Mazonakis M, Damilakis J, Varveris H, Fasoulaki M, Gourtsoyiannis N
Department of Medical Physics, University Hospital of Heraklion, Heraklion, Crete, Greece.
Int J Oncol. 2003 Jan;22(1):221-5.
The purpose of this study was to estimate the risk of thyroid cancer induction attributable to brain radiation therapy in adult and pediatric patients. An anthropomorphic phantom was used to simulate treatment of brain tumors with two lateral opposed fields. Thyroid dose was measured using thermoluminescent dosimeters. Phantom measurements were performed for all possible field sizes that may be applied during brain radiotherapy in adults and children. The dependence of the thyroid dose on the distance from the irradiation field and on the presence of beam modifiers in the primary beam was investigated. All phantom exposures were generated with a 6 MV photon beam. Thyroid dose was found to vary from 9.6 to 89.4 cGy and from 8.0 to 194.0 cGy depending upon the field size used and the thyroid location in respect to the field edge for adults and children respectively. The excess relative risk of thyroid cancer induction for exposed children was estimated to be 0.6-14.9. The corresponding excess relative risk for adults was 0.1-1.1. The introduction of lead blocks or wedges into the primary beam may result in a considerable increase of the risk of thyroid cancer due to the increase of the thyroid dose. This study shows that brain radiotherapy during childhood may be associated with an increased risk of secondary thyroid cancer while the risk in adult patients is much smaller.
本研究的目的是评估成人和儿童患者因脑部放射治疗导致甲状腺癌的风险。使用一个人体模型来模拟用两个对侧野治疗脑肿瘤的过程。使用热释光剂量计测量甲状腺剂量。针对成人和儿童脑部放射治疗期间可能应用的所有可能野大小进行了模型测量。研究了甲状腺剂量对距照射野距离以及原射线中射束修正器存在与否的依赖性。所有模型照射均使用6兆伏光子束产生。结果发现，根据所使用的野大小以及成人和儿童甲状腺相对于野边缘的位置，成人甲状腺剂量在9.6至89.4厘戈瑞之间变化，儿童甲状腺剂量在8.0至194.0厘戈瑞之间变化。估计受照射儿童诱发甲状腺癌的超额相对风险为0.6至14.9。成人相应的超额相对风险为0.1至1.1。由于甲状腺剂量增加，在原射线中引入铅挡块或楔形板可能会导致甲状腺癌风险显著增加。本研究表明，儿童期脑部放射治疗可能与继发性甲状腺癌风险增加有关，而成人患者的风险则小得多。
