Comparison of three Radiotherapy Techniques Volumetric Modulated Arc Therapy with Variable and Constant Dose Rate and Intensity-Modulated Radiotherapy for the Irradiation of Five Cancer Sites.

Background: Volumetric modulated arc therapy (VMAT) is mostly considered due to its superior tumor coverage and sparing of organs at risk (OAR) with shorter treatment delivery time.

Objective: This study aimed to explore the feasibility and potential benefits of VMAT with a constant dose rate (CDR).

Material and methods: In this analytical study, 75 cancer patients (15 from each cancer) were selected. Step and shoot intensity-modulated radiation therapy (S&S IMRT), CDR, and VDR VMAT (variable dose rate VMAT) plans were generated for each patient using the Monte Carlo algorithm on the Monaco treatment planning system for 6 MV photon energy. For dosimetric comparison, some variables were compared, including doses to the planning target volume (PTV), OAR, homogeneity index, conformity index (CI), treatment delivery time, and monitor units.

Results: CI was higher in CDR and VDR VMAT plans compared to IMRT without any significant variation for PTV coverage V95 and PTV mean dose. In the sparing of OAR, no significant variation was found between CDR, VDR, and IMRT for the brain, head-neck, oesophagus, lung, and prostate. The treatment delivery time was reduced more, i.e., by up to 72-80% in the CDR VMAT technique compared to IMRT.

Conclusion: CDR VMAT technique generates a clinically acceptable plan in terms of PTV coverage, dose conformity, and OAR sparing as IMRT and VDR VMAT in all five cancer sites.