SU‐E‐J‐161: In Vivo Dose Measurement During IGRT with KV Cone Beam CT

Purpose: The purpose of this study is to perform in vivo dose measurements during image guidance kV CBCT using MOSFET dosimeter. Methods: Dose measurements were performed on a Clinac 2100 C/D unit with the integrated kV CBCT.for patient positioning. CBCT imaging of head and neck is usually performed with full cone beam and half gantry rotation and that of breast and pelvis with half cone beam and full gantry rotation. In this study we used mobile MOSFET dosimeters along with dose verification system supplied by the BEST Medicals Canada. The MOSFETs used in this study are of high sensitivity, i.e 9 mV/cGy for standard and 30 mV/cGy for high bias setting. The mobile MOSFETs were calibrated against parallel plate ion chamber, with air kerma calibration factor (Nk) traceable to the primary standard. Radiation dose measurements during kV CBCT were performed for patients undergoing IGRT treatments for head & Neck, breast and pelvis. The kV CBCT doses to ipsi‐lateral and contralateral eyes were measured by placing the MOSFET on the eye lid for 15 patients. Similarly doses to ipsi‐lateral and contra‐lateral breasts for kV CBCT of breast patients and on the surface of the pelvis for prostate patients were measured. Results: The maximum doses to the contra‐lateral and ipsi‐lateral eyes were 4.0 mGy and 5.7 mGy respectively with an average of 2.0 and 3.0 mGy. Breast dose measurements performed on five patients showed maximum dose of 11 mGy and 9.1 mGy to the ipsi‐lateral and contra‐lateral breasts with an average of 10.7 mGy and 6.6 mGy respectively. The average dose to the surface of the pelvis was 31 mGy. Conclusion: The dose measurements performed in this study closely agrees with those of published values. Dose reduction strategies should be employed to reduce dose during IGRT. Funded by the Board of Research in Nuclear Sciences, Department of Atomic Energy, Govt. of India