigarh
Trends Number of Publications in Google Scholar2500200015001000 500 0 1990 1995 2000 2005 3 DCRT IMRT IGRT
Solutions ? Electrons Protons Neutrons Use alternative radiation Develop technologies to circumvent limitations modalities π- Mesons Heavy Charged Nuclei Antiprotons
Development TimelineTakahashi discusses conformal RT 1950 1st MLCs invented (1959) Proimos develops gravity oriented 1960 blocking and conformal field shaping Tracking Cobalt unit invented 1970 at Royal Free Hospital 1st inverse planning algorithm Brahame conceptualized inverse planning 1980 developed by Webb (1989) & gives prototype algorithm for (1982-88) Boyer and Webb develop Carol demonstrates NOMOS MiMIC (1992) principle of static IMRT (1991) Tomotherapy developed in Wisconsin (1993) 1990 Stein develops optimal dMLC equations First discussion of Robotic (1994) IMRT (1999)
Modulation: Examples Block: Wedge: Binary Modulation Uniform ModulationCoarse spatial and Fine spatialCoarse intensity coarse intensity Fine Spatial and Fine Intensity modulation
Conformal Radiotherapy Conformal radiotherapy (CFRT) is a technique that aims to exploit the potential biological improvements consequent on better spatial localization of the high- dose irradiation volume - S. Webb in Intensity Modulated Radiotherapy IOP
Problems in conformation Nature of the photon beam is the biggest impediment Has an entrance dose. Has an exit dose. Follows the inverse square law.
Types of CFRT Two broad subtypes : Techniques aiming to employ geometric ﬁeldshaping alone Techniques to modulate the intensity of ﬂuence across the geometrically- shaped ﬁeld (IMRT)
Modulation : Intensity or Fluence? Intensity Modulation is a misnomer – The actual term is Fluence Fluence referes to the number of “particles” incident on an unit area (m-2)
How to modulate intensity Cast metal compensator Jaw defined static fields Multiple-static MLC-shaped ﬁelds Dynamic MLC techniques (DMLC) including modulated arc therapy (IMAT) Binary MLCs - NOMOS MIMiC and in tomotherapy Robot delivered IMRT Scanning attenuating bar Swept pencils of radiation (Race Track Microtron - Scanditronix)
Step & Shoot IMRT Since beam is interrupted between movements leakage radiation is less. Easier to deliver and plan. More time consumingIntesntiy Distance
Dynamic IMRT Faster than Static IMRT Smooth intensity modulation acheived Beam remains on throughout – leakage radiation increased More susceptible to tumor motion related errors. Additional QA required for MLC motion accuracy.Intesntiy Distance
Caveats: Conformal Therapy Significantly increased expenditure: Machine with treatment capability Imaging equipment: Planning and Verification Software and Computer hardware Extensive physics manpower and time required. Conformal nature – highly susceptible to motion and setup related errors – Achilles heel of CFRT Target delineation remains problematic. Treatment and Planning time both significantly increased Radiobiological disadvantage: Decreased “dose-rate” to the tumor Increased integral dose (Cyberknife > Tomotherapy > IMRT)
How to Plan CFRT Patient positioning Volumetric Data Image Transfer and Immobilization acqusition to the TPS Target Volume DelineationTreatment QA Treatment Delivery Forward Planning Inverse Planning Dose distribution 3D Model Analysis generation
Positioning and Immobilization Two of the most important aspects of conformal radiation therapy. Basis for the precision in conformal RT Needs to be: Comfortable Reproducible Minimal beam attenuating Affordable Holds the Target in place while the beam is turned on
Types of Immobilization Invasive Frame based NoninvasiveImmoblization devices Frameless ➢Usually based on a combination of heat deformable “casts” of the part to be immobilized attached to a baseplate that can be reproducibly attached with the treatment couch. ➢The elegant term is “Indexing”
Cranial Immobilization BrainLab System TLC System Leksell Frame Gill Thomas Cosman System
Extracranial Immobilization Body Fix system Elekta Body Frame
Accuracy of systems System Techniqe Setup Accuracy Noninvasive Non invasive, 0.7– 0.8 mm (± 0.5–0.6 mm)Stereotactic frame mouthpiece Non invasive, x = 1.0 mm ± 0.7; y= 0.8 mm ± 0.8; z = 1.7 Latinen Frame nasion, earplugs mm ± 1.0 Non invasive, X = 0.35 mm ± 0.06; Y = 0.52 mm ± 0.09; GTC Frame mouthpiece Z= 0.34 mm ± 0.09Stereotactic Body Non invasive, X = 5 – 7 mm ,Y = 1 cm Z = 1.0 cm (mean) Frame vacccum based Non invasive,Heidelberg frame X = 5 mm,Y = 5 mm, Z = 10 mm (mean) vaccum based Non invasive, X = 0.4 ± 3.9 mm , Y = 0.1 ± 1.6 mm Z = 0.3 Body Fix Frame Vacccum based ± 3.6 mm. Rotation accuracy of 1.8 ± 1.6 with plastic foil degrees. With the precision of the body fix frame the target volume will be underdosed (< 90% of prescribed dose) 14% of the time!!!
