2063 - What is the Optimal Strategy for Re-Planning of Adaptive Radiotherapy of Head and Neck Cancer?
Presenter(s)
H. Enocson1,2, A. Anghede Haraldsson1,2, P. Engström2, S. Ceberg1, M. Gebre-Medhin3,4, G. Adrian3,4, and P. Munck af Rosenschold1,2; 1Medical Radiation Physics, Department of Clinical Sciences Lund, Lund University, Lund, Sweden, 2Radiation Physics, Department of Hematology, Oncology, and Radiation Physics, Skåne University Hospital, Lund, Sweden, 3Oncology, Department of Clinical Sciences Lund, Lund University, Lund, Sweden, 4Oncology, Department of Hematology, Oncology, and Radiation Physics, Skåne University Hospital, Lund, Sweden
Purpose/Objective(s): Adaptive radiotherapy (ART) adjusts treatment based on anatomical changes. We previously found that in head and neck squamous cell carcinoma (HNSCC), ART offers limited organ-at-risk (OAR) sparing without reduced planning target volume (PTV) margins, while increasing the need for ART to maintain target coverage. Different ART strategies have been proposed for HNSCC, with some suggesting a single adaptation (e.g., Figen et al., 2020), while others favor weekly over daily interventions to reduce clinical workload (e.g., Bobic et al., 2022). In this study, we simulated different ART strategies with reduced PTV margins to identify the approach that optimize target coverage and the number of ART plans.
Materials/Methods: A consecutive cohort of 33 HNSCC patients (928 fractions) treated with helical tomotherapy to 60.0-68.0 Gy in 2 Gy/fraction using a 5 mm CTV-PTV margin and daily kVCT imaging were retrospectively analyzed. Nominal plans with a 2 mm margin were generated.
Daily dose distributions were calculated on synthetic kVCT images with propagated contours, created from daily kVCT images, planning CT and deformable registration. Five ART strategies were simulated: none (nominal plan evaluated every fraction), twice (ART every 12th fraction), weekly (ART every fifth fraction), triggered (ART triggered when the previous fraction showed insufficient target coverage, D98%,CTV < 95%), and daily (online ART for every fraction). All adapted plans were generated using the same optimization constraints as the nominal plan.Results: Effective implementation of any ART-strategy depend on monitoring daily doses, which require offline processing. D98%,CTV was significantly different between ART strategies, with coverage improving as replans increased. Daily ART achieved the best target coverage with the largest difference compared to no-ART (-0.71%, p < 0.001). Only weekly and triggered ART showed statistically comparable D98%,CTV (p = 0.9) but with on average 5.1 fewer plans (p < 0.001) using triggered ART. The weekly and triggered strategies had a mean difference of 0.39% and 0.41%, respectively, compared to daily ART. D98%,CTV, number of fractions with D98%,CTV < 95%, and the number of unique plans are presented for each strategy the table.
Conclusion: All ART-strategies improved target coverage vs. no-ART, with more frequent adaptations providing greater improvements. Differences were dosimetrically small. Unless fully automated, triggered-ART offers comparable dose coverage to other ART-strategies with fewer re-plans and a reasonable clinical workload.
Abstract 2063 - Table 1| ART Strategy: | D98%,CTV Median (range) | Plans/patient Average (range) | Fractions/patient D98%,CTV<95% Average (range) | Total fractions D98%,CTV <95% |
| None: | 98.5 (79.5-101.8) | 1.0 (1-1) | 2.91 (0-21) | 96 |
| Twice: | 98.6 (80.3-102.3) | 3.0 (2-3) | 1.76 (0-13) | 58 |
| Weekly: | 98.8 (79.0-102.2) | 6.8 (6-7) | 0.82 (0-7) | 27 |
| Daily: | 99.1 (96.6-100.8) | 28.1 (23-32) | 0 | 0 |
| Triggered: | 98.68 (85.0-102.0) | 1.7 (1-7) | 1.0 (0-8) | 33 |