Impact of a contouring atlas on radiographer inter-observer variation in male pelvis radiotherapy.

PURPOSE/OBJECTIVE: To determine the impact of a MR-based contouring atlas for male pelvis radiotherapy delineation on inter-observer variation to support radiographer led real-time magnetic resonance image guided adaptive radiotherapy (MRgART). MATERIAL/METHODS: Eight RTTs contoured 25 MR images in the Monaco treatment planning system (Monaco 5.40.01), from 5 patients. The prostate, seminal vesicles, bladder, and rectum were delineated before and after the introduction of an atlas developed through multi-disciplinary consensus. Inter-observer contour variations (volume), time to contour and observer contouring confidence were determined at both time-points using a 5-point Likert scale. Descriptive statistics were used to analyse both continuous and categorical variables. Dice similarity coefficient (DSC), Dice-Jaccard coefficient (DJC) and Hausdorff distance were used to calculate similarity between observers. RESULTS: Although variation in volume definition decreased for all structures among all observers post intervention, the change was not statistically significant. DSC and DJC measurements remained consistent following the introduction of the atlas for all observers. The highest similarity was found in the bladder and prostate whilst the lowest was the seminal vesicles. The mean contouring time for all observers was reduced by 50% following the introduction of the atlas (53 to 27 minutes, p=0.01). For all structures across all observers, the mean contouring confidence increased significantly from 2.3 to 3.5 out of 5 (p=0.02). CONCLUSION: Although no significant improvements were observed in contour variation amongst observers, the introduction of the consensus-based contouring atlas improved contouring confidence and speed; key factors for a real-time RTT-led MRgART.

Geometric distortion caused by metallic femoral head prosthesis in prostate cancer imaging on an MR Linac: in-vivo measurements of spatial deformation.

OBJECTIVES: Metallic implants cause artefacts and distortion on MRI. To ensure accurate dose delivery and plan adaptation on an MR Linac, there is a need to evaluate distortion caused. METHODS: Participants were imaged on an MR Linac (Elekta Unity, Elekta AB Stockholm). Three sequences were evaluated. Two vendor supplied (T2W TSE 3D), and one T2W TSE 3D optimized to reduce metal artefact distortions. Images were rigidly registered to CT images by a single observer, using bony anatomy. Three coronal and three axial images were selected, and six paired, adjacent, bony landmarks were identified on each slice. Images bisecting treatment isocentre were included. Difference between landmark coordinates was taken to be measure of distortion. RESULTS: Five observers participated. Thirty six pairs of bony landmarks were identified. Median difference in position of landmarks was ≤3 mm (range 0.3-4.4 mm). One-way analysis of variance (ANOVA) between observer means showed no significant variation between sequences or patients (P = 1.26 in plane, P = 0.11 through plane). Interobserver intra class correlation (ICC) was 0.70 in-plane and 0.78 through-plane. Intra-observer ICC for three observers was 0.76, 0.81, 0.83, showing moderate to good reliability on this small cohort. CONCLUSIONS: This in-vivo feasibility study suggests distortion due to metallic hip prosthesis is not an obstacle for pelvic radiotherapy on an MR Linac. Research on the impact on plan quality is warranted. ADVANCES IN KNOWLEDGE: This work supports feasibility of treating patients with metallic hip prosthesis on an MR Linac.

The impact of an educational tool in cervix image registration across three imaging modalities.

OBJECTIVES: Accurate image registration is vital in cervical cancer where changes in both planning target volume (PTV) and organs at risk (OARs) can make decisions regarding image registration complicated. This work aims to determine the impact of a dedicated educational tool compared with experience gained in MR-guided radiotherapy (MRgRT). METHODS: 10 therapeutic radiographers acted as observers and were split into two groups based on previous experience with MRgRT and Monaco treatment planning system. Three CBCT-CT, three MR-CT and two MR-MR registrations were completed per patient by each observer. Observers recorded translations, time to complete image registration and confidence. Data were collected in two phases; prior to and following the introduction of a cervix registration guide. RESULTS: No statistically significant differences were noted between imaging modalities. Each group was assessed independently pre- and post-education, no statistically significant differences were noted in either CBCT-CT or MR-CT imaging. Group 1 MR-MR imaging showed a statistically significant reduction in interobserver variability (p=0.04), in Group 2, the result was not statistically significant (p=0.06). Statistically significant increases in confidence were seen in all three modalities (p≤0.05). CONCLUSIONS: At The Christie NHS Foundation Trust, radiographers consistently registered images across three different imaging modalities regardless of their previous experience. The implementation of an image registration guide had limited impact on inter- and intraobserver variability. Radiographers' confidence showed statistically significant improvements following the use of the registration manual. ADVANCES IN KNOWLEDGE: This work helps evaluate training methods for novel roles that are developing in MRgRT.

Evaluation of the palliative radiotherapy pathway in a single institute: Can an MR Linac improve efficiency?

BACKGROUND: Palliative radiotherapy (RT) is effectively used to relieve cancer related symptoms. The demand for these services is increasing worldwide. Rapid response clinics have been developed as a means to streamline the palliative RT radiotherapy process and increase efficiency and improve patient experiences. Key components to successful rapid response palliative RT are access to care, streamlined services and innovation. To successfully implement a rapid response RT programme, it is essential to identify gaps between currently provided care and ideal or enhanced care. The aims of this work are to audit the current palliative RT workflow at our institution both prior to and during the coronavirus pandemic. This work reports the impact of covid-19 on rate of palliative RT referrals and proposes a radiographer led, MR guided rapid response workflow to reduce wait times METHODS: A retrospective audit of palliative radiotherapy booking forms was completed over a two yearperiod (2019-2020) to assess the current pathway both prior to and during the covid-19 pandemic. This audit identified patients who had received urgent/emergency spinal RT in the specified timeframe. Further data on these patients was collected using departmental oncology information systems to form a detailed analysis of the pathway and wait times. Data was recorded and analysed using Microsoft Excel. RESULTS: A total of 813 patients met the inclusion criteria for this audit. Data was reported for 2019 and 2020 separately to determine any significant impact caused by the covid-19 pandemic. In 2020 there was an 11.5% increase in referrals for palliative radiotherapy with an equal portion (81%) of total referrals in each year being for single fractions. Timelines from referral to treatment delivery were reported, with those patients receiving same day single fraction RT palliative radiotherapy undergoing further analysis to determine the amount of time spent in the department. Mean wait time for these patients was 5 hours and 20 minutes in 2019 but increased by 20.9% in 2020. CONCLUSIONS: The increasing demand for palliative RT due to rising global cancer rates and extended life expectancy due to advanced systemic treatments may lead to increased wait times. An increase in both referrals and mean wait time was seen during the covid-19 pandemic. Improving efficiency and access to care is essential for this population. The MR Linac could play a role in streamlining palliative RT workflows due to its ability to employ a scan, plan and treat model in a single session. This work forms preliminary support for the development of a trial one stop palliative program on the MR Linac.