P0077 Risk assessment of radiation-induced secondary cancers when treating nasopharyngeal carcinoma with intensity modulated radiotherapy

Abstract

Background This study investigated a method to evaluate the risk of radiation-induced secondary cancer based on whole-body dose measurements in patients with nasopharyngeal carcinoma (NPC) undergoing intensity modulated radiotherapy (IMRT). Methods We determined the relative position and contour of organs with the RANDO phantom to obtain accurate dose assessments for organs out-of-field of radiation. The treatment planning was simulated for RANDO phantom after the verifications of clinical doctors. Thermoluminescent dosimeters (TLDs) were placed in the phantom to estimate the actual organ doses delivered by IMRT. In this treatment planning for NPC with IMRT, the planning target volume (PTV) was 1066cm 3 and the prescribed dose required to deliver 6996 cGy in 33 fractions was 212 cGy for each irradiation. Findings The dose evaluation for the patients with NPC receiving IMRT showed that the highest equivalent dose received by their lungs was 4013.31±381.19mSv. According to the tissue weighting factors 60 and 103, recommended by the International Commission on Radiological Protection (ICRP), had whole-body effective doses of 998.11±0.46. 75mSv and 961.99±46.24mSv, respectively. The corresponding risks of radiation-induced secondary cancer obtained were 4.99% Sv −1 and 3.85% Sv −1 , respectively. Interpretation We showed that the risk assessments of radiation-induced secondary cancer of NPC with IMRT supported previous studies.