Comparing four volumetric modulated arc therapy beam arrangements for the treatment of early-stage prostate cancer

Abstract

Introduction: This study compared four different volumetric modulated arc therapy (VMAT) beam arrangements for the treatment of early-stage prostate cancer examining plan quality and the impact on a radiotherapy department's resources.

Methods: Twenty prostate cases were retrospectively planned using four VMAT beam arrangements (1) a partial arc (PA), (2) one arc (1A), (3) one arc plus a partial arc (1A + PA) and (4) two arcs (2A). The quality of the dose distributions generated were compared by examining the overall plan quality, the homogeneity and conformity to the planning target volume (PTV), the number of monitor units and the dose delivered to the organs at risk. Departmental resources were considered by recording the planning time and beam delivery time.

Results: Each technique produced a plan of similar quality that was considered adequate for treatment; though some differences were noted. The 1A, 1A + PA and 2A plans demonstrated a better conformity to the PTV which correlated to improved sparing of the rectum in the 60-70 Gy range for the 1A + PA and 2A techniques. The time needed to generate the plans was different for each technique ranging from 13.1 min for 1A + PA to 17.8 min for 1A. The PA beam delivery time was fastest with a mean time of 0.9 min. Beam-on times then increased with an increase in the number of arcs up to an average of 2.2 min for the 2A technique.

Conclusion: Which VMAT technique is best suited for clinical implementation for the treatment of prostate cancer may be dictated by the individual patient and the availability of departmental resources.

Keywords: Prostate; RapidArc; VMAT; radiation therapy.

Figure 1

An example case displaying the planning target volume (in red) and the beam arrangement for the (A) partial arc (PA), (B) one arc (1A), (C) one arc plus a partial arc (1A + PA) and (d) two-arc (2A) volumetric modulated arc therapy (VMAT) techniques.

Figure 2

A series of dose volume histograms (DVHs) for an example case (Case 5) that plots the dose in cGy against the ratio of total structure volume (%) for the (A) planning target volume (PTV), (B) rectum, (C) bladder and (D) left head of femur for the partial arc (PA), one arc (1A), one arc plus a partial arc (1A + PA) and two-arc (2A) volumetric modulated arc therapy techniques.

Figure 3

The average optimisation, calculation and total planning time (in minutes) required for the; partial arc (PA), one arc (1A), one arc plus a partial arc (1A + PA) and two-arc (2A) volumetric modulated arc therapy (VMAT) techniques.