The experience of a developing country using an electronic portal imaging device for the verification of patient positioning and dosimetry in radiotherapy for prostate cancer

Abstract

AbstractPurposeThis is a retrospective study to evaluate the efficacy and safety of routine use of electronic portal imaging device (EPID) in intensity-modulated radiation therapy for localised prostate cancer.Materials and methodsData from 20 patients with localised prostate cancer treated by radical radiotherapy using intensity-modulated technique in Habib Bourguiba Hospital were analysed to define the action levels for pretreatment planer dose distribution of 100 treatment fields and the set-up errors of 418 portal imaging. Pretreatment planar dose distribution was measured with the EPID. The additional dose from repeated portal imaging was determined with treatment planning system.ResultsFor all 100 fields, the predicted and the measured planar dose distribution agrees well with mean±standard deviation value for γmax=2·31±0·57, γavg=0·36±0·07 and γ%≤1=98·94%±0·71%, respectively. For the evaluation of set-up errors, the mean total errors with 1 SD in the lateral, longitudinal and vertical directions were 0·11±0·44 cm; 0·02±0·37 cm and −0·02±0·21 cm, respectively. The imaging additional dose was evaluated as 1 cGy per monitor unit.ConclusionEPID is a useful tool to verify pretreatment dose distribution and to assess the correct field position without a significant increase in the absorbed dose due to the repetition of portal imaging.