The Measurement of Absorbed Dose in Thyroid, Parathyroid, Eye Lens and Gonads in Radiotherapy of Head and Neck Epithelial Tumors by Thermoluminescent Dosimeter (TLD) Method
Introduction: Owing to the abundance of head and neck epithelial tumors and their treatment by radiotherapy and the complications of ionizing rays on the organs that may be in the radiation field and/or in the vicinity of radiation field during radiotherapy as well as the sensitive organs such as gonads to the radiation, to be aware of the absorbed dose of such organs in radiotherapy of head and neck tumors and to reduce the absorbed dose of these organs seem a very crucial issue. This study aims to measure the absorbed dose of thyroid, parathyroid, eye lens and gonads (ovaries and testicles) in radiotherapy of head and neck epithelial tumors and to compare it with the tolerance dose values (TD5/5) of each organ.
Materials and Methods: In this research, the received dose to the thyroid, parathyroid, eye lens and gonads in designing a 2-D treatment was measured by TLD-100 for curing the head and neck cancers by Cobalt-60 Device on a tissue-equivalent human phantom and on 20 patients (10 men, 10 women) with head and neck epithelial cancer. The values of absorbed dose were compared using T-test at various depths in phantom and in the area of intended organs. Then, the results were analyzed on Excel®-2010.
Results: According to the measurements on phantom, the results of absorbed dose are 176.5±17.3cGy, 6.22±0.14 cGy, 0.37±0.07 cGy and 0.12±0.08 cGy for thyroid-parathyroid, eye lens, ovaries, and testicles, respectively. Meanwhile, the values of average absorbed dose based on measurements on patients are 145.4±12.7 cGy, 7.79±0.36 cGy, 0.26±0.03 cGy and 0.18±0.08 cGy for thyroid-parathyroid, eye lens, ovaries, and testicles, respectively.
Discussion and Conclusion: The measurements on phantom at various depths and the analysis of results showed that the absorbed dose does not entail a significant difference in the thyroid and parathyroid regions during the radiotherapy of head and neck epithelial tumors and in the assumed treatment fields (P-Value<0.05). There was a significant difference in the area of ovaries in the absorbed dose of various depths (P-Value<0.05). The average absorbed dose of above-mentioned organs is smaller than their tolerance dose (TD5/5).