Prostate morphological changes during external beam radiotherapy are poorly understood. Excellent soft-tissue visualisation offered by magnetic resonance image-guided radiotherapy (MRIgRT) provides an opportunity to better understand such changes. The aim of this study was to quantify prostate volume and dimension changes occurring during extreme and moderately hypofractionated schedules. Forty prostate cancer patients treated on the Unity 1.5 Tesla magnetic resonance linear accelerator (MRL) were retrospectively reviewed. The cohort comprised patients treated with 36.25 Gy in five fractions (n = 20) and 60 Gy in 20 fractions (n = 20). The volume of the delineated prostates on reference planning computed tomography (fused with MRI) and daily T2-weighted 2-min session images acquired on Unity were charted. Forty planning computed tomography and 500 MRL prostate volumes were evaluated. The mean absolute and relative change in prostate volume during radiotherapy was compared using a paired t-test (P value <0.01 considered significant to control for multiple comparisons). The maximum dimension of the delineated prostate was measured in three isocentric planes. Significant prostate volume changes, relative to MRL imaging fraction 1 (MRL#1), were seen at all time points for the five-fraction group. The peak mean relative volume increase was 21% (P < 0.001), occurring at MRL#3 and MRL#4 after 14.5 and 21.75 Gy, respectively. Prostate expansion was greatest in the superior-inferior direction; the peak mean maximal extension was 5.9 mm. The maximal extension in the left-right and anterior-posterior directions measured 1.1 and 2.2 mm, respectively. For the 20-fraction group, prostate volume increased relative to MRL#1, for all treatment time points. The mean relative volume increase was 11% (P < 0.001) at MRL#5 after 12 Gy, it then fluctuated between 8 and 13%. From MRL#5 to MRL#20, the volume increase was significant (P < 0.01) for 12 of 16 time points calculated. The peak mean maximal extension in the superior-inferior direction was 3.1 mm. The maximal extension in the left-right and anterior-posterior directions measured 1.7 and 3.7 mm, respectively. Significant prostate volume and dimension changes occur during extreme and moderately hypofractionated radiotherapy. The extent of change was greater during extreme hypofractionation. MRIgRT offers the opportunity to reveal, quantify and correct for this deformation.

The implementation of MRI-guided online adaptive radiotherapy has facilitated the extension of therapeutic radiographers’ roles to include contouring, thus releasing the clinician from attending daily treatment. Following undergoing a specifically designed training programme, an online interobserver variability study was performed. 117 images from six patients treated on a MR Linac were contoured online by either radiographer or clinician and the same images contoured offline by the alternate profession. Dice similarity coefficient (DSC), mean distance to agreement (MDA), Hausdorff distance (HD) and volume metrics were used to analyse contours. Additionally, the online radiographer contours and optimised plans (n = 59) were analysed using the offline clinician defined contours. After clinical implementation of radiographer contouring, target volume comparison and dose analysis was performed on 20 contours from five patients. Comparison of the radiographers’ and clinicians’ contours resulted in a median (range) DSC of 0.92 (0.86 – 0.99), median (range) MDA of 0.98 mm (0.2–1.7) and median (range) HD of 6.3 mm (2.5–11.5) for all 117 fractions. There was no significant difference in volume size between the two groups. Of the 59 plans created with radiographer online contours and overlaid with clinicians’ offline contours, 39 met mandatory dose constraints and 12 were acceptable because 95 % of the high dose PTV was covered by 95 % dose, or the high dose PTV was within 3 % of online plan. A clinician blindly reviewed the eight remaining fractions and, using trial quality assurance metrics, deemed all to be acceptable. Following clinical implementation of radiographer contouring, the median (range) DSC of CTV was 0.93 (0.88–1.0), median (range) MDA was 0.8 mm (0.04–1.18) and HD was 5.15 mm (2.09–8.54) respectively. Of the 20 plans created using radiographer online contours overlaid with clinicians’ offline contours, 18 met the dosimetric success criteria, the remaining 2 were deemed acceptable by a clinician. Radiographer and clinician prostate and seminal vesicle contours on MRI for an online adaptive workflow are comparable and produce clinically acceptable plans. Radiographer contouring for prostate treatment on a MR-linac can be effectively introduced with appropriate training and evaluation. A DSC threshold for target structures could be implemented to streamline future training.

IGRT in cervical cancer treatment delivery is complex due to significant target and organs at risk (OAR) motion. Implementing image assessment of soft-tissue target and OAR position to improve accuracy is recommended. We report the development and refinement of a training and competency programme (TCP), leading to on-line Radiation Therapist (RTT) led soft-tissue assessment, evaluated by a prospective audit. The TCP comprised didactic lectures and practical sessions, supported by a comprehensive workbook. The content was decided by a team comprised of Clinical Oncologists, RTTs, and Physicists. On completion of training, RTT soft-tissue review proficiency (after bony anatomy registration) was assessed against a clinician gold-standard from a database of 20 cervical cancer CBCT images. Reviews were graded pass or fail based on PTV coverage assessment and decision taken in concordance with the gold-standard. Parity was set at ≥80% agreement.The initial TCP (stage one) focussed on offline verification and decision making. Sixteen RTTs completed this stage, four achieved ≥80%. This was not sufficient to support clinical implementation.The TCP was redesigned, more stringent review guidelines and greater anatomy teaching was added. TCP stage two focussed on online verification and decision making supported by a decision flowchart. Twenty-one RTTs completed this TCP, all achieved ≥80%. This supported clinical implementation of RTT-led soft-tissue review under prospective audit conditions.The prospective audit was conducted between March 2017 and August 2017. Daily online review was performed by two trained RTTs. Online review and decision making proficiency was evaluated by a clinician. Thirteen patients were included in the audit. Daily online RTT-led IGRT was achieved for all 343 fractions. Two-hundred CBCT images were reviewed offline by the clinician; the mean number of reviews per patient was 15. 192/200 (96%) RTT image reviews were in agreement with clinician review, presenting excellent concordance. Multidisciplinary involvement in training development, redesign of the TCP and inclusion of summative competency assessment were important factors to support RTT skill development. Consequently, RTT-led cervical cancer soft-tissue IGRT was clinically implemented in the hospital.

