BACKGROUND:Head and neck (H&N) patients frequently undergo anatomical changes such as weight loss and tumour shrinkage during treatment, requiring repeat imaging and replanning to maintain accurate dose delivery. On-board cone-beam CT (CBCT) systems could support these workflows, however they have historically been limited by reduced Hounsfield unit accuracy, inferior image quality, and susceptibility to metal artifacts from dental hardware, all of which are critical for effective radiotherapy treatment planning and dose delivery. HyperSight CBCT offers improved image quality comparable to FBCT along with metal artifact reduction techniques, but its dosimetric performance in H&N patients, particularly in the presence of dental metal implants, has not yet been evaluated. PURPOSE:This work evaluates the dosimetric accuracy of the HyperSight CBCT system (Varian Medical Systems), including the impact of metal artifact reduction, to determine its reliability for H&N treatment planning. METHODS:Images of 25 H&N cancer patients were acquired on a conventional fan-beam CT (FBCT. GE Healthcare) and on two CBCT systems: an Ethos radiotherapy system equipped with HyperSight CBCT, which provides advanced iterative reconstruction (HS-Acuros) and metal artifact reduction reconstruction (HS-MAR) options, and a TrueBeam linear accelerator system with conventional CBCT, which uses filtered back projection reconstruction (Varian Medical Systems). For each patient, the CBCTs were rigidly registered to the FBCT, and the clinically accepted reference plans were forward calculated on all images. Gamma evaluations (3%/3 mm, 2%/2 mm, 1%/1 mm) for all CBCT modes were performed relative to FBCT on slices both unaffected and affected by metal artifacts, with the latter also analyzed as a function of the metal artifact index (AI). DVH metrics were assessed for the planning target volume (PTV), mandible, oral cavity, and parotid glands. RESULTS:For all gamma criteria, HS-Acuros images demonstrated significantly higher pass rates than both HS-MAR and TrueBeam CBCTs in the artifact-free slices (p ≤ 0.033). In artifact-affected slices, HS-MAR reconstructions performed the best in slices affected by metal artifacts (p ≤ 0.001), exhibiting the least reduction in gamma pass rates with increasing artifact index (AI). Conventional TrueBeam CBCT consistently yielded the lowest gamma pass rates in artifact-prone regions (p ≤ 0.005). Across all slices, the median 3D 3%/3 mm gamma passing rates were above 99.2%, 98.7% and 97.7% for HS-Acuros, HS-MAR and TrueBeam, respectively. Across all CBCT images, the median DVH-metric deviations relative to CTsim FBCT were within 2% for all structures and metrics except for PTV Dmax. CONCLUSIONS:HyperSight provides imaging suitable for direct dose calculation in H&N adaptive radiotherapy with iCBCT MAR improving accuracy in the presence of dental metal artifacts; however, iCBCT Acuros may be preferred when artifact reduction is not critical. This work highlights a significant advancement towards CBCT-based direct-dose calculation for adaptive radiotherapy.

BACKGROUND:Accurate Hounsfield units (HU) are critical for dose calculation and anatomical visualization, but are often affected by dental artifacts in head and neck (H&N) cancer patients. The HyperSight cone-beam computed tomography (CBCT) platform provides improved image quality over previous CBCT platforms and offers metal artifact reduction (iCBCT MAR) reconstruction. PURPOSE:This study evaluates the quality of HyperSight CBCT images compared to current clinical standards: TrueBeam CBCT for image guidance and fan-beam CT (FBCT) from a CT simulator for treatment planning, using images captured during H&N cancer treatment. METHODS:Images for 30 H&N cancer patients were acquired on a HyperSight CBCT, conventional TrueBeam and FBCT, with 24 patients exhibiting metal dental artifacts. The HyperSight images were reconstructed using iCBCT MAR and iterative (iCBCT Acuros) algorithms. The four image sets were rigidly registered and compared using the artifact index (AI) measured in the oral cavity and the percentile range (PR) measured in the oral cavity, brain, brainstem and eyes to assess image non-uniformity. The HU accuracy was calculated relative to FBCT (baseline) for soft tissues (oral cavity, brainstem, submandibular and parotid glands), and bone (mandible). The contrast relative to baseline was evaluated