ESTRO 2023 - Abstract Book

S1916

Digital Posters

ESTRO 2023

1 Johns Hopkins University, Radiation Oncology and Molecular Radiation Sciences, Baltimore, USA

Purpose or Objective The linear-quadratic (LQ) model has been the dominant tool in preclinical radiobiological modeling of cell survival as a function of dose. However, as a second-order polynomial approximation, it suffers from two well-known pitfalls: non- monotonic behavior and poor extrapolation, which manifest as negative β values and lead to unrealistic prediction results. This study systematically evaluated the prediction performance of the LQ model, the power model, and the linear model on post radiation cell survival data. Materials and Methods This study examined raw data of 253 sets of photons and 943 sets of ion radiation from the Particle Irradiation Data Ensemble (PIDE) project . Each set of data consists of a series of dose and cell survival data. The full or subsets of each data set were used as input data for the LQ model, the power model, and the linear model, and the data point with the highest dose was used as the test data, where the predictive performance of the models was evaluated using leave one out cross-validation (LOOCV) and 2-fold cross-validation. Results When fitted to the LQ model, 7.5% of the photon and 29.8% of the ion beam dose response data would result in negative β , compared to 0.77% and 2.0% reported in the literature. LQ model performed poorly in LOOCV compared to the alternative power model, and performed the worst among the three models in 2-fold cross-validation. Conclusion LQ model leads to unrealistic parameters, which are vastly under-reported in the literature, and performs poorly in standard cross-validation tests. Therefore, the LQ model is not a valid predicative dose-response model for cell survival. Alternative models need to be investigated. N. Dinapoli 1 , B. Fionda 1 , V. Lancellotta 1 , E. Placidi 1 , G.C. Mattiucci 2 , T. Greco 3 , C. Graci 3 , C. Perisano 3 , V. Valentini 1 , G. Maccauro 3 , L. Tagliaferri 1 1 Fondazione Policlinico Universitario Agostino Gemelli IRCCS, U.O.C. Radioterapia Oncologica, Dipartimento di Diagnostica per Immagini, Radioterapia Oncologica Ed Ematologia, Rome, Italy; 2 Mater Olbia Hospital, Radiotherapy Department, Olbia, Italy; 3 Fondazione Policlinico Universitario Agostino Gemelli IRCCS, Department of Ageing, Neurosciences, Head- Neck and Orthopedics Sciences, Orthopedics and Traumatology, Rome, Italy Purpose or Objective Adjuvant radiotherapy has proven to be particularly useful in case of Soft Tissue Sarcomas (STS) located in close relationship with the neurovascular structures, combining limb salvage strategy with the oncologic appropriate treatment. Aim of this paper is to present the results obtained with the use of HDR Interventional Radiotherapy (IRT, brachytherapy) followed external beam radiotherapy (ERT) in the multimodal treatment of STS of the extremities, in terms of Overall survival (OS), local recurrence (LR) and side effects. Materials and Methods We retrospectively analyzed 16 cases of STS of the extremities treated, between January 2003 and January 2016, with large or marginal surgical excision and adjuvant treatment with HDR IRT followed by ERT. Results The mean time between surgical excision and HDR IRT treatment was 7 days (range 5-15 days), with mean number of treatment fractions 4 (range 3-5 fractions) and mean overall dose of 18,5 Gy (range 15-20 Gy). The median survival was 34 months with a local control of 81.3%. The only significant side effect was mild sclerosis of the subcutaneous tissue and alterations of skin trophism. Conclusion Multimodal treatment with limb salvage surgery, HDR IRT and ERT has shown, in our series, positive results in lesions with a high-grade of malignancy with positive or marginal resection margins, for which a higher dose of radiations as allowed by IRT is desirable. Poster (Digital): Brachytherapy: Breast PO-2128 HDR perioperative interventional radiotherapy (brachytherapy) in soft tissue sarcomas of extremities

Poster (Digital): Brachytherapy: Gynaecology

PO-2129 Dose gradients between HR-CTV 100% and IR-CTV 50% in IGBT of GYN cancer: Tandem vs Needles

R. Kim 1 , S. Marcrom 1 , M. Yusuf 1 , J. Peacock 1 , Z. Iqbal 1

1 University of Alabama at Birmingham, Radiation Oncology, Birmingham, USA

Purpose or Objective