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The external beam radiotherapy and Image-guided radiotherapy (3)

The external beam radiotherapy and Image-guided radiotherapy (3). Somvilai Mayurasakorn , MD. Division of Therapeutic Radiology and Oncology, Faculty of Medicine, Chiang Mai University. Machine characteristics. 6 MV accelerator 3.5 MV: MVCT No flattening filter

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The external beam radiotherapy and Image-guided radiotherapy (3)

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  1. The external beam radiotherapy and Image-guided radiotherapy (3) SomvilaiMayurasakorn, MD. Division of Therapeutic Radiology and Oncology, Faculty of Medicine, Chiang Mai University

  2. Machine characteristics • 6 MV accelerator • 3.5 MV: MVCT • No flattening filter • Field Size in width: 40 cm • Treatment length: 160 cm 6 MV LINAC 64 leaf MLC Pitch = Distance Traveled Per Rotation Slice Width MVCT detector array

  3. Machine characteristics • TOMO Binary multileaf collimator • Optical sensors and pneumatic driven • Binary 64 leaf MLC • MLC leaf width: 6.25 mm (ISO) • Field Size in length: 1, 2.5 and 5 cm by a set of moveable jaws 100 times faster MLC Speed MLC leaves that move at 250 cm/s to open or shut in 20 milliseconds

  4. Machine characteristics • Treatment is delivered through the full 360° • This is approximated in the planning process • by 51 different beam directions • With a spacing of just over 7° • The rate of movement of the couch, relative to the • thickness of the fan beam, is referred to as the pitch Allows treatment of very long volumes without field junctions Slice width

  5. Helical Tomotherapy Process • Imaging / Contouring • Planning / Optimizing • In-room megavoltage CT imaging • Image Registration (IGRT) • Treatment delivery Adaptive RT: Dose Guidance (Recalculation / Reconstruction ) Dose Modification

  6. Helical Tomotherapy • The complex integrated technologies • With multiprofessional team • Physicist/dosimetrist • Radiation oncologist • Radiation therapist • Radiographer

  7. Helical Tomotherapy Clinical use : Rationale for patient selection • Treat patients who were considered likely to benefit from • IGRT : to inform repositioning • IMRT: complex target volume shapes, adjacent critical normal tissue structures • Combined IGRT/IMRT approach University of Cambridge /Burnet et al. Clinical Oncology 2010;22:294–312

  8. Helical Tomotherapy University of Cambridge /Burnet et al. Clinical Oncology 2010;22:294–312

  9. Helical Tomotherapy Treatment planning • Inverse planned IMRT concepts • Dose volume constraints : typically same as conventional IMRT planning • For all target and normal tissue structures

  10. Helical Tomotherapy Treatment planning Tomotherapy Planning Parameters • Field Size in length : Jaw size • 5, 2.5 or 1 cm • Modulation factor • ratio of maximum leaf opening time to mean leaf opening time • Pitch

  11. The external beam radiotherapy and Image-guided radiotherapy (4) SomvilaiMayurasakorn, MD. Division of Therapeutic Radiology and Oncology, Faculty of Medicine, Chiang Mai University

  12. Helical Tomotherapy • Smaller field widths, smaller pitches and higher modulation factors Tomotherapy Planning Parameters More conformal plans But increased treatment time !!

  13. Helical Tomotherapy Image acquisition and matching • MVCT fan-beam images • In-plane resolution of 0.78 mm at the bore center ; mean beam energy = 0.75 MeV • Set up slices thickness of 2, 4 or 6 mm • ‘fine’, ‘normal’ and ‘coarse’ settings • The scan length is kept as short as possible • always within the region of the PTV

  14. Helical Tomotherapy Image matching

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