between the oral cavity and nearby structures. Image-based metrics were computed relative to FBCT including structural similarity index measure (SSIM), mean-square error (MSE) and peak signal-to-noise ratio (PSNR). RESULTS:The HyperSight iCBCT MAR images showed a significant reduction in AI values compared to the other images (p < 0.0004), but higher PR values indicating decreased HU uniformity compared to HyperSight iCBCT Acuros and FBCT (p < 0.0002). The soft-tissue HU and contrast values were significantly closer to baseline in both HyperSight images compared to TrueBeam (HU: p < 0.001, contrast: p < 0.001). For soft-tissue the HU mean absolute deviation (MAD) from baseline was 16 ± 10 HU for HyperSight iCBCT Acuros, 15 ± 10 HU for HyperSight iCBCT MAR, and 35 ± 22 HU for TrueBeam. For bone, the HU MAD from baseline was 153 ± 233 HU, 185 ± 268 HU, and 214 ± 212 HU, respectively. The HyperSight iCBCT Acuros algorithm achieved significantly superior SSIM, MSE, and PSNR metrics compared to TrueBeam and HyperSight iCBCT MAR in regions with large amounts of bone and air. CONCLUSIONS:HyperSight iCBCT MAR significantly reduced artifacts compared to HyperSight iCBCT Acuros, TrueBeam and FBCT, making it particularly beneficial for patients with metal implants. Both HyperSight reconstructions demonstrated improved soft-tissue HU accuracy and contrast compared to TrueBeam, however the iCBCT Acuros algorithm may be preferred when metal-induced artifacts are not a concern. These results support the suitability of HyperSight images in adaptive treatment workflows requiring accurate image quality, even with severe metal artifacts.

Most follicular cell-derived differentiated thyroid carcinomas are regarded as low-risk neoplasms prompting conservative therapeutic management. Here, we provide consensus recommendations reached by a multidisciplinary group of endocrinologists, medical oncologists, pathologists, radiation oncology specialists, a surgeon and a medication reimbursement specialist, addressing more challenging forms of this malignancy, focused on radioactive iodine (RAI)-resistant or -refractory differentiated thyroid carcinoma (RAIRTC). In this document we highlight clinical, radiographic, and molecular features providing the basis for these management plans. We distinguish differentiated thyroid cancers associated with more aggressive behavior from thyroid cancers manifesting as poorly differentiated and/or anaplastic carcinomas. Treatment algorithms based on risk-benefit assessments of different multimodal therapy approaches are also discussed. Given the scarcity of data supporting management of this rare yet aggressive disease entity, these consensus recommendations provide much needed guidance for multidisciplinary teams to optimally manage RAIRTC.

Background: Delays in starting postoperative radiotherapy (PORT) have been established as negative predictors for clinical outcomes in head and neck squamous cell carcinomas (HNSCC). Our study aimed to examine the effect of delays during PORT, and the impact of national holidays in Canada, a publicly funded system, on oncologic outcomes such as Overall Survival (OS) and Local Recurrence (LR). Methods: The provincial cancer registry was queried to obtain demographic, pathologic, and outcomes data from cancer patients treated for all squamous cell carcinomas of the head and neck region treated between January 1, 2007 and November 30, 2019. All extracted information was cross-referenced and supplemented by chart review of patient electronic medical records. Extracted data were analyzed for OS and LR, in the context of Canadian national holidays causing delays during PORT. Results: 1433 patients treated for HNSCCs were identified, of whom 338 were treated curatively with surgery followed by PORT. 68.6% of patients experienced at least one day of interruption during treatments due to holidays. LR was 15.4% and OS was 59.6% at 5 years. Treatment interruptions by holidays were predictive of local recurrence (HR, 2.38; 95% CI 1.17-4.83; p = 0.017). Patients that developed early recurrence prior to PORT had very poor oncologic outcomes. Conclusion: Our findings were consistent with previously published studies in limiting the interval between surgery and PORT. We identified the novel finding of paired holidays as a significant predictor in determining LR, suggesting the importance of modifying RT delivery schedules and timing.

