ESTRO 2025 - Abstract Book

S2855

Physics - Dose prediction, optimisation and applications of photon and electron planning

ESTRO 2025

adaptive image-based dose escalation. Goal of this project is the dosimetric evaluation of the personalized dose escalation by 10-15% to the hypoxic regions based on the FMISO PET/CT in nonrandomized clinical trial (NCT05348486). Material/Methods: From May 2022 until September 2024, the strategy of hypoxia target volume delineation based on the FMISO PET/CT analysis before start of the radiotherapy with the adaptation after 11th fraction were used in 43 patients. A dose escalation of 79,2 Gy in 33 fractions to the hypoxic planning target volume (hPTV) was provided. Inclusion criteria were as follows: a pathologically proven new diagnosis of oropharyngeal p16 negative, or laryngeal/hypopharyngeal/oral cavity (independent of p16) squamous cell carcinoma of the clinical stage III or IV, evaluable tumor burden, eligible for definitive chemoradiation or hyperfractionated accelerated radiotherapy, not considered for primary surgery based on multidisciplinary tumor board decision, and Eastern Cooperative Oncology Group (ECOG) performance status of 0 or 1 performed within 10 days prior to receiving the first dose of study therapy. Results: At least one hypoxia region was found in 33 patients (77 %) and median hPTV was 1,6 ml (IQR 0,2-7,1). In the adaptive protocol, 13 of 43 patients (30 %) underwent replanning on the 11 th day of the radiotherapy. Median and maximal dose for hPTV were 79,2 Gy (IQR 76,2-79,2) and 80,4 Gy (IQR 77,7-81,4). Dose in the boost PTV (bPTV) as well as in the elective PTV (ePTV) were not affected by dose escalation and remained at 70 Gy and 55,9 Gy (IQR 54,9 57,0). Moreover, D95% for bPTV was 96,2 % (IQR 95,3-98,2). Median dose to the brainstem, spinal cord, spinal canal, and parotid glands were 25,2 Gy (IQR 21,8-31,3), 32,0 Gy (IQR 22,9-41,0), Gy 40,0 (IQR 33,0-47,2), and 25,3 Gy (IQR 23,2-33,6). There was no statistically significant higher dose for organs at risk in adaptive dose escalation protocol (Table 1).

Conclusion: Personalized dose escalation by 10-15% to the hypoxic regions based on the FMISO PET/CT evaluation is feasible and dose distribution was not negatively affected.

Keywords: hypoxia, FMISO, escalation

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