ESTRO 2020 Abstract Book

S19 ESTRO 2020

Conclusion Absolute verification for transit in vivo dosimetry enhanced detectable errors. The number of false positives was clearly lower for TrueBeam than for Clinac. The number of plan adjustments increased, showing the increased confidence in the system as a base for adaptive planning.

On multivariate analysis the presence of a neuroradiologist significantly influenced any change made during the PR meetings (OR 2.59; 95% CI 1.05-6.43; P=0.039). Conclusion PR amongst oncologists improves consistency of outlining for H&N cancer. However the addition of neuroradiology- based peer review significantly enhances this practice. We strongly recommend a collaborative approach of radiology and oncology at H&N peer review meetings. Further investigation into the specific cases where most benefit is seen is ongoing.

Poster discussion: CL: Head and neck 1

PD-0051 The impact of neuroradiology collaboration in head and neck cancer radiotherapy peer review R. Jadon 1 , R. Benson 1 , T. Das 2 , G. Barnett 1 1 Addenbrooke's Hospital- Cambridge, Department of Oncology, Cambridge, United Kingdom ; 2 Addenbrooke's Hospital- Cambridge, Department of Radiology, Cambridge, United Kingdom Purpose or Objective There is evidence for an association between radiotherapy contouring quality and clinical outcomes (1), especially in radiotherapy planning for head and neck (H&N) cancer. The Royal College of Radiologists (UK) recent guidance on peer review (PR) suggest the attendance of a radiologist “may be useful”, although this is not quantified (2). In this study we aim to determine the impact of the presence of a neuroradiologist on PR changes for H&N cancer radiotherapy. Material and Methods We report prospective data collected from scheduled weekly peer review meetings of H&N contouring. PR was completed after contouring and before treatment planning. Major, minor, and organ at risk (OAR) changes were recorded as well as any significant discussion (including dose, concurrent agents, fusion, choice of imaging sequence, choice of nodal levels etc.). A major change is defined as an alteration to the gross tumour volume (GTV) or high dose clinical target volume (CTV). A minor change is defined as an alteration to the elective- dose CTV (3). Differences in these changes in the presence or absence of a neuroradiologist was determined and chi- squared tests were performed to test statistical significance. Multivariate logistic regression was used to identify potential predictors of changes made during the PR meetings. Results All patients undergoing radical (chemo)radiotherapy for H&N cancer between October 2018 and September 2019 were included (n=171). Eleven patients with early larynx cancer were excluded. Prospective PR was performed in 125/160 (78%) of patients and full PR documentation was available in 120/160 (75%) of patients. Of the 120 patients with completed documentation, a specialist neuroradiologist was present in 53/120 (44%) of documented peer reviews.. 51/120 (42.5%) had a change made to any of the target volumes/OARs. Major changes were made in 43/120 (36%) of cases discussed (with 22% having changes in GTV). Minor changes were noted in 16/120 (13%), and 6/120 (5%) had changes in the OARs. 72/120 (60%) cases resulted in significant discussion. The differences in changes seen with or without the presence of a radiologist are summarised in the table below:

PD-0052 Interobserver variability in organ at risk delineation in head and neck cancer J. Van der Veen 1 , A. Gulyban 2 , S. Willems 3 , F. Maes 3 , S. Nuyts 1 1 University hospitals Leuven, Radiotherapy-Oncology, Leuven, Belgium ; 2 Jules Bordet Institute, Medical Physics Department, Brussels, Belgium ; 3 University hospitals Leuven, Medical Imaging research centre, Leuven, Belgium Purpose or Objective Inaccuracy in delineation of organs at risk (OARs) has an impact on dose-volume histograms which can affect evaluation of treatment plans and potentially lead to incorrect normal-tissue complication probability. Brouwer et al. showed significant interobserver variability (IOV) in OAR delineation in head and neck cancer (HNC), after which consensus delineation guidelines were published in 2015. The aim of our study was to identify the extent of IOV in delineation of OARs in HNC, in the presence of these guidelines. Material and Methods All radiotherapy departments in this national study were invited to complete an online survey and submit OAR contours for five HNC cases. Reference contours were delineated using the guidelines and compared to the contours from the different radiotherapy departments using DICE similarity coefficients (DSC) and median Hausdorff distances (HD50). Results Fourteen of 22 centres (64%) completed the survey and delineations. Thirteen centres used delineation guidelines and six confirmed the use of guidelines of Brouwer et al. Table 1 shows the median (and range) DSC and HD50 for all OARs in all five patients. The OARs that were delineated best were the mandible and brainstem followed by the parotid glands and submandibular glands. Table 1 also shows the number of times OARs were delineated. The supraglottic larynx was delineated least often (20 times) and the left parotid gland most often (62 times). Figure 1 shows DSC for every delineated OAR compared to the reference contour and the corresponding HD50. This figure shows that DSC and HD50 are negatively related and that there is clearly more IOV in some OARs compared to others. Especially cochlea’s, upper oesophagus, PCMs, supraglottis, and glottic area did poorly.