Somvilai Mayurasakorn, MD. Division of Therapeutic Radiology and Oncology, Faculty of Medicine, Chiang Mai University 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 Field Size in width: 40 cm Treatment length: 160 cm 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 MVCT detector array Pitch = Distance Traveled Per Rotation Slice Width

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 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

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 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

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

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

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 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

Helical Tomotherapy

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

Treatment planning Tomotherapy Planning Parameters 1.Field Size in length : Jaw size – 5, 2.5 or 1 cm 2.Modulation factor – ratio of maximum leaf opening time to mean leaf opening time 3.Pitch Treatment planning Tomotherapy Planning Parameters 1.Field Size in length : Jaw size – 5, 2.5 or 1 cm 2.Modulation factor – ratio of maximum leaf opening time to mean leaf opening time 3.Pitch Helical Tomotherapy

Somvilai Mayurasakorn, MD. Division of Therapeutic Radiology and Oncology, Faculty of Medicine, Chiang Mai University Somvilai Mayurasakorn, MD. Division of Therapeutic Radiology and Oncology, Faculty of Medicine, Chiang Mai University

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

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 Helical Tomotherapy

Image matching