Purpose/Objective(s) To determine the pattern of relapse, outcomes, and predictors of patients with head and neck squamous cell carcinoma (HNSCC), treated with surgery who had evidence of early recurrence prior to postoperative radiotherapy (PORT). Materials/Methods A retrospective review was performed for patients with squamous cell carcinoma of the oral cavity, oropharynx, larynx, hypopharynx, and nasal cavity (HNSCC), treated with curative intent surgery followed by PORT, with or without systemic therapy between 2007 and 2019. Patients were classified into 3 groups: (1) Early recurrence patients, who presented with recurrence at either the primary site, or the neck, before or shortly after planned PORT started, (2) Later recurrence patients, who recurred locoregionally, after completing PORT, with no evidence of recurrence before or during PORT, and (3) patients who, during and after PORT, had no evidence of local recurrence. Multivariable analysis (MVA) was performed to identify predictors of early recurrence, local recurrence, and overall survival (OS). Results Three hundred and thirty-eight patients were treated with surgery followed by PORT; 33 patients (9.76%) had early recurrence before PORT. On MVA, smoking (at any time) (OR, 3.916 (1.539-9.967); p = 0.0102), N category (pN3, OR 2.956 (1.427-6.126); p<0.0001), perineural invasion (OR 2.180 (1.219-3.899); p = 0.0086) and increasing time from surgery to starting radiotherapy (OR 1.316(1.181-1.467); p<0.0001), were predictive of early recurrence. The local recurrence rate in patients with early recurrence was 60.5% (95% CI = 39.3-76.4%) at 5 years, compared to 15.6% (95% CI =11.6-20.2%) in patients who did not have early recurrence. The five-year OS for patients with early recurrence, later recurrence, or no local recurrence was 15.3% (95% CI = 4.9-31.1%), 16.5% (95% CI = 7.1-29.2%) and 69.8% (95% CI = 63.3-75.4%), respectively (p<0.0001). Conclusion Patients with early recurrence have significantly higher rates of local failure, distant metastases, and poor overall survival, compared to patients without early recurrence. Treatment paradigms investigating strategies to improve local failure and distant failure appear warranted in this unique patient group.

BackgroundDifferentiated thyroid cancer (DTC) requires long-term follow-up due to the risk of delayed recurrence. Follow-up surveillance involves serial neck ultrasound (US) and thyroglobulin (Tg); however, the optimal frequency and diagnostic performance of neck US outside of specialized thyroid cancer centres in higher risk patients is not well defined. We sought to evaluate the diagnostic performance of US and serial Tg in advanced stage DTC.MethodsWe retrospectively reviewed our thyroid cancer database for patients with stage III and IV DTC from 2006 to 2018, total thyroidectomy, and at least 2 years follow-up to assess recurrence rates. Those with hemi-thyroidectomy or anti-Tg antibodies were excluded. Diagnostic performance of US and Tg were assessed using a composite reference standard of follow-up imaging and pathology. All relevant US were reviewed by a blinded expert radiologist for uniformity.ResultsOf 136 included patients (91 females, mean age 58.9), 26 (19%) had recurrence of DTC over median follow-up of 6.6 years (IQR 5.3-9.3). The sensitivity and specificity of US in diagnosing cervical recurrence were 73.3% (95% CI 0.51-0.96) and 68.3% (95% CI 0.60-0.77) based on historical reports, respectively, and 80% (95% CI 0.60-1.00) and 87.8% (95% CI 0.82-0.93) based on blinded expert review, respectively. Tg had a sensitivity of 95.5% (95% CI 0.89-1.0) and specificity of 96.2% (95% CI 0.92-0.99) in detecting cervical recurrence or distant metastases. False positive US findings on historical US and subsequent review occurred in 38 (28%) and 15 (11%) patients, respectively, while 5 (3.6%) had false positive Tg results.ConclusionSerial Tg has better sensitivity and specificity than US for detecting recurrence of advanced stage DTC. Furthermore, re-interpretation of abnormal findings using structured US reporting with a subspecialized reader may improve diagnostic performance of US and improve its utility in clinical care.

