Optimasi Penggunaan Bolus Berbahan Thermoplastic Elastomer Terhadap Distribusi Dosis Serap Radiasi Elektron pada Pesawat Linac di RSUP Prof. Dr. I.G.N.G Ngoerah

Abstract

Electron beam radiotherapy is widely used for superficial lesion treatment; however, surface dose distribution can be modified by the application of bolus material. This study aimed to evaluate the effect of a thermoplastic elastomer (TPE) bolus on absorbed dose at specific measurement depths for electron beam energies and to assess its feasibility as an alternative bolus material. An experimental phantom-based study was conducted using a slab phantom with five repeated measurements per condition. Electron beam energies of 4, 6, 8, and 10 MeV were evaluated under open field (without bolus) and with 1 cm TPE bolus conditions. Absorbed dose was calculated according to the IAEA TRS-398 protocol. The mean absorbed dose without bolus was 2.0486 ± 0.0019 Gy (4 MeV), 2.0199 ± 0.0019 Gy (6 MeV), 2.0636 ± 0.0007 Gy (8 MeV), and 2.0440 ± 0.0011 Gy (10 MeV). With TPE bolus application, the absorbed dose changed to 1.3012 ± 0.0024 Gy, 1.8396 ± 0.0074 Gy, 1.8835 ± 0.0013 Gy, and 2.0248 ± 0.0013 Gy, respectively. Coefficient of variation for all measurements was below 0.5%, indicating high reproducibility. Wilcoxon signed-rank test demonstrated significant differences between open and bolus conditions at all energies (Z ≈ −2.03; p < 0.05). The findings indicate that thermoplastic elastomer bolus significantly modifies electron beam absorbed dose, with greater absorbed dose reduction observed at lower energies. TPE demonstrates stable dosimetric performance.