3475 - Early Outcomes of Dose-Escalated Radiation Therapy for Pancreatic Cancer

02:30pm - 03:45pm PT

Hall F

Screen: 19

POSTER

Presenter(s)

I-Chia Liu, MD - Johns Hopkins Radiation Oncology Kimmel Cancer Center, Baltimore, Maryland

I. C. Liu¹, S. Sehgal¹, S. Mao¹, T. A. Lin², A. V. Reddy³, C. Hill⁴, G. Paparoidamis¹, M. B. Roumeliotis¹, J. J. Meyer¹, and A. Narang¹; ¹Department of Radiation Oncology and Molecular Radiation Sciences, Johns Hopkins University School of Medicine, Baltimore, MD, ²Department of Radiation Oncology, The University of Texas MD Anderson Cancer Center, Houston, TX, ³Northside Radiation Oncology Consultants, Canton, GA, ⁴Department of Radiation Oncology, New York University Grossman School of Medicine, New York, NY

Purpose/Objective(s):

In the setting of dose-escalated radiation therapy for pancreatic cancer, it is unclear whether target volume design should include at-risk volumes such as the recently described “Triangle” volume, which data has shown to be beneficial in the pre-operative setting. Additionally, optimal dose to such elective target volume is also unclear. Moreover, whether a biologically effective dose (BED) of 100 Gy is truly ablative remains uncertain. At our institution, for patients with unresectable pancreatic cancer, we have pursued a strategy of 75 Gy in 25 fractions (BED₁₀ of 98Gy) to gross disease while treating the “Triangle” volume to 45 Gy in 25 fractions. Herein, we report on patterns of failure with this approach, which may help answer the above questions.

Materials/Methods:

We retrospectively reviewed all localized pancreatic cancer patients who were diagnosed between 2022 and 2023 and were treated with multi-agent chemotherapy followed by dose-escalated radiation therapy using the prescription and target volume design noted above. Patients who proceeded to surgical resection after RT or did not have appropriate follow-up were excluded from the study. We collected baseline clinical characteristics, treatment details, and anatomical location of local failures in reference to the 75 Gy and 45 Gy isodose lines. We report patterns of failure with this approach.

Results:

There were 22 patients who met inclusion criteria, including 8 patients with locally advanced disease, 3 medically inoperable patients, and 11 patients with local recurrent disease after prior resection. With a median imaging follow-up of 10.5 months (range: 0.76 -27.9 months), there were seven (32%) local failures. Of the 7 failures, 6 represented with progression of gross disease, while one patient developed a deposit in a separate location of the pancreas parenchyma. Of the 6 cases of progression of gross disease, 5 demonstrated progression in an area of undercoverage due to proximity of a GI luminal organ and in which gross disease was therefore treated between 45 Gy and 75 Gy. Only one case demonstrated progression within the 75 Gy isodose line. There were two cases of progression in the “Triangle” volume, both in cases in which there was also concurrent progression of gross disease. No isolated progression of disease in the “Triangle volume” was noted.

Conclusion:

In a cohort of unresectable pancreatic cancer patients treated with definitive dose-escalated radiation along with microscopic dosing to the “Triangle” volume, progression of under-covered regions of gross disease was the most common pattern of failure. Elective targeting of the “Triangle” volume led to a lower risk of progression in this region, although further dose-escalation to the “Triangle” volume may also be needed for optimal local control. Longer follow-up with more patients is certainly needed.