Department of Radiation Oncology, University of California San Francisco, CA 94143, USA.
Radiother Oncol. 2012 Jul;104(1):83-90. doi: 10.1016/j.radonc.2011.09.024. Epub 2011 Dec 5.
To determine if image-guided radiotherapy (IGRT) ensures dose coverage to the target, and to assess the dosimetric impact of anatomic changes using megavoltage cone-beam CT (MVCBCT) for patient positioning during head and neck IMRT.
Forty-eight MVCBCT from 10 head and neck IMRT/IGRT patients were analyzed off-line. Target volumes and organs at risk (OARs) contours delineated on CT were transferred and adjusted on MVCBCT images. Each MVCBCT was processed to allow dose recalculation, resulting in 469 dose-volume histograms (DVHs). The concept of dosimetric latitude was introduced to provide a clinical perspective.
MVCBCT target DVHs showed a moderate level of difference in D95 (dose to ≥95% of volume), generally less than a 5% difference from the planned dose. Delivered-dose increases to the spinal cord and brainstem showed no apparent time trend. The 4mm margin around OARs was a useful precaution to prevent exceeding critical dose thresholds. The parotid glands showed progressive increases in mean dose related to shrinkage of the external contours.
IGRT repositioning ensured target volume coverage, but significant dose variations were observed for OARs. The dosimetric impact of anatomic changes during radiotherapy was of lesser importance than the effects of IGRT repositioning.
确定图像引导放疗（IGRT）是否能确保靶区的剂量覆盖，并评估使用用于头颈部调强放疗（IMRT）患者定位的兆伏锥形束 CT（MVCBCT）进行解剖变化的剂量学影响。
分析了 10 例头颈部 IMRT/IGRT 患者的 48 个 MVCBCT。在 CT 上勾画的靶区体积和危及器官（OAR）轮廓被转移并在 MVCBCT 图像上进行调整。对每个 MVCBCT 进行处理，以允许重新计算剂量，从而生成 469 个剂量体积直方图（DVH）。引入了剂量学裕度的概念，以提供临床视角。
MVCBCT 靶区 DVH 显示 D95（剂量达到体积的≥95%）存在中度差异，通常与计划剂量的差异小于 5%。脊髓和脑干的剂量增加没有明显的时间趋势。OAR 周围 4mm 的边界是防止超过临界剂量阈值的有用预防措施。由于外部轮廓的收缩，腮腺的平均剂量逐渐增加，与剂量相关。
IGRT 重新定位确保了靶区的覆盖，但 OAR 观察到显著的剂量变化。放射治疗期间解剖变化的剂量学影响不如 IGRT 重新定位的影响重要。
