Evaluation of Photon and Neutron Dose Distributions in a Mixed Radiation Field Using an Optically Stimulated Luminescence

光激發光劑量計在放射治療中光中子劑量之評估

邱筱文(Hsiao Wen Chiu) ； 丁健益(Chien Yi Ting) ； 蔡雅涵(Ya Han Tsai) ； 黎俊蔚(Chun Wei Li)

《台灣應用輻射與同位素雜誌》 15卷4期 (2019/12) Pp. 1799-1803

摘要

High-energy linear accelerators can produce neutrons when the output energy is greater than 10 MV, which could increase the additional dose in patients and workers. The aim of this study was to assess the radiation dose from neutrons and photons of workers and patients in different-sized fields using neutron-type optically stimulated luminescence dosimeters (OSLDs). Neutron and photon doses from a 10-MV photon energy Elekta synergy linear accelerator with different field sizes (10×10 cm2, 15×15 cm2, and 20×20 cm^2) were measured using OSLDs placed in a solid water phantom (20×20×20 cm^3) in this study. Neutron and photon doses were measured at the surface and at a depth of 5 cm in the phantom. The data were collected from three sites: the dress desk, mould cabinet, and proximal maze in the treatment room. The radiation dose was measured at two time points: immediately and 5 minutes after irradiation. The results showed that an increase in the field size caused an increase in neutron dose. However, no neutron dose was measured at a depth of 5 cm in the phantom. Instead, the photon dose at the 5 cm depth was about 1.16-1.8 times higher than that on the surface. The mean in-field doses were 942.1 mSv, 958.9 mSv, and 993.8 mSv in field sizes of 10×10 cm^2, 15×15 cm^2, and 20×20 cm^2, respectively. The mean out-field doses were 76.7 mSv, 113.6 mSv, and 137.8 mSv in field sizes of 10×10 cm^2, 15×15 cm^2, and 20×20 cm^2, respectively. Significant reductions (91.9%, 88.2%, and 86% in field sizes of 10×10 cm^2, 15×15 cm^2, and 20×20 cm^2, respectively) were found in out-field doses compared with in-field doses. After irradiation, the highest dose was found at the hospital dress desk; this was also the only site at which neutron radiation was found among the three investigated sites of the environment. Radiation doses reduced by 100%, 66.6%, and 99.6% at the proximal maze, mould cabinet, and hospital dress desk 5 minutes after irradiation, respectively. Neutrons are indeed generated when irradiated by a 10 MV linear accelerator. OSLDs can easily measure photons and neutrons. In order to reduce photon and neutron doses, appropriate protection is imperative for patients and workers. At the end of each radiotherapy session, the radiologist is suggested to wait for a few minutes before entering the treatment room to reduce unnecessary dose.

關鍵字

Radiation ； Neutron ； Dosimetry ； OSLD

並列摘要

高能量直線加速器超過10MV光子能量會產生中子，可能會額外增加工作人員及病人劑量。本研究目的使用中子型光激發光劑量計來評估工作人員及病人在不同輻射照野產生中子與光子之輻射劑量。本研究使用10MV直線加速器（Elekta synergy）進行量測，將中子型光激發光劑量計置放在20×20×20cm^3之水假體。改變不同輻射照野10×10、15×15和20×20cm^2，探討在表面及深度5公分之中子與光子輻射劑量之變化。另外也評估周圍環境劑量包括治療床、置物架及迷宮位置在治療後0分鐘及5分鐘之劑量。結果顯示隨著輻射照野增加中子輻射劑量也會增加，但在5公分假體深度位置並未量測到中子劑量之產生。在光子劑量部分，5公分深度劑量大於表面劑量約1.16-1.8倍。比較在輻射照野外及照野內光子輻射劑量之變化，在10×10cm^2,15×15cm^2, and 20×20cm^2輻射照野內平均為42.1mSv、958.9mSv和993.8mSv。照野外與照野內之輻射劑量相比平均降低91.9%,88.2%,及86%。在周邊環境光子劑量部分，在治療床之輻射劑量最高。另外比較治療後0分鐘及5分鐘輻射劑量之差異，5分鐘後輻射劑量在迷宮、置物櫃及治療床之劑量分別降低100%,66.6%, and 99.6%。當直線加速器光子能量超過10MV會產生中子，中子型光激發光劑量計可容一量測光子與中子劑量。為了降低光子與中子的劑量，可適當給予病人及工作人員防護。另外也建議治療後可等待幾分鐘後再進治療室可減少不必要的劑量。

並列關鍵字

輻射 ； 中子 ； 劑量 ； 光激發光劑量計