Implantable cardiac pacemaker failure by cumulative dose effects of flattening filter free beams

Abstract

Cumulative dose effects, which are one of the main causes of errors that occur when an implantable cardiac pacemaker (ICP) is irradiated with ionizing radiation, induce permanent failure in ICPs. Although flattening filter free (FFF) beams, which are often used in stereotactic radiotherapy, are known to have different characteristics from conventional (with flattening filter [WFF]) beams, the cumulative dose effects on ICPs with FFF beams have been under-investigated. This study investigates ICP failure induced by cumulative dose effects of FFF beams. When the ICP placed in the center of the irradiation field was irradiated with 10 MV-FFF at 24 Gy/min, the cumulative dose at which failure occurred was evaluated on the basis of the failure criteria associated with high cumulative dose as described in the American Association of Physicists in Medicine Task Group 203. The ICP failures such as a mild battery depletion at a cumulative dose of 10 Gy, pacing-output voltage change >25% at a cumulative dose of 122 Gy, and the loss of telemetry capability at cumulative dose 134 Gy were induced by cumulative dose effects. The cumulative doses by which the cumulative dose effects of FFF beams induced ICP failure were not very different from those reported in previous studies with WFF beams. Therefore, radiotherapy with FFF beams (and WFF beams) for patients with ICP requires appropriate management for minimizing the cumulative dose effects.

Keywords: FFF beams; cumulative dose effects; failure; implantable cardiac pacemaker (ICP); radiotherapy.

Fig. 1.

Experimental scheme. The ICP was positioned at a depth of 2.2 cm from the water’s surface in the water phantom filled with water at a source-to-axis distance of 100 cm and at the center of a 10 cm × 10 cm field. ICP parameters were recorded by an oscilloscope via a Y-adapter and a 500 Ω resistance and by telemetry using a programmer. ICP, implantable cardiac pacemaker

Fig. 2.

Battery impedance vs cumulative dose. The battery impedance was increased by approximately 77.8% from the initial value of 375 Ω to 667 Ω at a cumulative dose of 10 Gy and changed in the range of −3.1% to 4.7% at a cumulative dose of 10–134 Gy.

Fig. 3.

Battery voltage vs cumulative dose. The initial battery voltage was 2.69 V and decreased to 2.68 V and 2.67 V at cumulative doses of 30 and 90 Gy, respectively.

Fig. 4.

Pacing-output voltage vs cumulative dose. The pacing-output voltage was reduced by >15%, 30%, and 75% from its initial value at cumulative doses of 110, 122, and 134 Gy, respectively.

Fig. 5.

Lead impedance vs cumulative dose. The lead impedance fluctuated in the range of −1% to 4% at a cumulative dose of <130 Gy and became unreadable at a cumulative dose of 134 Gy.