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  1. 1. IMPROVISED BEAM MODIFICATION TECHNIQUES IN TELECOBALT - A Feasibility Study A comparison between cobalt and linear accelerator-based IMRT treatment plans <ul><li>Principal Investigator : </li></ul><ul><li>Dr. Lokesh Viswanath M.D </li></ul><ul><ul><li>Professor & Head of Unit II, Dept of Radiation Oncology </li></ul></ul><ul><ul><li>Kidwai Memorial Institute of Oncology, Bangalore </li></ul></ul>BOG 24June2011 Presentation
  2. 2. Investigating team (Co-investigators) <ul><li>Staff, Dept of Radiation physics </li></ul><ul><li>Dr. Bindu Venugopal </li></ul><ul><li>Dr. Padma </li></ul><ul><li>Dr. Lavanya </li></ul><ul><li>post-graduate student, MDRT.KMIO </li></ul>
  3. 3. <ul><li>2015 Developing countries - 10 million CA cases PA </li></ul><ul><li>2011 - India 289 radiation therapy centers </li></ul><ul><ul><li>270 telecobalt machines </li></ul></ul><ul><ul><li>250 linear accelerators </li></ul></ul>INTRODUCTION
  4. 4. <ul><ul><li>Imaging – 3D rendering </li></ul></ul><ul><ul><li>Image fusion : CT/MR/PET/others </li></ul></ul><ul><ul><li>Virtual simulation </li></ul></ul><ul><ul><li>TPS </li></ul></ul><ul><ul><li>Hardware : MLC, Portal Imaging, real time imaging </li></ul></ul><ul><ul><li>Mechanics </li></ul></ul><ul><li>…… . have translated conventional LA into Advanced Teletherapy Machines capable of delivering sophisticated treatments like 3DCRT, IMRT, IGRT etc . </li></ul>Recent advances in -
  5. 5. 3DCRT/IMRT/IGRT <ul><li>3 DCRT has evolved and established itself as the Standard of Care </li></ul><ul><li>In comparison to conventional 2D/ basic 3D field setups, these advanced technologies have demonstrated hitherto unexpected gains in terms of Dose escalation and better normal tissue sparing – which - translate into therapeutic gain </li></ul>
  6. 6. <ul><li>Telecobalt, though a 1970`s technology, continues to be used for Radiotherapy in many developing countries. </li></ul><ul><li>These machines are capable of set geometric field shapes and are provided with accessories like universal shielding bocks and wedges. </li></ul><ul><li>Most centers use 2D planning system or 3 D plans + conformal blocks </li></ul><ul><li>Plans to ensure homogenous dose distribution generally results in unintentional larger volume of normal tissue irradiation </li></ul>
  7. 7. 2 D planning systems <ul><li>2 D plans with unintentional greater normal tissue irradiation </li></ul>
  8. 8. Most often in our routine clinical practice: - <ul><ul><li>we have patients who by virtue of their tumor location need definitive treatment on LA with 3DCRT/IMRT techniques. </li></ul></ul><ul><ul><li>these poor and needy patients cannot afford Linear Accelerator treatment </li></ul></ul><ul><ul><li>The treating hospital has cobalt machine alone and due to existing economic situation the centre may not be able to refer the patient to centers with LA with 3D or IMRT facility </li></ul></ul><ul><ul><li>How can we help such poor patients ? </li></ul></ul>
  9. 9. RATIONALE FOR THE STUDY <ul><li>This study was initiated to see if improvised 3D treatment plans can be generated for Telecobalt Machines without MLC using locally available material (universal shielding blocks) & other facilities. </li></ul><ul><li>To look at the feasibility of being able to deliver such special plans on a Telecobalt machines. </li></ul>
  10. 10. <ul><li>Subjects - absolute indication for IMRT </li></ul><ul><ul><li>Proximity to normal structures </li></ul></ul><ul><ul><li>Re-irradiation etc </li></ul></ul>MATERIALS & METHODS
  11. 11. Mould room techniques <ul><li>Pt Positioning: Supine/Prone </li></ul><ul><li>Immobilization : </li></ul><ul><ul><li>Head rest & base plate </li></ul></ul><ul><ul><li>thermoplastic material </li></ul></ul>
  12. 12. CT simulation <ul><li>flat couch </li></ul><ul><li>Lasers </li></ul><ul><li>Markers </li></ul><ul><ul><li>Ant </li></ul></ul><ul><ul><li>Rt & Lt Lat </li></ul></ul>
  13. 13. <ul><li>Telecobalt Theratron 780C or E </li></ul><ul><ul><li>Without MLC </li></ul></ul><ul><ul><li>Universal Shielding Block & tray </li></ul></ul><ul><ul><li>+ Cerrobend Shielding Blocks and Tray </li></ul></ul>Machine
  14. 14. CT TPS <ul><li>Available 3d or IMRT Computer Treatment planning system like ECLIPSE with CO 60 beam parameters can be used </li></ul><ul><li>Centers which do not have planning system can transfer the patients simulation CT scan data to higher collaborating centers through CD or Internet and obtain the special plan for treatment execution at their respective centers </li></ul>
