Studies of dose distribution to Lung and Stomach and Estimation of Second Cancer Risk due to Outfi eld Dose in Radiotherapy with 60Co Teletherapy Beam

Abstract

A critical component of the radiation regimen for treating cancer patients is the precise dose delivery to the treatment organ while minimizing the dose to the healthy tissue. This study aims to evaluate in-fi eld organ dose and dose distribution outside the target organs to estimate the excess lifetime risk of second cancer. The study was carried out with a male Alderson Rando Phantom. 20 sets of thermoluminescence dosimeters (MTS-100) were used in this study. The in-fi eld organs absorbed dose was measured by inserting TLDs at diff erent geometrical depths of the left lung, right lung, and stomach, and for peripheral organs skin dose TLDs were placed at the surface of the corresponding organs. Target organs were irradiated at 100 cGy and 200 cGy by a 60Co teletherapy unit, and irradiated TLDs were read out by a RE-2000 TLD reader. For precise dose delivery to the cancerous organs by 60Co teletherapy, the depth dose correction factor for lung cancer treatment is 0.8667 ± 0.01, and for the stomach is 0.7856 ± 0.017. In the case of the treatment for the lung and stomach, the closest organs received signifi cant doses compared to the other distant organs. Thus, the risk of second cancer due to the peripheral dose is obtained. The stomach is at the highest risk when the lung is the target and the liver is at the highest risk when the stomach is the targeted organ.