Room: Exhibit Hall
Purpose: To retrospectively assess radiation therapy response in esophageal cancers using weekly cone beam CT (CBCT) data and relating the results to post-treatment clinical and pathological response on PET-CT or biopsy.
Methods: We conducted a retrospective analysis of CBCT data of 8 patients treated with radiation therapy from 2012 to 2017. All the patients received a total dose of 50.4 Gy in 28 fractions by external beam radiation therapy (21EX, Varian Medical Systems). The CBCT images were taken prior to each treatment using LINACâ€™s OBI system. The main purpose of CBCT imaging was to setup the patient accurately and reproducibly every day. CBCT images were registered with the planning CT and the initial GTV (Esophagus) volume was copied to the CBCT images for the starting point and then modified based on corresponding CBCT images of every 5th fraction. So no additional imaging was done on the patients for this study.
Results: Out of the 8 cases, 6 of them were complete responders and 2 were partial responders. The CBCT images show a reduction of GTV volumes from 20 % â€“ 33 % during full course of treatment in half of the cases. In the other half, there is no change in GTV throughout the treatment. The ones where tumor shrunk, it appeared after first 2 weeks and kept shrinking till completion of treatment.
Conclusion: The tumors were shrunk up to 33 % of initial volume, by the completion of treatment. This measured CBCT volume was correlated to treatment response. The results of this preliminary study indicated that the CBCT may have potential role in assessing treatment response and predicting prognosis. The preliminary study is promising and we are reviewing more number of patients to find statistical significance and uncertainties.
Not Applicable / None Entered.