Department of Radiation Medicine, Medical Physics Graduate Program, University of Kentucky, Lexington, KY, USA.
J Appl Clin Med Phys. 2020 Jun;21(6):83-92. doi: 10.1002/acm2.12868. Epub 2020 Apr 3.
Due to multiple beamlets in the delivery of highly modulated volumetric arc therapy (VMAT) plans, dose delivery uncertainties associated with small-field dosimetry and interplay effects can be concerns in the treatment of mobile lung lesions using a single-dose of stereotactic body radiotherapy (SBRT). Herein, we describe and compare a simple, yet clinically useful, hybrid 3D-dynamic conformal arc (h-DCA) planning technique using flattening filter-free (FFF) beams to minimize these effects.
Fifteen consecutive solitary early-stage I-II non-small-cell lung cancer (NSCLC) patients who underwent a single-dose of 30 Gy using 3-6 non-coplanar VMAT arcs with 6X-FFF beams in our clinic. These patients' plans were re-planned using a non-coplanar hybrid technique with 2-3 differentially-weighted partial dynamic conformal arcs (DCA) plus 4-6 static beams. About 60-70% of the total beam weight was given to the DCA and the rest was distributed among the static beams to maximize the tumor coverage and spare the organs-at-risk (OAR). The clinical VMAT and h-DCA plans were compared via RTOG-0915 protocol for conformity and dose to OAR. Additionally, delivery efficiency, accuracy, and overall h-DCA planning time were recorded.
All plans met RTOG-0915 requirements. Comparison with clinical VMAT plans h-DAC gave better target coverage with a higher dose to the tumor and exhibited statistically insignificance differences in gradient index, D , gradient distance and OAR doses with the exception of maximal dose to skin (P = 0.015). For h-DCA plans, higher values of tumor heterogeneity and tumor maximum, minimum and mean doses were observed and were 10%, 2.8, 1.0, and 2.0 Gy, on average, respectively, compared to the clinical VMAT plans. Average beam on time was reduced by a factor of 1.51. Overall treatment planning time for h-DCA was about an hour.
Due to no beam modulation through the target, h-DCA plans avoid small-field dosimetry and MLC interplay effects and resulting in enhanced target coverage by improving tumor dose (characteristic of FFF-beam). The h-DCA simplifies treatment planning and beam on time significantly compared to clinical VMAT plans. Additionally, h-DCA allows for the real time target verification and eliminates patient-specific VMAT quality assurance; potentially offering cost-effective, same or next day SBRT treatments. Moreover, this technique can be easily adopted to other disease sites and small clinics with less extensive physics or machine support.
由于高度调制容积弧形治疗（VMAT）计划中存在多个射束，因此在使用单次立体定向体部放射治疗（SBRT）治疗移动性肺病变时，与小射野剂量学和相互作用效应相关的剂量传递不确定性可能是一个问题。在此，我们描述并比较了一种简单但临床上有用的混合 3D 动态适形弧形（h-DCA）规划技术，该技术使用无均整滤波器（FFF）射束来最小化这些效应。
在我们的诊所中，有 15 名连续的早期 I-II 期非小细胞肺癌（NSCLC）患者接受了单次 30Gy 的治疗，使用了 3-6 个非共面 VMAT 弧形和 6X-FFF 射束。对这些患者的计划进行了重新规划，使用了具有 2-3 个不同权重的部分动态适形弧形（DCA）加 4-6 个静态射束的非共面混合技术。大约 60-70%的总射束权重分配给 DCA，其余部分分配给静态射束，以最大限度地提高肿瘤覆盖率并保护危及器官（OAR）。根据 RTOG-0915 方案，通过比较临床 VMAT 和 h-DCA 计划的适形性和 OAR 剂量来评估计划。此外，还记录了传递效率、准确性和整体 h-DCA 规划时间。
所有计划均符合 RTOG-0915 要求。与临床 VMAT 计划相比，h-DCA 提供了更好的靶区覆盖率，肿瘤剂量更高，梯度指数、D、梯度距离和 OAR 剂量差异具有统计学意义，但皮肤最大剂量除外（P=0.015）。对于 h-DCA 计划，观察到更高的肿瘤不均匀性和肿瘤最大、最小和平均剂量值，分别为 10%、2.8、1.0 和 2.0Gy，平均而言，与临床 VMAT 计划相比。平均射束开启时间减少了 1.51 倍。h-DCA 的整体治疗计划时间约为 1 小时。
由于靶区无射束调制，h-DCA 计划避免了小射野剂量学和 MLC 相互作用效应，通过提高肿瘤剂量（FFF 射束的特征）从而提高了靶区覆盖率。与临床 VMAT 计划相比，h-DCA 显著简化了治疗计划和射束开启时间。此外，h-DCA 允许实时靶区验证，并消除了特定于患者的 VMAT 质量保证；可能提供具有成本效益的、相同或次日的 SBRT 治疗。此外，该技术可以很容易地应用于其他疾病部位和小型诊所，这些诊所的物理或机器支持较少。
