Department of Radiation Oncology, University of Colorado School of Medicine, Aurora, Colorado 80045, USA.
Int J Radiat Oncol Biol Phys. 2012 Nov 15;84(4):1024-30. doi: 10.1016/j.ijrobp.2011.11.080. Epub 2012 May 12.
To describe regional lung tissue density changes in normal lung tissue of patients with primary and metastatic lung tumors who received stereotactic body radiation therapy (SBRT).
A total of 179 post-SBRT follow-up computed tomography (CT) scans of 62 patients who received SBRT between 2003 and 2009 were studied. Median prescription dose was 54 Gy (range, 30-60 Gy) in 3 to 5 fractions. SBRT-induced lung density changes on post-SBRT follow-up CT were evaluated at approximately 3, 6, 12, 18, 24, and 30 months after treatment. Dose-response curves (DRC) were generated for SBRT-induced lung damage by averaging CT number (HU) changes for regions of the lungs receiving the same dose at 5-Gy intervals.
For all follow-up interval periods, CT numbers linearly increased with dose until 35 Gy and were constant thereafter. For 3, 18, 24, and 30 months, the rate of relative electron density increase with dose was approximately 0.24% per Gy. At 6 months, the rate was also similar below 20 Gy but then rose to 0.6% per Gy above this threshold. After 6 months, DRCs were mostly time-independent. When split between patients treated with 3 fractions of 12 to 20 Gy (median, 20 Gy; average tumor volume, 12±16 cm3) and with >3 fractions of 6 to 12.5 Gy (median, 9 Gy; average tumor volume, 30±40 cm3), DRCs differed significantly. In both cases, CT changes at 3, 18, 24, and 30 months were identical to those of the population DRC; however, patients who received >3 fractions showed 6-month CT changes that were more than twice those for the group that received 3 fractions.
This analysis of SBRT-induced normal lung density changes indicates that lung normal tissue has more pronounced self-limited acute effects than late effects. Differences in acute CT changes following treatments in 3 fractions were considerably less than for treatments in >3 fractions.
描述接受立体定向体部放射治疗（SBRT）的原发性和转移性肺肿瘤患者正常肺部组织的区域性肺组织密度变化。
对 2003 年至 2009 年间接受 SBRT 的 62 名患者的 179 次 SBRT 后随访 CT 扫描进行了研究。中位处方剂量为 54 Gy（范围 30-60 Gy），分为 3-5 个部分。在治疗后约 3、6、12、18、24 和 30 个月时，评估 SBRT 后随访 CT 上 SBRT 引起的肺部密度变化。通过在 5 Gy 间隔内对接受相同剂量的肺部区域的 CT 数（HU）变化进行平均，生成 SBRT 诱导的肺损伤剂量反应曲线（DRC）。
对于所有随访间隔期，CT 数随剂量呈线性增加，直到 35 Gy，此后保持不变。对于 3、18、24 和 30 个月，相对电子密度随剂量的增加率约为 0.24%/Gy。在 6 个月时，低于 20 Gy 时的速率也相似，但在此阈值以上则上升至 0.6%/Gy。6 个月后，DRC 大多与时间无关。当分为接受 3 次 12-20 Gy（中位剂量 20 Gy；平均肿瘤体积 12±16 cm3）和 3 次以上 6-12.5 Gy（中位剂量 9 Gy；平均肿瘤体积 30±40 cm3）的患者时，DRC 存在显著差异。在这两种情况下，3、18、24 和 30 个月的 CT 变化与人群 DRC 相同；然而，接受 3 次以上治疗的患者在 6 个月时的 CT 变化是接受 3 次治疗的患者的两倍以上。
这项对 SBRT 诱导的正常肺部密度变化的分析表明，肺部正常组织具有比晚期效应更明显的自限性急性效应。3 次分割治疗后的急性 CT 变化差异明显小于 3 次以上分割治疗后的差异。
