2Department of Radiation Oncology, Koru Ankara Hospital, Ankara-Turkey
3Department of Radiation Oncology, Gazi University, Ankara-Turkey
4Department of Radiation Oncology, Gülhane Training and Research Hospital, Ankara-Turkey DOI : 10.5505/tjo.2019.1893 OBJECTIVE
The aim of the present study was to determine the electronic portal imaging (EPI) evaluation differences between the therapists in the reference of cone beam computed tomography (CBCT).
METHODS
In the present study, 62 EPI images belonging to 13 head and neck patients were evaluated separately by
four therapists as offline, and the amount of shift in the center of fields was determined. CBCT obtained
at the same time with the EPI images was accepted as reference, and the amount of shift in the center of
fields was compared separately for each therapist with the results of EPI.
RESULTS
According to our results, the amount of shift in the center of fields had changed between therapists with
0?9.4 mm in the reference of CBCT. The probability of shifting center of fields to be >3 mm was 60% for
the first therapist, 35% for the second therapist, 63% for the third therapist, and 50% for the fourth therapist.
The probability of shifting center of fields to be >5 mm was 24%, 8%, 27%, and 14.5%, respectively.
Analysis of variance for repeated measures test was applied to center shift values, and there were a significant
difference in the groups (sig. <0.05) and a significant difference between the groups (sig. <0.05).
CONCLUSION
The usage of CBCT for the verification of treatment fields eliminates the differences in interpersonal
evaluation. CBCT improves the set-up accuracy such that planning tumor volume expansion margin
can be safely dropped. Therefore, CBCT should be the preferred imaging modality in intensity-modulated
radiation therapy planning.