On the use of bolus for pacemaker dose measurement and reduction in radiation therapy

Abstract

Special attention is required in planning and administering radiation therapy to patients with cardiac implantable electronic devices (CIEDs), such as pacemaker and defibrillator. The range of dose to CIEDs that can induce malfunction is large among CIEDs. Clinically significant defects have been reported at dose as low as 0.15 Gy. Therefore, accurate estimation of dose to CIED and dose reduction are both important even if the dose is expected to be less than the often‐used 2‐Gy limit. We investigated the use of bolus in in vivo dosimetry for CIEDs. Solid water phantom measurements of out‐of‐field dose for a 6‐MV beam were performed using parallel plate chamber with and without 1‐ to 2‐cm bolus covering the chamber. In vivo dosimetry at skin surface above the CIED was performed with and without bolus covering the CIED for three patients with the CIED <5 cm from the field edge. Chamber measured dose at depth ~0.5–1.5 cm below the skin surface, where the CIED is normally located, was reduced by ~7–48% with bolus. The dose reduction became smaller at deeper depths and with smaller field size. In vivo dosimetry at skin surface also indicated ~20%–60% lower dose when using bolus for the three patients. The dose measured with bolus more accurately reflects the dose to CIED and is less affected by contaminant electrons and linac head scatter. In general, the treatment planning system (TPS) calculation underestimated the dose to CIED, but it predicts the CIED dose more accurately when bolus is used. We recommend the use of 1‐ to 2‐cm bolus to cover the CIED during in vivo CIED dose measurements for more accurate CIED dose estimation. If the CIED is placed <2 cm in depth and its dose is mainly from anterior beams, we recommend using the bolus during the entire course of radiation delivery to reduce the dose to CIED.

A Review and Analysis of Managing Commonly Seen Implanted Devices for Patients Undergoing Radiation Therapy

“…If the device sits within 5 cm proximal to the field edge, a bolus (1-2 cm thickness) on the top of the device for the entire course of treatment minimizes scatter and leakage because the photon spectra outside the treatment fields are in the kV range. 14 , 44 Chan et al reported that placement of bolus on the top of the ICD would reduce the dose to the device by 34% to 58% depending on the distance from the edge of the field. 14 Treatment planning techniques such as coplanar beam arrangement can also reduce entry and exit through the device.…”

Electron and Photon Energy Spectra Outside of 6 MV X-ray Small Radiotherapy Field Edges Produced by a Varian iX Linac

“…Consequently, the survival probability for patients to live enough for experimenting with late radiation effects has progressively increased [1]. So, knowing the peripheral (outside the field edge) low absorbed dose received by healthy surrounding organs becomes an important issue [2][3][4], principally if anatomical structures with tolerances to low absorbed dose are involved. From a biological standpoint, it is well known that for a given absorbed dose value, the radiobiological effect varies with the energy beams.…”

The effect of ionising radiation on the physical properties of 3D-printed polymer boluses

“…They are widely used in radiotherapy to alter the dose distribution of ionising radiation, especially during irradiation of superficial neoplastic lesions. Boluses provide additional absorption and scattering of ionising radiation, resulting in a more homogenous dose delivered to the area being treated (Hogstrom and Almond 2006 ; Łukowiak et al 2017 , 2016 ; Yan et al 2018 ; Stone et al 2003 ; Khan 2003 ).…”