  15. 15. Virtual Simulation <ul><li>CT Scan Data: DICOM format </li></ul><ul><li>ECLIPSE TPS :Ver 8.9 </li></ul><ul><li>Contouring : Normal Structures and GTV/CTV/PTV </li></ul><ul><li>PTV = Target volume </li></ul><ul><li>Co 60 Beam Parameters </li></ul>
  16. 16. TPS Planning Process <ul><ul><li>Optimal beam positions were selected taking into consideration the target volume & normal tissue to be spared. </li></ul></ul><ul><ul><li>Optimal field placements were chosen for Universal shielding block. </li></ul></ul><ul><ul><li>For oblique & lateral fields Customized Shielding tray for each field with cerrobends blocks with locking screws were planned selectively. </li></ul></ul><ul><ul><li>3D plans were generated. </li></ul></ul>
  17. 17. Conformal Radiation <ul><li>Two broad subtypes : </li></ul><ul><ul><li>Techniques aiming to employ geometric field shaping alone ( 3D-CRT) </li></ul></ul><ul><ul><li>Techniques to modulate the intensity of fluence across the geometrically-shaped field (IMRT) </li></ul></ul>Geometrical Field shaping Geometrical Field shaping with Intesity Modulation
  18. 18. <ul><li>Logical Manual optimal beam technique </li></ul><ul><ul><li>uses the concept of jaw based IMRT, where in the resolution of optimization is low compared to MLC/Micro MLC </li></ul></ul><ul><ul><li>Since manual forward plan technique was used, a lower resolution of 4 or 9 pixel was adapted </li></ul></ul><ul><ul><li>BEV: Blocking of normal structure in the selected quadrant / pixel is adopted </li></ul></ul><ul><ul><li>Field in Field Concept was also used to created sub fields with blocked zones </li></ul></ul><ul><ul><li>Field Weighting & optimization </li></ul></ul><ul><ul><li>Calculation was done using PBC ALGORITHM. </li></ul></ul>Improvisation of 3D plan
  19. 19. <ul><li>Gantry positions selected : to place the available universal shielding blocks </li></ul><ul><li>Each field: shielded zones transferred at tray position to OHP sheet for manual setup. </li></ul>
  20. 20. BEV : 4 Quadrant
  21. 21. BEV : 9 Quadrant
  22. 22. BEV : 9 Quadrant
  23. 23. <ul><li>Plan approval Process </li></ul><ul><li>Target volume TV = PTV: isodose coverage </li></ul><ul><ul><li>Cobalt Plans: ~ 90% </li></ul></ul><ul><ul><li>IMRT : PTV – 95% </li></ul></ul><ul><li>Field sizes noted </li></ul><ul><li>Tracing of fields and shielded areas were done on separate OHP sheets for each field </li></ul><ul><li>If there was a chance of universal shielding blocks sliding on the shielding tray, Slotted tray or perforated tray was used. </li></ul><ul><li>cerrobend shielding was prepared and anchored separately. </li></ul>
  24. 24. Case 1 <ul><li>Male </li></ul><ul><li>45 yrs </li></ul><ul><li>multiple myeloma – frontal bone </li></ul><ul><li>Current status - recurrence in the base skull and nasal cavity </li></ul><ul><li>Re-irradiation </li></ul>
  25. 26. Conventional 3 D Plan : Filed AP & 2 Lateral with shield
  26. 27. Improvised 3D Plan for Telecobalt
  27. 28. IMRT Plan : 95% isodose covering PTV Cobalt Plan: 90% isodose covering TV
  28. 29. IMRT Plan: Good coverage in other sections Cobalt Plan: Slight dipping of isodose lines near the lt eye due to fixed shielding block , can be improved with Cerrobent blocks
  29. 30. DVH : Cobalt plan has comparatively similar DVHG to IMRT with considerable normal issue low doses
  30. 31. Comparison of Mean Dose to PTV and adjacent Normal tissue
  31. 32. RT Technique used: Fields, Sub Fields and Shielded Zones: 8 Field
  32. 33. Field Positions: AP(2), RAO, LAO, Rt Lat (2), Lt Lat(2)
  33. 35. Plan Implementation and Treatment Delivery Verification
  34. 36. Setup Time <ul><li>Exposure time 8 fields - 2.85 minutes </li></ul><ul><li>Patient positioning, shield placement, gantry rotation- 8-10 minutes </li></ul><ul><ul><li>Total time- 10-12 minutes. </li></ul></ul>
  35. 37. CASE 2 <ul><li>Chondrosarcoma – medial wall of the orbit </li></ul><ul><li>Status Post Operative with + margin </li></ul>
  36. 45. CONCLUSION <ul><li>3DCRT/IMRT type of treatment plans are feasible on conventional telecobalt machine with meticulous planning. </li></ul><ul><li>It is possible to generate treatment plans similar to jaw based IMRT with a low resolution on telecobalt without multileaf collimator. </li></ul><ul><li>Further study with universal shielding blocks and conformal blocks with necessary QA checks are indicated to improve this technique. </li></ul><ul><li>Caution: This technique is not applicable for all patients. </li></ul>
  37. 46. thank you