ESTRO 2020 Abstract Book

S304 ESTRO 2020

PD-0547 National EndtoEnd (E2E) dosimetry intercomparison for lung stereotactic radiosurgery in Switzerland

Conclusion cPG D98% and high dose received by small OC volumes were found to impact most on G≥2 aSD, with age and smoking history acting as a dose-modifying factor. Findings on the development population were confirmed in a prospectively collected validation cohort, with peculiar validation of discriminative power and of effect size of dosimetric factors, thus gaining confidence on factors to be considered while optimizing RT.

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PD-0548 Quantitative Analysis of SCOPE 2 Trial 4DCT pre-accrual benchmark cases J. Kahan 1 , R. Carrington 2 , S. Cox 1 , G.J. Lewis 2 , S. Gwynne 3 1 Velindre Cancer Centre NHS trust, Clinical Oncology, Cardiff, United Kingdom ; 2 Velindre Cancer Centre NHS trust, Medical Physics, Cardiff, United Kingdom ; 3 South West Wales Cancer Centre, Clinical Oncology, Swansea, United Kingdom Purpose or Objective We have previously reported results of a qualitative analysis of the RTQA 4DCT benchmark cases within the SCOPE 2 trial (UK phase 2/3 trial looking at PET response and dose Escalation). Here we present a complementary quantitative analysis to explore whether automated assessment using conformity indices can expedite the time-to-approval of centres for use of 4DCT in the trial. Material and Methods Centres underwent pre-submission training and had access to a clear protocol. Submissions were classified as having acceptable or unacceptable variation based on pre- defined criteria. Cases were compared to a reference volume created from outlines from five experienced clinicians using the STAPLE algorithm. Future use of 4DCT was only permitted once a benchmark case had been satisfactorily completed. To date 21 cases were available for analysis, including the 14 original submissions. Of these, 3 (21%) were acceptable. Of the resubmissions, 5 (83%) were acceptable. One centre required a third attempt which was then considered acceptable. Qualitative analysis has previously shown that unacceptable variation usually occurs in the creation of ITV (the composite of CTVB volumes, edited to account for motion seen in 4DCT phases). Therefore, this analysis was limited to ITV. Investigator ITV (iITV) was compared to reference ITV (rITV) using Jaccard Conformity Index (JCI) and Geographical Miss Index (GMI). The GMI indicates the volume of rITV that is missed within the iITV, 0 indicates no volume has been missed. JCI indicates the concordance of rITV and iITV. 1 represents perfect concordance while 0 represents none. JCI of 0.7 is considered to represent excellent concordance in oesophageal cancer. Results For all cases submitted the median iITV JCI was 0.79 indicating very good conformity. Within the acceptable submissions; median JCI was 0.8, 100% had JCI >0.7 and 44% had JCI >0.8 (see table 1). Median GMI in these cases was 0.07 suggesting very little of the rITV was missed from the iITV. However, in those with unacceptable variation (12 cases) they also displayed high JCI values. Median iITV JCI was 0.76, 83% had a JCI >0.7 and 17% >0.8. These results were gained despite failure of volumes to account for appropriate motion in ITV which was identified on analysis of the volumes by the trials team. GMI in this case was 0.12 which indicates a larger volume missed from the iITV.

Poster discussion: PH: Implementation of new techniques 2

PD-0546 Ten years critical re-evaluation of a Failure mode effect analysis in a radiotherapy department P. Mancosu 1 , C. Signori 2 , E. Clerici 1 , T. Comito 1 , F. De Rose 1 , S. Ferrante 1 , M. Ferrara 1 , C. Galdieri 1 , C. Iftode 1 , P. Navarria 1 , A. Stravato 1 , M. Scorsetti 1,3 1 Humanitas Research Hospital, Radiotherapy and Oncology, Rozzano-Milano, Italy ; 2 Humanitas Research Hospital, Healthcare Directorate, Rozzano-Milano, Italy ; 3 Humanitas University, Biomedical Sciences, Pieve Emanuale-Milano, Italy Purpose or Objective The European directive 2013/59/EURATOM recommends that the quality assurance program in RT should include a study of the risk of accidental or unintended exposures. In our institute, a first failure mode and effects analysis (FMEA) was performed in 2008. The aim of this study was to critically re-evaluate the RT process after 10 years. At our knowledge, this is the first time an FMEA process was critically reviewed. Material and Methods A working group including radiation oncologists, physicists, RTTs, secretaries, and nurses performed a deep process analysis and evaluated the possible Failure Modes (FMs) of the RT process. For each FM, the estimated frequency of occurrence (O – range 1-4), the expected severity of the damage to the patient (S – range 1-5) and the detectability (D – range 1-4) were scored. Critical index (CI) was obtained as CI=OxSxD. Data were compared to the 2008 In 2008, the highest CIs were: (i) Error in patient identification (CI=48); (ii) incompleteness of the first examination (CI=29); (iii) prescription of an inadequate support therapy (CI=28). Actions adopted to reduce the first three CIs were: (i) a barcode verification system inside the bunker to check the patient identification and avoid mistreatments; (ii and iii) new information technology system with drop down menu and a reorganization of the physicians’ agenda. In the 2019 analysis, the first three CIs were reduced. In particular, patient identification CI was reduced to 13 (11 th CI score). The new highest CIs were: (a) non-adequate target contouring (CI=36) and (b) under-estimation of symptoms on other regions undergoing RT (CI=34). Possible reasons could be: (a) the higher dose conformity to the designed volume achievable thanks to the inverse modulated treatments, (b) the increase of long survivals that could require new RT treatments. Conclusion The FMEA analysis allowed taking actions to reduce the highest CI values. The 10 years analysis revealed new crucial points in a continuous iterative process. edition. Results