The Influence of the Minimum Dynamic Leaf Gap on VMAT Plans Quality

The aim of the present work is to investigate the influence of dynamic minimum leaf gap into Pinnacle3 on VMAT plans quality. Three treatment machines were modeled in our TPS with a different value of dynamic minimum leaf gap of 5, 10 and 20 mm. VMAT plans of AAPM TG-119 phantom and twenty clinical real cases were planned on each machine. Based on AAPM TG-119 guidelines, we compared the machine on their ability to fulfill the dose goals; the pretreatment quality assurance was done with COMPASS QA system (IBA dosimetry, Germany). In order to evaluate how the measured and the planned data from each machine are closed. The monitor units’ numbers for each site and machine were also compared. For simple plans, all the three machines easily meet the goals; however, for complex shape case, only the 5 and 10 mm minimum leaf gap machines allow the user to reach the goals. Otherwise, the 20 mm minimum leaf gap machine presents lower difference between planned and measured dose and the best gamma scores than the two others machines. It also has the lower MUs per clinical site. Based on this investigation, 10 mm is the best compromise value for the dynamic minimum leaf gap into Pinnacle. It allows the planner to reach high complex goals during planning process and in another hand gives good agreement between planned and measured doses.