Interdisciplinary Program in Radiation Applied Life Science, Seoul National University College of Medicine, Seoul, South Korea.
Med Phys. 2012 Oct;39(10):6185-91. doi: 10.1118/1.4752088.
To investigate dose perturbations for pacemaker-implanted patients in partial breast irradiation using high dose rate (HDR) balloon brachytherapy.
Monte Carlo (MC) simulations were performed to calculate dose distributions involving a pacemaker in Ir-192 HDR balloon brachytherapy. Dose perturbations by varying balloon-to-pacemaker distances (BPD = 50 or 100 mm) and concentrations of iodine contrast medium (2.5%, 5.0%, 7.5%, and 10.0% by volume) in the balloon were investigated for separate parts of the pacemaker (i.e., battery and substrate). Relative measurements using an ion-chamber were also performed to confirm MC results.
The MC and measured results in homogeneous media without a pacemaker agreed with published data within 2% from the balloon surface to 100 mm BPD. Further their dose distributions with a pacemaker were in a comparable agreement. The MC results showed that doses over the battery were increased by a factor of 3, compared to doses without a pacemaker. However, there was no significant dose perturbation in the middle of substrate but up to 70% dose increase in the substrate interface with the titanium capsule. The attenuation by iodine contrast medium lessened doses delivered to the pacemaker by up to 9%.
Due to inhomogeneity of pacemaker and contrast medium as well as low-energy photons in Ir-192 HDR balloon brachytherapy, the actual dose received in a pacemaker is different from the homogeneous medium-based dose and the external beam-based dose. Therefore, the dose perturbations should be considered for pacemaker-implanted patients when evaluating a safe clinical distance between the balloon and pacemaker.
研究使用高剂量率（HDR）球囊近距离放疗时，起搏器植入患者的剂量分布变化。
采用蒙特卡罗（MC）模拟方法计算 Ir-192 HDR 球囊近距离放疗中涉及起搏器的剂量分布。研究了不同球囊-起搏器距离（BPD=50 或 100mm）和球囊内碘对比剂浓度（体积比为 2.5%、5.0%、7.5%和 10.0%）对起搏器各部分（即电池和基板）的剂量分布影响。还使用电离室进行了相对测量，以验证 MC 结果。
在没有起搏器的均匀介质中，MC 和测量结果与发表数据在距球囊表面 2%至 100mm BPD 范围内一致。此外，它们带有起搏器的剂量分布也具有可比性。MC 结果表明，与没有起搏器的情况相比，电池上方的剂量增加了 3 倍。然而，在基板中间没有明显的剂量分布变化，但在钛胶囊与基板交界处的剂量增加了 70%。碘对比剂的衰减使起搏器接收到的剂量减少了 9%。
由于起搏器和对比剂的不均匀性以及 Ir-192 HDR 球囊近距离放疗中的低能光子，起搏器实际接收到的剂量与基于均匀介质的剂量和基于外部束的剂量不同。因此，在评估球囊与起搏器之间安全的临床距离时，应考虑起搏器植入患者的剂量分布变化。
