Radiation therapy in older patients with cancer.

The general population is aging, which expectedly will lead to a future increase in older patients with cancer. This review summarises the recent advances in radiotherapy. Technological advances have led radiotherapy to be an efficient and well-tolerated treatment option in older patient with cancer. Studies show no difference in toxicity and disease control rates compared with the ones in younger patients with cancer. MR-guided radiotherapy, proton therapy, and integration of artificial intelligence in treatment planning represent the latest advances in the field of radiotherapy and hold potential to further improve the treatment of older patients with cancer.

Impact of Stereotactic Body Radiotherapy on Thrombin Generation and Platelet Aggregation in Patients with Non-Small Cell Lung Cancer.

Patients with localized non-small cell lung cancer (NSCLC) considered unfit for surgery are at substantially increased risk of venous thromboembolism. Radiotherapy may further increase this risk. We aim to investigate the impact of stereotactic body radiotherapy (SBRT) on thrombin generation and platelet aggregation. We included 110 patients with localized NSCLC treated with SBRT. Blood samples were obtained prior to SBRT, immediately after SBRT completion, and 4-6 weeks following SBRT. Ex vivo and in vivo thrombin generations were analyzed using a calibrated automated thrombogram and commercial enzyme-linked immunosorbent assays. Platelet aggregation was evaluated using multiple electrode aggregometry. No significant differences were found in ex vivo or in vivo thrombin generation between blood samples before and immediately after SBRT treatment. Platelet aggregation was lower immediately after SBRT than before SBRT (TRAP: P = 0.04 and ASPI: P = 0.02) but remained within the reference interval. SBRT did not affect in vivo and ex vivo thrombin generation or platelet aggregation. SBRT did not cause prothrombotic changes in the coagulation in this study population of SBRT-treated patients with localized NSCLC.

A national repository of complete radiotherapy plans: design, Results, and experiences.

BACKGROUND: Previously, many radiotherapy (RT) trials were based on a few selected dose measures. Many research questions, however, rely on access to the complete dose information. To support such access, a national RT plan database was created. The system focuses on data security, ease of use, and re-use of data. This article reports on the development and structure, and the functionality and experience of this national database. METHODS AND MATERIALS: A system based on the DICOM-RT standard, DcmCollab, was implemented with direct connections to all Danish RT centres. Data is segregated into any number of collaboration projects. User access to the system is provided through a web interface. The database has a finely defined access permission model to support legal requirements. RESULTS: Currently, data for more than 14,000 patients have been submitted to the system, and more than 50 research projects are registered. The system is used for data collection, trial quality assurance, and audit data set generation.Users reported that the process of submitting data, waiting for it to be processed, and then manually attaching it to a project was resource intensive. This was accommodated with the introduction of triggering features, eliminating much of the need for users to manage data manually. Many other features, including structure name mapping, RT plan viewer, and the Audit Tool were developed based on user input. CONCLUSION: The DcmCollab system has provided an efficient means to collect and access complete datasets for multi-centre RT research. This stands in contrast with previous methods of collecting RT data in multi-centre settings, where only singular data points were manually reported. To accommodate the evolving legal environment, DcmCollab has been defined as a 'data processor', meaning that it is a tool for other research projects to use rather than a research project in and of itself.

Increased In Vivo Thrombin Generation in Patients with Localized Non-Small Cell Lung Cancer Unfit for Surgery.

Patients with lung cancer face a substantially increased risk of thromboembolic disease. Patients with localized non-small cell lung cancer (NSCLC) who are unfit for surgery due to age or comorbidity have additional thrombotic risk factors. Thus, we aimed to investigate markers of primary and secondary hemostasis, since this could assist in treatment decisions. We included 105 patients with localized NSCLC. Ex vivo thrombin generation was determined by calibrated automated thrombogram and in vivo thrombin generation was determined by measurement of thrombin-antithrombin complex (TAT) levels and prothrombin fragment F1 + 2 concentrations (F1 + 2). Platelet aggregation was investigated by impedance aggregometry. Healthy controls were used for comparison. TAT and F1 + 2 concentrations were significantly higher in NSCLC patients than in healthy controls (P < .001). The levels of ex vivo thrombin generation and platelet aggregation were not increased in the NSCLC patients. Patients with localized NSCLC considered unfit for surgery had significantly increased in vivo thrombin generation. This finding should be further investigated as it could be relevant for the choice of thromboprophylaxis in these patients.

