Tariq Mahin, Gomez Cindy, Riegel Adam C
St. Peter's Health Partners, Albany, NY 12208, United States.
Hofstra University, Hempstead, NY 11549, United States.
Phys Imaging Radiat Oncol. 2019 Sep 12;11:63-68. doi: 10.1016/j.phro.2019.08.004. eCollection 2019 Jul.
Studies have suggested that optically stimulated luminescent dosimeters (OSLDs) can be used for dosimetry of intensity-modulated radiation therapy (IMRT) and volumetric-modulated arc therapy (VMAT). Clinical uncertainties such as placement error have not been thoroughly investigated. The purpose of this work was to measure OSLD placement error in a clinical sample and analyze its dosimetric impact.
The analysis consisted of three parts: first, quantification of placement error in a clinical sample of 128 patients yielding 293 cone-beam CT (CBCT) with visible OSLDs registered to the treatment plan; Second, correlation of placement error and clinical OSLD measurements; third, simulation of dosimeter placement in the treatment plan and correlation of recalculated dose with placement error.
In the first analysis, average placement error was 9.7 ± 9.5 mm. In the second analysis, placement error and measured-to-planned dose agreement yielded no correlation (R = 0.02) for a subsample of 77 CBCTs of 55 head-and-neck patients. Average placement error was 7.0 ± 6.0 mm. Several factors, including image-guided shifts, introduced uncharacterized uncertainty to the measured-to-planned dose agreement. The third analysis isolated placement error from these other effects. Average dosimetric error was -2.4 ± 19.3%. Simulated dosimetric impact was weakly correlated with placement error (R = 0.39). Removing outliers reduced the average dosimetric error to -2.1 ± 10.9%, marginally improving the correlation (R = 0.44).
Placement error can substantially impact measured-to-planned dose agreement of OSLDs in high gradient regions, demonstrating the criticality of accurate dosimeter placement for IMRT and VMAT treatments.
研究表明，光激励发光剂量仪（OSLD）可用于调强放射治疗（IMRT）和容积调强弧形治疗（VMAT）的剂量测定。诸如放置误差等临床不确定性尚未得到充分研究。本研究的目的是测量临床样本中OSLD的放置误差，并分析其剂量学影响。
分析包括三个部分：第一，对128例患者的临床样本中的放置误差进行量化，这些患者产生了293幅与治疗计划配准的可见OSLD的锥形束CT（CBCT）；第二，放置误差与临床OSLD测量值的相关性；第三，在治疗计划中模拟剂量仪放置，并将重新计算的剂量与放置误差进行相关性分析。
在第一次分析中，平均放置误差为9.7±9.5毫米。在第二次分析中，对于55例头颈患者的77幅CBCT的子样本，放置误差与测量剂量与计划剂量的一致性之间没有相关性（R = 0.02）。平均放置误差为7.0±6.0毫米。包括图像引导移位在内的几个因素给测量剂量与计划剂量的一致性带来了未表征的不确定性。第三次分析将放置误差与其他这些影响因素隔离开来。平均剂量学误差为-2.4±19.3%。模拟的剂量学影响与放置误差弱相关（R = 0.39）。去除异常值后，平均剂量学误差降至-2.1±10.9%，相关性略有改善（R = 0.44）。
放置误差可显著影响高梯度区域中OSLD测量剂量与计划剂量的一致性，这表明IMRT和VMAT治疗中准确放置剂量仪至关重要。
