Harmon Grant, Diak Abbie, Shea Steven M, Yacoub Joseph H, Small William, Harkenrider Matthew M
Department of Radiation Oncology, Loyola University, Chicago, IL.
Department of Radiology, Loyola University, Chicago, IL.
Brachytherapy. 2016 Nov-Dec;15(6):825-831. doi: 10.1016/j.brachy.2016.08.010. Epub 2016 Sep 29.
To evaluate the dosimetric benefits of MRI-based brachytherapy in small and large high-risk clinical target volume (HR-CTV) in cervical cancer.
Twenty-eight fractions obtained from sixteen cervical cancer patients treated with MRI-based high-dose-rate brachytherapy with standard tandem and ovoid applicators were used; original fractions were optimized to HR-CTV D. Fractions were separated based on the median volume into small and large (HR-CTV <25 cm or >25 cm) lesion groups. Retrospective plans prescribed to Point A were created for each fraction. D, D, and International Commission of Radiation Unit and Measurements (ICRU) points were used to compare Point A vs. HR-CTV D plans for bladder, rectum, and sigmoid.
In the small lesion group, Point A plans vs. HR-CTV D plans had significantly higher D, D, and ICRU points for bladder, rectum, and sigmoid (p < 0.05). In the large lesion group, there was no significant difference between Point A and HR-CTV D plans for D, D, and ICRU points to the organs at risk (OARs).
The dosimetric advantages to OARs offered by MRI-based brachytherapy with prescription to HR-CTV D compared to Point A is most distinct for patients with smaller HR-CTV (<25 cm). This study demonstrates sufficient tumor coverage with lower doses to OARs in HR-CTV D vs. Point A plans in the small lesion group. These improvements were not seen in the large lesion group, indicating a lesser dosimetric advantage of HR-CTV D compared to Point A planning when the cervical lesion is >25 cm. Incorporation of interstitial needles for patients with larger HR-CTV is likely the best method to decrease dose to OARs and improve tumor coverage.
评估基于磁共振成像（MRI）的近距离放射治疗对宫颈癌中小高危临床靶区（HR-CTV）和大高危临床靶区的剂量学益处。
使用了16例接受基于MRI的高剂量率近距离放射治疗的宫颈癌患者的28个分次，采用标准的串联和卵圆形施源器；原始分次针对HR-CTV D进行了优化。根据中位体积将分次分为小病灶组和大病灶组（HR-CTV<25 cm或>25 cm）。为每个分次创建了针对A点的回顾性计划。使用D、D以及国际辐射单位与测量委员会（ICRU）点来比较A点与HR-CTV D计划对膀胱、直肠和乙状结肠的剂量。
在小病灶组中，A点计划与HR-CTV D计划相比，膀胱、直肠和乙状结肠的D、D以及ICRU点显著更高（p<0.05）。在大病灶组中，A点与HR-CTV D计划在危及器官（OARs）的D、D以及ICRU点方面没有显著差异。
与A点相比，基于MRI的近距离放射治疗并处方至HR-CTV D时，对OARs的剂量学优势在HR-CTV较小（<25 cm）的患者中最为明显。本研究表明，在小病灶组中，HR-CTV D计划与A点计划相比，能以较低剂量充分覆盖肿瘤，同时对OARs的剂量更低。在大病灶组中未观察到这些改善，这表明当宫颈病灶>25 cm时，与A点计划相比，HR-CTV D的剂量学优势较小。对于HR-CTV较大的患者，采用组织间插植针可能是降低OARs剂量并改善肿瘤覆盖的最佳方法。
