Ionoacoustic application of an optical hydrophone to detect proton beam range in water.
Ionoacoustic application of an optical hydrophone to detect proton beam range in water.
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光学水听器的离子声学应用来检测水中质子束的范围。
DOI：
10.1002/mp.16189
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发表时间：
2022
期刊：
影响因子：
3.8
通讯作者：
Taeko Matsuura
中科院分区：
文献类型：
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作者：
Shota Sueyasu;Taisuke Takayanagi;Koichi Miyazaki;Yasutoshi Kuriyama;Yoshihiro Ishi;Tomonori Uesugi;Mehmet Burcin Unlu;Nobuki Kudo;Ye Chen;Koki Kasamatsu;Masayuki Fujii;Masanori Kobayashi;Wolfgang Rohringer;Taeko Matsuura
背景质子射程的不确定性一直是限制质子治疗能力的主要因素，以集中剂量到肿瘤，以充分发挥其潜力。离子声（IA）范围验证是一种方法，以减少这种不确定性，通过检测热声波发射的照射体积后立即脉冲质子束输送，然而，信号的弱点一直是其临床应用的障碍。为了提高传统压电水听器的信噪比（SNR），需要较大的探测器灵敏体积，但这会缩小可用波束角的范围，并干扰波束传输过程中获得的真实的时间图像。目的为了防止这个问题，我们研究了一种利用激光干涉原理的毫米级光学水听器（OH）。对于两种类型的IA波[从布拉格峰（BP）发射的γ波和从金基准标记（GM）发射的具有谐振频率（SPIRE）的球形IA波]，在波形、SNR、范围检测精度和信号强度鲁棒性方面与PH进行了比较，以对抗小的检测器未对准，方法使用固定场交变梯度加速器产生具有27 ns脉冲宽度和4 mm射束尺寸的100-MeV质子射束，并照射到水模型。GM被设置在梁的中心轴上。不同厚度的丙烯酸板，最多12毫米，被设置在幻影的前面，以改变质子范围。将OH设置在射束的远端和侧面，使用γ波的飞行时间方法并通过与SPIRE IA波传输模拟得出的校准数据（SPIRE强度与GM和BP之间的距离）进行比较来估计范围。每脉冲剂量0.5-0.6戈伊。为了测量SPIRE振幅对水听器未对准的变化，水听器在横向方向上最大移动± 2 mm。ResultsOH尽管尺寸小，但可以检测到比传统PH（直径29 mm）更高SNR的γ波，并且单次测量足以检测水中亚毫米精度的波束范围。在SPIRE测量中，OH比我们先前研究中使用的聚焦PH（FPH）[5%/mm（OH）vs 80%/mm（FPH）]对探测器未对准更加稳健，并且测量的SPIRE强度与GM和BP之间的距离之间的相关性与模拟结果一致。然而，OH灵敏度低于FPH灵敏度，需要约5.6-戈伊剂量才能将测量值之间的强度变化降低到10%.ConclusionThe miniature OH was found to detect weak IA signals by proton beams with a BP dose used in hypofractionated regimens.在MHz制度下的OH灵敏度的改善是值得探索的下一步。
BackgroundProton range uncertainty has been the main factor limiting the ability of proton therapy to concentrate doses to tumors to their full potential. Ionoacoustic (IA) range verification is an approach to reducing this uncertainty by detecting thermoacoustic waves emitted from an irradiated volume immediately following a pulsed proton beam delivery; however, the signal weakness has been an obstacle to its clinical application. To increase the signal‐to‐noise ratio (SNR) with the conventional piezoelectric hydrophone (PH), the detector‐sensitive volume needs to be large, but it could narrow the range of available beam angles and disturb real‐time images obtained during beam delivery.PurposeTo prevent this issue, we investigated a millimeter‐sized optical hydrophone (OH) that exploits the laser interferometric principle. For two types of IA waves [γ‐wave emitted from the Bragg peak (BP) and a spherical IA wave with resonant frequency (SPIRE) emitted from the gold fiducial marker (GM)], comparisons were made with PH in terms of waveforms, SNR, range detection accuracy, and signal intensity robustness against the small detector misalignment, particularly for SPIRE.MethodsA 100‐MeV proton beam with a 27 ns pulse width and 4 mm beam size was produced using a fixed‐field alternating gradient accelerator and was irradiated to the water phantom. The GM was set on the beam's central axis. Acrylic plates of various thicknesses, up to 12 mm, were set in front of the phantoms to shift the proton range. OH was set distal and lateral to the beam, and the range was estimated using the time‐of‐flight method for γ‐wave and by comparing with the calibration data (SPIRE intensity versus the distance between the GM and BP) derived from an IA wave transport simulation for SPIRE. The BP dose per pulse was 0.5–0.6 Gy. To measure the variation in SPIRE amplitude against the hydrophone misalignment, the hydrophone was shifted by ± 2 mm at a maximum in lateral directions.ResultsDespite its small size, OH could detect γ‐wave with a higher SNR than the conventional PH (diameter, 29 mm), and a single measurement was sufficient to detect the beam range with a submillimeter accuracy in water. In the SPIRE measurement, OH was far more robust against the detector misalignment than the focused PH (FPH) used in our previous study [5%/mm (OH) versus 80%/mm (FPH)], and the correlation between the measured SPIRE intensity and the distance between the GM and BP agreed well with the simulation results. However, the OH sensitivity was lower than the FPH sensitivity, and about 5.6‐Gy dose was required to decrease the intensity variation among measurements to less than 10%.ConclusionThe miniature OH was found to detect weak IA signals produced by proton beams with a BP dose used in hypofractionated regimens. The OH sensitivity improvement at the MHz regime is worth exploring as the next step.