Secondary cancer risks in out-of-field organs for 3-D conformal radiation therapy

The risk of secondary cancers after radiation therapy has become an important issue, mainly because advanced treatment techniques such as 3-D conformal radiation therapy (CRT) and intensity-modulated radiation therapy (IMRT) tend to increase the radiation dose to out-of-field organs. Moreover, cancer patients' average survival period, following those advances in treatment techniques, also has increased, effectively raising the risks for the same levels of radiation exposure. In the present study, the secondary cancer risks to out-of-field organs were determined for some representative cases of 3-D CRT by measuring organ doses with LiF thermoluminescence (TL) dosimeters and an ATOM^TM male phantom. Our results show that the secondary cancer risks are similar (difference: < 20%) for 6 and 10 MV X-ray beams for the same prostate treatment case. The total secondary cancer risks of the out-of-field organs were on the order of 2-4% for the treatment cases considered in the present study. (author)