CT simulator 70 – 85 cm bore Scanning Field of View (SFOV) 48 cm – 60 cm – Allows wider separation to be imaged. Multi slice capacity: Speed up acquistion times Reduce motion and breathing artifacts Allow thinner slices to be taken – better DRR and CT resolution Allows gating capabilities Flat couch top – simulate treatment table
MRI Superior soft tissue resolution Ability to assess neural and marrow infiltration Ability to obtain images in any plane - coronal/saggital/axial Imaging of metabolic activity through MR Spectroscopy Imaging of tumor vasculature and blood supply using a new technique – dynamic contrast enhanced MRI No radiation exposure to patient or personnel
PET: Principle Unlike other imaging can biologically characterize a leison Relies on detection of photons liberated by annhilation reaction of positron with electron Photons are liberated at 180° angle and simultaneously – detection of this pair and subsequent mapping of the event of origin allows spatial localization The detectors are arranged in an circular array around the patient PET- CT scanners integrate both imaging modalities
PET-CT scanner PET scanner Flat couch top insert CT Scanner 60 cm Allows hardware based registration as the patient is scanned in the treatment position CT images can be used to provide attenuation correction factors for the PET scan image reducing scanning time by upto 40%
Markers for PET Scans Metabolic marker 2- 18 Fluoro 2- Deoxy Glucose Proliferation markers Radiolabelled thymidine: 18 F Fluorothymidine Radiolabelled amino acids: 11 C Methyl methionine, 11C Tyrosine Hypoxia markers Cu-diacetyl-bis(N-4- 60 methylthiosemicarbazone) (60Cu- ATSM) Apoptosis markers 99 m Technicium Annexin V PET Fiducials
Image Registration Technique by which the coordinates of identical points in two imaging data sets are determined and a set of transformations determined to map the coordinates of one image to another Uses of Image registration: Study Organ Motion (4 D CT) Assess Tumor extent (PET / MRI fusion) Assess Changes in organ and tumor volumes over time (Adaptive RT) Types of Transformations: Rigid – Translations and Rotations Deformable – For motion studies
Process: Image Registration The algorithm first measures the degree of mismatch between identical points in two images (metric). The algorithm then determines a set of transformations that minimize this metric. Optimization of this transformations with multiple iterations take place After the transformation the images are “fused” - a display which contains relevant information from both images.
Target Volume delineation The most important and most error prone step in radiotherapy. Also called Image Segmentation The target volume is of following types: GTV (Gross Target Volume) CTV (Clinical Target Volume) ITV (Internal Target Volume) PTV (Planning Target Volume) Other volumes: Targeted Volume Irradiated Volume Biological Volume
Target Volumes GTV: Macroscopic extent of the tumor as defined by radiological and clinical investigations. CTV: The GTV together with the surrounding microscopic extension of the tumor constitutes the CTV. The CTV also includes the tumor bed of a R0 resection (no residual). ITV (ICRU 62): The ITV encompasses the GTV/CTV with an additional margin to account for physiological movement of the tumor or organs. It is defined with respect to a internal reference – most commonly rigid bony skeleton. PTV: A margin given to above to account for uncertainities in patient setup and beam adjustment.
Definitions: ICRU 50/62 GTV CTV Treated Volume: Volume of the tumor and surrounding normal ITV tissue that is included in the isodose surface representing the irradiation TV dose proposed for the treatment (V95) Irradiated Volume: Volume included in an isodose surface with PTV IV a possible biological impact on the normal tissue encompassed in this volume. Choice of isodose depends on the biological end point in mind.
Organ at Risk (ICRU 62) Normal critical structures whose radiation sensitivity may significantly influence treatment planning and/or prescribed dose. A planning organ at risk volume (PORV) is added to the contoured organs at risk to account for the same uncertainities in patient setup and treatment as well as organ motion that are used in the delineation of the PTV. Each organ is made up of a functional subunit (FSU)
Biological Target Volume A target volume that incorporated data from molecular imaging techniques Target volume drawn incorporates information regarding: Cellular burden Cellular metabolism Tumor hypoxia Tumor proliferation Intrinsic Radioresistance or sensitivity
Biological Target Volumes Lung Cancer: 30 -60% of all GTVs and PTVs are changed with PET. Increase in the volume can be seen in 20 -40%. Decrease in the volume in 20 – 30%. Several studies show significant improvement in nodal delineation. Head and Neck Cancer: PET fused images lead to a change in GTV volume in 79%. Can improve parotid sparing in 70% patients.
