SU‐E‐T‐260: Risk of Second Cancer From Scattered Dose During the Radiation Therapy with Lung Cancer

Purpose: To compare the organ equivalent doses (OEDs) from scattered and leakage doses following intensity‐modulated radiotherapy (IMRT), volumetric arc therapy (VMAT) and tomotherapy (TOMO) in patients with lung cancer. Methods: IMRT, VMAT and TOMO were planned for the lung cancer patients. The OEDs are estimated from the measured corresponding secondary doses during irradiation at various points 20 to 80 cm from the iso‐center by using the radio‐photoluminescence glass dosimeter (RPLGD) on the surface. Results: The secondary dose per Gy from IMRT, VMAT and TOMO for lung cancer, measured 20 to 80 cm from the iso‐center, are less than 2.0, 1.5 and 1.0 cGy, respectively. The normalized mean values of relative OED of secondary dose of IMRT, VMAT and TOMO are 100%, 89% and 42% for thyroid, 100%, 82% and 42% for pancreas, 100%, 78% and 49% for bowel, 100%, 73% and 73% for rectum, 100%, 74% and 82% for prostate. The secondary dose and OED from TOMO became similar to those from IMRT and VMAT as the distance from the field edge increased. Conclusion: OED based estimation suggests that the secondary cancer risk from TOMO is less than or comparable to the risks from conventional IMRT and VMAT in patients with lung cancer.