Department of Radiation Oncology, University of Heidelberg, Germany.
Radiother Oncol. 2011 Dec;101(3):388-93. doi: 10.1016/j.radonc.2011.08.023. Epub 2011 Sep 30.
Volumetric modulated arc therapy (VMAT) has the potential to shorten treatment times for fluence modulated radiotherapy. We compared dose distributions of VMAT, step-and-shoot IMRT and serial tomotherapy for typical head and neck (H&N) planning target volumes (PTV) with sparing of one parotid, a complex paradigm and a situation often encountered in H&N radiotherapy. Finally, we validated the dosimetric accuracy of VMAT delivery.
Based on CT datasets of 10 patients treated for H&N cancer (PTV1:60 Gy/PTV2:56 Gy) with IMRT (7/9 fields), serial tomotherapy (MIMiC) and VMAT were compared with regard to plan quality and treatment efficiency. Plan quality was assessed by calculating homogeneity/conformity index (HI/CI), mean dose to parotid and brain stem and the maximum dose to the spinal cord. For plan efficiency evaluation, total treatment time (TTT) and number of monitor units (MU) were considered. A dosimetric evaluation of VMAT was performed using radiosensitive film, ion chamber and 2D-array.
For MIMiC/IMRT(7F)/IMRT(9F)/VMAT, mean CI was 1.98/2.23/2.23/1.82, HI(PTV1) was 1.12/1.20/1.20/1.11 and HI(PTV2) was 1.11/1.15/1.13/1.12. Mean doses to the shielded parotid were 19.5 Gy/14.1 Gy/13.9 Gy/14.9 Gy and the spinal cord received maximum doses of 43.6 Gy/40.8 Gy/41.6 Gy/42.6 Gy. The mean MU's were 2551/945/925/521 and the mean TTT was 12.8 min/7.6 min/8.5 min/4.32 min. The ion chamber measurements showed an absolute deviation of 0.08 ± 1.10% and 98.45 ± 3.25% pixels passed γ-analyses for 3%/3mm and 99.95 ± 0.09% for 5%/5mm for films. 2D-array measurements reported an agreement for 3%/3mm of 95.65 ± 2.47%-98.33 ± 0.65% and for 5%/5mm 99.79 ± 0.24%-99.92 ± 0.09% depending on the measurement protocol.
All treatment paradigms produced plans of excellent quality and dosimetric accuracy with IMRT providing best OAR sparing and VMAT being the most efficient treatment option in our comparison of treatment plans with high complexity.
容积调强弧形治疗（VMAT）有可能缩短调强放疗的治疗时间。我们比较了 VMAT、步进式调强放射治疗（step-and-shoot IMRT）和序列断层调强放射治疗（serial tomotherapy）在保护一个腮腺、复杂范式和头颈部放疗中常见情况的典型头颈部（H&N）计划靶区（PTV）中的剂量分布。最后，我们验证了 VMAT 传递的剂量学准确性。
基于 10 例接受 H&N 癌症治疗的患者的 CT 数据集（PTV1：60 Gy/PTV2：56 Gy），分别采用 IMRT（7/9 野）、序列断层调强放射治疗（MIMiC）和 VMAT 进行比较，评估计划质量和治疗效率。通过计算均匀性/适形性指数（HI/CI）、腮腺和脑干的平均剂量以及脊髓的最大剂量来评估计划质量。对于计划效率评估，考虑了总治疗时间（TTT）和监测单位（MU）的数量。使用放射敏感器件、电离室和二维阵列对 VMAT 的剂量学进行了评估。
对于 MIMiC/IMRT（7F）/IMRT（9F）/VMAT，平均 CI 分别为 1.98/2.23/2.23/1.82，HI（PTV1）分别为 1.12/1.20/1.20/1.11，HI（PTV2）分别为 1.11/1.15/1.13/1.12。屏蔽腮腺的平均剂量分别为 19.5 Gy/14.1 Gy/13.9 Gy/14.9 Gy，脊髓接受的最大剂量分别为 43.6 Gy/40.8 Gy/41.6 Gy/42.6 Gy。平均 MU 分别为 2551/945/925/521，平均 TTT 分别为 12.8 分钟/7.6 分钟/8.5 分钟/4.32 分钟。电离室测量结果显示，对于 3%/3mm 和 99.95 ± 0.09%，胶片的绝对偏差分别为 0.08 ± 1.10%和 98.45 ± 3.25%像素通过γ分析；对于 5%/5mm，分别为 95.65 ± 2.47%-98.33 ± 0.65%和 99.79 ± 0.24%-99.92 ± 0.09%。二维阵列测量报告，对于 3%/3mm，95.65 ± 2.47%-98.33 ± 0.65%和 5%/5mm，99.79 ± 0.24%-99.92 ± 0.09%，协议取决于协议的精度。
所有治疗方案均产生了高质量和剂量学准确性的计划，IMRT 提供了最佳的 OAR 保护，VMAT 是我们高复杂性治疗计划比较中的最有效治疗选择。
