Academic Radiation Oncology, The Christie NHS Foundation Trust, Manchester, UK.
Int J Radiat Oncol Biol Phys. 2012 Mar 1;82(3):e375-82. doi: 10.1016/j.ijrobp.2011.07.004. Epub 2011 Dec 22.
Parotid-sparing head-and-neck intensity-modulated radiotherapy (IMRT) can reduce long-term xerostomia. However, patients frequently experience weight loss and tumor shrinkage during treatment. We evaluate the use of kilovoltage (kV) cone beam computed tomography (CBCT) for dose monitoring and examine if the dosimetric impact of such changes on the parotid and critical neural structures warrants replanning during treatment.
Ten patients with locally advanced oropharyngeal cancer were treated with contralateral parotid-sparing IMRT concurrently with platinum-based chemotherapy. Mean doses of 65 Gy and 54 Gy were delivered to clinical target volume (CTV)1 and CTV2, respectively, in 30 daily fractions. CBCT was prospectively acquired weekly. Each CBCT was coregistered with the planned isocenter. The spinal cord, brainstem, parotids, larynx, and oral cavity were outlined on each CBCT. Dose distributions were recalculated on the CBCT after correcting the gray scale to provide accurate Hounsfield calibration, using the original IMRT plan configuration.
Planned contralateral parotid mean doses were not significantly different to those delivered during treatment (p > 0.1). Ipsilateral and contralateral parotids showed a mean reduction in volume of 29.7% and 28.4%, respectively. There was no significant difference between planned and delivered maximum dose to the brainstem (p = 0.6) or spinal cord (p = 0.2), mean dose to larynx (p = 0.5) and oral cavity (p = 0.8). End-of-treatment mean weight loss was 7.5 kg (8.8% of baseline weight). Despite a ≥10% weight loss in 5 patients, there was no significant dosimetric change affecting the contralateral parotid and neural structures.
Although patient weight loss and parotid volume shrinkage was observed, overall, there was no significant excess dose to the organs at risk. No replanning was felt necessary for this patient cohort, but a larger patient sample will be investigated to further confirm these results. Nevertheless, kilovoltage CBCT is a valuable tool for patient setup verification and monitoring of dosimetric variation during radiotherapy.
腮腺保护性头颈部强度调节放疗（IMRT）可减少长期口干。然而，患者在治疗过程中常经历体重减轻和肿瘤缩小。我们评估千伏（kV）锥形束 CT（CBCT）在剂量监测中的应用，并研究这些变化对腮腺和关键神经结构的剂量学影响是否需要在治疗过程中重新计划。
10 例局部晚期口咽癌患者接受对侧腮腺保护性 IMRT 联合铂类化疗。CTV1 和 CTV2 分别接受 65 Gy 和 54 Gy 的平均剂量，30 次分割。每周前瞻性采集 CBCT。每次 CBCT 与计划的等中心进行配准。在每个 CBCT 上勾画脊髓、脑干、腮腺、喉和口腔。在纠正灰度以提供准确的亨氏校准后，使用原始的 IMRT 计划配置，在 CBCT 上重新计算剂量分布。
计划的对侧腮腺平均剂量与治疗期间的剂量无显著差异（p>0.1）。同侧和对侧腮腺体积分别减少了 29.7%和 28.4%。脑干（p=0.6）和脊髓（p=0.2）的最大剂量、喉（p=0.5）和口腔（p=0.8）的平均剂量均无显著差异。治疗结束时平均体重减轻 7.5 公斤（基线体重的 8.8%）。尽管 5 例患者体重减轻≥10%，但对侧腮腺和神经结构无明显的剂量学改变。
尽管观察到患者体重减轻和腮腺体积缩小，但总体而言，危险器官的额外剂量没有显著增加。对于该患者组，无需重新计划，但将进一步研究更大的患者样本以进一步证实这些结果。然而，千伏 CBCT 是患者摆位验证和放射治疗期间剂量学变化监测的有价值工具。
