Radiobiological analysis of VMAT treatment plan with flattened and flattening filter free photon beam: an EUD and TCP based comparative study.

BACKGROUND

This study aimed to evaluate the dosimetric and radiobiological differences between 6MV flattened filter (FF) and flattening filter free (FFF) using volumetric modulated arc (VMAT) technique for head and neck (H&N) cancer patients.

MATERIALS AND METHODS

Fifteen patients with H&N carcinoma were selected and treated with VMAT with FF (VMAT) treatment plan. Retrospectively, additional VMAT treatment plans were developed using FFF beams (VMAT). Radiobiological parameters, such as equivalent uniform dose (EUD), tumor cure probability (TCP), and normal tissue complication probability (NTCP), were calculated using Niemierko's model for both VMAT and VMAT. Correlation between dosimetric and radiobiological data were analyzed and compared.

RESULTS

The conformity index (CI) was 0.975 ± 0.014 (VMAT) and 0.964 ± 0. 019 (VMAT) with p ≥ 0.05. Statistically, there was an insignificant difference in the planning target volume (PTV) results for TCP (%) values, with values of 81.20 ± 0.88% (VMAT) and 81.01 ± 0.92 (%) (VMAT). Similarly, there was an insignificant difference in the EUD (Gy) values, which were 71.53 ± 0.33 Gy (VMAT) and 71.46 ± 0.34 Gy (VMAT). The NTCP values for the spinal cord, left parotid, and right parotid were 6.54 × 10%, 8.04%, and 7.69%, respectively, in the case of VMAT. For VMAT, the corresponding NTCP values for the spinal cord, parotids left, and parotid right were 3.09 × 10%, 6.57%, and 6.73%, respectively.

CONCLUSION

The EUD and Mean Dose to PTV were strongly correlated for VMAT. An increased mean dose to the PTV and greater TCP were reported for the VMAT, which can enhance the delivery of the therapeutic dose to the target.