Abstract Disclosure: V. Munro: None. S. Mustafa: None. F.S. Siddiqi: None. M. Rajaraman: None. S.A. Imran: None. Background: Most guidelines recommend periodic cervical ultrasound (US) for ongoing surveillance of differentiated thyroid cancer (DTC). While recent studies do not support routine US surveillance in low-risk DTC, to date, no study has assessed the clinical utility of cervical US in advanced DTC. Methods: We conducted a retrospective study of our hospital DTC registry using the following criteria: a) AJCC stage III and IV, b) minimum follow-up of >4 years since total thyroidectomy +/-I-131 ablation, and c) at least one US per 3 years of follow-up. Patients with hemithyroidectomy only or positive anti-thyroglobulin antibody at the initial visit were excluded. Two years after initial treatment, patients were categorized by Dynamic Risk Stratification (DRS) as excellent, indeterminate, biochemically incomplete, or structurally incomplete response. Data obtained at each visit included: treatment response, thyroglobulin (TG) level, and US findings. Results: A total of 114 patients (85 AJCC stage III and 29 stage IV patients) met the inclusion criteria. Mean age (yrs) at diagnosis was 59, and 67% were female. Mean duration of follow-up was 8.5 years. Based on DRS, 73 patients had excellent response, 28 indeterminate, 8 biochemically incomplete, and 5 structurally incomplete. Recurrence or progression was detected in 20 patients (17.5%): 5 excellent response, 6 indeterminate, 5 biochemically incomplete, and 4 structurally incomplete. Recurrence sites included cervical region (14), distant metastases (5) and both (1). The TG rose from a mean of 4.76 ng/mL at baseline to 40.37 ng/mL at time of recurrence/progression. In those with structurally incomplete disease, US demonstrated progression in all 4 patients. However in other DRS categories, only 5/10 had definite US abnormalities. Of those without recurrence, 4 patients (4.3%) had false positive TG (mean baseline TG 0.08 rose to 11.8 ng/ml) without clinical/radiologic recurrence whereas the rate of false positive US abnormalities was 32% (37/114). The sensitivity and specificity of US vs. TG in diagnosing recurrence was 45% and 60% vs 100% and 95.7%, respectively. Conclusion: Our study suggests that routine cervical US surveillance after initial DRS does not improve the detection of recurrence in patients with excellent, indeterminate, or biochemically incomplete disease, and has a high false positive rate. Therefore, we suggest TG should be considered the mainstay of surveillance and any further imaging guided by DRS status and change in TG. Presentation Date: Saturday, June 17, 2023

ThyroidVol. 33, No. 11 Research LetterA Multicentre Retrospective Study of Anaplastic Thyroid Cancer in the Era of Targeted Therapy in a Public Health Care System: Canada's ExperienceMichael K. Gupta, Ana-Maria Misariu, Nadim Saydy, Anthony C. Nichols, Francisco Laxague, Antoine Eskander, Huaqi Li, Natalie Weisbrod, Jesse D. Pasternak, Bahar Golbon, Elaine Jin, Stan H.M. van Uum, Maryse Brassard, Florence Lévesque, Nader Sadeghi, Thavakumar Subramaniam, Aleksander M. Mlynarek, Gregoire Bernard Morand, Pierre H. Fortier, Laurent Fradet, Sana Ghaznavi, Shamir P. Chandarana, Eitan Prisman, Tareck Ayad, Apostolos Christopoulos, Joel C. Davies, Murali Rajaraman, Martin Corsten, Kye Rajaraman, and Anastasios ManiakasMichael K. GuptaAddress correspondence to: Michael Gupta, MD, Division of Otolaryngology—Head and Neck Surgery, McMaster University, 50 Charlton Avenue E, Hamilton L8N 4A6, Canada E-mail Address: [email protected]Division of Otolaryngology—Head and Neck Surgery, McMaster University, Hamilton, Canada.Search for more papers by this author, Ana-Maria MisariuDivision of Otolaryngology—Head and Neck Surgery, McMaster University, Hamilton, Canada.Search for more papers by this author, Nadim SaydyDivision of Otolaryngology—Head and Neck Surgery, Hôpital Maisonneuve-Rosemont, University of Montreal, Montreal, Canada.Search for more papers by this author, Anthony C. NicholsDepartment of Otolaryngology—Head and Neck Surgery and Western University, London, Canada.Search for more papers by this author, Francisco LaxagueDepartment of Head and Neck Surgery, Hospital Aleman of Buenos Aires, Buenos Aires, Argentina.Search for more papers by this author, Antoine EskanderDepartment of Otolaryngology—Head