planning systems in radiotherapy


Published on

Published in: Health & Medicine, Technology
No Downloads
Total views
On SlideShare
From Embeds
Number of Embeds
Embeds 0
No embeds

No notes for slide

planning systems in radiotherapy

  1. 1. Planning systems in Radiotherapy WFO Schmidt Institute for Radio-Oncology Donauspital Vienna
  2. 2. Contents Who is Mr. Schmidt ? Handbook for Teachers and Students, IAEA, May 2003 Chapter 7: Clinical Treatment Planning in External Beam Radiotherapy Chapter 11: Computerized Treatment Planning Systems for External Beam Radiotherapy AAPM Rep 85 (2004): Tissue inhomogeneity corrections for megavoltage Photon Beams Remark: this is a selection of some topics – not a total view of all aspects dealing with planning !
  3. 3. Personal data Dosimetry & Radioprotection at Inst Nucl Phys, Univ. Vienna 1977-1984 Medical Physics in Radiotherapy at the Univ. Vienna 1984 - 1995 Medical Physics in Radiotherapy at the Donauspital Vienna since 1995 PACS since 1993 in Diagnostics Stepping now into image fusion and image-guided radiotherapy (IGRT)
  4. 4. My relation to planning systems (TPSs): I do not develop planning systems but I´m an advanced and interested user. Main interest is to get new (and good) system into routine. systems working in our institute at present: CORVUS 6.1 PROWESS HELAX 6.2 Vs. 3.2 XiO (CMS) PLATO Vs 4.2 Vs14.2
  5. 5. What I will not talk about: specialized systems for: Brachytherapy Stereotactic radiosurgery with linac or GammaKnife Orthovoltage therapy Tomotherapy IMRT Intraoperative therapy Dynamic MLC D-shaped beams Total Body Irradiations Electron beam arc therapy MicroMLC Total Skin Electron Irradiations
  6. 6. Development of TPSs „historical“ dates: ~1980 :1D-planning (by hand) ~ 2000: 4D: taking also patient movement into ~1980 – 1990: 2D-planning account with computers, CT starts „Parallel“ developments: From ~1990: 2.5D-systems Inverse planning Eg missing knowledge how to handle scatter MonteCarlo-methods New algorithms (pencil-beam, convolution/superposition,...) ~1995: Real 3D available, getting exact
  7. 7. Clinical Treatment Planning: Definition of Volumes Definitions of GTV, CTV, ITV, PTV, OAR,... not discussed here Dose specifications: Min/max dose Mean dose ICRU-point not discussed here but play an important role when comparing planning from different systems !
  8. 8. Clinical Treatment Planning: Patient data for 2D-planning Single patient contour, eventually with lead wire markers, is transferred to a sheet of paper Simulation radiographs are taken for each field OARs identified and their position identified on radiographs Irregular field calculation Clarkson algorithm
  9. 9. Clinical Treatment Planning: Patient data for 3D-planning CT-data (5-10mm for thorax, 5mm pelvis, 3mm H&N) External contour on each slice Volumes drawn by oncologist OARs fully outlined !!! (DVHs) Other imaging information (fusion) Knowledge of inhomogeneities Comparison of radiographs with DRRs
  10. 10. Clinical Treatment Planning: Treatment simulation Determination of patient treatment position Identification of TVs & OARs Determination and verification of field geometries Generation of radiographs for comparison with portfilms/PI Acquisition of patient data for further planning
  11. 11. Clinical Treatment Planning: Patient positioning, immobilization Immobilization devices have 2 fundamental roles: Immobilising patient Reproducing patient position from CT/simulator and between fractions Usually for Head and H&N Additional devices (eg vacuum-based) needed for special treatments
  12. 12. Clinical Treatment Planning: Localization, Beam Geometries Localisation of (mostly invisible) PTVs and OARs Setting up and positioning the patient Taking geometrical data (FSD, angles, fieldsizes,... Taking radiographs Taking pictures (digitally) Taking data for irregular fields (eg with lead wires)
  13. 13. Clinical Treatment Planning: CT-Patient Data - Advantages Excellent soft tissue contrast Easy contouring Electron density planning TVs and OARs can easily be identified Scout views Position of TVs relative to bony anatomy fields conform TVs much better
