Wang Aoxiang, Zhu Ya-Nan, Setianegara Jufri, Lin Yuting, Hamaide Valentin, Pin Arnaud, Xiao Peng, Xie Qingguo, Gao Hao
Department of Biomedical Engineering, Huazhong University of Science and Technology, Wuhan, China.
Department of Radiation Oncology, University of Kansas Medical Center, Kansas City, USA.
Med Phys. 2025 Aug;52(8):e18031. doi: 10.1002/mp.18031.
Efficient delivery of intensity-modulated proton therapy (IMPT) plays a pivotal role in improving the effectiveness of proton therapy. Accelerating delivery not only increases patient throughput but also improves the ability to manage dynamic target motion and reduces uncertainties, thereby enhancing treatment accuracy. Additionally, rapid delivery enables the effective use of breath-hold techniques, allowing for smaller target margins and providing better protection for healthy tissues. Since energy layer switching time constitute the majority of delivery time, reducing the number of energy layers can be highly beneficial for improving delivery efficiency.
This work proposes a novel energy layer reduction method for rapid IMPT using a ridge filter.
The width of the Bragg peak (BP) is extended using a ridge filter, referred to as the extended Bragg peak (EBP). The machine file of the generated EBP is subsequently incorporated in our in-house treatment planning system for inverse planning. The extended peak width reduces the number of energy layers required for target coverage. However, relying solely on EBP can compromise the accuracy of energy modulation. To address this limitation, pristine BP is utilized to fill small gaps left by EBP and ensure rapid dose fall-off at the distal and proximal edges of the target. To optimize the selection of BP and EBP energies, the problem is formulated as a mathematical model incorporating a group sparsity constraint. The model is then solved by a variant of block orthogonal matching pursuit algorithm, which selects BP and EBP energies in a greedy manner.
The combined use of BP and EBP, referred to as the BP-EBP, considerably reduced the number of energy layers required compared to conventional IMPT. For example, in an abdomen case, the BP-EBP method decreased the energy layers from 79 to 28 (11 for BP and 17 for EBP) while maintaining comparable plan quality. Similarly, in a lung case, it reduced the energy layers from 70 to 30 (9 for BP and 21 for EBP), achieving slightly better plan quality than the conventional approach. Moreover, the BP-EBP reduced delivery time by more than 50% in both cases compared to conventional IMPT. Furthermore, the feasibility of BP-EBP was experimentally demonstrated on the ProteusONE proton therapy system.
A novel energy reduction method is proposed and experimentally demonstrated that leverages BP and EBP generated by a ridge filter that significantly decreases the number of energy levels required in IMPT, thereby enhancing delivery efficiency.
调强质子治疗（IMPT）的高效实施在提高质子治疗效果方面起着关键作用。加快治疗实施不仅能提高患者 throughput，还能增强应对动态靶区运动的能力，减少不确定性，从而提高治疗精度。此外，快速实施治疗能够有效利用屏气技术，缩小靶区边界，更好地保护健康组织。由于能量层切换时间占治疗实施时间的大部分，减少能量层数对提高治疗实施效率非常有益。
本研究提出一种利用脊形滤波器实现快速IMPT的新型能量层减少方法。
使用脊形滤波器扩展布拉格峰（BP）的宽度，称为扩展布拉格峰（EBP）。随后将生成的EBP的机器文件纳入我们内部的治疗计划系统进行逆向计划。扩展后的峰宽减少了覆盖靶区所需的能量层数。然而，仅依靠EBP可能会影响能量调制的精度。为解决这一局限性，利用原始BP填充EBP留下的小间隙，并确保在靶区远端和近端边缘实现快速剂量下降。为优化BP和EBP能量的选择，将该问题表述为一个包含组稀疏约束的数学模型。然后通过块正交匹配追踪算法的一个变体来求解该模型，该算法以贪婪方式选择BP和EBP能量。
与传统IMPT相比，联合使用BP和EBP（称为BP-EBP）大大减少了所需的能量层数。例如，在一个腹部病例中，BP-EBP方法将能量层数从79减少到28（BP为11层，EBP为17层），同时保持了相当的计划质量。同样，在一个肺部病例中，它将能量层数从70减少到30（BP为9层，EBP为21层），计划质量略优于传统方法。此外，与传统IMPT相比，BP-EBP在这两种情况下都将治疗实施时间缩短了50%以上。此外，在ProteusONE质子治疗系统上通过实验证明了BP-EBP的可行性。
提出并通过实验证明了一种新型能量减少方法，该方法利用脊形滤波器生成的BP和EBP，显著减少了IMPT中所需的能量层数，从而提高了治疗实施效率。
