用于肺部立体定向体部放疗应用的TrueBeam 10XFFF相空间文件的蒙特卡洛验证。

Teke Tony, Duzenli Cheryl, Bergman Alanah, Viel Francis, Atwal Parmveer, Gete Ermias

Medical Physics, BC Cancer Agency-Centre for the Southern Interior, Kelowna, British Columbia V1Y 5L3, Canada.

Medical Physics, BC Cancer Agency-Vancouver Centre, Vancouver, British Columbia V5Z 4E6, Canada.

Med Phys. 2015 Dec;42(12):6863-74. doi: 10.1118/1.4935144.

PURPOSE

To establish the clinical acceptability of universal Monte Carlo phase-space data for the 10XFFF (flattening filter free) photon beam on the Varian TrueBeam Linac, including previously unreported data for small fields, output factors, and inhomogeneous media. The study was particularly aimed at confirming the suitability for use in simulations of lung stereotactic ablative radiotherapy treatment plans.

METHODS

Monte Carlo calculated percent depth doses (PDDs), transverse profiles, and output factors for the TrueBeam 10 MV FFF beam using generic phase-space data that have been released by the Varian MC research team were compared with in-house measurements and published data from multiple institutions (ten Linacs from eight different institutions). BEAMnrc was used to create field size specific phase-spaces located underneath the jaws. Doses were calculated with DOSXYZnrc in a water phantom for fields ranging from 1 × 1 to 40 × 40 cm(2). Particular attention was paid to small fields (down to 1 × 1 cm(2)) and dose per pulse effects on dosimeter response for high dose rate 10XFFF beams. Ion chamber measurements were corrected for changes in ion collection efficiency (P(ion)) with increasing dose per pulse. MC and ECLIPSE ANISOTROPIC ANALYTICAL ALGORITHM (AAA) calculated PDDs were compared to Gafchromic film measurement in inhomogeneous media (water, bone, lung).

RESULTS

Measured data from all machines agreed with Monte Carlo simulations within 1.0% and 1.5% for PDDs and in-field transverse profiles, respectively, for field sizes >1 × 1 cm(2) in a homogeneous water phantom. Agreements in the 80%-20% penumbra widths were better than 2 mm for all the fields that were compared. For all the field sizes considered, the agreement between their measured and calculated output factors was within 1.1%. Monte Carlo results for dose to water at water/bone, bone/lung, and lung/water interfaces as well as within lung agree with film measurements to within 2.8% for 10 × 10 and 3 × 3 cm(2) field sizes. This represents a significant improvement over the performance of the ECLIPSE AAA.

CONCLUSIONS

The 10XFFF phase-space data offered by the Varian Monte Carlo research team have been validated for clinical use using measured, interinstitutional beam data in water and with film dosimetry in inhomogeneous media.

目的

确立瓦里安TrueBeam直线加速器上10XFFF（无均整器）光子束通用蒙特卡罗相空间数据的临床可接受性，包括此前未报告的小射野、输出因子和非均匀介质的数据。该研究尤其旨在确认其适用于肺部立体定向消融放疗治疗计划的模拟。

方法

将使用瓦里安MC研究团队发布的通用相空间数据，通过蒙特卡罗计算得出的TrueBeam 10 MV FFF射束的百分深度剂量（PDD）、横向轮廓和输出因子，与内部测量结果以及多个机构（来自八个不同机构的十台直线加速器）发布的数据进行比较。使用BEAMnrc创建位于准直器下方的特定射野大小的相空间。在水模体中，使用DOSXYZnrc计算1×1至40×40 cm²射野的剂量。特别关注小射野（低至1×1 cm²）以及高剂量率10XFFF射束的每脉冲剂量对剂量仪响应的影响。对离子室测量结果进行了校正，以考虑随着每脉冲剂量增加离子收集效率（P(ion)）的变化。将蒙特卡罗和ECLIPSE各向异性分析算法（AAA）计算得出的PDD与非均匀介质（水、骨、肺）中的Gafchromic胶片测量结果进行比较。

结果

在均匀水模体中，对于射野大小>1×1 cm²的情况，所有机器的测量数据与蒙特卡罗模拟结果在PDD和射野内横向轮廓方面的一致性分别在1.0%和1.5%以内。所有比较射野的80%-20%半值层宽度的一致性优于2 mm。对于所有考虑的射野大小，其测量和计算的输出因子之间的一致性在1.1%以内。对于10×10和3×3 cm²射野大小，蒙特卡罗计算得出的水/骨、骨/肺和肺/水界面以及肺内水的剂量结果与胶片测量结果的一致性在2.8%以内。这相对于ECLIPSE AAA的性能有了显著提高。