Abstract
An increasing number of patients undergoing proton radiotherapy have cardiac implantable electrical devices (CIEDs). We recently encountered a situation in which a high‐voltage coil on a lead from an implanted cardiac defibrillator was located within the clinical treatment volume for a patient receiving proton radiotherapy for esophageal cancer. To study the effects of the lead on the dose delivery, we placed a high‐Z CIED lead at both the center and the distal edge of a clinical spread‐out Bragg peak (SOBP) in a water phantom, in both a stationary position and with the lead moving in a periodic pattern to simulate cardiorespiratory movement. We then calculated planned doses using a commercial proton treatment planning system (TPS), and compared them with the doses delivered in the phantom, measured using radiographic film. Dose profiles from TPS‐calculated and measured dose distributions showed large pertubrations in the delivered proton dose in the vicinity of the CIED lead when it was not moving. The TPS predicted perturbations up to 20% and measurements revealed perturbations up to 35%. However, the perturbations were less than 3% when the lead was moving. Greater dose perturbations were seen when the lead was placed at the distal edge of the SOBP than when it was placed in the center of the SOBP. We conclude that although cardiorespiratory motion of the lead mitigates some of the perturbations, the effects of the leads should be considered and steps taken to reduce these effects during the treatment planning process.PACS numbers: 87.55.D‐,87.55.ne, 87.85.M
Highlights
14 Wootton et al.: Proton dose perturbations from a defibrillator in patients with cardiac implantable electrical devices (CIEDs)
Because of the coulombic nature of proton beam interactions with matter, the presence of multiple high-Z materials in the highvoltage (HV) shock coils and pacing ring electrodes of the leads in CIEDs directly affects the delivered dose distribution. (To prevent confusion, it should be noted that ‘lead’ and ‘leads’ in this text always refers to an electrical component of the CIED and never the element represented by the symbol ‘Pb’.) This is known to be the case for other high-Z materials that may be found in patients undergoing proton therapy
Studies of the effects on dose distribution in high-Z fiducial markers used for patient setup in radiotherapy for prostate cancer have reported dose perturbations ranging from 15% to 35% for stainless steel and titanium markers, depending on the size and orientation of the marker with respect to the treatment beam.[10,11,12] Because many different lead arrangements and types of leads with different geometries are commonly used for CIEDs, it is important to understand the possible effects of these leads on the dose delivered during proton beam radiotherapy
Summary
14 Wootton et al.: Proton dose perturbations from a defibrillator in patients with CIEDs. 14 Wootton et al.: Proton dose perturbations from a defibrillator in patients with CIEDs These procedures include keeping the device out of the radiation field, keeping the total dose to the device below manufacturer-recommended levels, estimating the dose delivered to the device (using thermoluminescent dosimeters, metal-oxide-semiconductor fieldeffect transistors, etc), and monitoring the function of the CIED on a daily or weekly basis. Even with these mitigating procedures, CIEDs could create problems during proton radiotherapy.
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