Gastrointestinal Cancer

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SU_7_2066 - A Prospective Pilot Study of Pencil Beam Scanning (PBS) Proton Radiation Therapy (RT) as a Component of Trimodality Therapy for Esophageal Cancer

Sunday, October 21
1:15 PM - 2:45 PM
Location: Innovation Hub, Exhibit Hall 3

A Prospective Pilot Study of Pencil Beam Scanning (PBS) Proton Radiation Therapy (RT) as a Component of Trimodality Therapy for Esophageal Cancer
C. L. Hallemeier1, K. W. Merrell2, J. A. Martenson1, M. A. Neben-Wittich1, H. H. Yoon3, S. H. Blackmon4, R. Shen4, E. J. Tryggestad1, B. Giffey1, B. D. Kazemba1, W. S. Harmsen5, and M. G. Haddock1; 1Department of Radiation Oncology, Mayo Clinic, Rochester, MN, 2Mayo Clinic, Rochester, MN, 3Department of Medical Oncology, Mayo Clinic, Rochester, MN, 4Department of Surgery, Mayo Clinic, Rochester, MN, 5Division of Biomedical Statistics and Informatics, Mayo Clinic, Rochester, MN

Purpose/Objective(s): To evaluate the safety and efficacy of PBS proton RT as a component of trimodality therapy for esophageal cancer.

Materials/Methods: Eligibility criteria were locally-advanced (T2-4 and/or N1-3) biopsy-proven adenocarcinoma (ACA) or squamous cell carcinoma (SCC) of the esophagus or gastroesophageal junction (GEJ), medically suitable for chemoRT (CRT) followed by planned esophagectomy. PBS (ProBeat, Hitachi) proton RT consisted of 25 fractions with dose-painting technique delivering 50 Gy (RBE 1.1) to the internal gross tumor volume + 1 cm and 45 Gy to a 3.5 cm longitudinal mucosal expansion and regional lymph nodes. Two posterior-oblique beams were typically utilized. Robust optimization was performed with uncertainties of 3-5 mm translational and 3-5% range. All pts had a treatable backup photon volumetric modulated arc therapy (VMAT) plan. Chemotherapy was weekly carboplatin (AUC=2) and paclitaxel (50 mg/m2). Restaging and esophagectomy were planned for 4-8 weeks after completion of CRT. The primary endpoint was the rate of acute grade 3 or higher adverse events (AEs) attributed to CRT.

Results: 35 pts were enrolled June 2015-April 2017, 5 withdrew prior to CRT (3 pts proton coverage denied, 2 pts metastatic disease), leaving 30 eligible/evaluable pts. Median age was 68 years (range 54-86) and 90% were male. Histology was ACA in 87% and location was distal esophagus/GEJ in 90%. Stage was T3-4 in 87% and N1-3 in 80%. Median tumor length was 5 cm. For all 30 patients, the treated PBS plan had lower mean dose to heart, lung, bowel, liver, and kidneys versus the VMAT comparison plan (heart: PBS mean 6.5 Gy (range 0.5-14) vs VMAT mean 23.1 Gy (range 13.5-34.0); lung: PBS mean 3.0 Gy (range 0.8-6.6) vs. VMAT mean 10.7 Gy (range 4.4-18). All 30 pts completed the planned RT dose. Acute grade 3 or higher AEs occurred in 9 pts (30%). Individual acute grade 3+ AEs were leukopenia 20%, neutropenia 10%, and dehydration 3%. 3 pts did not undergo esophagectomy (1 pt metastatic disease, 2 pts had clinical complete response and refused surgery (n=1) or explored and deemed technically unresectable (n=1)). 27 pts were evaluable for operative outcomes. Minimally invasive surgery was performed in 15%. Margin status was R0 is 93%. Pathologic complete response rate was 44%. Post-operative complications were cardiac 37%, pulmonary 22%, gastrointestinal 48%, wound/infection 22%. Severe post-operative complications (Clavien-Dindo score ≥ IV) occurred in 15%. Median hospital length of stay was 11 days (range 5-50). Postoperative mortality at 30 days was 3.7%. Median follow-up was 15 months (range 2-26). Kaplan–Meier survival estimate at 1 year was 78% (95% CI 62%-98%).

Conclusion: In this relatively elderly cohort of patients with esophageal cancer, PBS proton RT as a component of trimodality therapy resulted in promising acute AE profile and efficacy. Additional comparative clinical data with photon RT are needed.

Author Disclosure: C.L. Hallemeier: Research Grant; Mayo Clinic. K.W. Merrell: None. J.A. Martenson: None. M.A. Neben-Wittich: None. H.H. Yoon: None. S.H. Blackmon: None. R. Shen: None. E.J. Tryggestad: None. M.G. Haddock: Board Member; ISIORT.

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