Initial Clinical Experience with Electronic Portal Imaging Device-Based In Vivo Dosimetry for Radiotherapy in Gynecological Cancers

OBJECTIVE In this study, it was aimed to evaluate the performance and reliability of 3-dimensional (3D) in vivo electronic portal imaging device (EPID)-based dosimetry in radiotherapy (RT) of patients with gynecological cancer. METHODS The dose distributions and in vivo dosimetry results of patients with endometrial (n=10) and cervical (n=10) cancer who underwent external pelvic RT in our department were analyzed retrospectively. The RT planning and 3D in vivo dosimetry data were obtained from the treatment planning system and the iViewDose® (Elekta, Crawley, UK) in vivo quality assurance system. In addition, patient-specific phantom measurements were carried out for each patient with the Alderson Rando phantom. The results were evaluated with 3D gamma analysis method using iViewDose® software. We obtained γ_mean, γ_1%, and γ_≤1% values for each patient with the analysis. Acceptance criteria for these parameters were taken as 0.7, 2.0, and 90%, respectively. RESULTS The phantom measurements showed that all treatment plans were applicable. All patients met the passing criteria for γmean, γ_1%, and γ_≤1%. The mean gamma passing rate was 95.1%±1.7 and 96.3%±2.9 for patients with endometrial and cervical cancer, respectively. CONCLUSION The EPID-based in vivo dosimetry seems to be usable in clinical routine in the treatment of gynecological cancers. However, field size is the most important limitation of in vivo EPID dosimetry in cases requiring extended field RT.