Online adaptive radiotherapy: Assessment of planning technique and its impact on longitudinal plan quality robustness in pancreatic cancer

• Published in: Radiotherapy and oncology 2023-11, Vol.188, p.109869-109869, Article 109869
• Main Authors: Mittauer, Kathryn E, Yarlagadda, Sreenija, Bryant, John M., Bassiri, Nema, Romaguera, Tino, Gomez, Andres G, Herrera, Robert, Kotecha, Rupesh, Mehta, Minesh P, Gutierrez, Alonso N, Chuong, Michael D
• Format: Article
• Language: English
• Subjects: MR-guided radiotherapy; Online adaptive radiotherapy; Pancreatic radiotherapy; SBRT
• ISSN: 0167-8140; 1879-0887
• DOI: 10.1016/j.radonc.2023.109869

•An ablative MR online adaptive planning approach was implemented in pancreas cancer.•Adaptive plan quality was quantified across 5 fx course for 67 pancreas patients.•PARTS-a novel, global plan quality score for pancreas adaptive RT was implemented.•Online adaptive plans were robust and stable due to planning technique.•Findings are noteworthy given interfraction GI OAR differences in pancreas SBRT. Planning on a static dataset that reflects the simulation day anatomy is routine for SBRT. We hypothesize the quality of on-table adaptive plans is similar to the baseline plan when delivering stereotactic MR-guided adaptive radiotherapy (SMART) for pancreatic cancer (PCa). Sixty-seven inoperable PCa patients were prescribed 50 Gy/5-fraction SMART. Baseline planning included: 3–5 mm gastrointestinal (GI) PRV, 50 Gy optimization target (PTVopt) based on GI PRV, conformality rings, and contracted GTV to guide the hotspot. For each adaptation, GI anatomy was re-contoured, followed by re-optimization. Plan quality was evaluated for target coverage (TC = PTVopt V100%/volume), PTV D90% and D80%, homogeneity index (HI = PTVopt D2%/D98%), prescription isodose/target volume (PITV), low-dose conformity (D2cm = maximum dose at 2 cm from PTVopt/Rx dose), and gradient index (R50%=50% Rx isodose volume/PTVopt volume).A novel global planning metric, termed the Pancreas Adaptive Radiotherapy Score (PARTS), was developed and implemented based on GI OAR sparing, PTV/GTV coverage, and conformality. Adaptive robustness (baseline to fraction 1) and stability (difference between two fractions with highest GI PRV variation) were quantified. OAR constraints were met on all baseline (n = 67) and adaptive (n = 318) plans. Coverage for baseline/adaptive plans was mean ± SD at 44.9 ± 5.8 Gy/44.3 ± 5.5 Gy (PTV D80%), 50.1 ± 4.2 Gy/49.1 ± 4.7 Gy (PTVopt D80%), and 80%±18%/74%±18% (TC), respectively. Mean homogeneity and conformality for baseline/adaptive plans were 0.87 ± 0.25/0.81 ± 0.30 (PITV), 3.81 ± 1.87/3.87 ± 2.0 (R50%), 1.53 ± 0.23/1.55 ± 0.23 (HI), and 58%±7%/59%±7% (D2cm), respectively. PARTS was found to be a sensitive metric due to its additive influence of geometry changes on PARTS’ sub-metrics. There were no statistical differences (p > 0.05) for stability, except for PARTS (p = 0.04, median difference −0.6%). Statistical differences for robustness when significant were small for most metrics (