S2085
Physics - Image acquisition and processing
ESTRO 2026
Mini-Oral 4069
Astronomy E. Majorana, University of Catania, Catania, Italy
Spatial correlation of FDG PET and FAZA PET for head and neck cancer and its impact on more accessible hypoxia-driven dose escalation Laura A Rechner 1 , Christian Maare 1 , Henriette K Mortensen 1 , Kristin Skougaard 2 , Camilla K Lonkvist 1 , Jens Edmund 1 1 Department of Oncology, Copenhagen University Hospital - Herlev and Gentofte Hospital, Herlev, Denmark. 2 Department of Oncology, University Hospital Roskilde, Roskilde, Denmark Purpose/Objective: Hypoxia is a known negative prognostic factor for patients with head and neck cancer (HNC) [1]. The hypoxic volume (HV) could be targeted with dose- escalated radiotherapy (RT) [2], but hypoxia PET tracers such as FAZA have not reached widespread use due to feasibility and cost. Moderate correlation between FDG PET and hypoxia PET tracers has been reported [3], but the overlap of FDG PET-positive volumes and hypoxia PET HVs is not well understood. The purpose of this study was to explore dose escalation (DE) and spatial correlation of FDG volumes and FAZA HVs for patients with HNC. Material/Methods: Six patients with HNC were scanned for RT planning with FDG PET/CT further scanned with FAZA PET/CT to image hypoxia in the beginning, middle, and end of their RT course (H-19083440). All scans were acquired in treatment position with immobilization. Clinical FDG PET-positive volumes were delineated by a nuclear medicine specialist, and additional percentage-based contours of the FDG standard uptake volumes (SUV in g/ml) were created as 30%, 40%, and 50% of the maximum SUV within the GTV (FDG SUV30, 40 and 50). The HV within the GTV was defined as a FAZA signal ≥ 1.4x that of a reference tissue [4]. FAZA HVs were rigidly transferred to the FDG PET/CT and compared using Dice similarity coefficients (DSCs) and Booleans. DE treatment plans for 78Gy to the FDG-defined volumes (FDG Clinical and SUV40) were created and coverage metrics were extracted. Results: FAZA HVs were stable in location and reduced in volume (or eliminated) midway, and eliminated by the end of RT. FDG volumes were generally larger than FAZA HVs, and DSCs were consequently low (Figure 1). False negative volumes, i.e. hypoxic by FAZA but non- hypoxic by FDG, were small (0.0-2.7cm3) and false positive volumes, i.e. non-hypoxic regions by FAZA but within the FDG volume, were larger (1.2-21.4cm3). The FAZA HVs were well-covered by the dose-escalation to the FDG Clinical (V95%=[97-100%]) (Figures 1 and 2). Coverage was lower for the plans made for FDG SUV40 (V95%=[74-
Purpose/Objective: Surface Guided Radiation Therapy (SGRT) is increasingly adopted to enhance setup accuracy and patient positioning reproducibility. However, its specific benefit in lung radiotherapy compared to Image-Guided Radiation Therapy (IGRT) remains to be clarified. This study aimed to assess whether more accurate use of SGRT could reduce rotational setup errors detected by IGRT in lung cancer treatments. Material/Methods: Twenty patients with lung cancer treated with volumetric modulated arc therapy (VMAT) on a TrueBeam linear accelerator were analyzed. All patients were initially positioned using an SGRT system (VisionRT) and verified with cone-beam CT (CBCT). The first group of ten patients was treated using standard SGRT-based setup applying a tolerance of ±2° for rotational values. For the second group of ten patients, radiation therapists were specifically trained and encouraged to optimize SGRT positioning, aiming to maintain rotational deviations within ±1° for pitch, roll, and yaw. Rotational corrections obtained from daily CBCTs were recorded and compared between the two groups. Statistical analysis was performed using paired t-test, with significance set at p<0.05. Results: Despite targeted efforts to refine SGRT positioning, the residual rotational errors measured on CBCT remained comparable between the two groups of patients. No statistically significant differences were found in the mean rotational displacements detected by IGRT (p = 0.55, 0.41 and 0.31 for pitch, roll and yaw, respectively). These findings suggest that, for lung lesions located deep within the thorax and thus less correlated with surface anatomy, the contribution of SGRT to reducing rotational uncertainties is limited. IGRT remains essential to ensure accurate target localization in such cases. However, the frequency of CBCT-based corrections exceeding ±1° decreased by 14.3% with optimized SGRT. Conclusion: Although SGRT provides a reliable and efficient method for patient setup and monitoring, its effectiveness in minimizing rotational deviations for lung targets appears limited. The use of IGRT remains necessary in lung radiotherapy, where internal anatomical variations cannot be fully captured by surface guidance alone. Nevertheless, SGRT contributes to improve workflow efficiency by reducing patient setup time. The study is currently ongoing with an increasing number of patients to achieve greater statistical robustness. Keywords: SGRT, IGRT, Lung Radiotherapy
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