Secondary Cancer Risks in Out-of-field Organs for 3-D Conformal Radiation Therapy

Abstract

The introduction of more advanced radiation therapy techniques such as 3-D conformal radiation therapy (CRT) and intensity-modulated radiation therapy (IMRT) require higher monitor units per target dose to the patient, leading to significant increase of radiation doses to out-of-field organs. In the present study, the secondary cancer risks in the out-of-field organs were determined for several treatment cases of 3-D CRT using 6 MV and 10 MV x-ray beams. For this, 14 radiosensitive organs were defined in an ATOM adult male phantom and a total of 100 LiF:Mg,Ti thermoluminescence dosimeter (TLD) chips were inserted in the phantom to measure the radiation doses to the radiosensitive organs. The estimated values of total cancer risks in the out-of-field organs were within the range of 0.02-0.04 for the treatment cases considered in the present study. For the 6 MV x-ray beam, the chest treatment case showed higher cancer risk than the prostate and neck treatment cases, which is mainly due to the fact that, for the chest treatment case, the organs were located close to the target volume. Finally, the 10 MV x-ray beam showed slightly higher cancer risk than the 6 MV x-ray beam for the treatment case considered in the present study.