OC-0568: Necessity of using an image modality to improve IORT dosimetry

D. Bouzid, N. Boussion, P.F. Dupré, O. Pradier, P. Miglierini, D. Visvikis
2015 Radiotherapy and Oncology  
3rd ESTRO Forum 2015 S277 this study is to report the measured body exposures treated with single dose intra-operative electron radiation therapy (IOERT) in a large cohort of patients and to analyze which beam parameters impact the body exposure. Materials and Methods: During an almost 5-year period, more than 500 Partial Breast Irradiation (PBI) procedures have been performed with IOERT in our institution for pT1N0 unicentric ductal breast carcinoma. A dose of 21 Gy was prescribed at the 90%
more » ... cribed at the 90% isodose depth. Beam delivery was achieved with a Mobetron 1000 (Intraop, Sunnyvale, Ca). This mobile accelerator produces 4, 6, 9 and 12 MeV electron Beams with a 10Gy/min dose rate. Although the Mobetron is self-shielded device, a small component of straight X-rays radiation is always present during treatment delivery. In order to measure their body exposure coming from this straight radiation, three LiF Thermo-Luminescent Dosimeters (TLD) were positioned on each patient, respectively on the thyroid, on the contralateral breast and at the gonads level. The TLD were placed in an Aluminum container thick enough to provide electronic equilibrium and to stop any scattered electrons. TLDs were directly read just after PBI in a manual Harshaw reader under Nitrogen flow. As a comparison, the body exposure in a series of 30 BCT patients treated with 6 MV external beams was measured in the same way. Results: Mean doses for PBI treatments on the thyroid, contralateral breast and gonads were 0.82, 0.41 and 0.14 cGy respectively. Higher energy beam gives significant higher body exposure. The field size, ranging from 35 mm to 65 mm does not influence the body exposure. On the other hand, the treated quadrant has an impact on measured doses. Patients treated with external radiation received much higher body doses, from 25 times to more than 100 times higher for the contralateral breast. Conclusions: As radiation protection is concerned, IOERT is a safe procedure and gives very small body doses, unlikely to increase the carcinogenetic risk significantly, especially in the contralateral breast. Pregnant women might, in certain circumstances and with additional safety measures, be treated with the IOERT approach with an acceptable fetal dose. OC-0568 Necessity of using an image modality to improve IORT dosimetry
doi:10.1016/s0167-8140(15)40562-6 fatcat:526ldl575jcp3gj3g7oz4jdc4i