Implanted Cardiac Device Management for Total Skin Electron Therapy Patients
Abstract
Purpose
This project aimed to characterize a shielding technique for total skin electron therapy (TSET) patients with implanted cardiac devices (ICDs). Goals of the work included quantifying shielding effectiveness by quantifying and minimizing the dose delivered to the ICD.
Methods
Superflab bolus was selected as the shielding material due to its low atomic number (minimizing x-ray contamination), biocompatibility, and ease of customization. Multiple 1cm thick pieces of bolus were stacked, so the device (assumed depth of 7mm based on review of CTs) was beyond the practical range for 6MeV electrons on the patient’s surface (including 0.8cm acrylic beam spoiler). Delivery was simulated with an anthropomorphic phantom at treatment position, rotating through the six Stanford positions. Radiochromic films were placed on the surface of the bolus-shield and between each layer, with a PDD film placed behind shield between layers in phantom. Surface film and PDD films were placed on the contralateral chest to represent unshielded delivery. In vivo films were acquired on the patient's surface and top of shielding for two patients to confirm dose.
Results
The estimated dose to the simulated ICD was 43.1 cGy, ~3.6% of the prescribed dose. X-ray contamination of the delivery contributed to ~0.8% of the total dose from each beam delivery. In-vivo measurements indicate an ICD dose of <5% of prescription. Several TSE patients with ICDs have now been treated with this method.
Conclusion
These findings demonstrate that ~2 cm of bolus substantially reduces surface dose for 6 MeV TSET, limiting dose to superficial implanted cardiac devices. By providing appropriate shielding, the integrity of the implanted device is maximized for the patient, and in-vivo dosimetry informs the care team of potential follow-up treatment for their TSET.