ESTRO 2022 - Abstract Book

S217

Abstract book

ESTRO 2022

Conclusion The previously published ORN NTCP models with D 30% of the mandible and pre-RT dental extraction as independent factors were externally validated and lead to similarly good and comparable performance for the prediction of ORN I-IV and ORN IV. The CTP suggested a minor intercept update in order to match our cohort, most likely due to the lower ORN prevalence in this cohort. An explanation for this difference is subject of further investigation. Overall, these models can be used to optimize radiotherapy treatment planning, including patient selection for proton or photon therapy, aiming at prevention of mandibular osteoradionecrosis.

OC-0259 Focal boosting in prostate cancer: risk modelling for individualized therapy

K. Guricova 1 , V. Groen 2 , F. Pos 3 , E. Monninkhof 4 , K. Haustermans 5 , R.J. Smeenk 6 , J. van der Voort van Zyp 2 , C. Draulans 5 , S. Isebaert 5 , P.J. van Houdt 1 , L.G.W. Kerkmeijer 2,6 , U.A. van der Heide 1 1 Netherlands Cancer Institute (NKI-AVL), Radiation Oncology, Amsterdam, The Netherlands; 2 University Medical Center Utrecht, Radiation Oncology, Utrecht, The Netherlands; 3 Netherlands Cancer Insitute (NKI-AVL), Radiation Oncology, Amsterdam, The Netherlands; 4 University Medical Center Utrecht, Julius Center for Health Sciences and Primary Care, Utrecht, The Netherlands; 5 University Hospital Leuven, Radiation Oncology, Leuven, Belgium; 6 Radboud University Medical Center, Radiation Oncology, Nijmegen, The Netherlands Purpose or Objective The FLAME trial showed that radiotherapy with iso-toxic focal boosting to the intraprostatic lesion(s) in patients with intermediate and high-risk prostate cancer improves disease-free survival (DFS). Due to the strict adherence to organs at risk (OAR) constraints, a focal boost of D98% > 90 Gy was reached only in 20% of the patients (median D98% 84.7 Gy). To ensure the maximum treatment benefit without increasing OAR dose, more complex techniques to improve high focal boost delivery may be needed. Therefore, it is important to identify those patients who most likely require a high boost dose to achieve control. In this study, we designed a risk model which predicts the 5-year DFS based on individual clinical characteristics and the delivered boost dose. Materials and Methods The model was designed using data of the FLAME trial of 526 patients with available clinical data who were treated per protocol. The median follow-up was 72 months and clinical failure occurred in 99 patients. The considered set of model parameters consisted of the iPSA-value, cT-stage, ISUP grade group, age, use of hormonal therapy and the delivered boost dose. Penalized Cox regression was used for model development. Performance was evaluated with Harell’s C-index (discrimination), the calibration curve and calibration-in-the-large. To identify patients who would require a high boost dose to achieve control, we calculated the predicted 5-year DFS, assuming they were treated to a standard dose of 77 Gy. This was compared to predicted outcomes, assuming the same patients received D98% of 95 Gy.

Results