Joseph Kurian, Rose Brenda, Warkentin Heather, Yun Jihyun, Ghosh Sunita, Tankel Keith
Division of Radiation Oncology, Department of Oncology, University of Alberta & Cross Cancer Institute, Edmonton, Alberta, Canada.
Department of Medical Physics, Cross Cancer Institute, Edmonton, Alberta, Canada.
J Med Imaging Radiat Oncol. 2018 Oct;62(5):734-738. doi: 10.1111/1754-9485.12748. Epub 2018 May 23.
Skin bolus may routinely be used in the perineum to build up the surface dose in the treatment of anal cancer (ACC); this may contribute to significant acute skin toxicity. Skin bolus may not be needed with the introduction of modern radiotherapy techniques if these planning techniques would achieve adequate surface dose. Our study is to ascertain if appropriate skin dose can be achieved without the use of bolus when VMAT is used in the treatment of ACC.
The study includes 10 ACC patients treated with VMAT radiotherapy. Optically stimulated luminescence dosimeters (OSLD) are used to evaluate whether the calculated dose for the VMAT planning technique (VMAT-PT) accurately predicted the dose delivered to peri-anal target region without bolus. The OSLD recorded the dose at the anal verge or at the lower most extent of the tumour for each patient over two fractions. The OSLD was read after each of the two fractions, and the average value was reported. The mean dose over a volume centred on the anal marker was calculated in the treatment planning system (TPS).
The mean TPS-calculated dose was 186.1 cGy. The mean of the OSLD-measured doses was 205.7 cGy for a single fraction. The mean of the measured doses was 10.6% higher than the mean of the calculated doses.
The calculated dose for the VMAT-PT consistently under-predicted the dose delivered to the peri-anal target region without bolus. Routine use of skin bolus could be avoided with VMAT-PT when the patient is treated in a supine position.
在肛管癌（ACC）治疗中，会阴区常常规使用皮肤填充物以提高表面剂量；这可能会导致显著的急性皮肤毒性。如果现代放疗技术能实现足够的表面剂量，则可能无需使用皮肤填充物。我们的研究旨在确定在VMAT用于ACC治疗时，不使用填充物是否能达到合适的皮肤剂量。
本研究纳入10例接受VMAT放疗的ACC患者。使用光激励发光剂量计（OSLD）评估VMAT计划技术（VMAT-PT）计算的剂量是否能准确预测不使用填充物时传递至肛周靶区的剂量。OSLD记录每位患者两个分次中肛门边缘或肿瘤最下端的剂量。两个分次中的每次分次后读取OSLD，并报告平均值。在治疗计划系统（TPS）中计算以肛门标记为中心的体积内的平均剂量。
TPS计算的平均剂量为186.1 cGy。单次分次OSLD测量剂量的平均值为205.7 cGy。测量剂量的平均值比计算剂量的平均值高10.6%。
VMAT-PT计算的剂量始终低估了不使用填充物时传递至肛周靶区的剂量。当患者仰卧位接受治疗时，VMAT-PT可避免常规使用皮肤填充物。
