定量研究铅箔在射野平坦度剂量验证中的作用。

Quantification of the role of lead foil in flattening filter free beam reference dosimetry.

机构信息

Department of Radiation Physics, The University of Texas MD Anderson Cancer Center, Houston, Texas, USA.

出版信息

J Appl Clin Med Phys. 2023 Apr;24(4):e13960. doi: 10.1002/acm2.13960. Epub 2023 Mar 13.

DOI:10.1002/acm2.13960

PMID:36913192

原文链接:https://pmc.ncbi.nlm.nih.gov/articles/PMC10113695/

Abstract

PURPOSE

To quantify the potential error in outputs for flattening filter free (FFF) beams associated with use of a lead foil in beam quality determination per the addendum protocol for TG-51, we examined differences in measurements of the beam quality conversion factor k when using or not using lead foil.

METHODS

Two FFF beams, a 6 MV FFF and a 10 MV FFF, were calibrated on eight Varian TrueBeams and two Elekta Versa HD linear accelerators (linacs) according to the TG-51 addendum protocol by using Farmer ionization chambers [TN 30013 (PTW) and SNC600c (Sun Nuclear)] with traceable absorbed dose-to-water calibrations. In determining k , the percentage depth-dose at 10 cm [PDD(10)] was measured with 10×10 cm field size at 100 cm source-to-surface distance (SSD). PDD(10) values were measured either with a 1 mm lead foil positioned in the path of the beam [%dd(10) ] or with omission of a lead foil [%dd(10)]. The %dd(10)x values were then calculated and the k factors determined by using the empirical fit equation in the TG-51 addendum for the PTW 30013 chambers. A similar equation was used to calculate k for the SNC600c chamber, with the fitting parameters taken from a very recent Monte Carlo study. The differences in k factors were compared for with lead foil vs. without lead foil.

RESULTS

Differences in %dd(10)x with lead foil and with omission of lead foil were 0.9 ± 0.2% for the 6 MV FFF beam and 0.6 ± 0.1% for the 10 MV FFF beam. Differences in k values with lead foil and with omission of lead foil were -0.1 ± 0.02% for the 6 MV FFF and -0.1 ± 0.01% for the 10 MV FFF beams.

CONCLUSION

With evaluation of the lead foil role in determination of the k factor for FFF beams. Our results suggest that the omission of lead foil introduces approximately 0.1% of error for reference dosimetry of FFF beams on both TrueBeam and Versa platforms.

摘要

目的

根据 TG-51 附录协议，通过使用附加协议中的附加协议来确定束质转换因子 k 时，量化使用或不使用铅箔时，FFF 束的输出潜在误差。我们检查了在两种 FFF 束（6 MV FFF 和 10 MV FFF）中使用或不使用铅箔时测量 k 时的差异。

方法

根据 TG-51 附录协议，通过使用经溯源的水吸收剂量校准的 Farmer 电离室 [TN 30013（PTW）和 SNC600c（Sun Nuclear）]，在 8 台瓦里安 TrueBeam 和 2 台 Elekta Versa HD 直线加速器（linac）上对两种 FFF 束进行校准。在确定 k 时，使用 10×10 cm 射野在 100 cm 源皮距（SSD）处测量 10 cm 处的百分深度剂量 [PDD（10）]。要么在束流路径中放置 1 毫米铅箔测量 PDD（10）值[%dd（10）]，要么省略铅箔测量 PDD（10）值 [%dd（10）]。然后计算 %dd（10）x 值，并使用 TG-51 附录中针对 PTW 30013 室的经验拟合方程确定 k 因子。使用非常新的蒙特卡罗研究中的拟合参数，使用类似的方程计算 SNC600c 室的 k 因子。使用经验拟合方程。在使用和不使用铅箔的情况下，对于 6 MV FFF 束，k 因子的差异为 0.9±0.2%，对于 10 MV FFF 束，k 因子的差异为 0.6±0.1%。在使用和不使用铅箔的情况下，对于 6 MV FFF 束，k 因子的差异为-0.1±0.02%，对于 10 MV FFF 束，k 因子的差异为-0.1±0.01%。