3556 - Ablative Radiotherapy for Inoperable Non-Metastatic Pancreatic Cancer: Long-Term Results in a Single Center

Purpose/Objective(s): Stereotactic body radiation therapy (SBRT) with intent to definitive biological effective dose (BED), also known as ablative radiotherapy, has demonstrated promising local tumor control rates in the treatment of pancreatic cancer (PC). However, real-world data on ablative radiotherapy with 5-fraction SBRT protocol is limited. This study aims to evaluate the outcomes of patients with inoperable non-metastatic PC treated with 5-fraction SBRT at a high-volume center.

Materials/Methods: The study analyzed consecutive patients with inoperable non-metastatic PC who received ablative radiotherapy with 5-fraction SBRT protocol, where BED₁₀ (a/ß=10) was more than or equal to 100Gy, at a single center between 2016 and 2020. Ablative radiotherapy was delivered via a frameless robotic radiosurgery system, with 1 to 3 gold fiducials implanted in the lesion before treatment. Respiration synchronous tracking was used to monitor fiducial movement during simultaneous irradiation. Gross tumor volume (GTV) and organs at risk were contoured using multi-modal imaging. GTV included primary tumor and metastatic lymph nodes, with planning target volume (PTV) incorporating 0-5 mm expansion of GTV. The prescribed PTV dose was 50-55Gy in 5 fractions. The outcomes were overall survival (OS) and progression-free survival (PFS).

Results: 88 patients were enrolled, with a median age of 65 years (range, 36-84), including 55 males and 33 females. There were 55 cases in head and 33 cases in body/tail. At diagnosis, 29 and 59 patients had medically inoperable and locally advanced unresectable diseases, respectively. 82 patients received 50Gy/5f, while 6 received 55Gy/5f. The median GTV was 33.6 cm³ (range, 3.7-167.8). With a median follow-up of 20.2 months, the median OS (mOS) and median PFS (mPFS) from diagnosis were 19.2months [95% confidence interval (CI), 16.9-28.4] and 13.5 months (95% CI, 10.3-15.0), respectively. The mOS and mPFS from SBRT were 15.5 months (95% CI, 14.1-23.2) and 8.7 months (95% CI, 5.5-12.7), respectively. The 1-year, 2-year, and 3-year OS from diagnosis and SBRT were 77.5%, 36.9%, and 17.2% as well as 65.9%, 27.4%, and 10.4%, respectively. The mOS from diagnosis for medically inoperable and locally advanced unresectable disease were 18.0 months (95% CI, 17.0-NA) and 19.2 months (95% CI, 16.0-30.1), respectively, and that from SBRT for those were 18.0 months (95% CI, 14.1-NA) and 14.6 months (95% CI, 11.0-27.2), respectively. The mOS from diagnosis and SBRT for 55Gy/5f group were 15.3 months (95% CI, 14.9-NA) and 14.2 months (95% CI, 14.1-NA), respectively. For 50Gy/5f group, mOS from diagnosis and SBRT were 19.2 months (95% CI, 16.9-28.4) and 15.5 months (95% CI, 14.1-23.2), respectively. Grade 3 upper gastrointestinal bleeding occurred in 4 patients (4.5%), with no grade 4 or 5 events.

Conclusion: Ablative radiotherapy with 5-fraction SBRT with BED₁₀ (=100 Gy) provided durable locoregional tumor control and favorable survival outcomes in patients with inoperable non-metastatic PC.