Enhancing treatment precision through radiobiological modeling for evaluating complex VMAT plans in prostate and head-and-neck cancers

Regarding the importance of radiation therapy treatment planning in treatment outcomes, this study aimed to evaluate the quality of treatment plans for external radiotherapy of prostate and head-and-neck cancer patients using radiobiological modeling.

Treatment plans of five prostate and five head-and-neck cancer patients treated with volumetric modulated arc therapy were evaluated. The RADBIOMOD software tool was used to calculate tumor control probability (TCP) and normal tissue complications probability (NTCP). TCPs were calculated based on Poisson, Zaider-Minerbo, and equivalent uniform dose (EUD) models. Lyman-Kutcher-Burman (LKB) and EUD models were used to calculate NTCPs. Uncomplicated tumor control probability (UTCP) was also calculated.

For the evaluated prostate cancer treatment plans, the Zaider-Minerbo model achieved the highest TCP of 99.34%, while the Poisson model had the highest TCP of 97.78% for head-and-neck cases. The LKB model was effective in determining NTCP for cancer treatment plans being studied. Although acceptable values of calculated UTCP for both prostate and head-and-neck cancer cases were observed, the NTCP values obtained using the EUD model exceeded the permitted range for evaluated head-and-neck cases.

The acceptable quality of evaluated treatment plans was proved using calculated values of TCP, NTCP, and UTCP. These indices, along with the conventional dosimetric indicators obtained from dose volume histograms (DVHs), can help to assess the quality of treatment plans and to identify the optimal treatment plans. The observed varied TCP results across models, highlighting the importance of evaluating treatment plans with multiple models to ensure biologically guaranteed quality.