Snyder Jeffrey, Smith Blake, Aubin Joel St, Shepard Andrew, Hyer Daniel
Department of Radiation Oncology, University of Iowa Hospitals and Clinics, Iowa City, IA, United States.
Front Oncol. 2024 Jan 8;13:1325105. doi: 10.3389/fonc.2023.1325105. eCollection 2023.
This study simulates a novel prostate SBRT intra-fraction re-optimization workflow in MRIgART to account for prostate intra-fraction motion and evaluates the dosimetric benefit of reducing PTV margins.
VMAT prostate SBRT treatment plans were created for 10 patients using two different PTV margins, one with a 5 mm margin except 3 mm posteriorly (standard) and another using uniform 2 mm margins (reduced). All plans were prescribed to 36.25 Gy in 5 fractions and adapted onto each daily MRI dataset. An intra-fraction adaptive workflow was simulated for the reduced margin group by synchronizing the radiation delivery with target position from cine MRI imaging. Intra-fraction delivered dose was reconstructed and prostate DVH metrics were evaluated under three conditions for the reduced margin plans: Without motion compensation (no-adapt), with a single adapt prior to treatment (ATP), and lastly for intra-fraction re-optimization during delivery (intra). Bladder and rectum DVH metrics were compared between the standard and reduced margin plans.
As expected, rectum V18 Gy was reduced by 4.4 ± 3.9%, D1cc was reduced by 12.2 ± 6.8% (3.4 ± 2.3 Gy), while bladder reductions were 7.8 ± 5.6% for V18 Gy, and 9.6 ± 7.3% (3.4 ± 2.5 Gy) for D1cc for the reduced margin reference plans compared to the standard PTV margin. For the intrafraction replanning approach, average intra-fraction optimization times were 40.0 ± 2.9 seconds, less than the time to deliver one of the four VMAT arcs (104.4 ± 9.3 seconds) used for treatment delivery. When accounting for intra-fraction motion, prostate V36.25 Gy was on average 96.5 ± 4.0%, 99.1 ± 1.3%, and 99.6 ± 0.4 for the non-adapt, ATP, and intra-adapt groups, respectively. The minimum dose received by the prostate was less than 95% of the prescription dose in 84%, 36%, and 10% of fractions, for the non-adapt, ATP, and intra-adapt groups, respectively.
Intra-fraction re-optimization improves prostate coverage, specifically the minimum dose to the prostate, and enables PTV margin reduction and subsequent OAR sparing. Fast re-optimizations enable uninterrupted treatment delivery.
本研究在MRI引导的自适应放疗（MRIgART）中模拟一种新型前列腺立体定向体部放疗（SBRT）分次内重新优化工作流程，以考虑前列腺分次内运动，并评估减少计划靶体积（PTV）边界的剂量学益处。
为10例患者制定容积调强放疗（VMAT）前列腺SBRT治疗计划，使用两种不同的PTV边界，一种除后方为3 mm边界外其余为5 mm边界（标准边界），另一种使用统一的2 mm边界（缩小边界）。所有计划均规定分5次给予36.25 Gy，并适配到每个每日MRI数据集上。通过将放疗与电影MRI成像的靶区位置同步，为缩小边界组模拟了一种分次内自适应工作流程。重建分次内给予的剂量，并在三种情况下评估缩小边界计划的前列腺剂量体积直方图（DVH）指标：无运动补偿（无自适应）、治疗前单次自适应（ATP）以及最后在放疗期间进行分次内重新优化（分次内）。比较标准边界和缩小边界计划之间的膀胱和直肠DVH指标。
正如预期的那样，与标准PTV边界相比，缩小边界参考计划的直肠V18 Gy降低了4.4±3.9%，D1cc降低了12.2±6.8%（3.4±2.3 Gy），而膀胱的V18 Gy降低了7.8±5.6%，D1cc降低了9.6±7.3%（3.4±2.5 Gy）。对于分次内重新计划方法，平均分次内优化时间为40.0±2.9秒，少于用于治疗的四个VMAT弧之一的照射时间（104.4±9.3秒）。考虑分次内运动时，非自适应、ATP和分次内自适应组的前列腺V36.25 Gy平均分别为96.5±4.0%、99.1±1.3%和99.6±0.4%。非自适应、ATP和分次内自适应组分别有84%、36%和10%的分次中前列腺接受的最小剂量低于处方剂量的95%。
分次内重新优化可改善前列腺的覆盖范围，特别是前列腺的最小剂量，并能够减少PTV边界，进而减少危及器官（OAR）受量。快速重新优化可实现不间断的治疗。