  14. 14. Clinical Treatment Planning: Virtual Simulation Prior to scanning marking of a reference isocenter TVs and OARs are outlined directly at the CT Use of standard beam geometries or unorthodox techniques Defining the ICRU-point in the PTV Patient first is adjusted to the reference isocenter (stable markers), then the ICRU-point is set into the isocenter by moving the table to calculated coordinates Large opening necessary Best >80cm
  15. 15. Clinical Treatment Planning: Virtual Simulation - DRRs Digitally reconstructed radiographs from CT- dataset Mandatory for comparing patient images with portfilms or portal images Oftehn combined with Beam´s Eye Views (BEVs)
  16. 16. Clinical Treatment Planning: Virtual Simulation - BEVs BEVs are projections of the treatment beam axes onto (mostly) a DRR DRRs ideally should be transferred through image networks – but they contain colors ! Definition of new standard for radiotherapy – DICOM RT !
  17. 17. Clinical Treatment Planning: Conventional vs. Virtual Simulation Better soft tissue contrast in CT DRRs and BEVs in CT Setting anatomical landmarks Patient has only to be present at the CT – much shorter ! Do you still need a conventional simulator if you have your own CT ? Radiographs from treatment setup are fine !
  18. 18. Clinical Treatment Planning: Image Fusion MRI offers better contrast esp in soft tissues, but MRI cannot be used for planning Image fusion is standard now in all modern TPSs Other modalities also important (eg PET, US) MRI CT
  19. 19. Clinical Treatment Planning: Simulation - Summary
  20. 20. Clinical Treatment Planning: Simulation – Summary (cont.)
  21. 21. Clinical Treatment Planning: Treatment Aids - Wedges Wedge angles are defined at the 50% isodose line perpendicular to the central beam (sometimes in 10cm !!) Wedge factor: dose-ratio in 10cm depth with/without wedge HEEL: thick end; TOE: thin end (Error source !) Typical usage for compensation or to avoid overdosage
  22. 22. Clinical Treatment Planning: Treatment Aids–Bolus, Compensators Bolus: tissue equivalent material To increase the surface dose To compensate missing tissue Compensator: made of almost any material from wax to lead Gets new drive now, better calculaton algorithms, better 3D-cutting devices bolus – compensator IMRT ? difference
  23. 23. IMRT with compensators at the WSP Vienna F. Sommer1, H. Wetzel1, WFO. Schmidt2, M. Bobek1, B. Riemer1, I. Wedrich1, B. Hirn1 1 Inst for Radio-Oncology, Wilhelminenspital Vienna; 2 Inst for Radio-Oncology, Donauspital Vienna HVL- measurement Oct 27, 2001 Roses-Metal und Tin-grain (grainsize ~ 0.5mm) 100,0 90,0 % (100%=without perspex) 80,0 70,0 60,0 50,0 40,0 30,0 20,0 10,0 0,0 0 1 2 3 4 5 6 7 8 cm compensator thickness Future Work: Installation of CMS-planning system for IMRT-compensators Comp. planning/measurement with films and storage foils checks of production accuracy First patients expected in 2004 at a Mevatron (6MV) without MLC
  24. 24. Clinical Treatment Planning: Oblique Incidence, Inhomogeneities Different correction methods, partially integrated into planning systems, but mostly rough and may produce large errors Isodose shift method Effective attenuation coefficient method TAR method Equivalent TAR method
  25. 25. Clinical Treatment Planning: Beam Combinations Usual 1 beam Parallel opposed beams Multiple coplanar beams Rotational beams Multiple non-coplanar beams IMRT ? Positioning of adjacent beams
  26. 26. Clinical Treatment Planning: Hand Control of Plans Institute for Radio- Oncology HOSPITAL LINAC -- ISOZENTRIC Nobody loves it ! Physics´ Planning Patient + Reg.Nr Techn: Date : Physicians have to sign Physicist : Date : what they say ! Peak voltage (MV) : F1 F2 F3 F4 Focus-skin-distance FSD (cm) : Dosimetrists or technicians Fieldsize in reference distance (cm*cm) : Reference depth d (cm) : see it as an unnecessary Wedge angle (°) : Irregular field with perspex (y/n) : piece of work only Ref. dose Dref / fract/field in ICRU-point (Gy) : Physician : Reference value (Monitorunits/Gy for 10*10 - field; isocentric) RV= MU/Gy = Physicists have to run for Gantry angle : data and signatures – and 2* a* b FLeq = (a + b) always have to answer the Equivalent field : Outputfactor OF (Tab) : question: is it really Wedge-factor WF (Tab) : Tray-factor TF (Tab) : necessary ? 100 Μ = D ref * RV ** 1 * TMR-value for d, FLeq (Tab) : 1 TMR WF TF OF * 1 Monitor-units necess.:
