Background: Stereotactic radiotherapy (SRT) is a promising treatment option for patients with multiple brain metastases (BMs). Using one isocenter instead of a separate isocenter for each BM can reduce the treatment time. This work compares the calculated dose in the treatment planning system with the measured dose using film dosimetry of single-isocenter multi-target (SIMT) SRT for multiple BM.Methods: Fifty patients with 4 to 18 BMs (median = 6, in total 356 BMs) were treated with a single-isocenter non-coplanar LINAC-based treatment with six VMAT arcs. Treatment was performed using RayStation and Elekta Versa HD with Agility multileaf collimator, including a 6D robotic couch. Patient-specific QA measurements were performed with an in-house developed phantom using three layers of GafChromic EBT3 film. Film measurements were analyzed in DoseLab using global gamma with 3% and 1 mm distance-to-agreement criteria. Additionally, secondary dose calculations in Mobius3D were performed with similar gamma criteria.Results: The mean total Paddick conformity index and gradient index were 0.7 ± 0.10 and 5.2 ± 1.9, respectively. Monitor units used were 6321 ± 2510, and mean irradiation time was 600 ± 90 s. The mean global gamma passing rate for all measured films was 94.5 ± 4.6% with 3% and 1 mm criteria, while that of the dose calculations in Mobius3D was 98.2 ± 1.2% with the same criteria. A dependence of gamma passing rates of film measurements on the total PTV volume was observed, whereas such dependence was minimal for Mobius3D.Conclusions: The results demonstrate good agreement between the TPS, film measurements, and independent dose calculations, supporting the dosimetric accuracy of single-isocenter multi-target SRT for treating multiple BMs.
背景：立体定向放射治疗（SRT）是多发性脑转移瘤（BMs）患者的一种前景广阔的治疗选择。采用单一等中心点而非为每个脑转移灶设置独立等中心点可缩短治疗时间。本研究通过胶片剂量测定法，比较了治疗计划系统计算的剂量与实测剂量，以评估多发性脑转移瘤单等中心点多靶点（SIMT）SRT的剂量学准确性。 方法：对50例患有4至18个脑转移灶（中位数=6，总计356个病灶）的患者实施基于直线加速器的单等中心点非共面治疗，采用六弧容积旋转调强放疗（VMAT）。治疗使用RayStation计划系统和配备Agility多叶准直器（含六维机器人治疗床）的Elekta Versa HD直线加速器执行。患者特异性质量保证（QA）测量采用自主研发的模体配合三层GafChromic EBT3胶片完成。胶片测量数据在DoseLab软件中采用全局伽马分析法进行评估，标准为3%剂量偏差与1mm距离一致性。同时，使用Mobius3D进行次级剂量计算，并采用相同伽马标准验证。 结果：平均总Paddick适形指数和梯度指数分别为0.7±0.10和5.2±1.9。治疗使用监测单位为6321±2510，平均照射时间为600±90秒。所有胶片测量的平均全局伽马通过率为94.5±4.6%（3%/1mm标准），而Mobius3D剂量计算的通过率为98.2±1.2%（相同标准）。观察到胶片测量的伽马通过率与计划靶区总体积存在相关性，而Mobius3D计算结果的此类相关性较弱。 结论：研究结果表明治疗计划系统、胶片测量和独立剂量计算三者间具有良好的一致性，这支持了单等中心点多靶点SRT治疗多发性脑转移瘤的剂量学准确性。
肿瘤(癌症)患者之家