Department of Radiation Oncology, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA.
Int J Radiat Oncol Biol Phys. 2013 Oct 1;87(2):375-82. doi: 10.1016/j.ijrobp.2013.05.048.
To assess the dosimetric impact caused by the interplay between intrafraction prostate motion and the intermittent delivery of proton pencil beam scanning (PBS).
A cohort of 10 prostate patients was treated with PBS using a bilateral single-field uniform dose (SFUD) modality. Bilateral intensity-modulated proton therapy (IMPT) plans were generated for comparison. Because beam-on time in PBS was intermittent, the actual beam-on time was determined from treatment logs. Prostate motion was generalized according to real-time Calypso tracking data from our previously reported prospective photon trial. We investigated potential dose deviations by considering the interplay effect resulting from the worst-case scenario motion and the PBS delivery sequence.
For both bilateral-field SFUD and IMPT plans, clinical target volume (CTV) D99% coverage was degraded <2% owing to prostate intrafraction motion when averaged over the course of treatment, but was >10% for the worst fraction. The standard deviation of CTV D99% distribution was approximately 1.2%. The CTV coverage of individual fields in SFUD plans degraded as time elapsed after the initial alignment, owing to prostate drift. Intensity-modulated proton therapy and SFUD demonstrated comparable results when bilateral opposed fields were used. Single-field SFUD plans that were repainted twice, which could reduce half of the treatment time, resulted in similar CTV coverage as bilateral-field plans.
Intrafraction prostate motion affects the actual delivered dose to CTV; however, when averaged over the course of treatment, CTV D99% coverage degraded only approximately 2% even for the worst-case scenario. The IMPT plan results are comparable to those of the SFUD plan, and similar coverage can be achieved if treated by SFUD 1 lateral field per day when rescanning the field twice to shorten the treatment time and mitigate intrafraction motion.
评估前列腺内运动与质子笔束扫描（PBS）间歇性输送之间相互作用引起的剂量学影响。
对 10 例前列腺患者进行 PBS 治疗，采用双侧单野均匀剂量（SFUD）模式。生成双侧强度调制质子治疗（IMPT）计划进行比较。由于 PBS 中的束流开启时间是间歇性的，实际束流开启时间是根据治疗记录确定的。根据我们之前报道的前瞻性光子试验中实时 Calypso 跟踪数据对前列腺运动进行了概括。我们研究了由于最糟糕情况下的运动和 PBS 输送顺序引起的相互作用效应而导致的潜在剂量偏差。
对于双侧野 SFUD 和 IMPT 计划，当平均治疗过程时，由于前列腺内运动，CTV D99%覆盖度降低<2%，但最差分次时>10%。CTV D99%分布的标准差约为 1.2%。由于前列腺漂移，SFUD 计划中各野的 CTV 覆盖度随着初始对准后时间的流逝而降低。当使用双侧对侧野时，IMPT 和 SFUD 表现出相似的结果。可以将治疗时间减少一半的两次重画单野 SFUD 计划导致与双侧野计划相似的 CTV 覆盖度。
前列腺内运动影响CTV 的实际接受剂量；然而，当平均治疗过程时，即使在最坏情况下，CTV D99%覆盖度也仅降低约 2%。IMPT 计划的结果与 SFUD 计划相当，如果每天治疗 SFUD 1 个侧野，并两次重新扫描该野以缩短治疗时间并减轻内运动，可以实现相似的覆盖度。
