Factors Affecting “Organs at Risk” Doses in 3 Dimensional Brachytherapy (3D BRT) of Cervical and Endometrium Cancers

Abstract

In brachytherapy, both the tumor and organ at risk may have intrafractional and interfractional anatomical differences. In this study, we aimed to investigate the factors affecting Organs at Risk (OAR) doses in adaptive 3D BRT applications. A total of 55 patients that underwent intracavitary brachytherapy with the diagnosis of a gynecological tumor between September 2012 and December 2013 were evaluated retrospectively. The effect of the surgery, applicator type, bladder, rectum and sigmoid on D2cc, D1cc, D0.1cc values were investigated. The median age was 55 years. While there was no statistically significant difference between 1st and 2nd fractions measurements, the sigmoid D1cc values between the 1st and 3rd fractions were found to be statistically significant (p = 0.004). When the effect of the interfractional change of bladder filling on OAR doses in the first three fractions was examined, it was not statistically significant however, its effect on bladder, sigmoid and rectum D2cc, D1cc, D0.1cc values were observed in some fractions. The bladder point dose was found to be statistically significant in operated patients (p= 0.005). When the comparison was made according to the application type, the bladder dose was found to be statistically significant in roller applications than the other two applicator treatments (p= 0.001). 3D BRT provides maximum protection of healthy tissues while giving a high dose to the target as a result of adaptive planning by performing computed tomography in each fraction. The sigmoid is the OAR that makes the most distinctive interfraction. To obtain higher treatment accuracy in each fraction, routine preparation and tomographic imaging followed by adaptive planning should be done.