Dosimetric perturbations due to an implanted cardiac pacemaker in MammoSite® treatment

Purpose: To investigate dose perturbations for pacemaker‐implanted patients in partial breast irradiation using high dose rate (HDR) balloon brachytherapy. Methods: 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. 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%. Conclusions: 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.