Instantaneous in vivo distal edge verification in intensity-modulated proton therapy by means of PET imaging.

Medical physics Pub Date : 2025-05-02 DOI:10.1002/mp.17850
Brian Zapien-Campos, Zahra Ahmadi Ganjeh, Giuliano Perotti-Bernardini, Jeffrey Free, Stefan Both, Peter Dendooven
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引用次数: 0

Abstract

Background: Intensity-modulated proton therapy (IMPT) holds promise for improving outcomes in head-and-neck cancer (HNC) patients by enhancing organ-at-risk (OAR) sparing. A key challenge in IMPT is ensuring an accurate dose delivery at the distal edge of the tumor, where the steep dose gradients make treatment precision highly sensitive to uncertainties in both proton range and patient setup. Thus, IMPT conformality is increased by incorporating robust margins in the treatment optimization. However, an increment in the plan robustness could lead to an OAR overdosing. Therefore, an accurate distal edge verification during dose delivery is crucial to increase IMPT conformality by reducing optimization settings in treatment planning.

Purpose: This work aims to evaluate, in a quasi-clinical setting, a novel approach for accurate instantaneous proton beam distal edge verification in IMPT by means of spot-by-spot positron emission tomography (PET) imaging.

Methods: An anthropomorphic head and neck phantom CIRS-731 HN was irradiated at the head and neck region. The targets were defined as 4 cm diameter spheres. A 60-ms delay was introduced between the proton beam spots in order to enable the spot-by-spot coincidence detection of the 511-keV photons resulting from positron annihilation following the positron emission from very short-lived positron-emitting, mainly 12N (T1/2  = 11.0 ms). Additionally, modified irradiations were carried out using solid water slabs of 2 and 5 mm thickness in the beam path to assess the precision of the approach for detecting range deviations. The positron activity range (PAR) was determined from the 50% distal fall-off position of the 1D longitudinal positron activity profile derived from the 2D image reconstructions. Furthermore, Monte Carlo (MC) simulations were performed using an in-house RayStation/GATE MC framework to predict the positron activity images and verify the PAR measurements.

Results: PAR measurements achieved a precision between 1.5 and 3.6 mm (at 1.5σ clinical level) at the beam spot level within sub-second time scales. Measured PAR shifts of 1.6-2.1  and 4.2--.7 mm were observed with the 2- and 5-mm thickness range shifters, respectively, aligning with the corresponding proton dose range (PDR) shifts of 1.3-1.8 and 3.9-4.3 mm. The simulated PAR agrees with the measured PARs, showing an average range difference of ∼0.4 mm.

Conclusion: This study demonstrated the feasibility of instantaneous distal edge verification using PET imaging by introducing beam spot delays during dose delivery. The findings represent a first step toward the clinical implementation of instantaneous in vivo distal edge verification. The approach contributes to the development of real-time range verification aimed at improving IMPT treatments by mitigating range and setup uncertainties, thereby reducing dose to organs-at-risk and ultimately enhancing patient outcomes.

利用PET成像技术在调强质子治疗中的瞬时体内远端边缘验证。
背景:强度调节质子治疗(IMPT)有望通过增强危险器官(OAR)保护来改善头颈癌(HNC)患者的预后。IMPT的一个关键挑战是确保肿瘤远端边缘的准确剂量递送,那里陡峭的剂量梯度使治疗精度对质子范围和患者设置的不确定性高度敏感。因此,通过在治疗优化中纳入稳健的边缘,提高了IMPT的一致性。然而,计划稳健性的增加可能导致桨叶过量。因此,在给药过程中精确的远端边缘验证对于通过减少治疗计划中的优化设置来提高IMPT的一致性至关重要。目的:本研究旨在评估在准临床环境下,通过逐点正电子发射断层扫描(PET)成像,在IMPT中精确瞬时质子束远端边缘验证的新方法。方法:在头颈区照射拟人化头颈假体CIRS-731 HN。目标定义为直径为4厘米的球体。在质子束点之间引入60 ms的延迟,以实现对极短正电子发射(主要是12N (T1/2 = 11.0 ms))正电子湮灭后产生的511 kev光子的逐点重合检测。此外,在光束路径中使用2和5 mm厚度的固体水板进行改进照射,以评估该方法检测距离偏差的精度。正电子活度范围(PAR)由二维图像重建得出的一维纵向正电子活度剖面的50%远端下降位置确定。此外,使用内部RayStation/GATE MC框架进行蒙特卡罗(MC)模拟,以预测正电子活动图像并验证PAR测量结果。结果:在亚秒的时间尺度上,PAR测量的精度在1.5 ~ 3.6 mm之间(临床水平为1.5σ)。实测PAR位移为1.6-2.1和4.2—。2 mm和5 mm厚度范围移位器分别观察到7 mm,对应的质子剂量范围(PDR)移位为1.3-1.8和3.9-4.3 mm。模拟的PAR与测量的PAR一致,显示出约0.4 mm的平均范围差异。结论:本研究表明,通过在剂量传递过程中引入束斑延迟,使用PET成像进行瞬时远端边缘验证是可行的。这些发现代表了临床实现瞬时体内远端边缘验证的第一步。该方法有助于实时范围验证的发展,旨在通过减轻范围和设置的不确定性来改善IMPT治疗,从而减少对危险器官的剂量,最终提高患者的预后。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
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