3 D TPS Treatment planning systems are complex computer systems that help design radiation treatments and facilitate the calculation of patient doses. Several vendors with varying characteristics Provide tools for: Image registration Image segmentation: Manual and automated Virtual Simualtion Dose calculation Plan Evaluation Data Storage and transmission to console Treatment verification
Planning workflow Total Dose Total Time of delivery of dose Define a dose objective Total number of fractions Choose Number of Beams Organ at risk dose levels Choose beam angles and couch angles Choose Planning Technique Forward Planning Inverse Planning
“Forward” Planning A technique where the planner will try a variety of combinations of beam angles, couch angles, beam weights and beam modifying devices (e.g. wedges) to find a optimum dose distribution. Iterations are done manually till the optimum solution is reached. Choice for some situations: Small number of fields: 4 or less. Convex dose distribution required. Conventional dose distribution desired. Conformity of high dose region is a less important concern.
“Inverse” Planning Inverse Planning 1. Dose distribution specifiedForward Planning 3. Beam Fluence modulated to recreate 2. Intensity map created intensity map
Optimization Refers to the technique of finding the best physical and technically possible treatment plan to fulfill the specified physical and clinical criteria. A mathematical technique that aims to maximize (or minimize) a score under certain constraints. It is one of the most commonly used techniques for inverse planning. Variables that may be optimized: Intensity maps Number of beams Number of intensity levels Beam angles Beam energy
Optimization Criteria Refers to the constraints that need to be fulfilled during the planning process Types: Physical Optimization Criteria: Based on physical dose coverage Biological Optimization Criteria: Based on TCP and NTCP calculation A total objective function (score) is then derived from these criteria. Priorities are defined to tell the algorithm the relative importance of the different planning objectives (penalties) The algorithm attempts to maximize the score based on the criteria and penalties.
Why 4D Planning? Organ motion types: Types of movement: Interfraction motion Translations: Intrafraction motion Craniocaudal Lateral Even intracranial structures can move – 1.5 mm shift Vertical when patient goes from Rotations: sitting to supine!! Roll Pitch Yaw Shape: Flattening Balloning Pulsation
Interfraction Motion Prostate: Rectum: Motion max in SI and AP Diameter: 3 – 46 mm SI 1.7 - 4.5 mm Volumes: 20 – 40% AP 1.5 – 4.1 mm In many studies decrease in volume found Lateral 0.7 – 1.9 mm SV motion > Prostate Bladder: Uterus: Max transverse diameter mean 15 mm variation SI: 7 mm SI displacement 15 mm AP : 4 mm Volume variation 20% - Cervix: 50% SI: 4 mm
Intrafraction Motion Liver: Lung: Normal Breathing: 10 – 25 Quiet breathing mm AP 2.4 ± 1.3 mm Deep breathing: 37 – 55 mm Lateral 2.4 ± 1.4 mm Kidney: SI 3.9 ± 2.6 mm Normal breathing: 11 -18 2° to Cardiac motion: 9 ± 6 mm mm lateral motion Deep Breathing: 14 -40 mm Tumors located close to the chest wall and in upper lobe Pancreas: show reduced interfraction motion. Average 10 -30 mm Maximum motion is in tumors close to mediastinum
IGRT: Solutions Imaging techniques USG based Video based Planar X-ray CT MRI ●BAT ●AlignRT ●Sonoarray ●Photogrammetry ●I-Beam ●Real Time Video guided Fan Beam Cone Beam ●Resitu IMRT ●Video substraction ●Tomotherapy ●In room CT MV CT KV CT ●Siemens ●Mobile C arm KV X-ray OBI ●Varian OBI ●Elekta ●Siemens Inline Gantry Mounted Room Mounted MV X-ray●Varian OBI ●Cyberknife EPI ●●Elekta Synergy ●RTRT (Mitsubishi)●IRIS ●BrainLAB (Exectrac)
IGRT: Solution Comparision DOF = degrees of freedom – directions in which motion can be corrected – 3 translations and 3 rotations
EPI Uses of EPI: Correction of individual interfraction errors Estimation of poulation based setup errors Verification of dose distribution (QA) Problems with EPI: Poor image quality (MV xray) Increased radiation dose to patient Planar Xray – 3 dimensional body movement is not seen Tumor is not tracked – surrogates like bony anatomy or implanted fiducials are tracked.
Types of EPID Liquid Matrix Ion Chamber* Camera based devices Amorphous silicon flat panel detectors Amorphous selenium flat panel detectors Electrode High voltage applied connected to high voltage “Output” Output read out Liquid 2,2,4 - ionized liquid electrode by the lower trimethylpentane electrodes
4 D CT acqusition Axial scans are acquired with the use of a RPM camera attached to couch.The “cine” mode of the scanner is used toacquire multiple axial scans atpredetermined phases of respiratory cyclefor each couch position
RPM SystemPatient imaged with the RPM system to ascertain baseline motion profile A periodicity filter algorithm checks the breathing periodicity Breathing comes to a rythm Breathing cycle is recorded
Problems with 4 D CT The image quality depends on the reproducibility of the respiratory motion. The volume of images produced is increased by a factor of 10. Specialized software needed to sort and visualize the 4D data. Dose delivered during the scans can increase 3-4 times. Image fusion with other modalities remains an unsolved problem
4D Target delineation Target delineation can be done on all images acquired. Methods of contouring: Manual Automatic (Deformable Image Registration) Why automatic contouring? Logistic Constraints: Time requirement for a single contouring can be increased by a factor of ~ 10. Fundamental Constraints: To calculate the cumulative dose delivered to the tumor during the treatment. However the dose for each moving voxel needs to be integrated together for this to occur. So an estimate of the individual voxel motion is needed.
