论文标题
基于蒙特卡洛计算
Dosimetric investigation of 103Pd permanent breast seed implant brachytherapy based on Monte Carlo calculations
论文作者
论文摘要
目的：使用103PD的永久性乳腺种子植入物（PBSI）正在成为早期乳腺癌的有效辅助辐射技术。但是，临床剂量评估遵循水性TG-43方法，其近似值相当大。为了临床采用高级TG-186基于模型的剂量评估，本研究对PBSI进行了全面研究，以考虑靶标和正常组织剂量。 METHODS: Dose calculations are performed with the free open-source Monte Carlo (MC) code, egs_brachy, using 2 types of virtual patient models: TG43sim (simulated TG-43 conditions: all water with no interseed attenuation) and MCref (heterogeneous tissue modelling from patient CT, interseed attenuation, seeds at implant angle) for 35 patients.评估了剂量度量对种子取向的敏感性以及腺/脂肪组织分割的阈值。结果：在目标体积中，MCREF的D90平均比TG43SIM低14.1％。相反，MCREF的正常组织剂量通常高于TG43SIM，例如皮肤D1CM2的22％，肋骨DMAX为82％，心脏D1CM3的肋骨为71％。 MCREF和TG43SIM剂量之间的差异在患者队列以及所考虑的组织和度量方面有所不同。剂量对腺/脂肪组织分割阈值敏感，目标D90的差异为几％。皮肤剂量对种子方向敏感。结论：TG-43剂量评估通常低估了关键的正常器官/组织的剂量，同时高估了靶剂量。 MCREF和TG43SIM在患者的基础上存在很大差异，这表明临床采用患者特定的MC剂量计算是动机的。本文介绍的MCREF框架为高级TG-186剂量计算的临床实施提供了一种一致的建模方法。
PURPOSE: Permanent breast seed implant (PBSI) using 103Pd is emerging as an effective adjuvant radiation technique for early-stage breast cancer. However, clinical dose evaluations follow the water-based TG-43 approach with its considerable approximations. Towards clinical adoption of advanced TG-186 model-based dose evaluations, this study presents a comprehensive investigation for PBSI considering both target and normal tissue doses. METHODS: Dose calculations are performed with the free open-source Monte Carlo (MC) code, egs_brachy, using 2 types of virtual patient models: TG43sim (simulated TG-43 conditions: all water with no interseed attenuation) and MCref (heterogeneous tissue modelling from patient CT, interseed attenuation, seeds at implant angle) for 35 patients. Sensitivity of dose metrics to seed orientation and the threshold for glandular/adipose tissue segmentation are assessed. RESULTS: In the target volume, D90 is 14.1% lower with MCref than with TG43sim, on average. Conversely, normal tissue doses are generally higher with MCref than with TG43sim, e.g., by 22% for skin D1cm2, 82% for ribs Dmax, and 71% for heart D1cm3. Discrepancies between MCref and TG43sim doses vary over the patient cohort, as well as with the tissue and metric considered. Doses are sensitive to the glandular/adipose tissue segmentation threshold with differences of a few percent in target D90. Skin doses are sensitive to seed orientation. CONCLUSIONS: TG-43 dose evaluations generally underestimate doses to critical normal organs/tissues while overestimating target doses. There is considerable variation in MCref and TG43sim on a patient-by-patient basis, suggesting that clinical adoption of patient-specific MC dose calculations is motivated. The MCref framework presented herein provides a consistent modelling approach for clinical implementation of advanced TG-186 dose calculations.