Introduction Prostate cancer (PCa) is the most common cancer in men. Recurrence may occur in up to half of patients initially treated with curative intent for high-risk localised/locally advanced PCa. Pelvic nodal recurrence is common in this setting, but no clear standard of care exists for these patients, with potential therapeutic approaches including stereotactic body radiotherapy (SBRT) to the involved node(s) alone, extended nodal irradiation (ENI) to treat sites of potential micrometastatic spread in addition to involved node(s) and androgen deprivation therapy with or without additional systemic anticancer therapies. Based on observational studies, ENI is associated with promising metastasis-free survival (MFS) compared with SBRT and appears to result in low rates of severe late toxicity. Methods and analysis Pelvis Or Involved Node Treatment: Eradicating Recurrence in Prostate Cancer is a UK multicentre, open-label, phase III randomised controlled trial, which will deliver much needed, high-quality evidence of the impact on metastatic progression from ENI compared with SBRT in patients with PCa pelvic nodal recurrence. The trial will also evaluate the long-term toxicity of 5-fraction ENI compared with a standard 20-fraction schedule. The trail will randomise 480 participants in a ratio of 2:1:1 to SBRT, 5-fraction ENI or 20-fraction ENI from 35 to 40 UK radiotherapy sites over 4 years. Coprimary endpoints are MFS at 3 years and participant-reported late bowel toxicity at 3 years. Secondary endpoints include overall survival, biochemical progression-free survival, failure-free survival, patterns of failure, participant-reported/clinician-reported toxicity and health-related quality of life. Collection of blood and tissue samples will enable future evaluation of biomarkers of disease and toxicity and support stratification of salvage therapeutic approaches. Ethics and dissemination Ethical approval was obtained from NHS Health Research Authority, East of England – Cambridgeshire and Hertfordshire Research Ethics Committee (24/EE/0099). Trial results will be published in peer-reviewed journals and adhere to International Committee of Medical Journal Editors guidelines. Trial registration number ISRCTN11089334, registered on 23 September 2024.

Introduction: We aimed to establish if stereotactic body radiotherapy to the prostate can be delivered safely using reduced clinical target volume (CTV) to planning target volume (PTV) margins on the 1.5T MR-Linac (MRL) (Elekta, Stockholm, Sweden), in the absence of gating.Methods: Cine images taken in 3 orthogonal planes during the delivery of prostate SBRT with 36.25 Gray (Gy) in 5 fractions on the MRL were analysed. Using the data from 20 patients, the percentage of radiotherapy (RT) delivery time where the prostate position moved beyond 1, 2, 3, 4 and 5 mm in the left-right (LR), superior-inferior (SI), anterior-posterior (AP) and any direction was calculated.Results: The prostate moved less than 3 mm in any direction for 90% of the monitoring period in 95% of patients. On a per-fraction basis, 93% of fractions displayed motion in all directions within 3 mm for 90% of the fraction delivery time. Recurring motion patterns were observed showing that the prostate moved with shallow drift (most common), transient excursions and persistent excursions during treatment.Conclusion: A 3 mm CTV-PTV margin is safe to use for the treatment of 5 fraction prostate SBRT on the MRL, without gating. In the context of gating this work suggests that treatment time will not be extensively lengthened when an appropriate gating window is applied.

Objectives: To measure the magnitude of intra-fraction prostate motion (IFPM) during stereotactic radiotherapy (SBRT) delivered without intra-fraction tracking. To assess if current margins adequately cover IFPM. To derive margins using new guidelines. Methods: IFPM was determined in 20 patients receiving 36.25 Gy in 5 fractions using 97 pairs of pre- and post-treatment cone beam CT (CBCT) scans. Correlation of time between CBCT acquisitions and motion was determined. The magnitude of IFPM was compared to current margins (6 mm isotropic, 3 mm posterior). Margins were calculated using IFPM alone and updated guidelines. Results: The averaged 3D root mean square IFPM was 2.5 mm (4.2 mm). Independent prostate motion was predominantly posterior (70%) and inferior (63%). There was weak correlation between posterior (ρ = 0.38) and inferior (ρ = 0.36) IFPM and time. IFPM greater than current margins occurred in 8 of 97 fractions, six in the posterior direction. Margins were ≤3.5 mm using IFPM alone and ≤3.3 mm Left 3.5 mm Right, 7.0 mm inferior, 3.7 mm superior, 4.4 mm anterior and 3.3 mm posterior using new guidelines, compensating for motion in 92% of fractions. Conclusions: Our current SBRT margins account for 92% of IFPM, predominantly posterior and inferior. Although updated guidelines suggest an increase in margins inferiorly, any increase must be balanced against the possibility of increased toxicity, particularly if biochemical control and side-effects are favourable with current practice. Advances in knowledge: The difference between current clinical margins and those determined using updated guidance is demonstrated. The implications must be considered against clinical outcomes.