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摘要:
目的 探讨二维电离室矩阵系统MatriXX用于近距离治疗剂量分布验证的可行性。 方法 利用井式电离室测量有效测量点60 s的照射量, 结合电离室本身的刻度因子及环境修正因子计算出放射源192Ir的活度。使用该放射源通过Valencia皮肤施源器、等效固体水模, 完成对EBT3免洗胶片的刻度, 获取剂量灰度曲线, 找到经过Valencia皮肤施源器均整后的192Ir辐射野中轴的百分深度剂量(percentage depth dose, PDD)曲线后, 即可对MatriXX进行刻度, 得到剂量刻度因子Kuser。采用Freiburg Flap施源器和插植针及固体水建立模体, 获取CT图像, 在计划系统内完成管道重建以及剂量分布计算, 传输至后装治疗机执行计划, 通过MatriXX获取特定冠状层面内的剂量分布与计划系统所得剂量分布进行比较, 利用软件分析测量与计划剂量分布结果。 结果 经Valencia皮肤施源器均整后的192Ir辐射场的剂量分布类似加速器的射野, 横向及纵向对称性分别为0.17%和0.16%, PDD参考剂量点位于施源器表面下3 mm处, 施源器表面下11.6 mm处的PDD为46.5%。经该辐射场刻度的MatriXX测量的剂量分布与治疗计划系统模体中计算平面相比较, γ分析(3 mm/3%)结果显示, γ ≤ 1的剂量点所占比例为97.67%, 绝对点剂量与治疗计划系统内剂量偏差保持在±5%以内。 结论 MatriXX作为近距离治疗剂量分布的验证工具具有重复性好、避免使用胶片验证的成本损耗等优点, 是目前较为快速、便捷的近距离治疗剂量学质量保证工具。 Abstract:Objective To investigate the feasibility of two-dimensional ionization chamber array MatriXX for brachytherapy plan verification. Methods The well-type ion chamber was used to verify the source activity of 192Ir though the result of 60-second readout by calibration factor. The radioactive source was used to complete the calibration of EBT3 film through the Valencia skin applicator and water equivalent solid phantom. After the dose gray curve was obtained, the percentage depth dose(PDD) curves under Valencia skin applicator was drawn and then applied to calibrate the two-dimensional ionization chamber array MatriXX and get a calibration factor Kuser. The Freiburg Flap applicator with the needle was inserted, and then combined with solid water to build a phantom. After CT scanning, the catheter reconstruction and dose distribution calibration were completed in the treatment planning system (TPS). The planned dose distribution and measurement dose distribution were analyzed by software. Results The 192Ir dose distribution under Valencia skin applicator was similar to accelerator beam. The transverse and longitudinal symmetries were 0.17% and 0.16%, respectively. The reference dose was at 3 mm under the applicator surface, and the PDD value at 11.6 mm under the applicator surface was 46.5%. The measured dose distribution and TPS calculated dose plane was compared using gamma analysis method (3 mm/3%). The ratio of pixels within γ ≤ 1 was 97.67%, and the absolute dose measurement and calculation of dose deviation remained in 5%. Conclusions MatriXX has good repeatability when used as a brachytherapy dose distribution verification tool. It avoids using film and is more rapid and convenient for brachytherapy dosimetry quality assurance. -
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