Estimation of fetal dose from IMRT and VMAT plans from various treatment sites using radio-photoluminescent glass dosimeter

Abstract

The purpose of this study was to estimate the fetal dose from IMRT and VMAT plans from various treatment sites (Brain, Head & Neck, Breast, Lung, and Liver) using radio-photoluminescent glass dosimeters (RPLGDs). A Varian Halcyon™ linear accelerator with a 6 MV FFF beam and RPLGDs (GD-302M) was used to measure the fetus dose. To assess the effects of target volume, three target volumes (2.5 cm³, 5 cm³, 10 cm³) were used in a simple-geometry in solid water phantom, and the out-of-field (OOF) doses were measured at different distances. Subsequently, 45 treatment plans were generated using the Eclipse Treatment Planning System (version 16.1), and doses were calculated with the Acuros XB algorithm. Fetus dose measured by copying the plans to the Rando phantom images, with multiple RPLGDs inserted at the uterine level (slice 28) and compared with the TPS calculations dose. The results indicated that the fetal dose decreased significantly with increasing distance from the treatment regions in both techniques. VMAT consistently delivered a lower fetal dose than IMRT across five regions. In the Brain and the H&N regions, the RPLGD-measured dose per prescribed dose was 0.25 ± 0.03 mSv/Gy and 0.91± 0.18 mSv/Gy for VMAT, while 0.66 ± 0.10 mSv/Gy and 2.05 ± 0.43 mSv/Gy for IMRT. The maximum TPS-calculated dose and RPLPGD-measured dose were observed in the Liver region for both techniques, with 90.42 ± 160.31 mSv/Gy and 22.08 ± 21.13 mSv/Gy for IMRT and 77.60 ± 130.48 mSv/Gy and 25.03 ± 26.70 mSv/Gy for VMAT. The TPS-calculated dose underestimates at the longest distance and overestimates at the shortest distance. Recommend VMAT over IMRT for pregnant patients due to less dose to the fetus. TPS calculation alone is insufficient; direct measurement with RPLGDs is required for accurate fetal dose estimation.