and Neck Surgery, Sunnybrook Health Sciences Centre, University of Toronto, Toronto, Canada.Search for more papers by this author, Huaqi LiDepartment of Otolaryngology—Head and Neck Surgery, Sunnybrook Health Sciences Centre, University of Toronto, Toronto, Canada.Search for more papers by this author, Natalie WeisbrodDepartment of Otolaryngology—Head and Neck Surgery, Sunnybrook Health Sciences Centre, University of Toronto, Toronto, Canada.Search for more papers by this author, Jesse D. PasternakDepartment of Surgery, Toronto General Hospital, University of Toronto, Toronto, Canada.Search for more papers by this author, Bahar GolbonDepartment of Surgery, Toronto General Hospital, University of Toronto, Toronto, Canada.Search for more papers by this author, Elaine JinDepartment of Surgery, Toronto General Hospital, University of Toronto, Toronto, Canada.Search for more papers by this author, Stan H.M. van UumDivision of Endocrinology, Western University, London, Canada.Search for more papers by this author, Maryse BrassardDivision of Endocrinology, Department of Medicine, Université Laval, Quebec City, Canada.Search for more papers by this author, Florence LévesqueDivision of Endocrinology, Department of Medicine, Université Laval, Quebec City, Canada.Search for more papers by this author, Nader SadeghiDepartment of Otolaryngology, Head and Neck Surgery, McGill University Health Centre, Montreal, Canada.Search for more papers by this author, Thavakumar SubramaniamDepartment of Otolaryngology, Head and Neck Surgery, McGill University Health Centre, Montreal, Canada.Search for more papers by this author, Aleksander M. MlynarekDepartment of Otolaryngology Head and Neck Surgery, Jewish General Hospital, McGill University, Montreal, Canada.Search for more papers by this author, Gregoire Bernard MorandDepartment of Otolaryngology Head and Neck Surgery, Jewish General Hospital, McGill University, Montreal, Canada.Department of Otolaryngology, University of Zurich, Zurich, Switzerland.Search for more papers by this author, Pierre H. FortierDepartment of Otolaryngology—Head and Neck Surgery, Centre Hospitalier de l'Universite Sherbrooke, Sherbrooke, Canada.Search for more papers by this author, Laurent FradetDepartment of Otolaryngology—Head and Neck Surgery, Centre Hospitalier de l'Universite Sherbrooke, Sherbrooke, Canada.Search for more papers by this author, Sana GhaznaviDivisions of Endocrinology and University of Calgary, Calgary, Canada.Search for more papers by this author, Shamir P. ChandaranaDivisions of Otolaryngology, University of Calgary, Calgary, Canada.Search for more papers by this author, Eitan PrismanDivision of Otolaryngology, University of British Columbia, Vancouver, Canada.Search for more papers by this author, Tareck AyadDivision of Otolaryngology—Head and Neck Surgery, Centre Hospitalier de l'Université de Montréal, Université de Montréal, Montreal, Canada.Search for more papers by this author, Apostolos ChristopoulosDivision of Otolaryngology—Head and Neck Surgery, Centre Hospitalier de l'Université de Montréal, Université de Montréal, Montreal, Canada.Search for more papers by this author, Joel C. DaviesDepartment of Otolaryngology, Mount Sinai Hospital, University of Toronto, Toronto, Canada.Search for more papers by this author, Murali RajaramanDepartment of Radiation Oncology and Dalhousie University, Halifax, Canada.Search for more papers by this author, Martin CorstenDivision of Otolaryngology, Dalhousie University, Halifax, Canada.Search for more papers by this author, Kye RajaramanFaculty of Medicine, Saint Mary's University, Halifax, Canada.Search for more papers by this author, and Anastasios Maniakashttps://orcid.org/0000-0002-4354-2841Division of Otolaryngology—Head and Neck Surgery, Hôpital Maisonneuve-Rosemont, University of Montreal, Montreal, Canada.Department of Head and Neck Surgery, The University of Texas MD Anderson Cancer Center, Houston, Texas, USA.Search for more papers by this authorPublished Online:13 Nov 2023https://doi.org/10.1089/thy.2023.0088AboutSectionsView articleView Full TextSupplemental MaterialPDF/EPUBView Supplemental Data Permissions & CitationsPermissionsDownload CitationsTrack CitationsAdd to favorites Back To Publication ShareShare onFacebookXLinked InRedditEmail View articleFiguresReferencesRelatedDetails Volume 33Issue 11Nov 2023 InformationCopyright 