Evaluating impact of medium variation on dose calculated through planning system in a low cost in-house phantom

Abstract

Purpose: In radiotherapy, accuracy in dose estimation of dose calculation methods is critical. The influence of deformity on radiation dose calculations derived by planning system is evaluated in present study. The goal of 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 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. Phantom was scanned in Computed Tomography (CT) scanner and image set was sent to the planning workstation. The depth dose evaluations were performed using ionization chamber and Gafchromic film with 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 results was reported for photon 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: Low-cost in-house phantoms can be utilised to assess point and planar doses during patient-specific quality assurance in centres that don't have accessibility to phantoms due to the high cost of commercially available tools.

Evaluation of Radiation Treatment Planning Algorithms in IMRT and VMAT: A Comparative Dosimetric Study in Lung Equivalent Heterogeneous Medium

“…However, the variation with PBA was greater than MCA-generated VMAT plan, with a minimal permissible deviation of 0.8%, related to the lower accuracy of algorithm in simulating the enhanced transverse scattering phenomenon in low-density mediums. Saini A et al [ 18 ] showed that the greatest dose variation predicted by the PB method was -11.6% of the observed Gafchromic film dose in 15 MV photon energy. The maximal variation in dose was similarly large in all other energies.…”