Goddard Lee C, Brodin N Patrik, Bodner William R, Garg Madhur K, Tomé Wolfgang A
1 Department of Radiation Oncology, Montefiore Medical Center , Bronx, NY , United States.
2 Institute for Onco-Physics, Department of Radiation Oncology, Albert Einstein College of Medicine , Bronx, NY , United States.
Br J Radiol. 2018 May;91(1085):20180010. doi: 10.1259/bjr.20180010. Epub 2018 Mar 2.
To investigate whether photon or proton-based stereotactic body radiation therapy (SBRT is the preferred modality for high dose hypofractionation prostate cancer treatment. Achievable dose distributions were compared when uncertainties in target positioning and range uncertainties were appropriately accounted for.
10 patients with prostate cancer previously treated at our institution (Montefiore Medical Center) with photon SBRT using volumetric modulated arc therapy (VMAT) were identified. MRI images fused to the treatment planning CT allowed for accurate target and organ at risk (OAR) delineation. The clinical target volume was defined as the prostate gland plus the proximal seminal vesicles. Critical OARs include the bladder wall, bowel, femoral heads, neurovascular bundle, penile bulb, rectal wall, urethra and urogenital diaphragm. Photon plan robustness was evaluated by simulating 2 mm isotropic setup variations. Comparative proton SBRT plans employing intensity modulated proton therapy (IMPT) were generated using robust optimization. Plan robustness was evaluated by simulating 2 mm setup variations and 3% or 1% Hounsfield unit (HU) calibration uncertainties.
Comparable maximum OAR doses are achievable between photon and proton SBRT, however, robust optimization results in higher maximum doses for proton SBRT. Rectal maximum doses are significantly higher for Robust proton SBRT with 1% HU uncertainty compared to photon SBRT (p = 0.03), whereas maximum doses were comparable for bladder wall (p = 0.43), urethra (p = 0.82) and urogenital diaphragm (p = 0.50). Mean doses to bladder and rectal wall are lower for proton SBRT, but higher for neurovascular bundle, urethra and urogenital diaphragm due to increased lateral scatter. Similar target conformality is achieved, albeit with slightly larger treated volume ratios for proton SBRT, >1.4 compared to 1.2 for photon SBRT.
Similar treatment plans can be generated with IMPT compared to VMAT in terms of target coverage, target conformality, and OAR sparing when range and HU uncertainties are neglected. However, when accounting for these uncertainties during robust optimization, VMAT outperforms IMPT in terms of achievable target conformity and OAR sparing. Advances in knowledge: Comparison between achievable dose distributions using modern, robust optimization of IMPT for high dose per fraction SBRT regimens for the prostate has not been previously investigated.
探讨基于光子或质子的立体定向体部放射治疗（SBRT）是否是高剂量低分割前列腺癌治疗的首选方式。在适当考虑靶区定位不确定性和射程不确定性的情况下，比较可实现的剂量分布。
确定了10例先前在我们机构（蒙特菲奥里医疗中心）接受过使用容积调强弧形治疗（VMAT）的光子SBRT治疗的前列腺癌患者。与治疗计划CT融合的MRI图像有助于准确勾画靶区和危及器官（OAR）。临床靶区定义为前列腺加近端精囊。关键OAR包括膀胱壁、肠道、股骨头、神经血管束、阴茎球部、直肠壁、尿道和泌尿生殖膈。通过模拟2mm各向同性的摆位变化来评估光子计划的稳健性。采用稳健优化方法生成了采用调强质子治疗（IMPT）的对比质子SBRT计划。通过模拟2mm摆位变化和3%或1%的亨氏单位（HU）校准不确定性来评估计划的稳健性。
光子和质子SBRT可实现相当的最大OAR剂量，然而，稳健优化导致质子SBRT的最大剂量更高。与光子SBRT相比，1%HU不确定性的稳健质子SBRT的直肠最大剂量显著更高（p = 0.03），而膀胱壁（p = 0.43）、尿道（p = 0.82）和泌尿生殖膈（p = 0.50）的最大剂量相当。质子SBRT对膀胱和直肠壁的平均剂量较低，但由于侧向散射增加，对神经血管束、尿道和泌尿生殖膈的平均剂量较高。实现了相似的靶区适形度，尽管质子SBRT的治疗体积比略大，质子SBRT为>1.4，光子SBRT为1.2。
在忽略射程和HU不确定性的情况下，与VMAT相比，IMPT在靶区覆盖、靶区适形度和OAR保护方面可生成相似的治疗计划。然而，在稳健优化过程中考虑这些不确定性时，VMAT在可实现的靶区适形度和OAR保护方面优于IMPT。知识进展：此前尚未研究过使用现代稳健优化的IMPT对前列腺高剂量单次分割SBRT方案可实现的剂量分布之间的比较。
