S71
Saturday 13 May
ESTRO 2023
respectively), stage (p <0.0001 and 0.0005 respectively), and surgery before CIRT (p=0.042 and 0.042). Performance status (p<0.0001), age (p=0.006) and GTV (p<0.0001) were additional prognostic factors for OS. Interestingly, worse OS was reported for pts with any GTV at preCIRT MRI compared to macroscopically resected pts (p=0.008), with shorter OS in pts after debulking surgery and unresected pts (43% and 54% 5 yrs OS) compared to R1 postoperative pts with macroscopic disease at pre CIRT MRI (78% OS) and pts with microscopic disease (93%, p=0.014). At multivariate analysis prognostic factors for OS were large GTV volume (0cc, vs <50cc, vs >50cc, p=0.006), site (higher risk for sub-lingual glands vs others, p=0.02), stage (IV vs G3 was reported. Interestingly, higher acute toxicity was reported for the patients with tumor located at the minor salivary glands (p=0.03) and with flap reconstruction after surgery (p=0.04). Late maximum toxicity reported during follow up was G0 in 11%, G1 in 23%, G2 in 48%, G3 in 15%, G4 in 2% and G5 in 1% of the pts. Conclusion CNAO data for ACC are in line with other CIRT facilities. A multidisciplinary effort is required for better selecting pts for CIRT. Our results point out that CIRT might be offered as an alternative curative option to surgery in locally advanced cases deemed to be R2. OC-0111 Results of multi-centric 4DCT QA audit: evaluating the accuracy and consistency of 4D imaging M. Burghelea 1 , J. Bakkali 2 , M. Kyndt 3 , A. Gulyban 4 , J. Dhont 1 , J. Szkitsak 5 , E. Bogaert 6 , N. Reynaert 1 , D. van Gestel 7 1 Institute Jules Bordet, Medical Physics, Brussels, Belgium; 2 GasthuisZusters Antwerpen Ziekenhuizen, Medical Physics Department, Antwerp, Belgium; 3 MIM Software Inc., Development , Brussels, Belgium; 4 Institute Jules Bordet, Medical Physics , Brussels, Belgium; 5 Universit¨atsklinikum Erlangen, Department of Radiation Oncology, Erlangen, Germany; 6 Ghent University Hospital, Department of Radiotherapy-Oncology, Ghent, Belgium; 7 Institute Jules Bordet, Radiation Oncology, Brussels, Belgium Purpose or Objective In this study, a multi-institutional multi-vendor 4DCT audit was initiated to assess the accuracy of current 4DCT imaging protocols. Materials and Methods The audit consisted of a validated, comprehensive, and automatic 4DCT QA workflow; five regular and three irregular breathing patterns were applied on a 2cm sphere inside a dynamic Thorax phantom (CIRS, Norfolk, USA). 4DCT acquisitions followed the institution’s own protocol with the in-house breathing monitoring system. No manual intervention was allowed during acquisition. To comply with the automated workflow each participating institution was asked to reconstruct a static, 10-phase, MaxIP, and AvgIP image set per breathing pattern. Post-acquisition, the sphere was automatically segmented in all relevant image sets and an ITV structure was automatically created through a summation of the sphere in each phase. CT number accuracy, volume deviation, amplitude deviation, and spatial integrity were assessed per pattern using both the segmented volumes and line profiles. Ten institutions (8 in Belgium and 2 in France) were asked to participate in the 4DCT audit and provide the image sets for analyses. Results Eleven institutions (three vendors, six CT scanner types, and three breathing monitoring systems) participated in the audit (7 site visits, 3 remote). Four out of five regular breathing patterns showed relatively accurate results across all institutions (Table), with mean volume and CT number deviations below 2% and 3 HU, respectively. However, outliers in certain phases did occur. For the regular pattern with the highest velocity, substantial blurring of the sphere was observed in some phases leading to an incorrect tumor shape across all institutions (HV-R in Figure A-B). Proffered Papers: QA and auditing
Results with all irregular patterns show more variation across the institutions (Figure A-B). Volume and HU deviations co-