Dosimetric comparison between the prostate intensity-modulated radiotherapy (IMRT) and volumetric-modulated arc therapy (VMAT) plans using the planning target volume (PTV) dose-volume factor

Background We demonstrated that our proposed planning target volume (PTV) dose-volume factor (PDVF) can be used to evaluate the PTV dose coverage between the intensity-modulated radiotherapy (IMRT) and volumetric-modulated arc therapy (VMAT) plans based on 90 prostate patients. Purpose PDVF were determined from the prostate IMRT and VMAT plans to compare their variation of PTV dose coverage. Comparisons of the PDVF with other plan evaluation parameters such as D-5%, D-95%, D-99%, D-mean, conformity index (CI), homogeneity index (HI), gradient index (GI) and prostate tumour control probability (TCP) were carried out. Methods and materials Prostate IMRT and VMAT plans using the 6 MV photon beams were created from 40 and 50 patients, respectively. Dosimetric indices (CI, HI and GI), dose-volume points (D-5%, D-95%, D-99% and D-mean) and prostate TCP were calculated according to the PTV dose-volume histograms (DVHs) of the plans. All PTV DVH curves were fitted using the Gaussian error function (GEF) model. The PDVF were calculated based on the GEF parameters. Results From the PTV DVHs of the prostate IMRT and VMAT plans, the average D-99% of the PTV for IMRT and VMAT were 741 and 745 Gy, respectively. The average prostate TCP were 0956 and 0958 for the IMRT and VMAT plans, respectively. The average PDVF of the IMRT and VMAT plans were 0970 and 0983, respectively. Although both the IMRT and VMAT plans showed very similar prostate TCP, the dosimetric and radiobiological results of the VMAT technique were slightly better than IMRT. Conclusion The calculated PDVF for the prostate IMRT and VMAT plans agreed well with other dosimetric and radiobiological parameters in this study. PDVF was verified as an alternative of evaluation parameter in the quality assurance of prostate treatment planning.