Minimising pacemaker exposure in thoracic radiotherapy: a comparative study of IMRT, VMAT, and helical tomotherapy

Patients with cardiac implantable electronic devices (CIEDs) increasingly require thoracic radiotherapy, but comparative evidence guiding technique selection remains limited. This study evaluated CIED dose, target coverage, organ-at-risk (OAR) sparing, and delivery efficiency across IMRT, VMAT, and helical tomotherapy in matched thoracic cases.

Eighty patients with left-sided subclavicular pacemakers were planned using five techniques: IMRT, VMAT, and tomotherapy with 1 cm, 2.5 cm, and 5 cm field widths. All plans used 6 MV FFF photons with harmonised dose constraints. CIED endpoints included Dmax, D0.03 cc, and Dmean. Secondary endpoints included PTV coverage, homogeneity, conformity, lung and heart dose metrics, monitor units, and beam-on time. Statistical comparisons were performed using repeated-measures ANOVA with Holm-Bonferroni correction.Out-of-field dose was validated using OSLDs in a RANDO phantom.

Target coverage was comparable across techniques (PTV D95 ≈ 98.5–99.2%). CIED dose was significantly reduced with tomotherapy, with mean Dmax decreasing from 1.86 ± 0.43 Gy (IMRT) and 1.68 ± 0.38 Gy (VMAT)to 1.10 ± 0.25 Gy for the 1 cm field width (p < 0.01). Mean heart dose decreased from 8.2 Gy to 3.8 Gy, and mean lung dose from 9.4 Gy to 7.6 Gy. VMAT required fewer monitor units (500 vs. 910 for IMRT) and shorter delivery (1–1.5 min), whereas tomotherapy ranged from 140 to 500 s.

Helical tomotherapy improves CIED sparing and selected OAR metrics while maintaining target coverage. However, VMAT offers superior delivery efficiency. Technique selection should therefore be individualised, balancing dosimetric benefit against intrafraction motion risk, target geometry, and patient-specific clinical priorities.