Al-Booz Hoda, Boiangiu Ion, Appleby Helen, French Chris, Coomber Helen, Humphery Pauline, Cornes Paul
The Department of Clinical Oncology, Bristol Haematology and Oncology Centre, Bristol, United Kingdom. hodabooz@doctors,org.uk
J Egypt Natl Canc Inst. 2006 Jun;18(2):156-60.
To identify organs at risk (OAR) and analyze the dose volume histograms (DVHs) for intracavitary brachytherapy in cancer of the cervix. Late toxicities are our concern in treatment of cancer cervix especially as it is presenting in younger age population.
Patients with cancer of the cervix were treated using CT and MRI compatible, high dose rate, (HDR) applicators. CT images were acquired with the intra-uterine tube and colpostats in place and subsequently imported into Varian Brachyvision planning software. We identified the gross tumour volume (GTV) and organs at risk (OARs) and analyzed the dose distribution using dose volume histograms (DVHs). Doses were calculated according to ICRU 38. Critical tissue DVHs were analysed following the American Brachytherapy Society rules. Dose points are recorded as the dose encompassed by the greatest contiguous 1 cm3, 2 cm3, and 5 cm3 volumes in the plan.
We found the sigmoid colon to be a relatively immobile structure that repeatedly received doses in excess of 70% of the intended point A dose. The only solution in order to bring sigmoid DVHs within 5% toxicity limits was to reduce the dose to point A. Planning images and DVHs for the OARs are shown as an example of our work.
The recto-sigmoid colon is identified as an unexpected OAR in a majority of cervix brachytherapy plans. A new consensus on the DVH limit of this structure will be needed in the era of CT planned brachytherapy, if arbitrary dose reductions to point A are to be the solution to the problem of sigmoid DVHs that exceed conventional tolerance limits.
识别宫颈癌腔内近距离放射治疗中的危及器官（OAR）并分析剂量体积直方图（DVH）。晚期毒性是我们在宫颈癌治疗中所关注的问题，尤其是在年轻人群中。
宫颈癌患者采用与CT和MRI兼容的高剂量率（HDR）施源器进行治疗。在子宫内导管和阴道柱状施源器就位的情况下采集CT图像，随后导入Varian Brachyvision治疗计划软件。我们识别大体肿瘤体积（GTV）和危及器官（OAR），并使用剂量体积直方图（DVH）分析剂量分布。剂量根据ICRU 38进行计算。按照美国近距离放射治疗学会的规则分析关键组织的DVH。剂量点记录为计划中最大连续1 cm³、2 cm³和5 cm³体积所包含的剂量。
我们发现乙状结肠是一个相对固定的结构，反复接受超过A点预期剂量70%的剂量。为了使乙状结肠的DVH处于5%毒性限值以内，唯一的解决办法是降低A点的剂量。OAR的计划图像和DVH作为我们工作的一个示例展示。
在大多数宫颈癌近距离放射治疗计划中，直肠乙状结肠被识别为一个意外的OAR。在CT计划近距离放射治疗时代，如果对A点进行任意剂量降低是解决乙状结肠DVH超过传统耐受限值问题的方法，那么就需要对该结构的DVH限值达成新的共识。
