Dosimetric delivery validation of dynamically collimated pencil beam scanning proton therapy.
Dosimetric delivery validation of dynamically collimated pencil beam scanning proton therapy.
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DOI：
10.1088/1361-6560/acb6cd
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发表时间：
2023-02-20
影响因子：
3.5
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中科院分区：
文献类型：
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Objective.能量层特定准直可以改善双束扫描（PBS）质子治疗靶区剂量符合性。一种这样的准直器是动态准直系统（DCS），其由四个镍微调刀片组成，当扫描束接近目标的横向范围时，所述微调刀片拦截扫描束。虽然DCS的剂量学益处已通过计算治疗计划研究得到证实，但对于复合多能量层场，这些益处还有待实验验证。这项工作的目的是剂量表征和实验验证的输送动态准直质子治疗的DCS配备到临床PBS系统。Approach.使用Monte Carlo剂量计算生成3 × 3 × 3 cm 3靶体积的优化单场、均匀剂量治疗计划，深度范围为5 - 15 cm，修整器至表面距离范围为5 - 18.15 cm，有和没有4 cm厚的聚乙烯范围移位器。然后使用原型DCS和IBA专用喷嘴系统将治疗计划输送到水模体，并使用Zebra多层电离室、MatriXX PT电离室阵列和Gafchromic™ EBT 3薄膜进行测量。主要结果。对于在SOBP内进行的测量，在所有测量的未准直和准直计划中，MatriXX PT的平均2D伽马通过率超过98.5%，在2%/2 mm标准下，胶片的平均2D伽马通过率超过96.5%。为了验证半暗带宽度减少与准直，胶片与Monte Carlo一致，平均差异在0.3 mm以内，而MatriXX PT为0.9 mm。意义我们已经通过实验验证了使用临床PBS系统和常用剂量计的DCS准直场的交付，并且还确定了受陡峭剂量梯度影响的剂量计的潜在弱点。
Objective. Pencil beam scanning (PBS) proton therapy target dose conformity can be improved with energy layer-specific collimation. One such collimator is the dynamic collimation system (DCS), which consists of four nickel trimmer blades that intercept the scanning beam as it approaches the lateral extent of the target. While the dosimetric benefits of the DCS have been demonstrated through computational treatment planning studies, there has yet to be experimental verification of these benefits for composite multi-energy layer fields. The objective of this work is to dosimetrically characterize and experimentally validate the delivery of dynamically collimated proton therapy with the DCS equipped to a clinical PBS system. Approach. Optimized single field, uniform dose treatment plans for 3 × 3 × 3 cm3 target volumes were generated using Monte Carlo dose calculations with depths ranging from 5 to 15 cm, trimmer-to-surface distances ranging from 5 to 18.15 cm, with and without a 4 cm thick polyethylene range shifter. Treatment plans were then delivered to a water phantom using a prototype DCS and an IBA dedicated nozzle system and measured with a Zebra multilayer ionization chamber, a MatriXX PT ionization chamber array, and Gafchromic™ EBT3 film. Main results. For measurements made within the SOBPs, average 2D gamma pass rates exceeded 98.5% for the MatriXX PT and 96.5% for film at the 2%/2 mm criterion across all measured uncollimated and collimated plans, respectively. For verification of the penumbra width reduction with collimation, film agreed with Monte Carlo with differences within 0.3 mm on average compared to 0.9 mm for the MatriXX PT. Significance. We have experimentally verified the delivery of DCS-collimated fields using a clinical PBS system and commonly available dosimeters and have also identified potential weaknesses for dosimeters subject to steep dose gradients.
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