The impact of dose grid resolution during VMAT planning on COMPASS pass rate / 中华放射医学与防护杂志

ABSTRACT

Objective To investigate the impact of adopting different dose grid resolution during volumetric modulated arc therapy (VMAT) planning on COMPASS pass rate.Methods A total of 10 patients with cervical cancer were enrolled.Four types of VMAT plans (plan1,plan2,plan3,plan4) were designed for each patient,with dose grid resolution of 0.2 cm × 0.2 cm × 0.2 cm,0.3 cm × 0.3 cm ×0.3 cm,0.4 cm ×0.4 cm ×0.4 cm and 0.5 cm ×0.5 cm ×0.5 cm,respectively.The plans were exported to Linac and conducted,then measured by COMPASS.The discrepancies were analyzed,which were obtained by comparing reconstructed dose from COMPASS and dose from TPS optimization.Results For tumor volume,the mean value of Dmean and D95 were ＜ 0.5％ and ＜ 1.3％ respectively,and the standard deviation were both ＜ 1.0％.For organs at risk (OAR),the max discrepancies were Dmean of femur with-6.7％,-7.0％,-8.0％,-5.8％,and V35 of rectum with 4.9％,-6.3％,-6.1％,-5.7％ in four types of VMAT plans.The γ (3％,3 am) rate of tumor volume was ＞95％ with standard deviation ＜ 2.5％,with no statistically significant difference among the four types of plans (P ＞0.05).The γ (3％,3 mm) rate of OARs were ＞ 98％ except femur (＞ 95％),and the standard deviations were within 1.9％-6.1％,with no statistical significance (P ＞0.05).The average γ rate of tumor volume and OARs were ＜ 0.4 except femur (＞ 0.4),with no statistically significant difference among four types of VMAT plans (P ＞ 0.05).Conclusions COMPASS pass rate was not influenced by the dose grid resolution between 0.2 ～ 0.5 cm for VMAT plan.