2023, Mary Ann Liebert, Inc., publishersTo cite this article:Michael K. Gupta, Ana-Maria Misariu, Nadim Saydy, Anthony C. Nichols, Francisco Laxague, Antoine Eskander, Huaqi Li, Natalie Weisbrod, Jesse D. Pasternak, Bahar Golbon, Elaine Jin, Stan H.M. van Uum, Maryse Brassard, Florence Lévesque, Nader Sadeghi, Thavakumar Subramaniam, Aleksander M. Mlynarek, Gregoire Bernard Morand, Pierre H. Fortier, Laurent Fradet, Sana Ghaznavi, Shamir P. Chandarana, Eitan Prisman, Tareck Ayad, Apostolos Christopoulos, Joel C. Davies, Murali Rajaraman, Martin Corsten, Kye Rajaraman, and Anastasios Maniakas.A Multicentre Retrospective Study of Anaplastic Thyroid Cancer in the Era of Targeted Therapy in a Public Health Care System: Canada's Experience.Thyroid®.Nov 2023.1374-1377.http://doi.org/10.1089/thy.2023.0088Published in Volume: 33 Issue 11: November 13, 2023Online Ahead of Print:November 1, 2023Online Ahead of Editing: September 19, 2023PDF download

Aim: To assess the implementation of an electronic patient reported outcomes (ePRO) application across a multi-center radiation oncology department. Process: Dalhousie University's Department of Radiation Oncology (DRO) is composed of four radiotherapy (RT) centres (Halifax, Sydney, Saint John, Charlottetown) across three provinces. The implementation of ePRO across our centres has been made possible by several key events: In 2009, a Canadian Partnership Against Cancer (CPAC) grant enabled 2 centres to begin paper-based distress screening using the Canadian Problem Checklist (CPC) and Edmonton Symptom Assessment System (ESASr). In 2015, a PRO retreat included representatives from all 4 centres to devise an action plan for ePRO implementation. In 2017, Accreditation Canada mandated routine evaluation of patient outcomes and in 2019, three DRO centres were awarded CPAC funding to launch ePROs. The fourth centre now hopes to use lessons learned in order to facilitate their ePRO implementation. Within the ePRO application (Noona) Canadian Partnership for Quality Radiotherapy (CPQR)-endorsed PRO tools are used to capture patient responses including CPC, ESASr, and the Brief Pain Inventory (BPI). Needs assessments were conducted in the areas of human resource (e.g. administrative support) as well as staff and patient education. Clinic workflows were revised to include an ePRO assessment at consultation, first and last RT review as well as follow-up in clinic or remotely. Official roll-out began in November 2021 with a phased approach across centres and tumors sites to allow for stakeholder and user feedback and to facilitate continued project planning. Benefits/Chellenges: Multi-centre and multi-disciplinary collaboration has been a major enabler of this project with significant potential to expand our Department's clinical and research programs. While the challenge of coordinating such a large-scale initiative was aggravated by constantly changing pandemic restrictions, project priority was escalated across the institutions with recognition of the electronic platform as a powerful tool to assess patient distress/symptoms remotely. While implementation of an ePRO program has been feasible, it has also been complex. Approvals from Privacy Impact Assessments to IT architectural reviews were required. An advisory board was formed to facilitate multi-stakeholder feedback including patient representatives, project managers, clinical clerks, nurses, radiation therapists, radiation oncologists, industry representatives, IT and legal. The project has been dependent on support from cancer program leadership to front line staff. Given that implementation of an ePRO application has introduced change in clinic workflow, change management strategies have been required to obtain buy-in for a system that aims to ultimately improve the quality and efficiency of patient care. Impact / Outcomes: PROs capture the patient perspective on physical, emotional and practical impacts of treatment, with the literature showing benefits to include improved patient-provider communication, patient quality of life and even survival. Future evaluation of the program will hopefully confirm that uptake and efficiency of PROs improves with use of the electronic versus paper system. More importantly, we await data collection and analysis to determine whether our multiple RT centres see improved patient outcomes through use of ePROs.

