SU‐E‐T‐447: Electronic Brachytherapy (EBT) Treatment of Cervical Cancer – First Clinical Experience

Abstract

Purpose: To study the first trial patient in which an electronic brachytherapy (EBT) x‐ray source is utilized for treatment of cervical cancer. Methods: During patient treatment, a miniaturized x‐ray source was used in combination with a customized titanium tandem and ovoid applicator set. The semi‐specialized source was modeled with formalisms outlined by AAMP Task Group 43. Multiple models were used to compensate for variable attenuation conditions as a function of source positions. Varian Brachyvision treatment planning software was utilized on CT data sets for dose calculations prior to treatment delivery. The dose was prescribed to “point A” as defined by American Brachytherapy society. Additional treatments plans were created from those clinically utilized in patient care and were recalculated for an existing Ir‐192 source model. Dose volume histograms (DVH) and point dose calculations were compared between the modalities for the clinical condition present in patients treated with EBT. Results: Clinical treatment times, though longer than those typically experienced by Ir‐192 users, were manageable. Instantaneous dose rates at personal positions within the treatment vault were lower than those measured during intra operative radiation therapy and breast EBT treatments. Due to lower average photon energy in EBT, dose gradients within the treatment plans were as expected steeper than those observed in Ir‐192 based brachytherapy. DVH comparisons between Ir‐192 and EBT treatments showed an expected decrease in the integral dose to normal tissues of interest for EBT. In comparing plans created for EBT delivery with those calculated for Ir‐192, average dose values for EBT were more than 4%, 11%, and 9% lower at predefined bladder, rectum and “point B” positions, respectively. Conclusion: For the first time, we have demonstrated that the utilizing electronic brachytherapy system for tandem and ovoid based treatment of cancer of the cervix is feasible, and potentially beneficial, in clinical environment.