Center for Proton Therapy, Paul Scherrer Institute, 5232, Villigen PSI, Germany,
Strahlenther Onkol. 2013 Dec;189(12):1020-5. doi: 10.1007/s00066-013-0432-0. Epub 2013 Sep 21.
Mesenchymal tumours require high-dose radiation therapy (RT). Small bowel (SB) dose constraints have historically limited dose delivery to paraspinal and retroperitoneal targets. This retrospective study correlated SB dose-volume histograms with side-effects after proton radiation therapy (PT).
Between 1997 and 2008, 31 patients (mean age 52.1 years) underwent spot scanning-based PT for paraspinal/retroperitoneal chordomas (81%), sarcomas (16%) and meningiom (3%). Mean total prescribed dose was 72.3 Gy (relative biologic effectiveness, RBE) delivered in 1.8-2 Gy (RBE) fractions. Mean follow-up was 3.8 years. Based on the pretreatment planning CT, SB dose distributions were reanalysed.
Planning target volume (PTV) was defined as gross tumour volume (GTV) plus 5-7 mm margins. Mean PTV was 560.22 cm(3). A mean of 93.2% of the PTV was covered by at least 90% of the prescribed dose. SB volumes (cm(3)) receiving doses of 5, 20, 30, 40, 50, 60, 70, 75 and 80 Gy (RBE) were calculated to give V5, V20, V30, V40, V50, V60, V70, V75 and V80 respectively. In 7/31 patients, PT was accomplished without any significant SB irradiation (V5=0). In 24/31 patients, mean maximum dose (Dmax) to SB was 64.1 Gy (RBE). Despite target doses of >70 Gy (RBE), SB received >50 and >60 Gy (RBE) in only 61 and 54% of patients, respectively. Mean SB volumes (cm(3)) covered by different dose levels (Gy, RBE) were: V20 (n=24): 45.1, V50 (n=19): 17.7, V60 (n=17): 7.6 and V70 (n=12): 2.4. No acute toxicity ≥ grade 2 or late SB sequelae were observed.
Small noncircumferential volumes of SB tolerated doses in excess of 60 Gy (RBE) without any clinically-significant late adverse effects. This small retrospective study has limited statistical power but encourages further efforts with higher patient numbers to define and establish high-dose threshold models for SB toxicity in modern radiation oncology.
间质瘤需要高剂量放射治疗（RT）。小肠（SB）剂量限制历来限制了脊柱旁和腹膜后靶区的剂量传递。本回顾性研究将 SB 剂量-体积直方图与质子放射治疗（PT）后的副作用相关联。
1997 年至 2008 年间，31 例患者（平均年龄 52.1 岁）接受了脊柱旁/腹膜后脊索瘤（81%）、肉瘤（16%）和脑膜瘤（3%）的点扫描式 PT。平均总处方剂量为 72.3Gy（相对生物效应，RBE），分 1.8-2Gy（RBE）剂量分次给予。平均随访 3.8 年。根据治疗前计划 CT，重新分析了 SB 剂量分布。
计划靶区（PTV）定义为大体肿瘤体积（GTV）加 5-7mm 边界。平均 PTV 为 560.22cm³。93.2%的 PTV 至少被 90%的处方剂量覆盖。计算了 SB 体积（cm³）接受 5、20、30、40、50、60、70、75 和 80Gy（RBE）的剂量，分别得到 V5、V20、V30、V40、V50、V60、V70、V75 和 V80。在 31 例患者中，有 7 例（7/31）PT 完成时 SB 无明显照射（V5=0）。在 24 例患者中，SB 的平均最大剂量（Dmax）为 64.1Gy（RBE）。尽管靶剂量大于 70Gy（RBE），但只有 61%和 54%的患者分别接受了 SB 大于 50 和 60Gy（RBE）的剂量。不同剂量水平（Gy，RBE）覆盖的 SB 平均体积（cm³）为：V20（n=24）：45.1，V50（n=19）：17.7，V60（n=17）：7.6 和 V70（n=12）：2.4。未观察到任何≥2 级的急性毒性或晚期 SB 后遗症。
小肠非环形小体积可耐受 60Gy（RBE）以上剂量，无任何临床显著的晚期不良影响。这项小的回顾性研究统计学效能有限，但鼓励进一步努力增加患者数量，以确定和建立现代放射肿瘤学中 SB 毒性的高剂量阈值模型。
