Purpose/Objective(s)Volumetric Modulated Arc Therapy (VMAT) has become a staple of modern head and neck (HN) radiation planning, but there may exist unexpected failure modes in which VMAT plans are less robust than typically expected. We identify and characterize one such potential instability (to our knowledge not previously described) that can occur at the interface between target volume (e.g. a mucosal primary tumor) and internal air (e.g. pharyngeal lumen, sinuses, nasal cavity, etc.), where the lack of a sufficient region for full dose buildup can lead to development of unexpected hotspots with even minor variations in target geometry.Materials/MethodsPlans for ten HN patients treated with curative-intent VMAT radiation therapy (RT) at our institution in 2023 were reviewed. All patients received 60-69.96 Gy in 30-33 daily fractions with 6MV photons, with plans created in a technology company treatment planning system and calculated with an advanced dose calculation algorithm (version 16.1). To model the effect of swelling or tumor growth at the internal air/tumor interface, verification plans were run in which internal air within 3 mm of the planning target volume (PTV) was overridden to soft tissue density (Hounsfield Unit [HU] = 0), and resulting hotspots were assessed. A modified planning technique was employed to increase robustness, wherein the plan was initially optimized with the luminal air density on CT overridden to HU = -300, before being re-calculated and re-normalized with the original CT HU values. Finally, the modified plan was then assessed for robustness in the event of tissue filling by again overriding luminal air to HU = 0.ResultsAlthough hotspots were well controlled in clinically treated plans at baseline (median 110%, range 109%-114%), relatively minor changes at the tumor-air interface (within 3 mm of PTV) resulted in development of significant unexpected hotspots (median 131%, range 115%-155%). With the proposed robust planning technique, plans were similar at baseline (median hotspot 110%, range 108%-114%, p=0.275 relative to original plan), but significantly more robust in the event of changes at the internal air-tumor interface (median hotspot 110%, range 108%-114%, p=0.001 relative to non-robust plan) while maintaining stable target coverage (D95% of 99.1% to 100.2%).ConclusionIn cases requiring full dose to the interface between target volume and luminal air, standard VMAT plans can exhibit unstable behavior due to insufficient region for dose buildup, resulting in clinically unacceptable hotspots with even minor variations in target geometry—variations that are well under thresholds that would conventionally trigger replanning. A density override planning technique can mitigate this effect, creating VMAT plans that differ minimally at baseline but are substantially more robust against the development of unexpected hotspots. This technique is worthy of further consideration, particularly for HN plans with high dose regions abutting luminal air.

Purpose: Significant heterogeneity exists in clinical quality assurance (QA) practices within radiation oncology departments, with most chart rounds lacking prospective peer-reviewed contour evaluation. This has the potential to significantly affect patient outcomes, particularly for head and neck cancers (HNC) given the large variance in target volume delineation. With this understanding, we incorporated a prospective systematic peer contour-review process into our workflow for all patients with HNC. This study aims to assess the effectiveness of implementing prospective peer review into practice for our National Cancer Institute Designated Cancer Center and to report factors associated with contour modifications. Methods and materials: Starting in November 2020, our department adopted a systematic QA process with real-time metrics, in which contours for all patients with HNC treated with radiation therapy were prospectively peer reviewed and graded. Contours were graded with green (unnecessary), yellow (minor), or red (major) colors based on the degree of peer-recommended modifications. Contours from November 2020 through September 2021 were included for analysis. Results: Three hundred sixty contours were included. Contour grades were made up of 89.7% green, 8.9% yellow, and 1.4% red grades. Physicians with >12 months of clinical experience were less likely to have contour changes requested than those with <12 months (8.3% vs 40.9%; P < .001). Contour grades were significantly associated with physician case load, with physicians presenting more than the median number of 50 cases having significantly less modifications requested than those presenting <50 (6.7% vs 13.3%; P = .013). Physicians working with a resident or fellow were less likely to have contour changes requested than those without a trainee (5.2% vs 12.6%; P = .039). Frequency of major modification requests significantly decreased over time after adoption of prospective peer contour review, with no red grades occurring >6 months after adoption. Conclusions: This study highlights the importance of prospective peer contour-review implementation into systematic clinical QA processes for HNC. Physician experience proved to be the highest predictor of approved contours. A growth curve was demonstrated, with major modifications declining after prospective contour review implementation. Even within a high-volume academic practice with subspecialist attendings, >10% of patients had contour changes made as a direct result of prospective peer review. Published by Elsevier Inc. on behalf of American Society for Radiation Oncology.

Local control was excellent with SBRT delivered to metastatic disease, particularly for lesions receiving a BED≥100 Gy. High-grade toxicity was rare in our patient population. Patients with 5 or fewer metastatic sites have a significantly better OS compared to > 5 sites. Future prospective trials with multi-institutional collaboration will be necessary to evaluate appropriate patient selection and the optimal radiation dose regimen.

Cumulative incidence of radiation-induced BPP after re-irradiation was 17% at 1 year. Dmax > 106 Gy, higher V80/V90, and the use of concurrent cisplatin during re-irradiation, were associated with increased risk of BPP.