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Relative Neutron Damage to Cardiovascular Implantable Electronic Devices: A Monte Carlo Study

M Studenski

M Studenski1*, A Ezzati2 , (1) University of Miami, Miami, FL, (2) University of Tabriz, Tabriz, Iran


SU-I-GPD-T-348 (Sunday, July 30, 2017) 3:00 PM - 6:00 PM Room: Exhibit Hall

Purpose: Recent data demonstrates that cardiac implantable electric device (CIED) failure is more likely related to neutron damage than photon dose. MCNPX was used along with silicon damage response functions and ICRP neutron dose conversion factors to quantify the relative neutron damage induced in a CIED from a clinical 18 MV photon beam and to calculate damage probability based on neutron dose or fluence as a function of field size, off-axis distance and depth.

Methods: Using MCNPX, neutron dose and fluence maps were calculated as a function of field size, depth, and off-axis distance. Second, neutron damage maps were determined which were used to calculate damage-to-dose and damage-to-fluence ratios. Particular attention was devoted to the modelling of the Varian 2100C/D linear accelerator to ensure accurate contamination neutron spectra.

Results: The neutron fluence does not have its maximum depth at the surface, rather it is at a depth of around 4 cm and that as the field size increases, the neutron fluence increases. Beyond an off-axis distance of about 30 cm, the neutron fluence is independent of field size. Neutron dose is maximum near the surface and by increasing the depth and off axis distance, the dose decreases. Neutron damage is a complex function that is dependent on both depth and off-axis distance. By increasing the depth and off-axis distance the probability of damage decreases, but the relationship is not linear. The damage probability must take into account neutron energy spectra and intensity. Finally, the probability of damage is never zero regardless of off-axis distance and depth.

Conclusion: There is no linear relationship between neutron dose or fluence and the damage to a CIED. Care must be taken when treating patients with high energy photons as there is always the possibility for damage.

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