Ates Ozgur, Uh Jinsoo, Pirlepesov Fakhriddin, Hua Chia-Ho, Merchant Thomas E, Krasin Matthew J
St. Jude Children's Research Hospital, Memphis, TN 38105, USA.
Cancers (Basel). 2023 Aug 22;15(17):4200. doi: 10.3390/cancers15174200.
(1) Background: Synthetic CT images of the pelvis were generated from daily CBCT images to monitor changes in water equivalent path length (WEPL) and determine the dosimetric impact of anatomy changes along the proton beam's path; (2) Methods: Ten pediatric patients with pelvic tumors treated using proton therapy with daily CBCT were included. The original planning CT was deformed to the same-day CBCT to generate synthetic CT images for WEPL comparison and dosimetric evaluation; (3) Results: WEPL changes of 20 proton fields at the distal edge of the CTV ranged from 0.1 to 12 mm with a median of 2.5 mm, and 75th percentile of 5.1 mm for (the original CT-rescanned CT) and ranged from 0.3 to 10.1 mm with a median of 2.45 mm and 75th percentile of 4.8 mm for (the original CT-synthetic CT). The dosimetric impact was due to proton range pullback or overshoot, which led to reduced coverage in CTV Dmin averaging 12.1% and 11.3% in the rescanned and synthetic CT verification plans, respectively; (4) Conclusions: The study demonstrated that synthetic CT generated by deforming the original planning CT to daily CBCT can be used to quantify proton range changes and predict adverse dosimetric scenarios without the need for excessive rescanned CT scans during large interfractional variations in adaptive proton therapy of pediatric pelvic tumors.
(1) 背景：从每日的锥形束CT（CBCT）图像生成骨盆的合成CT图像，以监测水等效路径长度（WEPL）的变化，并确定沿质子束路径的解剖结构变化对剂量学的影响；(2) 方法：纳入10例接受质子治疗的小儿盆腔肿瘤患者，每日进行CBCT扫描。将原始计划CT变形为当日CBCT，以生成用于WEPL比较和剂量学评估的合成CT图像；(3) 结果：在CTV远端边缘的20个质子野的WEPL变化范围为0.1至12毫米，中位数为2.5毫米，（原始CT-重新扫描CT）的第75百分位数为5.1毫米，（原始CT-合成CT）的范围为0.3至10.1毫米，中位数为2.45毫米，第75百分位数为4.8毫米。剂量学影响是由于质子射程拉回或超射，这导致CTV Dmin的覆盖范围分别在重新扫描和合成CT验证计划中平均降低了12.1%和11.3%；(4) 结论：该研究表明，通过将原始计划CT变形为每日CBCT生成的合成CT可用于量化质子射程变化，并预测不良剂量学情况，而无需在小儿盆腔肿瘤的自适应质子治疗中进行过多的重新扫描CT扫描。
