S2605
Radiobiology - Radiobiological modelling
ESTRO 2026
References: [1] Jeong, J., et al., Modeling the Cellular Response of Lung Cancer to Radiation Therapy for a Broad Range of Fractionation Schedules. International Journal of Radiation Oncology, Biology, Physics, 2017. 99(2): p. 464-473.[2] Menegakis, A., et al., A Novel Lineage-Tracing Tool Reveals that Hypoxic Tumor Cells Drive Tumor Relapse After
Radiotherapy. Cancer Cell, 2024. 42(3): p. 512-527. Keywords: Mechanistic Modelling, Quiescence, TCP
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Cumulative Dose Evaluation between External Beam Radiation Therapy and Radioligand Therapy: A Case Study with ¹⁷⁷Lu- PSMA Sara Panebianco 1 , Demetrio Aricò 2 , Elisa Bonanno 1 , Giuseppina Rita Borzì 1 , Nina Cavalli 1 , Martina Pace 1 , Giuseppe Stella 3 , Lucia Zirone 1 , Carmelo Marino 1 1 Medical Physics Department, Humanitas - Istituto Clinico Catanese, Misterbianco, Italy. 2 Nuclear Medicine Department, Humanitas - Istituto Clinico Catanese, Misterbianco, Italy. 3 Physics and Astronomy E. Majorana, University of Catania, Catania, Italy Purpose/Objective: Radioligand therapy (RLT) is among the most innovative method in Theranostics, a discipline that integrates diagnosis and therapy into a single personalized approach [1]. A clinically relevant application is the 177Lu-PSMA treatment for patients with metastatic Castration- Resistant Prostate Cancer (mCRPC), an advanced disease stage. These patients, previously treated with External Beam Radiation Therapy (EBRT), hormone therapy, or chemotherapy, are enrolled in 177Lu-PSMA treatment according to the VISION trial criteria [2]. This study aims to evaluate the cumulative dose between EBRT and RLT to analyse the dose distribution in Organs at Risk (OAR) and lesions, and to correlate these with the patient outcomes. This assessment is performed by testing the capabilities of the MIM SurePlanTM MRT Treatment Planning System (TPS). Material/Methods: The cumulative dose is assessed by analyzing the distribution of the Biological Effective Dose (BED) for EBRT and RLT. The patient received hypofractionated EBRT (6 Gy x 5 fractions) on a perianal lesion, which shows weak tracer uptake during the PET scan at the time of enrolment for RLT treatment. For EBRT, the theoretical BED is calculated using the conventional formula, with an assumed α / β ratio of 10 for the lesion. The determinations are performed using the MAESTRO® extension of MIM
software. For RLT, an additional Lea-Catcheside factor (G), ranging from 0 to 1, is introduced to account the dose rate and the repair time T(rep).
The parameters C(Gy/h) and λ (1/h) are derived from the exponential fit of the dose rate curve. Two parameter sets are compared: (1) the American Association of Physicists in Medicine (AAPM) TG-137, assuming T(rep)=0.27 h and the α / β =3 for lesion [3]; (2) 90Y
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