ESTRO 2023 - Abstract Book

S635

Monday 15 May 2023

ESTRO 2023

Conclusion The recently published close correlation between irradiated breast volume and 3-year risk of breast induration from the DBCG PBI trial [2] was validated in the DBCG HYPO trial. However, it was demonstrated in both trials that this correlation was only present in older pts, whilst pts <65 years with large irradiated breast volume have no increased risk of breast induration. In the HYPO trial, similar volume effects were observed with the two fractionation schemes whereas smoking was associated with a doubled risk of induration irrespective of irradiated volume and age.

[1] doi: https://doi.org/10.1200/jco.20.01363 [2] doi: https://doi.org/10.1016/radonc.22.09.024

OC-0769 Radio-induced lung injury: clinical and dosimetric risk factors in a subset of the CANTO RT cohort A. Gueiderikh 1 , T. Sarrade 2 , Y. Kirova 3 , B. De La Lande 4 , F. De Vathaire 5 , G. Auzac 1 , A.L. Martin 6 , S. Everhard 7 , B. Duchemann 8 , R. Allodji 5 , S. Rivera 1 1 Gustave Roussy, Radiotherapy, Villejuif, France; 2 Tenon Hospital, Radiotherapy, Paris, France; 3 Curie Institute Hospital, Radiotherapy, Paris, France; 4 Curie Saint Cloud Hospital, Radiotherapy, Saint Cloud, France; 5 Gustave Roussy, Centre for research in epidemiology and population health, Villejuif, France; 6 UNICANCER, Data departement, Kremlin Bicêtre, France; 7 UNICANCER, Data department, Kremlin Bicêtre, France; 8 Avicenne Hospital, Pulmonology, Bobigny, France Purpose or Objective Radio-induced Lung Injury (RILI) has been shown to be associated with various clinical conditions and dosimetric parameters. Former studies led to reduce radiotherapy (RT) dose to the lung and favored the discontinuation of tamoxifen during RT. However, the monocentric design and variability of dosimetric parameters chosen by those studies limited further improvement. The aim of our study was to assess the incidence of RILI in nowadays practice and to determine clinical and dosimetric risk factors associated with RILI occurrence. Materials and Methods Data from 3 out of the 10 centers included in the CANTO-RT prospective longitudinal cohort were analysed retrospectively for RILI occurrence. This cohort included invasive cT0-3cN0-3M0 breast cancer patients from 2012 to 2018 and recorded prospectively the occurrence of treatments side effects by questionnaires and medical visits at the end of treatments and up to 60 months after. Dosimetric data and RT planning CT scans with contoured volumes were available for all patients. We considered V5Gy, V10Gy, V15Gy, V20Gy, V25 Gy, V30 Gy, V35 Gy, V40 Gy and Dmean to the homolateral lung. RILI events were defined in all patients by the association of clinical symptoms and compatible medical imaging. Results Within the 5 first years afterRT, RILI was found in 38/1565 (2.4%) patients. Grade 2 RILI represented 15/38 events (39%) and 2/38 events (6%) were grade 3 or 4. There were no grade 5. The incidence of ≥ grade 3 events was 0.1% of the total cohort, confirming favourable safety profile of breast radiotherapy in CANTO. Treatment was performed mainly in conformational 3D RT (96%). In an univariate analysis, we confirmed the association of RILI occurrence with pulmonary medical history, chemotherapy use, nodal RT. All dosimetric parameters were highly correlated and had close predictive value but the V30Gy was the most predictive of RILI occurrence in our dataset (ROC curve AUC=0.68). In the multivariate analysis, only pulmonary medical history (OR=2.2, p=0.02) and high V30Gy (OR=2.05, p=0.04) remained predictive factors for RILI occurrence. The best threshold for V30Gy in our study was V30Gy < 13%. We confirmed the data from Lee and al. 2020, showing that V30Gy < 10% would have a better predictive value than V30Gy<20%. We noted that RILI occurrence was often poorly identified. Pulmonary medical history associated with RILI occurrence were mainly COPD, infectious pneumonitis or interstitial syndrome. On the contrary, the RILI group presented less cardiac medical history.