ESTRO 2023 - Abstract Book

S1427

Digital Posters

ESTRO 2023

Purpose or Objective Build, train and validate a Knowledge-Based prediction model devoted to Cranio-Spinal Irradiation (CSI) of pediatric CNS tumors based on the experience of three Italian Institutions (C1, C2 and C3). Test the KBP model as decision support tools in a simulated centralized RT QA program. Materials and Methods 110 CSI treatments of pediatric patients (age 13.23 ± 8.07 [2.26; 41.88] years) were collected by three highly experienced Italian Institutions. The KBP library included different diseases (Medulloblastoma, Xantoastrocitoma, Pinealoblastoma, Ependimoma), two treatment modalities (multi-isocentric VMAT: 59%, Helical Tomotherapy (HT): 41%) and different fractionation schemes, ranging from 39Gy/30fx to 23.4Gy/13fx. Accrual volume was approximately similar: C1 35 pats (60% VMAT, 40% HT), C2 45 pats (VMAT only) and C3 30 pats (HT only). Patients were contoured following PNET-5 trial specifications. To ensure the homogeneity of the contouring practices, the target structures of 3 patients were independently contoured by each center and the contours compared through Volume and Dice Index. A first KBP model was populated with 40 VMAT and 12 HT. This model was used to compare the consistency of the planning habits of the three centers and the two planning techniques. Exploiting the KBP model capability, a preliminary trend was found for mean doses of Heart, Lungs, Kidneys and Lenses, as a function of the patient's age. Results The contouring comparison yielded mean volume differences lower than 8% and mean Dice Index equal to 0.896. Target coverage, homogeneity and OARs sparing showed comparable results across centers and treatment modalities (see Table).

The preliminary KBP model, trained on 42 patients, showed an acceptable degree of predictivity: goodness-of-fit statistics R ² and X ² ranged in [0.385;0.772] and [1.083;1.135] for Heart, Lungs, Kidneys and Lenses. The KBP predicted OARs mean dose, obtained for each of the patients included in the KBP library, were averaged over age classes to obtain trends. The figure reports these age trends, for each treatment case included in the model library planned mean dose is reported as comparison.