3440 - Pancreatic Reirradiation: A Multi-Institutional Retrospective Analysis of Feasibility, Tolerability and Clinical Outcomes

02:30pm - 03:45pm PT

Hall F

Screen: 18

POSTER

Presenter(s)

Helen Hou, - Massachusetts General Hospital, Boston, MA

H. X. Hou¹, H. J. Roberts¹, P. S. Pathak², H. J. Mamon³, J. D. Mancias³, J. L. Koenig¹, T. S. Hong¹, C. R. Blaszkowsky¹, L. S. Blaszkowsky², A. R. Parikh², J. N. Allen², J. W. Clark², C. Weekes², R. van Dams³, and J. Y. Wo¹; ¹Department of Radiation Oncology, Massachusetts General Hospital, Harvard Medical School, Boston, MA, ²Division of Medical Oncology, Department of Medicine, Massachusetts General Hospital, Harvard Medical School, Boston, MA, ³Department of Radiation Oncology, Brigham and Women’s Hospital/Dana-Farber Cancer Institute, Boston, MA

Purpose/Objective(s):

With improvements in systemic therapy for pancreatic cancer, the role of radiation to optimize local control has increased. The tolerability and outcomes for RT for PC are well described; but data on feasibility, tolerability and clinical outcomes after pancreatic reirradiation (re-RT) remain limited. This study retrospectively reviews a multi-institutional experience of pancreatic re-RT.

Materials/Methods:

A retrospective review of two academic institutions for patients who received pancreatic re-RT was conducted. The cohort comprised: adenocarcinoma (n=25), adenosquamous (n=1), colloid carcinoma (n=1). Electronic medical records were reviewed, and descriptive statistics calculated. The primary study endpoint was local failure-free survival (LFFS) from time of completion of re-RT. Secondary endpoints included progression free survival (PFS), distant metastasis free survival (DMFS), chemotherapy-free interval, overall survival (OS) and acute toxicity, graded according to CTCAEv5.0. Kaplan-Meier method and Cox regression were performed.

Results:

Between 2012-2024, 27 patients who underwent prior pancreatic radiotherapy and later received abdominal re-RT were identified. Indications for re-RT were local recurrence (n=17) after resection with adjuvant chemoRT (n=3) or RT (n=1), or neoadjuvant chemoRT (n=9) or RT (n=4), local progression after definitive RT for unresectable pancreatic cancer (n=7), positive margin after initial surgery (n=2), and for repeat GI bleed (n=1). Median BED for initial RT was 59.5 Gy (range, 28.0-72.0) delivered in a median of 10 fractions (range, 3-33). Median BED for pancreatic re-RT was 54.8 Gy (range, 8.5-97.9) delivered in a median of 20 fractions (range, 3-28), with 74% (n=20) receiving concurrent chemotherapy. RT technique of re-RT included: 3D-CRT (n=1), IMRT/VMAT (n=13), SBRT (n=10), and proton RT (n=3).

96% (26/27) completed re-RT; one patient discontinued due to tumor-related fistula. Median follow-up after re-RT was 6.2 months (range, 0.2-59.4). 37% (10/27) had metastatic disease at the time of re-RT. Neoadjuvant chemotherapy was administered to 56% (15/27) patients prior to re-RT. After re-RT, 13 patients received chemotherapy, with a median chemotherapy-free interval of 5.7 months (range, 0-35.5), 6 and 3 patients had 6-mo and 12-mo chemotherapy-free intervals. The 6-mo and 12-mo LFFS after re-RT was 60.3% and 54.3%. The 6-mo PFS, DMFS, and OS after re-RT were 36.5%, 50.5%, 65.6%, respectively. Grade =3 toxicities occurred in three patients, including anorexia, dysphagia, and GI bleed.

Conclusion:

Pancreatic re-RT is feasible and may offer promising local control and time off chemotherapy for select patients. Future studies should refine patient selection criteria for pancreatic re-RT, and improvement on RT delivery with online adaptive therapy may further minimize toxicity.