离线自适应技术在鼻咽癌放射治疗中的剂量学分析

目的 基于每周定位CT分析鼻咽癌离线自适应放射治疗(ART)过程中靶区和危及器官体积及剂量差别，探讨放疗再计划的必要性以及离线自适应技术在鼻咽癌放疗中的靶区及危及器官的剂量学改善。方法 选取2021年10月—2022 年10月在我院行根治性放疗的鼻咽癌患者10例，进行容积旋转调强计划设计，并在患者治疗时每周行CT扫描一次，将每周CT图像与原始计划CT图像刚性配准后进行变形配准，勾画出每幅CT的靶区和危及器官，比较分析靶区和危及器官在放疗过程中体积的变化。将原始计划剂量映射到每周CT图像上，得出每周CT靶区和危及器官的分次剂量，与原始计划分次剂量进行对比分析。利用变形配准建立起来的变形矢量场，将每周分次剂量变形累加到计划CT图像上，得到靶区和危及器官整体剂量的分布后，比较真实实施总剂量与计划剂量的不同。在合适的时间制定新的自适应计划，与原始计划剂量进行对比分析。结果 10例患者均发现头颈部轮廓缩小。在最后一次CT图像上观察，与原体积相比，GTVnx、GTVnd平均缩小了13.17%、13.95%，左腮腺、右腮腺平均缩小了17.05%、24.53%，脑干体积变化在±5%以内，脊髓体积变化在±3%以内。利用最后一周CT映射出的分次剂量，与原计划分次剂量相比，GTVnx和GTVnd的D95量差别不大，在±3%以内，左腮腺、右腮腺的D50平均升高了10.66%、12%，脑干和脊髓剂量基本无差别。患者真实实施总剂量与计划总剂量相比，GTVnx和GTVnd的D95差别均在±0.03%以内，左腮腺、右腮腺的D50平均增加了9.6%、5.1%，脑干和脊髓的总剂量无变化。经过自适应计划后，与原计划剂量相比，GTVnx和GTVnd的D95、D98、D2差别均在±2%以内，左腮腺、右腮腺的Dmean平均降低了6.76%、6.36%，脑干或脊髓剂量有所降低。结论 晚期鼻咽癌患者放疗过程中靶区和危及器官的位置和体积均会发生变化，靶区和腮腺体积变化较大，脑干和脊髓体积基本无变化，腮腺会受到超过预期剂量的照射，在治疗后期有必要修改治疗计划，提高患者的生活质量

Dosimetric analysis of offline adaptive technology in nasopharyngeal carcinoma radiotherapy

Objective To research on patients with advanced nasopharyngeal for offline adaptive radiotherapy based on weekly CT images,analyze the volume and dose changes of the tumor and organs at risk in the whole treatment and investigate the necessity of radiotherapy replanning and the dosimetric improvement of tumour and organs at risk by off-line adaptive technique in radiotherapy for nasopharyngeal carcinoma. Methods A total of 10 patients with nasopharyngeal carcinoma who received radical radiotherapy in our hospital from October 2021 to October 2022 were selected. The volume rotation intensity modulation plan was designed and CT scan was performed once a week during treatment. The weekly CT images were rigidly registered with the original planned CT images for deformation registration, and the target areas and organs at risk of each CT were outlined, and the volume changes of the target areas and organs at risk during radiotherapy were compared and analyzed. The original planned dose was mapped to the weekly CT images to obtain the weekly CT fractional dose of the target area and organs at risk, and compared with the original planned fractional dose. By using the deformation vector field established by deformation registration, the weekly fractional dose deformation was added to the planned CT images to obtain the overall dose distribution in the target area and the organs at risk, and the difference between the actual total dose and the planned dose was compared. At the appropriate time, a new adaptive schedule was developed and compared with the original planned dose. Results The contours of the head and neck were reduced in all 10 patients. Compared with the original volume, GTVnx and GTVnd were reduced by 13.17% and 13.95% on average, the left parotid gland and right parotid gland were reduced by 17.05% and 24.53% on average, the brain stem volume changed within ±5%, and the spinal cord volume changed within ±3%. According to the fractional dose mapped by CT in the last week, compared with the original planned fractional dose, the D95 amount of GTVnx and GTVnd was little different, within ±3%, the D50 of left parotid gland and right parotid gland increased by 10.66% and 12% on average, and there was basically no difference in brain stem and spinal cord doses. Compared with the planned total dose, the difference in D95 of GTVnx and GTVnd was within ±0.03%, the D50 of left parotid gland and right parotid gland increased by 9.6% and 5.1% on average, and the total dose of brain stem and spinal cord did not change. After adaptive planning, the difference in D95, D98 and D2 of GTVnx and GTVnd was within ±2% compared with the original planned dose. The Dmean of left parotid gland and right parotid gland was decreased by 6.76% and 6.36% on average, and the dose of brain stem or spinal cord was decreased.Conclusion In the course of radiotherapy for patients with advanced nasopharyngeal carcinoma, the location and volume of the target area and the organs at risk will change, the volume of the target area and parotid gland will change greatly, the volume of the brain stem and spinal cord will remain basically unchanged, and the parotid gland will receive more than the expected dose of radiation, so it is necessary to modify the treatment plan in the later stage of treatment to improve the quality of life of patients