Radiological Assessment after Neoadjuvant SBRT in Pancreatic Cancer

Abstract

<h3>Purpose/Objective(s)</h3> Localized pancreatic cancer is often treated with neoadjuvant SBRT. Patients showing radiological response after SBRT can be considered for surgical resection. Here, we assess the difference in radiological assessment between 8 and 12 weeks post-SBRT. <h3>Materials/Methods</h3> Patients were prospectively enrolled on a phase 1/2 randomized controlled trial of SBRT with or without a vasospasm. The trial was designed to assess the maximal tolerated dose of SBRT in patients with borderline resectable or locally advanced pancreatic cancer. All patients received neoadjuvant chemotherapy and SBRT with 50 or 55Gy in 5 fractions. Following neoadjuvant therapy, patients underwent CT scanning at weeks 8 and 12 post-SBRT. Response was assessed using the modified RECIST criteria: partial response (PR) was considered when the tumor showed at least a 30% decrease in diameter, and disease progression was considered with the tumor showed at least a 20% increase in diameter. We analyzed response/progression between baseline and week 8, and baseline and week 12, and compared the difference between the two timepoints. <h3>Results</h3> In total, 20 patients had CT assessments at 8 and 12 weeks post-SBRT. Compared to baseline, only 1 patient (5%) showed PR at week 8, but 5 patients (25%) showed PR at week 12. The median decrease in diameter for those 5 patients was 24.8% at week 8 vs 35.9% at week 12. Moreover, 1 patient (5%) showed disease progression at week 8, with a 45.3% diameter increase, but showed stable disease compared to baseline at week 12 (6.3% diameter increase). Lastly, when looking at any change in tumor diameter, 11 patients (55%) had a larger decrease in tumor diameter at week 12 compared to week 8 (median decrease week 8: 6.5% vs week 12: 22.1%). <h3>Conclusion</h3> Re-assessing patients at week 12 post-SBRT could show better response rates compared to week 8, and allow more patients to undergo surgical resection. Larger studies are still needed to better assess ideal SBRT follow-up.