Stanley D N, Popp T, Ha C S, Swanson G P, Eng T Y, Papanikolaou N, Gutiérrez A N
Department of Radiation Oncology, Cancer Therapy & Research Center at The University of Texas Health Science Center San Antonio, San Antonio, Texas.
Department of Radiation Oncology, Scott & White Healthcare, Temple, Texas.
Pract Radiat Oncol. 2015 Nov-Dec;5(6):e625-33. doi: 10.1016/j.prro.2015.06.012. Epub 2015 Jul 7.
The purpose of this study was to dosimetrically compare 6- and 10-MV photon beam energies in high-risk prostate cancer patients of various body habitus using a volumetric modulated arc therapy (VMAT) radiation delivery technique. The objectives of the study were to evaluate whether dosimetric differences exist and to investigate whether differences are dependent on patient body habitus.
Forty patients with various body habitus who had previously received treatment to the prostate and pelvic lymph nodes with VMAT techniques were chosen. Patients were planned in the Pinnacle(3) treatment planning system with double or triple SmartArc plans with 6- and 10-MV photon energies. All patients were optimized with the same planning objectives and normalized such that 95% of the planning target volume (PTV) received the prescription dose. Patients were evaluated for PTV and organ at risk (OAR) parameters for the bladder, rectum, small bowel, penile bulb, and sigmoid colon. Metrics used for comparison were D2%, D98%, homogeneity, conformity, and dose falloff for the PTV and D(2%), D(mean), V(80%), V(60%), and V(40%) for OARs. Statistical differences were evaluated with a paired-sample Wilcoxon signed rank test with a significance level of .05.
For the PTV, there were no statistically significant differences in D(mean), D(2cc), conformation number, and homogeneity index values, but the dose falloff parameters, R50 and R25, showed a median improvement of 6.7% (P<.01) and 6.2% (P<.01), respectively, with 10 MV. A correlation between patient anterior-posterior distance (d(AP)) and percentage reduction in R50 of 0.436% per centimeter (P<.01) was determined. For OARs, statistically significant reductions in dose metrics were found in the small bowel and bladder, but increases in the D(2cc) of 3.5% in the penile bulb (P<.01) and 0.2% in the rectum (P=.02) were shown with 10 MV. The use of 10 MV also demonstrated a statistically significant reduction in the total number of monitor units of 15.9% (P<.01) compared with 6 MV.
The study showed that 10 MV provides a faster dose falloff than 6 MV for patients whose prostate and pelvic lymph nodes are treated using a VMAT technique irrespective of body habitus; however, the improvement in dose falloff is dependent on body habitus and increases as the patient body habitus increases.
本研究旨在使用容积调强弧形放疗（VMAT）技术，对不同体型的高危前列腺癌患者进行6兆伏和10兆伏光子束能量的剂量学比较。本研究的目的是评估是否存在剂量学差异，并调查这些差异是否取决于患者体型。
选择40例此前接受过前列腺和盆腔淋巴结VMAT技术治疗的不同体型患者。患者在Pinnacle(3)治疗计划系统中采用双弧或三弧计划，光子能量为6兆伏和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95%的计划靶体积（PTV）接受处方剂量。评估患者的PTV以及膀胱、直肠、小肠、阴茎球部和乙状结肠等危及器官（OAR）的参数。用于比较的指标包括PTV的D2%、D98%、均匀性、适形度和剂量跌落，以及OAR的D(2%)、D(平均)、V(80%)、V(60%)和V(40%)。采用配对样本Wilcoxon符号秩检验评估统计学差异，显著性水平为0.05。
对于PTV，D(平均)、D(2立方厘米)、适形数和均匀性指数值无统计学显著差异，但剂量跌落参数R50和R25在10兆伏时分别显示中位数改善了6.7%（P<0.01）和6.2%（P<0.01）。确定患者前后径（d(AP)）与R50每厘米降低0.436%之间的相关性（P<0.01）。对于OAR，小肠和膀胱的剂量指标有统计学显著降低，但10兆伏时阴茎球部的D(2立方厘米)增加了3.5%（P<0.01），直肠增加了0.2%（P=0.02）。与6兆伏相比，使用10兆伏还显示监测单位总数有统计学显著减少，减少了15.9%（P<0.01）。
该研究表明，对于使用VMAT技术治疗前列腺和盆腔淋巴结的患者，无论体型如何，10兆伏的剂量跌落比6兆伏更快；然而，剂量跌落的改善取决于体型，且随着患者体型增加而增加。
