四川省调强放疗光子线束吸收剂量和二维剂量分布验证研究

目的 用粉末热释光剂量计（TLD）和胶片测量调强放疗（IMRT）光子线束吸收剂量和二维剂量分布验证研究。方法 用国际原子能机构（IAEA）提供的聚苯乙烯固体模体，经CT扫描，影像传给放射治疗计划系统（TPS）制定放疗计划，源皮距90 cm，深度10 cm，照射野5 cm×5 cm，计算吸收剂量6 Gy相应的监督单位（MU）。根据四川省各个地域医疗水平、放射治疗开展情况和物理师技术力量等因素选择了7家三级甲等医院，每家医院选取1台常用的加速器，7台加速器生产厂家分别为瓦里安、医科达和西门子，并分别实施调强放疗计划。医院使用的均质固体模体，尺寸30 cm×30 cm，25 cm×25 cm的胶片放在模体上，厚度>20 cm的固体模体板覆盖在胶片上面，射线束中心对准胶片中心，实施调强放疗计划的验证。结果 7台加速器中，TLD吸收剂量与TPS计划剂量相对偏差分别为1.4%、3.7%、-2.5%、-0.3%、4.9%、4.9%和5.0%，满足IAEA要求的±5%以内；胶片吸收剂量与TPS计划剂量相对偏差分别为4.7%、4.3%、1.5%、3.9%、-1.6%、3.3%和-1.3%，满足IAEA要求的±5%以内；5台加速器胶片二维剂量分布3 mm/3%通过率分别为99.9%、98.5%、98.5%、97.9%和70.0%，其中4台加速器满足IAEA要求的通过率为90%以上，1台不满足要求。结论 用TLD和胶片测量调强放疗光子线束野吸收剂量和二维剂量分布验证，科学实用，经济方便，可为放射治疗计划提供质量保证。

Verification of photon beam field absorbed dose and two-dimensional dose distribution in intensity modulated radiotherapy in Sichuan province

Objective To measure absorbed dose and verify two-dimensional dose distribution from IMRT MLC using thermoluminescence dosimeters (TLDs) and films. Methods The teflon phantom was scanned by CT and its images were transmitted to TPS for planning. The 6 Gy-corresponding MUs were calculated at 90 cm SSD and 10 cm depth and on 5 cm×5 cm radiation field. All the plans were implemented at 7 medical linear accelerators, which were produced by Varian, Elekta and Siemens and selected from 7 third-grade first-class hospitals according to the technical conditions of various regions in Sichuan province. The homogeneous solid phantoms used in hospitals were covered by 30 cm×30 cm and 25 cm×25 cm films. Then, the films were covered by thicker-than-20 cm phantoms. Finally, the plans were implemented by aligning the center of beams to the films center. Results The relative deviations of the measured absorbed dose to TPS-planned dose were 1.4%, 3.7%, -2.5%, -0.3%, 4.9%, 4.9%, 5.0% for TLDs and 4.7%, 4.3%, 1.5%, 3.9%, -1.6%, 3.3%, -1.3% for films, respectively, all consistent with the limit of less than 5%. The passing rates of 2D dose distribution (3 mm/3%) were 99.9%, 98.5%, 98.5%, 97.9% and 70.0% for 5 accelerators, with only one not consistent with the requirements. Conclusions It is convenient to measure the absorbed dose to photon beam field and verify two-dimensional dose distribution using TLDs and films, which can provide quality assurance for radiation treatment plans.