Secondary cancer risk estimations following the gastric cancer radiotherapy

Advances in gastric cancer radiotherapy have led to overall survival increments. Despite the radiotherapy advantages, there is a risk of developing secondary cancers caused by unintended radiations inside the out-of-field organs. This study aims to evaluate the risk of subsequent secondary cancers after the 3D-conformal radiotherapy of gastric cancer. The absorbed doses inside the out-of-field organs for 30 patients were measured by performing the generalized equivalent uniform dose formalism. Furthermore, the Monte Carlo simulation approach using the MCNPx code was applied to calculate the absorbed dose in more non-target organs through ICRP-110 voxelized phantom. Finally, secondary malignancies risks were estimated via NCRP-116 and BEIR VII risk models. The obtained results indicated that all distant organs from the treatment field had a negligible dose distribution compared with near organs to the tumor. In the case of dose volume histogram (DVH), the spinal cord had the largest absorbed dose, while the maximum equivalent dose of about 38.9 ± 0.03% Sv was found for liver through MC simulation. The highest risk of secondary cancers in this study was found for liver with the use of the BEIR risk model. Furthermore, by performing the NCRP-116 model, the spinal cord and left kidney had the maximum risk of developing secondary cancers. The calculated risks for most of the near organs to the tumor were relatively higher than those for distant organs. So, reducing the received dose by these healthy organs during the radiotherapy is quite mandatory by sparing these healthy organs from the radiation field using appropriate shields.