Rangarajan Ramya
Department of Radiation Oncology, Government Royapettah Hospital, Chennai, Tamil Nadu, India.
J Med Phys. 2018 Jan-Mar;43(1):23-27. doi: 10.4103/jmp.JMP_90_17.
Since anatomical and geometric variations occur with every fraction, planning, and dose optimization is necessary for every fraction of high-dose rate intracavitary brachytherapy of carcinoma cervix. In this study, we have tried to quantify the differences in doses to organs at risk (OAR) for each fraction of brachytherapy.
One hundred and seventy computed tomography datasets of cervical cancer patients receiving intracavitary brachytherapy at our institution between January and April 2015 were analyzed. The volumes of the high-risk clinical target volume and OAR contoured were recorded for every insertion. Dose-volume histograms were generated and D90 and D100CTV and D0.1, D1, and D2cc were recorded for bladder, rectum, and sigmoid for each insertion.
Sixty-one percent had a decrease in bladder volume in the second fraction, 35% had an increase in bladder volume and 4% had no change in bladder volume. There was a strong positive correlation between increase in volume and dose (D2cc), which was statistically significant, = 0.441, = 0.013. Nearly 49.4% of patients had an increase in rectal volume during the second fraction. 45.9% had decrease in rectal volume during the second fraction. There was a positive correlation between the increase in volume and dose (D2cc), which was statistically significant, = 0.393, = 0.010. About 63.5% of the patients had a decrease in sigmoid volume during the second fraction, whereas 30.6% had an increase in volume and 5.9% had no change in volume.
First, this study emphasizes the importance of imaging and planning for every fraction of brachytherapy to quantify the exact doses to the target and OAR s. Second, it is important to follow a uniform bladder protocol for every fraction, and adequate bowel preparation is needed for every fraction to minimize the interfraction variations. Finally, it also opens the realm of an adaptive planning strategy in cervical cancers which are known for rapid tumor regression during radiotherapy.
由于每次分次治疗时都会出现解剖学和几何学变化，因此对于子宫颈癌高剂量率腔内近距离放射治疗的每次分次治疗，都需要进行计划制定和剂量优化。在本研究中，我们试图量化近距离放射治疗每次分次时危及器官（OAR）所接受剂量的差异。
分析了2015年1月至4月期间在我们机构接受腔内近距离放射治疗的170例宫颈癌患者的计算机断层扫描数据集。记录每次插入时高危临床靶区体积和勾画的OAR体积。生成剂量体积直方图，并记录每次插入时膀胱、直肠和乙状结肠的D90、D100CTV以及D0.1、D1和D2cc。
61%的患者在第二次分次治疗时膀胱体积减小，35%的患者膀胱体积增加，4%的患者膀胱体积无变化。体积增加与剂量（D2cc）之间存在强正相关，具有统计学意义，r = 0.441，P = 0.013。近49.4%的患者在第二次分次治疗时直肠体积增加。45.9%的患者在第二次分次治疗时直肠体积减小。体积增加与剂量（D2cc）之间存在正相关，具有统计学意义，r = 0.393，P = 0.010。约63.5%的患者在第二次分次治疗时乙状结肠体积减小，而30.6%的患者体积增加，5.9%的患者体积无变化。
首先，本研究强调了对近距离放射治疗的每次分次进行成像和计划制定以量化靶区和OAR确切剂量的重要性。其次，每次分次遵循统一的膀胱方案很重要，并且每次分次都需要充分的肠道准备以尽量减少分次间差异。最后，这也开启了针对在放疗期间肿瘤快速消退的宫颈癌采用自适应计划策略的领域。
