Dosimetric verification analysis for intensity modulated radiation therapy based on Mapcheck2

Abstract

Objective To investigate the relationship between dosimetric verification and target homogeneity index (HI), target conformality index (CI) and isocenter dose gradient (DGref) of intensity-modulated radiation therapy (IMRT). Methods Dosimetric verification was performed on 532 IMRT plans based on Mapcheck2 (two-dimensional diode detector arrays). By setting the passing rate of gamma (3%/3 mm) and the absolute value of isocenter cumulative dose deviation (Dacc) as judge criterion, 532 IMRT plans were divided into qualified plan(control group) and unqualified plan (group A: passing rate of gamma 3%; group C: Dacc>3%). The HI, CI and DGref of all unqualified groups were calculated and compared with control group. Results There was no significant difference in HI, CI or DGref between group A and control group (P>0.05). There were significant differences in HI, CI and DGref between group B and control group (P<0.05). There was no significant difference in HI or CI between group C and control group while the DGref of group C was significantly higher than that in control group (P<0.01). After re-optimization, the unqualified plans were identified as qualified plan. There were no significant difference in HI, CI or DGref between the re-optimization plans and control group. Conclusions When designing the IMRT plan, the location of beam isocenter should be placed in the target area with smaller dose gradient. For the plan with higher HI and lower CI, the beam amount, beam direction, optimization parameters and optimization algorithm should be checked carefully to avoid the reduction of the gamma pass rate of dosimetric verification. Key words: Mapcheck2; Dosimetric verification; Gamma analysis; Homogeneity index; Conformality index; Isocenter dose gradient