技术说明：使用质量保证测试图案对质子笔形束点扫描的晕轮建模进行验证。

Technical Note: Validation of halo modeling for proton pencil beam spot scanning using a quality assurance test pattern.

作者信息

Lin Liyong, Huang Sheng, Kang Minglei, Solberg Timothy D, McDonough James E, Ainsley Christopher G

机构信息

Department of Radiation Oncology, University of Pennsylvania, 3400 Civic Center Boulevard, Philadelphia, Pennsylvania 19104.

出版信息

Med Phys. 2015 Sep;42(9):5138-43. doi: 10.1118/1.4928157.

DOI:10.1118/1.4928157

PMID:26328965

Abstract

PURPOSE

The purpose of this paper is to demonstrate the utility of a comprehensive test pattern in validating calculation models that include the halo component (low-dose tails) of proton pencil beam scanning (PBS) spots. Such a pattern has been used previously for quality assurance purposes to assess spot shape, position, and dose.

METHODS

In this study, a scintillation detector was used to measure the test pattern in air at isocenter for two proton beam energies (115 and 225 MeV) of two IBA universal nozzles (UN #1 and UN #2). Planar measurements were compared with calculated dose distributions based on the weighted superposition of location-independent (UN #1) or location-dependent (UN #2) spot profiles, previously measured using a pair-magnification method and between two nozzles.

RESULTS

Including the halo component below 1% of the central dose is shown to improve the gamma-map comparison between calculation and measurement from 94.9% to 98.4% using 2 mm/2% criteria for the 115 MeV proton beam of UN #1. In contrast, including the halo component below 1% of the central dose does not improve the gamma agreement for the 115 MeV proton beam of UN #2, due to the cutoff of the halo component at off-axis locations. When location-dependent spot profiles are used for calculation instead of spot profiles at central axis, the gamma agreement is improved from 98.0% to 99.5% using 2 mm/2% criteria. The two nozzles clearly have different characteristics, as a direct comparison of measured data shows a passing rate of 89.7% for the 115 MeV proton beam. At 225 MeV, the corresponding gamma comparisons agree better between measurement and calculation, and between measurements in the two nozzles.

CONCLUSIONS

In addition to confirming the primary component of individual PBS spot profiles, a comprehensive test pattern is useful for the validation of the halo component at off-axis locations, especially for low energy protons.

摘要

目的

本文旨在展示一种综合测试模式在验证包含质子笔形束扫描（PBS）光斑晕轮成分（低剂量尾部）的计算模型方面的效用。这种模式此前已用于质量保证目的，以评估光斑形状、位置和剂量。

方法

在本研究中，使用闪烁探测器在等中心空气中测量两种IBA通用喷嘴（UN #1和UN #2）的两种质子束能量（115和225 MeV）下的测试模式。将平面测量结果与基于位置无关（UN #1）或位置相关（UN #2）光斑轮廓加权叠加计算出的剂量分布进行比较，这些光斑轮廓此前使用双放大法在两个喷嘴之间进行了测量。

结果

对于UN #1的115 MeV质子束，使用2 mm/2%标准时，包含低于中心剂量1%的晕轮成分可使计算与测量之间的伽马图比较从94.9%提高到98.4%。相比之下，对于UN #2的115 MeV质子束，包含低于中心剂量1%的晕轮成分并未改善伽马一致性，这是由于晕轮成分在离轴位置被截断。当使用位置相关的光斑轮廓而非中心轴处的光斑轮廓进行计算时，使用2 mm/2%标准，伽马一致性从98.0%提高到99.5%。直接比较测量数据表明，115 MeV质子束的通过率为89.7%，这两个喷嘴显然具有不同的特性。在225 MeV时，相应的伽马比较在测量与计算之间以及两个喷嘴的测量之间一致性更好。