使用双光子能量调强放疗对肝脏立体定向体部放疗计划中的剂量跌落进行剂量学量化。
Dosimetric quantification of dose fall-off in liver SBRT planning using dual photon energy IMRT.
作者信息
Henry J, Moreno C, Crownover R L, Baacke D, Papanikolaou N, Gutierrez A N
机构信息
Department of Radiation Oncology, School of Medicine, Cancer Therapy and Research Center at The University of Texas Health Science Center San Antonio, San Antonio, TX 78229, USA.
出版信息
J Radiosurg SBRT. 2016;4(2):145-151.
INTRODUCTION
The purpose of this study was to dosimetrically compare 6 MV, 10 MV and a hybrid of 6 and 10 MV photon beam energies in liver stereotactic body radiotherapy (SBRT) patients using a fixed-field IMRT technique. The objectives of the study were to evaluate dosimetric differences in the target volume and investigate if dose fall-off could be improved with 10MV beam energy.
METHODS AND MATERIALS
Sixteen (n=16) liver SBRT patients previously treated using a non-coplanar, fixed-field IMRT technique with 6 MV were replanned using 10 MV and dual photon energy (DE). Plans were generated in Pinnacle using a Novalis Tx with HD120 MLC. For each patient, three plans with the same beam geometry were created using 6 MV, 10 MV and DE. For DE plans, the central axis effective depth from each beam was calculated and the values averaged. Beams with an effective depth greater than the average were assigned to 10 MV. All patients were optimized with the same planning objectives and normalized such that 98% of the target received 100% of prescription dose. Metrics used for comparison were the homogeneity index, conformity indices, and dose fall-off parameters at various isodose levels.
RESULTS
The three techniques showed comparable PTV conformity and inhomogeneity for all patients-differences in the median values 「0.6%. With regard to dose fall-off, no statistically significant differences were noted among the techniques for R, R and R; however, 10 MV showed statistical significance in the lowest median values of R, R, and R. Ten MV and DE plans also demonstrated a statistically significant reduction in the total number of monitor units (MU) of 14.9% (p 「0.01) and 12.0% (p 「0.01) as compared to 6 MV, respectively.
CONCLUSION
Both dual energy and 10 MV photon beams had similar PTV dosimetric characteristics to 6 MV for liver SBRT but findings show faster dose fall-off for 10 MV and DE plans at the 40%, 30%, and 20% prescription isodose levels.
引言
本研究的目的是使用固定野调强放射治疗（IMRT）技术，对肝脏立体定向体部放射治疗（SBRT）患者的6兆伏、10兆伏以及6兆伏和10兆伏混合光子束能量进行剂量学比较。本研究的目标是评估靶区体积的剂量学差异，并研究10兆伏束能量是否能改善剂量下降情况。
方法与材料
16例先前使用非共面固定野IMRT技术、6兆伏能量进行治疗的肝脏SBRT患者，重新使用10兆伏和双光子能量（DE）进行计划制定。计划在Pinnacle中使用带有HD120多叶准直器的Novalis Tx生成。对于每位患者，使用6兆伏、10兆伏和DE创建三个具有相同射束几何形状的计划。对于DE计划，计算每个射束的中心轴有效深度并求平均值。有效深度大于平均值的射束分配为10兆伏。所有患者均以相同的计划目标进行优化，并进行归一化处理，使98%的靶区接受100%的处方剂量。用于比较的指标有均匀性指数、适形指数以及不同等剂量水平下的剂量下降参数。
结果
对于所有患者，这三种技术显示出可比的计划靶体积（PTV）适形性和不均匀性——中位数差异「0.6%。在剂量下降方面，三种技术在R、R和R上未观察到统计学显著差异；然而，10兆伏在R、R和R的最低中位数上显示出统计学显著性。与6兆伏相比，10兆伏和DE计划的监测单位总数也分别有统计学显著减少，减少了14.9%（p「0.01）和12.0%（p「0.01）。
结论
对于肝脏SBRT，双能量和10兆伏光子束与6兆伏具有相似的PTV剂量学特征，但研究结果表明，在40%、30%和20%处方等剂量水平下，10兆伏和DE计划的剂量下降更快。
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