The Influence of Treatment Energy on Cardiac Devices in Patients Undergoing Intensity Modulated Radiation Therapy (IMRT) for Prostate Cancer

Abstract

We previously reported an increased risk of a cardiac device malfunction in patients undergoing IMRT for prostate cancer (DiBiase SJ, et al, IJROBP 81; 2011). In that report, high-energy photons were associated with device malfunction. We now review a subsequent cohort of prostate cancer patients who underwent IMRT utilizing low-energy photons to evaluate the influence of energy on cardiac device malfunction. Between 2009 and 2012, 955 patients underwent IMRT for prostate cancer at a single treatment center. Of these 955 patients, 44 patients (4.6%) had cardiac devices (pacemakers and defibrillators). All patients had their cardiac devices interrogated before treatment and at the completion of treatment. Some patients underwent IMRT using 18-MV (high-energy) photons and others underwent IMRT using 6MV (low-energy) photons. The initial group of patients treated from 2009-2011 (Group A) received both low and high-energy photons, and patients treated from 2011-2012 (Group B) received only low-energy photons based on a change in center protocol. A two proportion comparison test was used to check statistical significance of energy type on the development of device malfunction between Group A and Group B. Of the 24 cardiac device patients in Group A who were treated with IMRT utilizing both high-energy and low-energy photons, 6 patients (25%) experienced a device malfunction. Of the 24 patients in Group A, 8 patients received high-energy photons and 16 patients received low-energy photons. Of the 8 patients who received high-energy photons, 6 patients (75%) developed a cardiac malfunction. None of the 16 patients who received low-energy photons experienced a device malfunction. In a subsequent group (Group B) of 20 device patients who underwent low-energy IMRT between 2011 and 2012, none of the Group B patients experienced a cardiac device malfunction. A statistically significant difference at the 5% level was noted between low-energy and high-energy IMRT for developing a cardiac device malfunction (P value = 0.0005). The use of low-energy IMRT appears to reduce the risk of cardiac device malfunction in men undergoing treatment for prostate cancer. Energies above 6MV should be avoided in patients with cardiac devices undergoing IMRT.