Department of Physics and Applied Physics, University of Massachusetts Lowell, Massachusetts 01854, USA.
Med Phys. 2010 Aug;37(8):4038-45. doi: 10.1118/1.3458720.
To study the effects of the breast-air and breast-lung interfaces on the absorbed dose within the planning target volume (PTV) of a MammoSite balloon dose delivery system as well as the effect of contrast material on the dose rate in the PTV.
The Monte Carlo MCNP5 code was used to simulate dose rate in the PTV of a 2 cm radius MammoSite balloon dose delivery system. The simulations were carried out using an average female chest phantom (AFCP) and a semi-infinite water phantom for both Yb-169 and Ir-192 high dose rate sources for brachytherapy application. Gastrografin was introduced at varying concentrations to study the effect of contrast material on the dose rate in the PTV.
The effect of the density of the materials surrounding the MammoSite balloon containing 0% contrast material on the calculated dose rate at different radial distances in the PTV was demonstrated. Within the PTV, the ratio of the calculated dose rate for the AFCP and the semi-infinite water phantom for the point closest to the breast-air interface (90 degrees) is less than that for the point closest to the breast-lung interface (270 degrees) by 11.4% and 4% for the HDR sources of Yb-169 and Ir-192, respectively. When contrast material was introduced into the 2 cm radius MammoSite balloon at varying concentrations, (5%, 10%, 15%, and 20%), the dose rate in the AFCP at 3.0 cm radial distance at 90 degrees was decreased by as much as 14.8% and 6.2% for Yb-169 and Ir-192, respectively, when compared to that of the semi-infinite water phantom with contrast concentrations of 5%, 10%, 15%, and 20%, respectively.
Commercially available software used to calculate dose rate in the PTV of a MammoSite balloon needs to account for patient anatomy and density of surrounding materials in the dosimetry analyses in order to avoid patient underdose.
研究乳腺-空气和乳腺-肺界面对 MammoSite 球囊剂量输送系统计划靶区（PTV）内吸收剂量的影响，以及对比材料对 PTV 内剂量率的影响。
使用蒙特卡罗 MCNP5 代码模拟 2cm 半径 MammoSite 球囊剂量输送系统的 PTV 内剂量率。模拟使用平均女性胸部体模（AFCP）和半无限水体模，用于 Yb-169 和 Ir-192 高剂量率近距离治疗源。引入胃造影剂以研究对比材料对 PTV 内剂量率的影响。
展示了含有 0%对比材料的 MammoSite 球囊周围材料密度对 PTV 不同径向距离计算剂量率的影响。在 PTV 内，最接近乳腺-空气界面（90 度）的点的计算剂量率与最接近乳腺-肺界面（270 度）的点的计算剂量率之比，对于 Yb-169 和 Ir-192 的 HDR 源，分别小于 11.4%和 4%。当在不同浓度下（5%、10%、15%和 20%）将对比材料引入 2cm 半径的 MammoSite 球囊时，与半无限水体模的对比浓度分别为 5%、10%、15%和 20%相比，Yb-169 和 Ir-192 在 90 度 3.0cm 径向距离处的 AFCP 剂量率分别降低了 14.8%和 6.2%。
为了避免患者剂量不足，用于计算 MammoSite 球囊 PTV 内剂量率的商业可用软件需要在剂量分析中考虑患者解剖结构和周围材料的密度。