4D Manual Contouring The tumor is manually contoured in end expiration and end inspiration The two volumes are fused to generate at MIV – Maximum Intensity Volume The projection of this to a DRR is called MIP (Maximum Intensity Projection) End Inspiration MIV End Expiration
Automated Contouring Technique by which a single moving voxel is matched on CT slices that are taken in different phases of respiration The treatment is planned on a reference CT – usually the end expiration (for Lung) Matching the voxels allows the dose to be visualized at each phase of respiration Several algorithms under evaluation: Finite element method Optical flow technique Large deformation diffeomorphic image registration Splines thin plate and b
Automated Contouring Individaul Pixels + =Day 1 Image Day 2 Image Due to the changes in shape of the object the same pixel occupies a different coordinate in the 2nd image Deformable Image registration circumvents this problems
4D Treatment Planning A treatment plan is usually generated for a single phase of CT. The automatic planning software then changes the field apertures to match for the PTV at each respiratory phase. MLCs used should be aligned parallel to the long axis of the largest motion.
Limitations of 4D Planning Computing resource intensive – Parallel calculations require computer clusters at present No commercial TPS allows 4 D dose calculation Respiratory motion is unpredictable – calculated dose good for a certain pattern only Incorporating respiratory motion in dynamic IMRT means MLC motion parameters become important constraints Tumor tracking is needed for delivery if true potential is to be realized The time delay for dMLC response to a detected motion means that even with tracking gating is important
4D Treatment delivery Options for 4D delivery Ignore motion Freeze the motion Follow the motion (Tracking) Patient breaths normally Breathing is controlled Respiratory Gating Breath holding (DIBH) Jet Ventilation Active Breathing control
Minimizing Organ Motion Abdominal Compression(Hof Breath Hold technique: et al. 2003 – Lung tumors): Patients instructed to hold Cranio-caudal movement of breath in one phase tumor 5.1±2.4 mm. Usually 10 -13 breath holding Lateral movement 2.6±1.4 sessions tolerated (each 12 -16 sec) Anterior-posterior movement 3.1±1.5 mm Reduced lung density in irradiated area – reduced volume of lung exposed to high dose Tumor motion restricted to 2-3 mm (Onishi et al 2003 – Lung tumors)
Minimizing Organ Motion Active Breathing Control Consists of a spirometer to “actively” suspend the patients breathing at a predetermined postion in the respiratory cycle A valve holds the respiratory cycle at a particular phase of respiration Breath hold duration : 15 -30 sec Usually immobilized at moderate DIBH (Deep Inspiration Breath Hold) – 75% of the max inspiratory capacity Max experience: Breast Intrafractional lung motion reduced Mean reproducibility 1.6 mm
Tracking Target motion Also known as Real-time Postion Management respiratory tracking system (RPM) Various systems: Video camera based tracking (external) Radiological tracking: Implanted fiducials Direct tracking of tumor mass Non radiographic tracking: Implanted radiofrequncy coils (tracked magnetically) Implanted wireless transponders (tracked using wireless signals) 3-D USG based tracking (earlier BAT system)
Adaptive Radiotherapy (ART) Adaptive radiotherapy is a technique by which a conformal radiation dose plan is modified to conform to a mobile and deformable target. Two components: Adapt to tumor motion (IGRT) Adapt to tumor / organ deformation and volume change. 4 ways to adapt radiation beam to tracked tumor motion: Move couch electronically to adapt to the moving tumor Move a charged particle beam electromagnetically Move a robotic lightweight linear accelerator Move aperture shaped by a dynamic MLC
ART: Concept 1. 2. 3. ●Offline ART●Conventional Rx ➢ Individual patient based ●Online ART ➢ Individual patient based➢ Sample Population based margins margins ➢ Frequent imaging of margins ➢ Daily imaging of patients➢ Accomadates variations of patients ➢ Daily error corrected setup for the populations ➢ Estimated systemic error➢ No or infrequent imaging corrected based on prior to the treatment ➢ Smallest margin➢ Largest margin repeated measurements ➢ A small margin kept for required ➢ Plans adapted to the random error ➢ Plans adapted to average changing anatomy daily! changes
ART: Why ? Due to a change in the contours (e.g. Weight Loss) the actual dose received by the organ can vary significantly from the planned dose despite accurate setup and lack of motion.
