Screen: 4
Toxicity was reported during FU using SOMA/LENT scoring. The study endpoint was moderate-severe late toxicity consisting of Fibrosis-Atrophy-Telangiectasia-Pain (FATP G2+) developed within 42 months after RT completion.
Automatic delineation of skin and DVH extraction were accomplished by scripting using the MIM_assistant software. Also, the impact of changes in the dose calculation algorithms during enrolment time was quantified.
A logistic model was created by combining multifactorial variables, considering both clinical factors and the absolute skin DVH (cc). Variance Inflation Factor (VIF) was performed to reduce the multicollinearity. Repeated 5-fold cross-validation with SMOTE approach to overcome the class unbalance was applied for model feature selection. The predictive model was then developed on the entire population due to the limited G2+ events.
Results: The FATP G2+ rate was 3.8% with 40/1066 experiencing late toxicity. Among them, a 40% had already developed acute symptoms after RT completion showing a consequential effect.
The multicollinearity analysis selected 27 clinical-treatment-dosimetric factors. After repeated (20 times) 5-fold cross-validation, the best-performing model included Post-Surgery Cosmetic alterations, Aromatase Inhibitors (as a protective factor), V20 Gy (50% of the prescribed dose - DVH plateau region) and V42 Gy (105% of the prescribed dose - DVH high-dose tail). Accuracy and f1-score were 0.76 and 0.58 in both training and test sets, providing good reliability for selected variables. AUC for the final model on the entire population was 0.76+/-0.04.
Conclusion: We quantified the association between fibrosis and skin DVH when delivering 40Gy in 15fr. The model suggested an independent role of V20 and V42 Gy and a heavy risk modulation by surgical effects and aromatase inhibitors. This last factor could interfere with adipose tissue and water-content distribution within the breast. For this purpose, a CT-based densitometry characterization of toxicity patients is ongoing.
Abstract 2364 - Table 1
Variables | Coeff. | OR | p-value | Sub-Groups Tox Rate |
Cosmesis (post Surgery) | 1.65 | 5.20 | <0.0001 | 1.0% vs 16.0% (good vs poor cosmesis) |
V 20 Gy (cc) | 0.02 | 1.02 | <0.0001 | 2.0% vs 5.4% (below vs above median=205 cc) |
V 40 Gy (cc) | 0.08 | 1.09 | 0.05 | 3.4% vs 6.5% (below vs above Q3=1.5 cc) |
Aromatase Inhibitors | -0.63 | -0.53 | <0.0001 | 5% vs 2.7% (no drug vs drug) |
Constant | -6.76 | |||
AUC = 0.76 Calib Plot = 0.00 + 1.05*x, HL-test = 0.88 |
Tiziana Rancati, MS
Fondazione IRCCS - Istituto Nazionale dei Tumori
Milan, Lombardia