ESTRO 2020 Abstract book

S590 ESTRO 2020

Conclusion These results highlight the limitation of CBCT images for daily online replanning in thoracic tumours. Though our results need to be validated with on-board MR-images, they suggest that there could be clear advantages to using daily MR-guided radiotherapy for cardiac SABR, where precise delivery of radiotherapy would result in optimal dose whilst minimising risk of complications. Further investigation is needed to determine the best MR sequences required for daily MR-based adaptive replanning for cardiac SABR. PO-1021 Stereotactic radiotherapy for unresectable locally advanced non small cell lung cancer F. Arcidiacono 1 , P. Anselmo 1 , F. Trippa 1 , M. Casale 1 , M. Italiani 1 , L. Draghini 1 , S. Terenzi 1 , S. Fabiani 1 , A. Di Marzo 1 , E. Maranzano 1 1 Radiotherapy Oncology Centre, Santa Maria Hospital, Terni, Italy Purpose or Objective Conventional fractionated radiotherapy (cRT) concurrent with chemotherapy (ChT) is the standard of care in unresectable locally advanced non small cell lung cancer (LA-NSCLC).The majority of patients (pts) cannot tolerate this treatment due to its toxicity, so sequential ChT followed by cRT is the more frequent choice in clinical practice. Recently, stereotactic radiotherapy (SBRT) has been used instead of cRT in NSCLC offering superior control with less toxicity. We present our experience with SBRT in LA-NSCLC. Material and Methods Between June 2015 and April 2019, 30 LA-NSCLC pts who underwent SBRT were analyzed . 24/30 (80%) pts received neoadjuvant ChT before SBRT. All pts had CT-PET before SBRT. In pts submitted to neoadjuvant ChT the target volume was the residual disease defined on the basis of CT-PET images. The technique was intensity modulated arc therapy(IMAT) and volumetric modulated arc therapy (VMAT) in 14(46%) and 16 (54%) pts, respectively. A specific treatment planning (IMRT-SIB) for primary tumor (T) and lymph-node/s (N) was done for 16(53%) pts, while in remaining 14(47%)the planning target volume (PTV) included both T and N. All pts repeated CT-PET 3 months after treatment and thereafter every 4-6 months. The toxicity was evaluated using CTCAE scale. Results Median age was 73 years (54-86). 9(30%), 15(50%) and 6(20%) pts had clinical N1, N2 and N3 stage at diagnosis, respectively. 27 (90%) and 3 (10%) had central and peripheral primary tumor. Median PTV for T and N separately treated were 58.07 cc (8.7-673) and 15.02cc (5.84-72.3), while for T and N treated in the same target was 105.15 cc (53.2-733). Median prescribed dose was 40 Gy (35-55) and 40 Gy (35-45) in 5 fractions to T and N, respectively.After a median follow-up of 12 months (4-51) 7 of 30 (23%) pts had local recurrence (LR), 9 (30%) regional node (RN) recurrence and 10 (30%) distant progression (DP). Median LR free survival (FS), RN-FS and DP-FS were 9 months (4-48), 9 months (4-48) and 9 months (4-48), respectively. Median overall and cancer specific survival were 12 months (4-48). Of note 2 patients who had hemoptysis before SBRT resolved the symptom after treatment. No patients developed > grade 2 toxicity. Conclusion SBRT was a feasible,safe and effective treatment in selected unresectable LA-NSCLC pts. Although clinical outcomes were very promising both in terms of results and toxicity,larger and more mature studies are needed to adopt this treatment in clinical practice. PO-1022 Clinical-dosimetric assessment with Prodvh software after adjuvant radiotherapy for MPM E. Salah ElDin Tantawi 1 , P. Borghetti 1 , C. Cozzaglio 2 , M. Bonù 1 , N. Pasinetti 1 , D. Greco 1 , M. Maddalo 1 , A. Baiguini 1 ,

Material and Methods We chose three patients from an institutional lung cancer database. Each patient had a set of diagnostic MR images (T1 with fat saturation, a sequence we can acquire with the MR-linac), a planning CT and a CBCT. We ask five observers (three radiographers and two clinicians) to contour two thoracic structures (heart and esophagus) on the three sets of images of the three patients (figure 1). The volunteers used a five-point visual grading scale (1 = very unconfident, 2 = unconfident; 3 = confident with reservations, 4 = confident, 5 = very confident) to indicate their confidence when contouring (figure 2).

Results The mean confidence for the heart contours (n=15) in the MR, planning CT and CBCT images was 4.33±0.49, 4.27±0.59 and 2,33±0.46, respectively, and for the esophagus contours (n=15) was 4.07±0.8, 3.8±0.68 and 1.33±0.49, respectively. The grade of confidence in contouring heart and esophagus was significatively higher with MR than with CBCT (p<0.01 in both cases). No statistically significant differences were observed between MR and planning CT contours.