Department of Oncology, St Thomas' Hospital, Guy's and St Thomas' NHS Foundation Trust, London, UK.
Br J Radiol. 2014 Feb;87(1034):20130532. doi: 10.1259/bjr.20130532. Epub 2013 Nov 28.
To investigate if cone beam CT (CBCT) can be used to estimate the delivered dose in head and neck intensity-modulated radiotherapy (IMRT).
15 patients (10 without replan and 5 with replan) were identified retrospectively. Weekly CBCT was co-registered with original planning CT. Original high-dose clinical target volume (CTV1), low-dose CTV (CTV2), brainstem, spinal cord, parotids and external body contours were copied to each CBCT and modified to account for anatomical changes. Corresponding planning target volumes (PTVs) and planning organ-at-risk volumes were created. The original plan was applied and calculated using modified per-treatment volumes on the original CT. Percentage volumetric, cumulative (planned dose delivered prior to CBCT + adaptive dose delivered after CBCT) and actual delivered (summation of weekly adaptive doses) dosimetric differences between each per-treatment and original plan were calculated.
There was greater volumetric change in the parotids with an average weekly difference of between -4.1% and -27.0% compared with the CTVs/PTVs (-1.8% to -5.0%). The average weekly cumulative dosimetric differences were as follows: CTV/PTV (range, -3.0% to 2.2%), ipsilateral parotid volume receiving ≥26 Gy (V26) (range, 0.5-3.2%) and contralateral V26 (range, 1.9-6.3%). In patients who required replan, the average volumetric reductions were greater: CTV1 (-2.5%), CTV2 (-6.9%), PTV1 (-4.7%), PTV2 (-11.5%), ipsilateral (-10.4%) and contralateral parotids (-12.1%), but did not result in significant dosimetric changes.
The dosimetric changes during head and neck simultaneous integrated boost IMRT do not necessitate adaptive radiotherapy in most patients.
Our study shows that CBCT could be used for dose estimation during head and neck IMRT.
研究锥形束 CT（CBCT）是否可用于估计头颈部调强放疗（IMRT）中的剂量。
回顾性选择 15 例患者（10 例未行再计划和 5 例行再计划）。每周进行 CBCT 与原始计划 CT 配准。将原始高剂量临床靶区（CTV1）、低剂量 CTV（CTV2）、脑干、脊髓、腮腺和外轮廓复制到每个 CBCT 上，并进行修改以考虑解剖结构变化。创建相应的计划靶区（PTV）和计划危及器官（OAR）体积。使用原始 CT 上修改后的每次治疗体积对原始计划进行应用和计算。计算每个每次治疗计划与原始计划之间的体积比、累积（在 CBCT 之前的自适应剂量+在 CBCT 之后的自适应剂量）和实际剂量（每周自适应剂量的总和）的剂量差异。
与 CTV/PTV（1.8%至 5.0%）相比，腮腺的体积变化更大，平均每周差异在-4.1%至-27.0%之间。累积剂量差异的平均值如下：CTV/PTV（范围，-3.0%至 2.2%）、同侧腮腺接受≥26Gy 的体积（V26）（范围，0.5%至 3.2%）和对侧 V26（范围，1.9%至 6.3%）。需要再计划的患者，CTV1（-2.5%）、CTV2（-6.9%）、PTV1（-4.7%）、PTV2（-11.5%）、同侧（-10.4%）和对侧腮腺（-12.1%）的体积平均减少量较大，但并未导致显著的剂量变化。
在头颈部同步推量调强放疗中，大多数患者不需要自适应放疗。
本研究表明，在头颈部调强放疗中，CBCT 可用于剂量估计。
