Assessment of Dose Calculation Accuracy of TiGRT Treatment Planning System Versus BEAMnrc Simulation in Nasopharyngeal Carcinoma: A Phantom study

Abstract

Background: 

Accurate dose calculations in radiotherapy are essential, especially in complex anatomical areas such as the nasopharynx, where heterogeneous tissue compositions can greatly influence treatment outcomes. This study assesses the accuracy of the full scatter convolution (FSC) algorithm within the TiGRT treatment planning system by comparing it to the BEAMnrc Monte Carlo (MC) simulation using a head phantom.

Methods: 

EBT3 film was strategically placed in the nasopharyngeal region to enable direct comparisons between experimental results and those derived from the FSC and MC methods. Various metrics, including the dose difference index, two-dimensional gamma index, and horizontal and vertical dose profiles, were employed for the analysis. The heterogeneous regions were classified into bone, air, and soft-tissue components. For dosimetric evaluation, the irradiated areas were segmented into four regions based on isodose values: Field region (FR), irradiated region (IR), penumbra region (PR), and out-of-FR (OOFR).

Results: 

The greatest computational discrepancies observed between the FSC algorithm and MC simulations in the air region of the FR were -5.12% ± 1.10% and 1.93% ± 1.45%, respectively. Notable underestimations occurred in the air and soft-tissue regions of the IR, PR, and OOFR when using the FSC algorithm, with a minimum discrepancy of -9.33% ± 5.51% and a maximum of -77.28% ± 8.19%. Conversely, doses calculated for the bone region were overestimated by 53.64% ± 5.65%. In comparison, the MC calculations in the IR region revealed discrepancies of 1.90% ± 1.55% (air), including a maximum underestimation of -8.82% ± 1.18% in the bone area within the PR. The gamma pass rates for different tissue types under local and global modes, using 3%-3 mm gamma criteria, demonstrate that the MC method consistently outperformed the TiGRT method across all tissue types, especially in the air (99.9%) and bone (99.8%) regions.

Conclusions: 

The findings reveal that the FSC algorithm tends to underestimate doses in soft tissue and air while overestimating doses in bone. In contrast, there was excellent agreement between MC calculations and experimental measurements, highlighting the FSC algorithm’s lower consistency.