Estimation of Absorbed Dose to the Organs with High Risk of Radiation Exposure During External Radiotherapy of Esophageal Cancer

External radiotherapy is one of the treatments of cancer in which the risk of radiation exposure of organs is a continue concern. The goal of present study was to measure surface and depth doses in an anthropomorphic phantom and surface dose in patients suffering upper esophageal cancer undergoing radiotherapy. In this study, surface and depth doses and surface doses was measured in phantom and patients, respectively. The phantom had some places to insert thermoluminescence dosimeters (TLDs) in eye, parotid, submandibular glands, and thyroid, spine, sternum and trachea areas. As this treatment performs in two phases, the dosimetry was done in both phases. In phase I, treatment was performed using parallel opposed (AP-PA) technique with a dose of 2 Gy/ fraction and in phase II, treatment was done with three beam technique (an oblique and AP-PA) with a dose of 1.8 Gy/fraction in 5 fractions. In regions out of treatment field such as parotid and eye, measured doses were in the range of 1.36-7.5 cGy. Thyroid doses differ in two phases; in phase I thyroid was in treatment field and its dose in the phantom was 30.84±0.88 cGy and in phase II it was in the outside of the treatment field and its dose was 5.04±0.11 cGy, whereas in patients in phase I the dose was 107.78±10.84 cGy and in phase II was 6.73±1.17 cGy. In other measurement points, there were no significant differences between measured and calculated values with TLDs and treatment planning system, respectively. Discussion & Comparing calculated doses obtained from treatment planning system and measured doses by TLDs, it was observed that these values have little differences in regions out of the treatment field which is due to scattered radiation. According to our results, given the critical role of thyroid and its high risk of radiation exposure, it is necessary to consider thyroid for defining radiation fields.