ART: Problem Real time adaptive RT is not possible “today”
Helical Tomotherapy Gantry dia 85 cm Integrated S Band LINAC 6 MV photon beam No flattening filter – output increased to 8 Gy/min at center of bore Independant Y - Jaws are provided (95% Tungsten) Fan beam from the jaws can have thickness of 1 -5 cm along the Y axis
Helical Tomotherapy LINAC Binary MLCs are provided – 2 positions – open or closed Cone Beam Pneumatically driven 64 leaves Y jaw Open close time of 20 msBinary MLC Width 6.25 mm at isocenter 10 cm thickY jaw Interleaf transmission – 0.5% in field and 0.25% out field Maximum FOV = 40 cm Fan Beam However Targets of 60 cm dia meter can be treated.
Helical Tomotherapy Flat Couch provided allows automatic translations during treatment Target Length long as 160 cm can be treated “Cobra action” of the couch limits the length treatable Manual lateral couch translations possible Automatic longitudinal and vertical motions possible
Helical Tomotherapy Integrated MV CT obtained by an integrated CT detector array. MV beam produced with 3.5 MV photons Allows accurate setup and image guidance Allows higher image resolution than cone beam MV CT (3 cm dia with 3% contrast difference) Tissue heterogenity calculations can be done reliably on the CT images as scatter is less (HU more reliable per pixel) Not affected by High Z materials (implant) Dose 0.3 – 3 Gy depending on slice thickness Dose verification possible
Prostate Cancer Rectal Toxicity: Grade 2: 7 patients (1.5%); Grade 3: 3 patients (less than 1%) The 8-year actuarial likelihood of late grade 2 or greater rectal toxicity 1.6%. Urinary Toxicity: Grade 2 chronic urethritis in 50 patients (9%); Urethral stricture requiring dilation (grade 3) developed in 18 patients (3%). The 8-year actuarial likelihood of late grade 2 or greater urinary toxicities was 15%. 47% patient developed ED (43% IMRT alone; 57% ADT) No 2nd cancers!
Prostate Cancer Arcangeli et al (2007) WP-IMRT 91% with Prostate boost 71% N = 55; All had NAADT, Risk of 63% nodal mets > 15% Dose: 55 – 59 Gy (Pelvis) 66 – 80 Gy (Prostate) 33 – 40 fractions No Gr III toxicity Late Gr II toxicity: Rectum: 2 yr actuarial probablity 8%
Head and Neck Cancers Author Year N CCT Dose Result Huang 2003 41 (I) Yes 70/60/50 (2.18 68% Stage IV; 31% Gr III mucositis; (P,NR) Gy per #) 7% Gr IV mucositis; Gr II xerostomia 58.5%; 2 yr Locoregional control 89% ; 2 yr OS 89% Wendt 2006 39 (I) Yes 60-70 Gy / 48 Gr III mucositis 11%; 12% Gr III (P,NR) -54 Gy (I) xerostomia at 6 months; 2yr Crude LC 70%; 50 % recurrences outside high dose regionYao (P,NR) 2007 90 (I) Yes 70/60/54 Gy All N2/N3 disease; 71% Oropharynx; (SIB) 3 yr LC 96%; OS 67.5%; PET useful in patient selection for ND (10) Arruda 2006 50 (I) Yes 70 / 59.4 -54 Gy All oropharynx; 92% ≥ St III; 33% (P,NR) (76% - SIB) Gr II xerostomia (1 yr); Gr III mucositis 38%; 2 yr LRC 88%; OS 98% Table showing Results of IMRT in H&N Ca
Head and Neck CancersAuthor Year N CCT Dose Result Chao 2003 126 Yes 72 -68/ 64 -60 Gy 59% Post op IMRT; 67% St IV; 2 yr(P,NR) (I) (30%) (SIB) LRC 85% ; 89% (Post ND)Thorstad 2005 356 Yes 70/56 Gy – Def.; 63% Post op; 90% ≥ St III; 5 Yr LRC (P,NR) (I) (40%) 64/54 Gy – 76%; 14% of the failures were Postop marginal. All marginal failures in post op patients.Wolden 2005 79 (I) Yes 70 Gy (59 – All Npx; 80% ≥ Stage III; 3 yr(P,NR) Hyperfractionated actuarial LC 91%; OS 83%; Gr III ; 15 - SIB) hearing loss 15%; 32% Gr II xerostomia at 1 yr; distant mets dominant form of therapy Daly 2007 69 (I) Yes 66 Gy -Def (2.2 33% Post op; 2 yr LC and OS 92% and(P,NR) Gy per #); 60.2 – 74%(Def); 87% and 87% (Post op); Post op (2.15 per Mean xerstomia significantly improved #) than CRTSchwartz 2007 49 (I) Yes 60 / 50 Gy (25#) All Stage III/IV; Gr III mucositis 55%, (P,NR) - SIB Gr III dermatitis 8%; 2 yr LC 83% ; OS 80% Table showing results of IMRT in H& N Ca
