Department of Radiology, Himalayan Institute of Medical Sciences, HIHT University, C-I-5, HIHT Campus, Swami Ram Nagar, P.O. Doiwala, Jolly Grant, Dehradun, Uttarakhand 248140, India.
Phys Med. 2013 Mar;29(2):171-7. doi: 10.1016/j.ejmp.2012.01.004. Epub 2012 Feb 18.
To verify the dosimetric accuracy of treatment plans in high dose rate (HDR) brachytherapy by using Gafchromic EBT2 film and to demonstrate the adequacy of dose calculations of a commercial treatment planning system (TPS) in a heterogeneous medium.
Absorbed doses at chosen points in anatomically different tissue equivalent phantoms were measured using Gafchromic EBT2 film. In one case, tandem ovoid brachytherapy was performed in a homogeneous cervix phantom, whereas in the other, organ heterogeneities were introduced in a phantom to replicate the upper thorax for esophageal brachytherapy treatment. A commercially available TPS was used to perform treatment planning in each case and the EBT2 films were irradiated with the HDR Ir-192 brachytherapy source.
Film measurements in the cervix phantom were found to agree with the TPS calculated values within 3% in the clinically relevant volume. In the thorax phantom, the presence of surrounding heterogeneities was not seen to affect the dose distribution in the volume being treated, whereas, a little dose perturbation was observed at the lung surface. Doses to the spinal cord and to the sternum bone were overestimated and underestimated by 14.6% and 16.5% respectively by the TPS relative to the film measurements. At the trachea wall facing the esophagus, a dose reduction of 10% was noticed in the measurements.
The dose calculation accuracy of the TPS was confirmed in homogeneous medium, whereas, it was proved inadequate to produce correct dosimetric results in conditions of tissue heterogeneity.
使用 Gafchromic EBT2 胶片验证高剂量率（HDR）近距离放射治疗计划的剂量准确性，并证明商业治疗计划系统（TPS）在非均匀介质中剂量计算的充分性。
使用 Gafchromic EBT2 胶片测量在解剖学上不同的组织等效体模中选定点的吸收剂量。在一种情况下，在均匀的宫颈体模中进行了子宫颈双腔球囊近距离放射治疗，而在另一种情况下，在体模中引入了器官不均匀性以模拟用于食管近距离放射治疗的上胸部。使用商业上可用的 TPS 对每种情况进行治疗计划，并使用 HDR Ir-192 近距离放射治疗源对 EBT2 胶片进行照射。
在宫颈体模中的胶片测量值与 TPS 计算值在临床相关体积内的差异在 3%以内。在胸部体模中，周围不均匀性的存在并未影响治疗体积中的剂量分布，而在肺表面观察到轻微的剂量扰动。与胶片测量值相比，TPS 对脊髓和胸骨骨的剂量高估和低估分别为 14.6%和 16.5%。在面对食管的气管壁处，测量值中注意到剂量减少了 10%。
TPS 的剂量计算准确性在均匀介质中得到了确认，而在组织不均匀性的情况下，它被证明不足以产生正确的剂量学结果。
