ESTRO 2020 Abstract Book

S89 ESTRO 2020

Results Percentual dose differences (average ± σ) in ΔPTV Dmean were (3.1 ± 1.7)% for PIVD and (2.8 ± 1.7)% for EDIVD; in ΔCord DMax were (4.7 ± 3.3)% for PIVD and (10.3 ± 8.9)% for EDIVD and in Δ Parotid Dmean were (5.1% ± 3.1) for PIVD and (15.2 ± 10.1)% for EDIVD. In five cases Cord Dmax exceeded alarm level of 44 Gy with EDVD, but only three violations were find out with PIVD. In four cases, Parotid Dmean exceeded alarm level of 26 Gy, but only one violation was highlighted by PIVD.

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

Figure2: In this figure TPS and in vivo doses computed using plannig CT (PCT) e elastically deformed planing CT (EDCT) were compared in PTV, Cord and Parotid gland. Conclusion The use of EDCT for modeling patient anatomy improved the evaluation of dose differences in critical organ at risk. PCT produced results in agreement with EDCT for evaluation of dose difference in the PTV. PD-0183 Does the detector resolution influence correlations between complexity metrics and VMAT QA results? S. Russo 1 , G. Della Gala 2 , V. Hernandez 3 , M. Esposito 1 , S. Pini 1 , A. Ghirelli 1 , J. Saez 4 , H.O. Ghafour 5 , G. Zatelli 1 1 Azienda USL Toscana Centro, SC Fisica Sanitaria - Firenze, Bagno a Ripoli - Firenze, Italy ; 2 Università degli