Head and Neck CancersAuthor Year N CCT Dose Result Huang 2003 41 (I) Yes 70/60/50 68% Stage IV; 31% Gr III mucositis; 7% (P,NR) (2.18 Gy per Gr IV mucositis; Gr II xerostomia 58.5%; #) 2 yr Locoregional control 89% ; 2 yr OS 89% Jabbari 2004 30 (I), No 60-78 Gy (I); At 12 months, median XQ and HNQOL (P,NR) 10 (C) 63 -76.8 (C) scores were lower (better) in the IMRT compared with the standard RT patients by 19 and 20 points, respectivelyPow (P,R) 2006 24 No 68-70 / 66- All Stage II Npx; At 1 yr 83% had (I),21 68(I); 68 / 66 recovered 25% of the pre RT parotid flow (C) (C) in IMRT (9.5% in Conv RT arm). Subscale scores for role-physical, bodily pain, and physical function were significantly higher in the IMRT group Braam 2006 30 (I), No I – 69/66/54 83% in I arm treated definitively (23% in (P,NR) 26 (C) (30#), C – 50 C arm);mean parotid flow ratio was 18% -70/46-50(25 (C) and 64% (I); parotid gland – 35#) complication rate was 81% (C) and 56% (I) (p = 0.04). Table showing Salivary sparing and QOL improvement with IMRT
Breast Cancer Largest randomized trial Donovan et al (2007) 305 patients – 156(standard) and 150 (IMRT) 1997 – 2000 Aim:Impact of improved radiation dosimetry with IMRT in terms of external assessments of change in breast appearance and patient self-assessments of breast discomfort, breast hardness and quality of life. Dose: 50 Gy / 25# with 10 Gy boost
Breast Cancer➢ The control arm had 1.7 times (95% CI 1.2–2.5) more likely to have had some change than the IMRT arm, p = 0.008.➢ Areas with dose > 105% have 1.9 times higher risk of any change in cosmesis
Breat Cancer Leonard et al 2007 – APBI 55 patients , Non randomized All patients stage I Dose: 34 Gy (n=7) / 38.5 (n = 48) BID over 5 days Median F/U – 1 yr Good to excellent cosmesis: Patient assessed: 98% (54) Physician assessed: 98% (54) Considered a reasonable option for patients who have large target volumes and/or target volumes that are in anatomic locations that are very difficult to cover.
Lung Cancer Author Year N CCT Dose ResultYom et al 2005 37 (I) Yes 63 Gy (median) 7% incidence of Gr III (R, NR) pneumonitisYorke et al 2005 78 No Dose escalation 22% incidence of Gr III (P, NR) (3D) (50.7 – 90 Gy); pneumonitis above doses of 70 Gy.Videtec (R, 2006 28 (I) No 50 Gy in 5 fraction 64% T1; 2.6% Gr II pneumonitis, NR) (SBRT) no Gr III reactions; LC and OS at 1 yr 96.4% and 93% respectivelyScarbrough 2006 17 (I) Yes 71.2 Gy (69–73.5 Mean age 70; 73% IIIB, FU 1 yr, (R, NR) Gy) No Gr III tox, 2 yr OS 66%Jensen (P, 2007 17 (I) Yes 66 Gy Patients no suited for CCRT. 1 Gr NR (citux) III esophagitis; 79% response (6 mo)Yom et al 2007 68 (I), Yes 63 Gy (median); 60% stage IIIB, FU = 8 mo (R, NR) 222 Dose > 60 Gy (median); Gr III pneumonitis 8% (3D) 84% (I), 63% (32% for 3D CRT); V20 35% (I) vs (3D) 38%(3D) (p = 0.001) Table showing results of IMRT in Lung Cancer
Brain Tumors Author Year N Dose ResultSultanem 2004 25 60 Gy (GTV); 40 All GBM,Post op volume < 110 cc; Gy (CTV); 20 # Majority RPA class 4/5; The 1-year overall survival rate is 40%, Median survial 9 mo. No late toxicity. Luchi 2006 25 48 – 68 Gy 2 AA patients; Median KPS 70; 2 yr PFS (GTV); 40 Gy 53.6%; 2 yr survival 55.6%; Pattern of (CTV1); 32 Gy death – CSF dissemination most (CTV2); 8 # common cause of death!Narayana 2006 58 60 Gy (PTV); 70% GBM; 1 yr OS 30% (2 yr 0%) for 30# GBM; No Gr III late toxicity; Pattern of failure – local Table showing results of IMRT in brain tumors
Cervical CancerAuthor Year N CCT Dose Result Mundt 2003 36 Y 45 Gy (1.8 80% stage I-II; PTV S3 to L4/5 (P,NR) (53%) Gy/#) interspace; Chronic GI toxicity 15% (n= 3; 1 Gr II, 2 Gr I); 50% incidence in Conventional Mundt 2002 40 Y 45 Gy (1.8 60% Acute Gr II toxicity (90% Gr II in (P,NR) Gy/#) Conv.); Less GU toxicity (10% vs 20%); Patients not requiring antidiarrheal halved! Chen 2007 33 Y 50.4 Gy / All Stage I -II; All Post Hysterectomy; 1 (P,NR) 28# yr LRC 93%; Acute GI toxicity 36% (Gr I- II); Acute Gu toxicity 30% (Gr I-II) Beriwal 2007 36 Y 45 Gy 2 Yr LC 80%; 2 yr OS 65%; 11 had (P,NR) (EFRT) + recurrences – 9 distant; Gr III toxicity – 10-15 Gy 10% boostKochanski 2005 62 Y 45 Gy (1.8 29% Post op; 20 Stage IIB-IIIB; 3 yr DFS (64%) Gy /#) 72.7%; 3 yr pelvic control 87.5%; 5% Gr II or higher late toxicity