Purpose:Outside of randomized clinical trials, it is difficult to develop clinically relevant evidence-based recommendations for radiation therapy (RT) practice guidelines owing to lack of comprehensive real-world data. To address this knowledge gap, we formed the Learning from Analysis of Multicenter Big Data Aggregation consortium to cooperatively implement RT data standardization, develop software solutions for data analysis, and recommend clinical practice change based on real-world data analyzed. The first phase of this "Big Data" study aimed at characterizing variability in clinical practice patterns of dosimetric data for organs at risk (OARs) that would undermine subsequent use of large-scale, electronically aggregated data to characterize associations with outcomes. Evidence from this study was used as the basis for practical recommendations to improve data quality. Methods and Materials:Dosimetric details of patients with head and neck cancer treated with radiation therapy between 2014 and 2019 were analyzed. Institutional patterns of practice were characterized, including structure nomenclature, volumes, and frequency of contouring. Dose volume histogram (DVH) distributions were characterized and compared with institutional constraints and literature values. Results:Plans for 4664 patients treated to a mean plan dose of 64.4 ± 13.2 Gy in 32 ± 4 fractions were aggregated. Before implementation of TG-263 guidelines in each institution, there was variability in OAR nomenclature across institutions and structures. With evidence from this study, we identified a targeted and practical set of recommendations aimed at improving the quality of real-world data. Conclusions:Quantifying similarities and differences among institutions for OAR structures and DVH metrics is the launching point for next steps to investigate potential relationships between DVH parameters and patient outcomes.

Abstract Background Medullary thyroid carcinoma (MTC) constitutes around 1-2% of all thyroid cancer with a paucity of published data. Distinctively, MTC has a strong genetic component with oncogene mutations. For AJCC stages I, II, III, and IV, 5-year overall survival (OS) rates are 100, 90, 86.5 and 55.5%. The aims of this study are to report outcomes of the MTC patient cohort managed at a single tertiary cancer centre and specifically that of the subset of patients who have a biochemically incomplete response to primary surgical management. Objectives Explore the incidence and outcome of MTC including demographics, stage, genetic mutation status, dynamic risk stratification (DRS), and OS rate. Compare the outcome of MTC patients found to have low detectable post-op calcitonin (POC) levels (10-200 pg/ml=Grp B)) with those who have undetectable (< 10 pg/ml=Grp A) and significantly high-level POC levels (>200 pg/ml=Grp C). Methods Patients with MTC were identified from the Interdisciplinary Thyroid Oncology Clinic (ITOC) prospective database. Data was extracted and completed with a chart review. Results 35 cases with MTC were identified from 1570 cases. 21/35 were males. The diagnosis was made between 1988 and 2019 with a median age at diagnosis of 50 years (range=15 to 77) and a median follow-up of 8 years. Distribution (and 5-year OS, p=0.515) across Stages I, II, III, IV were 23% (100%), 14% (100%), 17% (100%) and 32% (90%) respectively with 14% unknown. 10 (29%) tested positive for RET gene mutations. Post-operative DRS response to initial treatment for 29 cases found 48%, 35%, and 17% were classified into excellent (E=undetectable calcitonin), biochemical incomplete (B=only detectable calcitonin), or structural incomplete (S=structural disease present) respectively. The 29 cases with available POC and DRS were divided into Groups A, B, and C based on POC levels as above. The final status at last follow up for Grp A was 13/14 (93%) with E and 1 (7%) with S, for Grp B 6/9 (67%) with B, 3/9 (33%) with S, and for Grp C 6/6 (100%) with S. The DRS for Grp A, B and C was 100% E, 89% B and 11% S, and 33% B and 67% S. The 5-year OS for Grp A, B, C was 100%, 89%, 100% (p=0.223) respectively. Conclusion This cohort of MTC cases failed to show significant differences in OS by stage and POC levels but did exhibit a higher rate of genetic mutations (29%) than those from other regions of Canada. Additionally, a biochemically incomplete response with a POC level above 200 pg/ml was highly suggestive of progressive structural disease as final outcome. This study will provide the template for a national survey of MTC in Canada facilitating analysis of a larger dataset. Presentation: No date and time listed