J Niedzielski*, S Beddar, R Martin, L Perles, N Rebueno, E Holliday, G Smith, B Minsky, E Ludmir, P Das, E Koay, C Taniguchi, A Koong, G Sawakuchi, UT MD Anderson Cancer Center, Houston, TX

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  J Niedzielski

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SU-B-TRACK 6-6 (Sunday, 7/25/2021) 11:30 AM - 12:30 PM [Eastern Time (GMT-4)]

Purpose: To evaluate the benefit of daily adaptive re-planning for pancreas SBRT by using either daily plan re-optimization or fractional dose-escalation to attain maximal tumor coverage.

Methods: Eight pancreatic cancer patients, originally treated with SBRT (36–40 Gy, 5 fractions) using daily CT-on-rails image guidance and breath-hold motion management, were re-planned on the daily treatment CT-on-rails images using 2 different techniques: (i) all patients had each of their 5 fractional plans re-optimized to preserve clinical target coverage and meet OAR constraints; and (ii) all patients were re-planned on each fraction to receive dose-escalated SBRT, using an iterative strategy that consisted of a dose-escalated PTV (DE-PTV), as well as simultaneous integrated boosts to both the tumor-vessel-interface (TVI) and gross-tumor-volume (GTV), while meeting organ-at-risk (OAR) constraints. Both the original and dose-escalated treatment plans, using the original planning CT, were recalculated on each treatment’s CT-on-rails image and accumulated dose was calculated. Additionally, dose was accumulated using the 5 daily re-plans, for both strategies, and then compared to the clinically delivered and the dose-escalated treatment plans.

Results: When compared to the accumulated dose from the original clinical plan, daily re-optimization resulted in an average 7.1% /6.7% increase in D100% of the GTV/TVI (p=0.17/0.12). Compared to the accumulated dose from the dose-escalated treatment plan, the daily adaptive dose-escalation approach had an average 10.7%/21.2%/20.4% increase in D100% for the GTV/TVI/DE-PTV (p=0.20/0.02*/0.03*), respectively. The daily adaptive dose-escalated approach was able to deliver an average 22.4%/32.8% increase to the GTV/TVI (p=0.007*/0.0001*), when compared to the delivered dose of the original clinical plan. Without daily adaptation, dose-escalated plans would violate the D1.0cc<35Gy OAR constraint in 5/1/1 patients for the duodenum/stomach/small bowel, according to accumulated dose.

Conclusion: Daily re-optimization of pancreas SBRT treatments leads to superior plan quality. Daily adaptive re-planning can maximize dose escalation, without violating OAR constraints.

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