Tumor Response after Preoperative Chemoradiation Therapy Using Volumetric Arc Therapy with Dose Escalated Simultaneous Integrated Boost in Locally Advanced Rectal Cancer

Tuesday, Nov. 28 12:45PM - 1:15PM Room: RO Community, Learning Center Station #6

Mustafa Adli, MD, Istanbul, Turkey (Presenter) Nothing to Disclose
Mehmet C. Koc, MD, PhD, Erzurum, Turkey (Abstract Co-Author) Nothing to Disclose
Hilal Alkis, Istanbul, Turkey (Abstract Co-Author) Nothing to Disclose
Merve Sevindik, Istanbul, Turkey (Abstract Co-Author) Nothing to Disclose
Abolfazl Asadollahi Arbatani, Istanbul, Turkey (Abstract Co-Author) Nothing to Disclose
Ayse Dagli, Istanbul, Turkey (Abstract Co-Author) Nothing to Disclose
Rashad Rzazade, Istanbul, Turkey (Abstract Co-Author) Nothing to Disclose
Sevket C. Yegen, Istanbul, Turkey (Abstract Co-Author) Nothing to Disclose

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Purpose/Objective(s): This single center retrospective study investigated the efficacy of preoperative dose escalation using volumetric arc therapy with simultaneous integrated boost (VMAT-SIB), concomitant with capecitabine chemotherapy in locally advanced rectal cancer.Materials/Methods: Between February 2015 and September 2016, 35 patients with operable stage II-III rectal adenocarcinoma received preoperative VMAT with pelvic dose of 50.4 Gy and simultaneously delivered 56 Gy to the tumor in 28 fractions, concomitant with capecitabine, 825 mg/m2 bid, including weekends. Treatment response rates were analyzed.Results: Median age was 60 (30-82). Female/male ratio was 10/25. Tumor location was distal rectum in 12 patients, mid-rectum in 14, and proximal rectum in 9. Thirty patients underwent surgical resection. Median time to surgery from the completion of radiotherapy was 9 (6-24) weeks. Five patients refused surgery or were medically inoperable. Biopsy-proven clinical complete response (n=3) and pCR (n=6) was achieved in 9 (25.7%) patients. In another 4 (11.4%) patients microscopic disease only (“few tumor cells”) was reported. Resection margins were free in all operated patients. The sphincter preservation rate for the low rectal tumors was 50%, including two patients with clinical complete response. Metastatic pelvic lymph nodes were reported in 8 (22.8%) patients, pathologic lymph node status was unknown in one patient due to local excision only. There were not any Grade =3 acute toxicities, except diarrhea in one patient, which resolved after capecitabine discontinued. Early postoperative complications were not reported. Conclusion:  Preoperative chemoradiotherapy with dose escalation using VMAT-SIB is well tolerated, with a low acute toxicity profile, and can achieve a high rate of pCR or near-complete response and downstaging in locally advanced rectal cancer patients. Further studies with larger patient number and longer follow-ups are needed.