  27. 27. Clinical Treatment Planning: Dose Statistics Describing not the spatial information but: Min dose to the PTV Max dose to the PTV Mean dose to PTV Dose received by at least 95% of the volume Volume irradiated by at least 95% of the prescribed dose
  28. 28. Clinical Treatment Planning: Dose Volume Histograms (DVHs) Computer is summing voxels of known size in a certain dose range Direct or differential DVHs Cumulative or integrals DVHs Differential DVH Cumulative DVHs are more popular But always keep in mind: DVH (one line) also means loss of spatial informaTION Cumulative DVH
  29. 29. Clinical Treatment Planning: Portal Imaging Fluoroscopic detectors like simulator image intensifier Ionisation chamber detectors Amorphous silicon detectors Like fluoro detectors, light photons from metal plate produce electron- hole pairs in the photodiodes whose quantity is proportional to the intensity and is „translated“ into an image
  30. 30. Clinical Treatment Planning: Portal Films Localisation films (fast films) Generally produce better images Good for small fields or complex arrangements Verification films (slow films) Esp. for larger fields Single/double exposure
  31. 31. Computerized TPS for External Beam Radiotherapy (EBRT) Typical TPS hardware Central Processing Unit (CPU) Graphics display (typically 17“ – 21“), sometimes 2 monitors Memory and archiving functions (floppies, CDs, ODs, DVDs, rewritable harddisks, tapes,...) Digitizing devices (digitizers, scanners,...) Output devices (printers, plotters,...) Uninterruptable Power Supplies (UPS) Communications hardware (networks, modem,...) Air conditioning !
  32. 32. Computerized TPS for EBRT Configurations Possible Smaller TPSs normally have a stand-alone lay- out But also some communi- cation necessary for eg CTs and/or data transfer Backup ? Larger systems operate in a hospital-wide network Backing up on servers Specially trained personal necessary
  33. 33. Computerized TPS for EBRT Calculation Algorithms Proper understanding of manual dose calculation is mandatory ! Some listing of chronological development in ICRU 42 Present approach is to decompose the radiation beam into primary and secondary (scatter) components. Convolution/superposition algorithms Pencil beam algorithms MonteCarlo methods
  34. 34. Computerized TPS for EBRT Beam Modifiers Photons: Electrons: Jaws (eventually moving Cones or movable jaws) collimators Blocks (mostly made Shielding for irregular from lead or low melting metal-compositions fields with perspex blocks or Rose´s metal MLC with/without backuo – Take care on burning leafs) the skin at block edges Wedges Bolus materials Compensators ... ...
  35. 35. Computerized TPS for EBRT Data Acquisition – Machine Data Have to be entered prior to entering scanned curves Gantry-, couch-, collimator-, jaw- and table- movements, wedge directions and their limits Data for MLC, blocks, trays,... Electron cone data This work is often underestimated and leads to avoidable errors !
  36. 36. Computerized TPS for EBRT Data Acquisition – Beam Data Beam data required must be well understood Also, how the system works with them internally ! Photon scanning data typically contain depth doses and profiles with/without wedges and blocks. Scanning measurements for electrons are more difficult ! Non-scanning data like peak- or total scatter factors as well as absolute doses normally are measured with chambers and controlled with a second device. Data entry possible via digitizing tablet, keyboard or electronically Data-fitting outside the planning system is dangerous !
  37. 37. Computerized TPS for EBRT Commissioning and QA EN 62083 ! Comparison of input and output data ! Hardcopy of all curves, archiving in a logbook Control of hardware, eg digitizing tablet Control of communication, eg R&V system, CT, cutter Make your own plans (eg with oblique incidence or a combination photons/electrons) and try to verify it. ..........
  38. 38. Computerized TPS for EBRT Commissioning and QA (cont) Spot checks eg for determination of correct wedge calculation Written documentations of normalization and beam- weightings for usual plannings Same for DVHs and plan optimization Training (eg user meetings) and documentation for hard- and software I don´t like software changes by modem ! Scheduled QA (daily. weekly, monthly,...)
  39. 39. AAPM 85 TG 65, Aug ´04
  40. 40. AAPM 85, list of TPS Vendors and Algorithms