ESTRO 2024 - Abstract Book

S4550

Physics - Machine learning models and clinical applications

ESTRO 2024

2543

Mini-Oral

Characterization of the oxygen transport variation with dose on a cohort of breast cancer patients

Alessandra Catalano 1 , Alessandro Cicchetti 1 , Martina Scotti 1 , Maria Carmen De Santis 2 , Riccardo Ray Colciago 2 , Eliana La Rocca 2 , Fabio Badenchini 3 , Eliana Gioscio 1 , Luca Possenti 1 , Tommaso Giandini 4 , Sophie Veronique Materne 1 , Tiziana Rancati 1 1 Fondazione IRCCS Istituto Nazionale Tumori di Milano, Data Science Unit, Milan, Italy. 2 Fondazione IRCCS Istituto Nazionale Tumori di Milano, Radiation Oncology, Milan, Italy. 3 Fondazione IRCCS Istituto Nazionale Tumori di Milano, Medial Oncology 1, Milan, Italy. 4 Fondazione IRCCS Istituto Nazionale Tumori di Milano, Medical Physics, Milan, Italy

Purpose/Objective:

Radiotherapy damages the microcirculation system, perturbing the capillary functionality and affecting the surrounding tissue. Several studies considered microcirculation in animal studies and computational models to extrapolate clinical relationships (1,2). Here, we aimed to study the alterations of oxygen transport in skin microcirculation as a function of dose through in vivo non-invasive measurements of variation in haemoglobin concentration [Hb] in a cohort of breast cancer patients treated with whole breast irradiation. Such clinical evidence will enrich a pre-existing computational microcirculation model (3,4), enabling it to describe morphological and functional variations in blood capillaries caused by radiotherapy.

Material/Methods:

We recruited 180 breast patients undergoing adjuvant radiotherapy between November 2020 and July 2023. Patients received 40-42.4 Gy to the whole breast, delivered with tangential fields RT or VMAT, without dose boost.

We evaluated haemoglobin concentration using cutaneous spectrophotometry. This non-invasive tool provided reflectance measurements in the 400-700 nm range. Following (5), we estimated the melanin contribution and deconvolved the reflectance spectra, leading to an estimation of the haemoglobin concentration, which describes the perfusion level of the capillary network.

We acquired the reflectance measures in three standardized zones of the treated breast. We repeated measurements at the beginning, middle and end of radiotherapy.

Three regions of interest, i.e., three "skin" volumes, were contoured on the CT scan images in the same standardised positions. We chose 5 mm thick volumes, describing the sensitive depth covered by the instrument and representative of the epidermis, dermis and hypodermis. We assumed that the accumulated dose at the time of measurement was the mean dose in these volumes computed by the Treatment Planning System (TPS).

To study the relationship between the variation of haemoglobin concentration ([Hb]) and the absorbed dose, we used a Linear Mixed Model (LMM). This model included fixed and random (patient-specific) effects. The fixed effects