Anal Canal Author Year N CCT Dose ResultSalama et 2006 40 (I) Yes 45 Gy WP + 9 Gy 12.5% Gr III GI toxicity, 0 Gr IIIal (R, NR) boost skin toxicity, 2 year colostomy- free, disease free, and overall survival 81%, 73%, and 86%Milano et al 2005 17 (I) Yes 45 Gy WP + 9 Gy 53% Gr II GI toxicity, No Gr III (P, NR) boost acute or late complications. 82% CR rate, the 2-year CFS, PFS, and overall survial are: 82%, 65%, and 91% Devisetty 2006 34 (I) Yes 45 Gy WP + 9 Gy 17% Acute GI toxicity; volume of (P,NR) boost bowel receiving 22 Gy (V22) was correlated with toxicity (31.8% acute GI toxicity for V22 > 563 cc vs. 0% for V22 ≤ 563 cc) Hwang 2006 12 (I) Yes 30.6 Gy WP + 42% Gr III dermal toxicity, 8% Gr (P,NR) 14.4 Gy Low III GI toxicity, 83% CR rate Pelvic + 9 Gy boost
New Techniques inStereotacticRadiation therapy
Stereotaxy Derived from the greek words Stereo = 3 dimensional space and Taxis = to arrange. A method which deﬁnes a point in the patient’s body by using an external three-dimensional coordinate system which is rigidly attached to the patient. Stereotactic radiotherapy uses this technique to position a target reference point, deﬁned in the tumor, in the isocenter of the radiation machine (LINAC, gamma knife, etc.). Units used: Gamma Knife LINAC with special collimators or mico MLC Cyberknife Neutron beams
Stereotactic Radiation Rigid application of a Two braod groups:stereotactic frame to the patient Radiosurgery: Single treatment fraction3 D Volumetric imaging with the Radiotherapy: Multiple frame attached fractions Frameless stereotacticTarget delineation and Treatment radiation is possible in one planning system – cyberknife Postioning of patinet with the Sites used: frame after verification Cranial Extracranial QA of treatment and delivery of therapy
Sterotactic Radiation The first machine used by Leksell in 1951 was a 250 KV Xray tube. In 1968 the Gamma knife was available LINAC based stereotactic radiation appeared in 1980 Other machines using protons (1958) and heavy ions – He (1978) were also used for stereotactic postioning of the Braggs Peak
Gamma Knife Designed to provide an overall treatment accuracy of 0.3 mm 3 basic components Spherical source housing 4 types of collimator helmets Couch with electronic controls 201 Co60 sources (30 Ci) Unit Center Point 40 cm Dose Rate 300 cGy/min
LINAC Radiosurgery Conventional LINAC aperture modified by a tertiary collimator. Two commercial machines Varian Trilogy Novalis
Cyberknife Roof mounted KV X-ray Robotic arm with 6 degrees of 6 MV LINAC freedon Circular Collimator attached to headFrameless patient Floor mounted Amorphousimmobilization couch silicon detectors
Advantages of Cyberknife An image-guided, frameless radiosurgery system. Non-isocentric treatment allows for simultaneous irradiation of multiple lesions. The lack of a requirement for the use of a head-frame allows for staged treatment. Real time organ position and movement correction facility Potentially superior inverse optimization solutions available.
Cyberknife 185 published articles till date; 5000 patients treated. 73 worldwide installations Areas where clinically evaluated: Intracranial tumors Trigeminal neuralgia and AVMs Paraspinal tumors – 1° and 2° Juvenile Nasopharyngeal Angiofibroma Perioptic tumors Localized prostate cancer However till date maximum expirence with Intracranial or Peri-spinal Stereotactic RT
Results Tumor Year N Result Brain mets 2004 333 (164 Survival advantage for patients with single (Andrews et al) SRT / 164 brain mets (Median survival 6.5 – 4.9 mo); C) Better functional status at follow up – SRT with WBRT Rx in single brain mets (RTOG 9508) Benign brain 2003 285 95% tumor control (media F/U 10 yr); actuarial tumors tumor control rate at 15 years was 93.7%.( Kondziolka et al) Normal facial nerve function was maintained in 95% with aucostic neuromasMalignant Glioma UP 203 SRT + EBRT + BCNU did not result in significant (Souhami et al) survial advantage – 13.6 vs 13.5 mo (RTOG 9305)Malignant Glioma 2002 203 SRT + EBRT + BCNU did not result in significant (Souhami et al) improvement in Quality adjusted survival (RTOG 9305) The only randomized trial comparing stereotactic radiation therapy boosthas failed to reveal a significant survival benefit for patients with malignant gliomas. (RTOG 9305). However 18% of the patients in the stereotactic radiotherapy arm had significant protocol deviations.
