Inova Schar Cancer Institute, Inova Health System, Fairfax, Virginia, USA.
RaySearch Laboratories, Stockholm, Sweden.
Med Phys. 2023 Apr;50(4):1999-2008. doi: 10.1002/mp.16254. Epub 2023 Feb 15.
Pencil beam scanning (PBS) proton therapy allows for far superior dose conformality compared with passive scattering techniques. However, one drawback of PBS is that the beam delivery time can be long, particularly when treating superficial disease. Minimizing beam delivery time is important for patient comfort and precision of treatment delivery. Mini-ridge filters (MRF) have been shown to reduce beam delivery time for synchrotron-based PBS. Given that cyclotron systems are widely used in proton therapy it is necessary to investigate the potential clinical benefit of mini-ridge filters in such systems.
To demonstrate the clinical benefit of using a MRF to reduce beam delivery time for patients with large target volumes and superficial disease in cyclotron-based PBS proton therapy.
A MRF beam model was generated by simulating the effect of a MRF on our clinical beam data assuming a fixed snout position relative to the isocenter. The beam model was validated with a series of measurements. The model was used to optimize treatment plans in a water phantom and on six patient DICOM datasets to further study the effect of the MRF and for comparison with physician-approved clinical treatment plans. Beam delivery time was measured for six plans with and without the MRF to demonstrate the reduction achievable. Plans with and without MRF were reviewed to confirm clinical acceptability by a radiation oncologist. Patient-specific QA measurements were carried out with a two-dimensional ionization chamber array detector for one representative patient's plan optimized with the MRF beam model.
Results show good agreement between the simulated beam model and measurements with mean and maximum deviations of 0.06 mm (0.45%) and 0.61 mm (4.9%). The increase in Bragg peak width (FWHM) ranged from 2.7 mm at 226 MeV to 6.1 mm at 70 MeV. The mean and maximum reduction in beam delivery time observed per field was 29.1 s (32.2%) and 79.7 s (55.3%).
MRFs can be used to reduce treatment time in cyclotron-based PBS proton therapy without sacrificing plan quality. This is particularly beneficial for patients with large targets and superficial disease such as in breast cancer where treatment times are generally long, as well as patients treated with deep inspiration breath hold (DIBH).
铅笔束扫描（PBS）质子治疗相比于被动散射技术能够实现更好的剂量适形性。然而，PBS 的一个缺点是束流传输时间可能会很长，尤其是在治疗浅层疾病时。最小化束流传输时间对于患者的舒适度和治疗交付的精确性非常重要。已经证明，微型脊滤波器（MRF）可以减少基于同步加速器的 PBS 的束流传输时间。鉴于回旋加速器系统在质子治疗中广泛使用，因此有必要研究 MRF 在这种系统中的潜在临床益处。
证明在基于回旋加速器的 PBS 质子治疗中，对于具有大靶区和浅层疾病的患者，使用 MRF 来减少束流传输时间的临床益处。
通过模拟 MRF 对我们的临床束流数据的影响，生成了 MRF 束流模型，假设 MRF 相对于等中心的位置固定。通过一系列测量验证了束流模型。该模型用于在水模体和六个患者 DICOM 数据集上优化治疗计划，以进一步研究 MRF 的影响，并与医生批准的临床治疗计划进行比较。测量了六个有和没有 MRF 的计划的束流传输时间，以展示可实现的减少量。由一名放射肿瘤学家审查了有和没有 MRF 的计划，以确认临床可接受性。对一位使用 MRF 束流模型优化的代表性患者的计划进行了患者特异性 QA 测量，使用二维电离室阵列探测器进行测量。
结果表明，模拟束流模型与测量结果之间具有良好的一致性，平均偏差和最大偏差分别为 0.06 毫米（0.45%）和 0.61 毫米（4.9%）。布拉格峰宽度（FWHM）的增加范围为 226 MeV 时的 2.7 毫米到 70 MeV 时的 6.1 毫米。每个射野观察到的束流传输时间的平均和最大减少量分别为 29.1 秒（32.2%）和 79.7 秒（55.3%）。
在基于回旋加速器的 PBS 质子治疗中，可以使用 MRF 来减少治疗时间，而不会牺牲计划质量。对于具有大靶区和浅层疾病（如乳腺癌）的患者，以及接受深吸气屏气（DIBH）治疗的患者，这尤其有益，因为这些患者的治疗时间通常较长。
