Vol. 8, Issue 1, Part A (2026)

Purpose: In external beam radiation therapy, accuracy in dose estimation of dose calculation methods is critical. The influence of deformity on radiation dose calculations derived by a treatment planning system is investigated in this study. The goal of this study was to create a low-cost inhomogeneous phantom for measuring absorbed dose using an Ionisation chamber and Gafchromic film, which was validated using treatment planning system (TPS) dose outcome.

Methods and Materials: The central axis dose calculations were computed using the Pencil Beam Convolution algorithm (PBC), Collapsed Cone Convolution (CCC) and Monte Carlo (MC)algorithm in the Monaco treatment planning system using an In-house phantom (20x20x20cm³) made up of acrylic sheet containing water and inhomogeneous material wooden powder equivalent to lung. The phantom is scanned with a Computed Tomography (CT) scanner, and the image data set is sent to the treatment planning workstation. The depth dose measurements were performed using cylindrical ionization chamber and Gafchromic film for depth dose computations, with the same beam settings and monitor units in every setup. Following that, the calculated doses obtained from TPS and measured depth doses were compared.

Results: The x-ray beams passed through the various media, interacting with the densities of the inhomogeneous material and depositing dose. The results reported in this study for photon beam energies 6MV, 10MV, 15MV, 6FFF and 10FFF at varying field sizes of 4X4 cm², 5x5 cm², 10x10 cm², and 15x15 cm². MC maximum dose variation predicted was 2.06% in 15MV of measured chamber dose and -2.06% of measured gafchromic film dose in 6MVFFF. CCC maximum dose variation predicted was 2.68% of measured chamber dose in 6MV and 3.31% of measured gafchromic film dose in 6MV whereas PB maximum dose variation predicted was -5.94% in 15MV of measured chamber dose and -11.6% of measured gafchromic film dose in 6MVFFF.

Conclusion: The results of this study showed that the inhouse phantom can be used with different inhomogeneities and can be used for pretreatment plan verification. The low cost inhouse phantoms can be used in assessment of point and planar doses during patient specific quality assurance in centers having no such facility of phantoms available for QA due to expensive tools available into the market.