ESTRO 2020 Abstract book

S99 ESTRO 2020

patients with indication for radiation should be screened for a therapy in deep inspiration and treated accordingly. PD-0181 Relationship between low dose to heart substructures and heart damage within SAFE trial (NCT2236806) I. Desideri 1 , G. Francolini 1 , I. Meattini 1 , L. Dominici 1 , S. Lucidi 1 , V. Maragna 1 , V. Salvestrini 1 , E. Scoccimarro 1 , G. Stocchi 1 , M.A. Teriaca 1 , G.A. Barletta 2 , L. Livi 1 1 University of Florence, Radiotherapy Department- Careggi Hospital, Firenze, Italy ; 2 University of Florence, Cardiology Department- Careggi Hospital, Firenze, Italy Purpose or Objective Adjuvant radiotherapy may increase risk of cardiovascular comorbidity in breast cancer patients, especially if left sided. However, no threshold dose has been evidenced in literature, and no data about heart substructures have been collected so far. Patients undergoing adjuvant treatment for breast cancer in our institute are included in a study protocol aimed to reduce cardiovascular morbidity and based on periodic follow up with heart speckle tracking ultrasound US (SAFE 2014, NCT2236806). We recently assessed the interobserver variability in heart substructures delineation in patients included in this trial and here we present the relationship between dose received by heart substructures and occurrence of subclinical heart damage. Material and Methods Heart substructures of 17 left sided patients treated within SAFE trial were delineated according to a pre‐existing contouring guideline [4]. All patients underwent 3d conformal radiotherapy (3dCRT). Data about Dmean, Dmax, D98% and D2% were collected and reported for whole heart (WH), Left Atrium (LA), Right Atrium (RA), Right Ventricle (RV) and Left Ventricle (LV). Dose parameters were reported also for left ventricle segments: Anterior (Ant), Lateral (Lat), Apical (Api), Inferior (Inf) and Septal (Sep). Patients were assessed at 6, 12 and 24 months from enrollment with speckle tracking US. Variations in terms of 3D Left Ventricle Ejection Fraction (LVEF), End Diastolic Volume Index (EDVI), End Systolic Volume Index (ESVI) and Global linear Strain (GLS) between baseline and last available US were calculated. Receiver Operator Characteristic (ROC) curves were plotted to test the accuracy of different dose parameter to each heart substructure in predicting any subclinical damage. Results Overall, a significant variation in 3D LVEF, EDVI, ESVI and GLS was found in 12,9,9 and 8 patients, respectively. 3d LVEF was significantly affected by LV D98%, Lat Dmean, Lat Dmax, Lat D2%, Inf Dmean, Inf D98%. A significant impact on EDVI and ESVI was found for WH Dmean, WH Dmax, RV Dmean, RV D98%, RV D2%, RA Dmean, Lat Dmean, Inf Dmean, Sep D98%, Api D98%. GLS was affected only by LA Dmax. Dose significantly related to decrease in 3D LVEF, EDVI, ESVI and GLS are also reported (Table 1). No significant association was found between subclinical heart damage and other measured dose parameters.

Conclusion To our knowledge, this is the first analysis of relationship between dosimetric assessment of heart substructures and subclinical heart damage. Heart is indeed a complex organ, as demonstrated by the fact that low dose to its different substructure significantly affect its functionality and may predict heart morbidity before clinical evidence. Of note, right chambers dosimetry warrants further analysis within the context of SAFE trial. These data may be useful to understand which heart substructure are mostly involved in heart morbidity after adjuvant radiotherapy for breast cancer. PD-0182 Elastically deformed planning CT improves in vivo dosimetry results for Head and Neck treatments M. Esposito 1 , A. Ghirelli 2 , S. Pini 2 , S. Russo 2 , P. Alpi 3 , R. Barca 3 , S. Fondelli 3 , B. Grilli Leonulli 3 , L. Paoletti 3 , F. Rossi 3 , P. Bastiani 3 1 USL CENTRO TOSCANA, S.C. Fisica Sanitaria, Bagno a Ripoli, Italy ; 2 Azienda Sanitaria USL Toscana Centro, S.C. Fisica Sanitaria, Bagno a Ripoli, Italy ; 3 Azienda Sanitaria USL Toscana Centro, S.C. Radioterapia, Bagno a Ripoli, Italy Purpose or Objective Back‐projection EPID in vivo dosimetry (IVD) algorithms need the model of patient daily anatomy. Planning CT (PCT) and Cone Beam CT (CBCT) are commonly used; however, PCT could not reproduce daily anatomy changes and CBCT needs complex calibration of Hounsfield Units. In this work we tested the use of the elastically deformed planning CT(EDCT), for modeling daily anatomy for EPID in vivo dosimetry. Material and Methods Nine Head and Neck treatments were tested. EDCT were computed applying multimodal elastic deformation between PCT and daily pre‐treatment kV CBCT. EDCT was automatically contoured by applying elastic deformation to planning contours. Elastic deformations were computed with the software MIM 6.8. Planned 3D doses, computed by TPS Monaco 5.11 were compared with the IVD 3D doses reconstructed using PCT (PIVD) and EDCT (EDIVD). IVD was computed with the commercial software Dosimetry Check 5.4, equipped with collapsed cone dose computation algorithm. The dose differences were computed in the PTVs Dmean (ΔPTV Dmean), Spinal Cord Dmax (ΔCord DMax), Parotids Dmean (ΔParotid Dmean). Poster discussion: PH: Dose measurement and dose calculation

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