Institute of Radiation Physics, Lausanne University Hospital and Lausanne University, Lausanne, Switzerland.
Accuray Incorporated, Madison, Wisconsin, USA.
J Appl Clin Med Phys. 2024 Oct;25(10):e14478. doi: 10.1002/acm2.14478. Epub 2024 Aug 8.
Treatment delivery safety and accuracy are essential to control the disease and protect healthy tissues in radiation therapy. For usual treatment, a phantom-based patient specific quality assurance (PSQA) is performed to verify the delivery prior to the treatment. The emergence of adaptive radiation therapy (ART) adds new complexities to PSQA. In fact, organ at risks and target volume re-contouring as well as plan re-optimization and treatment delivery are performed with the patient immobilized on the treatment couch, making phantom-based pretreatment PSQA impractical. In this case, phantomless PSQA tools based on multileaf collimator (MLC) leaf open times (LOTs) verifications provide alternative approaches for the Radixact® treatment units. However, their validity is compromised by the lack of independent and reliable methods for calculating the LOT performed by the MLC during deliveries.
To provide independent and reliable methods of LOT calculation for the Radixact® treatment units.
Two methods for calculating the LOTs performed by the MLC during deliveries have been implemented. The first method uses the signal recorded by the build-in detector and the second method uses the signal recorded by optical sensors mounted on the MLC. To calibrate the methods to the ground truth, in-phantom ionization chamber LOT measurements have been conducted on a Radixact® treatment unit. The methods were validated by comparing LOT calculations with in-phantom ionization chamber LOT measurements performed on two Radixact® treatment units.
The study shows a good agreement between the two LOT calculation methods and the in-phantom ionization chamber measurements. There are no notable differences between the two methods and the same results were observed on the different treatment units.
The two implemented methods have the potential to be part of a PSQA solution for ART in tomotherapy.
在放射治疗中，为了控制疾病和保护健康组织，治疗的实施安全和精确至关重要。对于常规治疗，会进行基于体模的患者特定质量保证（PSQA），以在治疗前验证交付。自适应放射治疗（ART）的出现给 PSQA 增加了新的复杂性。事实上，在患者固定在治疗床上的情况下，进行危及器官和靶区重新轮廓勾画、计划重新优化和治疗实施，使得基于体模的预处理 PSQA 变得不切实际。在这种情况下，基于多叶准直器（MLC）叶片开启次数（LOT）验证的无体模 PSQA 工具为 Radixact®治疗单元提供了替代方法。然而，由于缺乏用于计算治疗过程中 MLC 执行 LOT 的独立且可靠的方法，这些工具的有效性受到了影响。
为 Radixact®治疗单元提供 LOT 计算的独立且可靠方法。
实施了两种用于计算治疗过程中 MLC 执行 LOT 的方法。第一种方法使用内置探测器记录的信号，第二种方法使用安装在 MLC 上的光学传感器记录的信号。为了将这些方法校准到真实情况，在 Radixact®治疗单元上进行了体模内电离室 LOT 测量。通过将 LOT 计算与在两个 Radixact®治疗单元上进行的体模内电离室 LOT 测量进行比较，对这些方法进行了验证。
研究表明，两种 LOT 计算方法与体模内电离室测量结果之间具有良好的一致性。两种方法之间没有明显差异，并且在不同的治疗单元上观察到相同的结果。
这两种已实施的方法有可能成为 Tomotherapy 中 ART 的 PSQA 解决方案的一部分。
