Slessinger Eric, Pepin Eric, Zhao Qingya, Zhao Li, Das Indra
Indiana University Simon Cancer Center, Indiana University School of Medicine, Indiana.
J Contemp Brachytherapy. 2012 Jun;4(2):106-10. doi: 10.5114/jcb.2012.29367. Epub 2012 Jun 30.
To evaluate the dosimetric impact of lung tissue in Ir-192 APBI.
In a 40 × 40 × 40 cm(3) water tank, an Accelerated Partial Breast Irradiation (APBI) brachytherapy balloon inflated to 4 cm diameter was situated directly below the center of a 30 × 30 × 1 cm(3) solid water slab. Nine cm of solid water was stacked above the 1 cm base. A parallel plate ion chamber was centered above the base and ionization current measurements were taken from the central HDR source dwell position for channels 1, 2, 3 and 5 of the balloon. Additional ionization data was acquired in the 9 cm stack at 1 cm increments. A comparable data set was also measured after replacing the 9 cm solid water stack with cork slabs. The ratios of measurements in the two phantoms were calculated and compared to predicted results of a commercial treatment planning system.
Lower dose was measured in the cork within 1 cm of the cork/solid water interface possibly due to backscatter effects. Higher dose was measured beyond 1 cm from the cork/solid water interface, increasing with path length up to 15% at 9 cm depth in cork. The treatment planning system did not predict either dose effect.
This study investigates the dosimetry of low density material when the breast is treated with Ir-192 brachytherapy. HDR dose from Ir-192 in a cork media is shown to be significantly different than in unit density media. These dose differences are not predicted in most commercial brachytherapy planning systems. Empirical models based on measurements could be used to estimate lung dose associated with HDR breast brachytherapy.
评估肺组织在铱-192加速部分乳腺照射（APBI）中对剂量测定的影响。
在一个40×40×40 cm³的水箱中，一个直径膨胀至4 cm的加速部分乳腺照射近距离放射治疗球囊直接位于一块30×30×1 cm³固体水板中心下方。在1 cm厚的底部上方堆叠9 cm厚的固体水。一个平行板电离室位于底部上方中心位置，并从球囊通道1、2、3和5的中心高剂量率（HDR）源驻留位置进行电离电流测量。在9 cm厚的堆叠中以1 cm的增量获取额外的电离数据。在用软木板替换9 cm厚的固体水堆叠后，也测量了一组可比数据。计算了两个体模中的测量比值，并与商业治疗计划系统的预测结果进行比较。
在软木/固体水界面1 cm范围内的软木中测量到较低剂量，这可能是由于反向散射效应。在距软木/固体水界面1 cm以外测量到较高剂量，在软木中9 cm深度处随路径长度增加高达15%。治疗计划系统未预测到这两种剂量效应。
本研究调查了用铱-192近距离放射治疗乳腺时低密度材料的剂量测定。结果表明，铱-192在软木介质中的高剂量率剂量与单位密度介质中的剂量有显著差异。大多数商业近距离放射治疗计划系统未预测到这些剂量差异。基于测量的经验模型可用于估计与高剂量率乳腺近距离放射治疗相关的肺剂量。