Brachytherpy An inherently conformal method of radiation delivery Relies on the inverse square law for the conformity Unlike traditional EBRT brachytherapy is both : Physically conformal Biologically conformal Rapid dose fall off from the radio-isotope Recent advances haveDose focused on better method of target identification and radio-isotope placement. Distance
Brachytherapy: Whats New Image Based Brachytherapy Image Assisted Image Guided Brachytherapy Brachytherapy Robotic Brachytherapy‡ Electronic Brachytherapy* Image Based Brachytherapy: Technique where advanced imaging modalites are used to gain information about the volumetric dose delivery by brachytherapy Image Guided Brachytherapy: Technique where imaging is used to guide brachytherapy source placement as well give information regarding the volumetric dose distribution
Image Assisted Brachytherapy Principle: Cross sectional imaging utilized to plan and analyze a brachytherapy procedure Steps: Image assisted provisional treatment planning Image guided application Image assisted definitive treatment planning Image assisted quality control of dose delivery Provisional planning refers to the planning of the implant prior to the placement of the applicator in situ – important to realize the significant anatomical distrortions 2° to the applicator placement. Definitive planning refers to the definitve treatment planning with the applicator in situ.
Image Acqusition Images should be acquired in 3 dimensions parallel and perpendicular to the axis of the applicator This minimizes reconstruction related artifacts The best modality in this respect is the MRI CE MRI can provide excellent soft tissue contrast too Para Sagittal Para Coronal Para Axial
Tumor Delineation Tumor delineation requires a good clinical examination in brachytherapy: Mucosal infiltration is usually picked up on visual inspection only. The ideal imaging modality for soft tissue resolution : MRI Tumors are usually contoured in the T2 weighted image T1 images are better for detection of lymphadenopathy
Target Volumes The target volumes as defined by ICRU 58 are similiar to the ICRU 62 recommendations Modifications specific to brachytherapy: PTV generally “approximates” CTV as applicators are considered to maintain positional accuracy. If the patient is treated with EBRT / Sx prior to brachy the CTV is the initial tumor volume (GTV) prior to treatment. The GTV for brachytherapy should be recorded seperately in such cases. Due to high dose gradient organ delineation is meaningful if done in the vicinity of the applicator For luminal structures wall delineation can give a better idea about the dose received as compared to the whole volume
Image based brachytherapyDose Distribution at level of 3 D view of the ovoids and tandem applicator geometry Bladder Rectum 3 D Dose distribution
Provisional Planning Beaulieu et al reported on 35 cases (IJROBP 2002) Prostate contours were created in a preplan setting as well as in the operating room (OR). In 63% of patients the volume of the prostate drawn had changed. These changes in volume and shape resulted in a mean dose coverage loss of 5.7%. In extreme cases, the V100 coverage loss was 20.9%. At present applied clinically for prostate cancer only. For both intraluminal and intracavitary significant changes of the anatomy on application preclude provisional planning.
Image Guided BrachytherapyRadiation Oncologist Contouring and dose acquiring sectional planning being done The finalized plan with USG images on the TPS the superimposed grid on the template indicated the point of placement of each needle
Image Guided Brachytherapy “Seed afterloader” with the needle containing the in postion. Needles being inserted into the prostate under direct USGA machine called the guidance seed loader can receive instructionsfrom the TPS directly
Image Guide Brachytherapy Final Seed placement View of the B Mode Stepped USG device with the template for insertion of the needles. Some needles have been placed already
Results Keasten et al (IJROBP 2006) 564 patients of prostate CA – IGRT or IGBRT (5 yr FU) 5-year BC rates were similar in both groups (78–82% for IGRT vs 80–84% for IGBRT) IGRT higher chronic grade≥2 GI toxicity (22% vs 12% for EBRT+HDR) EBRT+HDR higher chronic grade≥2 GU toxicity (30% vs 17% for IGRT) Nandalur et al (IJROBP 2006) 479 Prostate cancer patients IGRT vs IGBT 5 yr biochemical control rates > 90% (GR III toxicity ~ 4-6%!!) C-IGBT patients experienced significantly less chronic grade 2 GI toxicity and sexual dysfunction.
Electronic Brachytherapy AXXENT Customized Ballon Applicator X ray Source Assembly KV Xray Tube
Conclusions Conformal radiation therapy requires a good imaging guidance and better machines for delivery – development expensive and time consuming Dosimetric results invariably show superiorty of conformal avoidance IMRT the best conformal EBRT technique can allow new methods of radiotherapy – bringing hypofractionation back into fashion Several unresolved questions – sparse but emerging clinical data Cancers of developing nations – stand maximum to gain from Conformal radiation therapy Approach – Cautious Embrace?
Thank YouRadiotherapy can treat 30% cancers while Chemo/Biotherapy 2% - But considered as the “sticking plaster” of oncology” S. Webb
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