Dose-volume consistency and radiobiological characterization between prostate IMRT and VMAT plans

Abstract

Purpose: Dose-volume consistency of the planning target volume (PTV) and rectum for the prostate intensity modulated radiotherapy (IMRT) and volumetric modulated arc therapy (VMAT) plans were evaluated and compared. Dependences of radiobiological parameters of the prostate and rectum on the PTV and rectal volume were also investigated. Methods: From 40 prostate IMRT and 50 VMAT patients treated with the same prescription (78 Gy per 39 fractions) and dose-volume criteria in the inverse planning, the prostate tumour control probability (TCP), rectal equivalent uniform dose (EUD) and rectal normal tissue complication probability (NTCP) were calculated. The dose-volume consistency of the PTV and rectum, demonstrating the variability of dose-volume histogram (DVH) among patients, was defined and calculated as per the deviation between the corresponding and mean DVH. Results: For the IMRT plans, the prostate TCP was found increasing with the PTV with a rate equal to 1.05 × 10 -3 % cm -3 , which was lower than 1.11 × 10 -3 % cm -3 for the VMAT plans. Both the rectal EUD and rectal NTCP were found decreasing with the rectal volume. The decrease rates for the IMRT plans (EUD = 0.47 × 10 -3 Gy cm -3 and NTCP = 3.94 × 10 -2 % cm -3 ) were higher than those for the VMAT (EUD = 0.28 × 10 -3 Gy cm -3 and NTCP = 2.61 × 10 -2 % cm -3 ). Conclusion: For the dose-volume consistency, small prostate TCP variation could be achieved by decreasing the dose-volume variability among the IMRT and VMAT plans. However, dependences of the rectal EUD and rectal NTCP on the dose-volume variability were not significant. It is concluded that maintaining a good dose-volume consistency in prostate plans can decrease the prostate TCP variation among the IMRT and VMAT patients. However, dose-volume variability is not affected by variations of the rectal EUD and rectal NTCP.