Department of Radiation Oncology, University of Washington Medical Center, Seattle, WA, 98195, USA.
Department of Radiation Oncology, Rush University Medical Center, Chicago, IL, 60612, USA.
Med Phys. 2018 Jul;45(7):3275-3286. doi: 10.1002/mp.12985. Epub 2018 Jun 10.
We propose a novel compensator-based IMRT system designed to provide a simple, reliable, and cost-effective adjunct technology, with the goal of expanding global access to advanced radiotherapy techniques. The system would employ easily reusable tungsten bead compensators that operate independent of a gantry (e.g., mounted in a ring around the patient). Thereby the system can be retrofitted to existing linac and cobalt teletherapy units. This study explores the quality of treatment plans from the proposed system and the dependence on associated design parameters.
We considered Co-based plans as the most challenging scenario for dosimetry and benchmarked them against clinical MLC-based plans delivered on a linac. Treatment planning was performed in the Pinnacle treatment planning system with commissioning based on Monte Carlo simulations of compensated beams. Co-compensator IMRT plans were generated for five patients with head-and-neck cancer and five with gynecological cancer and compared to respective IMRT plans using a 6 MV linac beam with an MLC. The dependence of dosimetric endpoints on compensator resolution, thickness, position, and number of beams was assessed. Dosimetric accuracy was validated by Monte Carlo simulations of dose distribution in a water phantom from beams with the IMRT plan compensators.
The Co-compensator plans had on average equivalent PTV coverage and somewhat inferior OAR sparing compared to the 6 MV-MLC plans, but the differences in dosimetric endpoints were clinically acceptable. Calculated treatment times for head-and-neck plans were 7.6 ± 2.0 min vs 3.9 ± 0.8 min (6 MV-MLC vs Co-compensator) and for gynecological plans were 8.7 ± 3.1 min vs 4.3 ± 0.4 min. Plan quality was insensitive to most design parameters over much of the ranges studied, with no degradation found when the compensator resolution was finer than 6 mm, maximum thickness at least 2 tenth-value-layers, and more than five beams were used. Source-to-compensator distances of 53 and 63 cm resulted in very similar plan quality. Monte Carlo simulations suggest no increase in surface dose for the geometries considered here. Simulated dosimetric validation tests had median gamma pass rates of 97.6% for criteria of 3% (global)/3 mm with a 10% threshold.
The novel ring-compensator IMRT system can produce plans of comparable quality to standard 6 MV-MLC systems. Even when Co beams are used the plan quality is acceptable and treatment times are substantially reduced. Co-compensator IMRT plans are adequately modeled in an existing commercial treatment planning system. These results motivate further development of this low-cost adaptable technology with translation through clinical trials and deployment to expand the reach of IMRT in low- and middle-income countries.
我们提出了一种基于补偿器的新型调强放射治疗（IMRT）系统，旨在提供一种简单、可靠且具有成本效益的辅助技术，以扩大全球先进放射治疗技术的应用范围。该系统将采用易于重复使用的钨珠补偿器，这些补偿器独立于治疗头（例如，安装在患者周围的环形结构中）运行。因此，该系统可以 retrofit 到现有的直线加速器和钴 60 治疗机上。本研究探讨了该系统提出的治疗计划的质量以及对相关设计参数的依赖性。
我们将 Co 基计划视为剂量学方面最具挑战性的情况，并将其与在直线加速器上进行的临床多叶准直器（MLC）计划进行了基准比较。在 Pinnacle 治疗计划系统中进行治疗计划制定，采用基于补偿射束的蒙特卡罗模拟进行验证。我们为 5 例头颈部癌症患者和 5 例妇科癌症患者生成了 Co 补偿器 IMRT 计划，并与使用 6 MV MLC 治疗头的相应 IMRT 计划进行了比较。评估了补偿器分辨率、厚度、位置和射束数量对剂量学终点的依赖性。通过在水模体中对具有 IMRT 计划补偿器的射束的剂量分布进行蒙特卡罗模拟，验证了剂量学准确性。
Co 补偿器计划的 PTV 覆盖率平均等效，OAR 保护稍差于 6 MV-MLC 计划，但剂量学终点的差异在临床可接受范围内。头颈部计划的计算治疗时间为 7.6 ± 2.0 分钟，而 6 MV-MLC 计划为 3.9 ± 0.8 分钟（Co 补偿器）；妇科计划分别为 8.7 ± 3.1 分钟和 4.3 ± 0.4 分钟。在研究的大部分范围内，计划质量对大多数设计参数不敏感，当补偿器分辨率小于 6mm、最大厚度至少为 2 个 10 层值和使用超过 5 个射束时，未发现计划质量下降。源至补偿器距离为 53cm 和 63cm 时，计划质量非常相似。蒙特卡罗模拟表明，对于这里考虑的几何形状，表面剂量没有增加。模拟剂量验证测试的中位数伽马通过率为 97.6%，标准为 3%（全局）/3mm，阈值为 10%。
新型环形补偿器 IMRT 系统可以生成与标准 6 MV-MLC 系统相当的高质量计划。即使使用 Co 射束，计划质量也是可接受的，并且治疗时间大大缩短。Co 补偿器 IMRT 计划在现有的商业治疗计划系统中得到了充分的建模。这些结果为这种低成本、适应性强的技术的进一步发展提供了动力，该技术通过临床试验进行转化并部署，以扩大调强放射治疗在低收入和中等收入国家的应用范围。