Causal relation between heart irradiation and survival of lung cancer patients after radiotherapy.

INTRODUCTION: In a recent study, setup uncertainties in the direction of the heart were shown to impact the overall survival of non-small cell lung cancer (NSCLC) patients after radiotherapy, indicating the causal effect between heart irradiation and survival. The current study aims to externally evaluate this observation within a patient cohort treated using daily IGRT. METHOD: NSCLC patients with locally-advanced disease and daily CBCT were included. For all treatment fractions, the distance between the isocenter and the heart was evaluated based on the clinical setup registrations. The variation in heart position between planning and treatment (DeltaDistance) was estimated from these registrations. The possible impact of DeltaDistance on survival was analysed by a multivariable Cox model of overall survival, allowing for a time-dependent impact of DeltaDistance to allow for toxicity latency. RESULTS: Daily CBCT information was available for 489 patients at Odense University Hospital. The primary Cox model contained GTV volume, patient age, performance status, and DeltaDistance. DeltaDistance significantly impacted overall survival approximately 50 months after radiotherapy. Subanalyses indicated that the observed effect is mainly present among the patients with the least clinical risk factors. CONCLUSION: Our results confirm the impact of setup variations in the direction of the heart on the survival of NSCLC patients, even within a cohort using daily CBCT setup guidance. This result indicates a causal effect between heart irradiation and survival. It will be challenging to reduce the setup uncertainty even further; thus, increased focus on dose constraints on the heart seems warranted.

Veliparib Plus Carboplatin and Paclitaxel Versus Investigator's Choice of Standard Chemotherapy in Patients With Advanced Non-Squamous Non-Small Cell Lung Cancer.

BACKGROUND: This open-label Phase III trial (NCT02264990) evaluated the PARP inhibitor, veliparib, combined with carboplatin/paclitaxel versus chemotherapy alone for first-line treatment of patients with advanced non-squamous non-small cell lung cancers (NSCLC). A 52-gene expression classifier (LP52) previously shown to identify patients more likely to respond to veliparib was evaluated as a planned correlative analysis. MATERIALS AND METHODS: Adult current or former smokers with advanced non-squamous NSCLC were randomized 1:1 to veliparib (120 mg daily for 7 days/cycle) with carboplatin and paclitaxel or to investigators' choice of platinum doublet chemotherapy (up to 6, 21-day cycles), with optional pemetrexed maintenance. Prospective analysis of the LP52 signature was conducted using a clinical Qiagen/HTG assay. The primary endpoint was overall survival (OS) in LP52+ patients. RESULTS: Overall, 595 patients received veliparib + carboplatin/paclitaxel (n = 298) or chemotherapy alone (n = 297); 13% (n = 40) in each arm were LP52+. The primary endpoint was not met; median OS was 11.2 months with veliparib + carboplatin/paclitaxel versus 9.2 months with chemotherapy alone in the LP52+ subgroup (hazard ratio [HR] 0.644, 95% confidence interval [CI]: 0.396-1.048; P = .113). In the overall population, median OS was 12.1 months in both arms (HR 0.986, 95% CI: 0.827-1.176; P = .846). No new safety signals were observed. CONCLUSION: In patients with non-squamous NSCLC, there was no significant improvement in OS with veliparib + carboplatin/paclitaxel versus chemotherapy alone, although a trend toward improved OS in the LP52+ population suggests this subgroup may benefit from veliparib. Statistical power was limited due to the small sample size.

Outcomes of prophylactic cranial irradiation in patients with small cell lung cancer in the modern era of baseline magnetic resonance imaging of the brain.

BACKGROUND: For decades many patients with small cell lung cancer (SCLC) have been offered prophylactic cranial irradiation (PCI) to prevent brain metastases (BM). However, the role of PCI is debated in the modern era of increased brain magnetic resonance imaging (MRI) availability. BM in SCLC patients may respond to chemotherapy, and if a negative MRI is used in the decision to use of PCI in the treatment strategy, the timing of brain MRI may be crucial when evaluating the effect of PCI. This retrospective study investigates the impact of PCI outcomes in patients with SCLC staged with brain MRI prior to chemotherapy. MATERIALS AND METHODS: This study included 245 patients diagnosed SCLC/mixed NSCLC-SCLC treated between 2012 and 2019. The population was analyzed separately for limited disease (LS-SCLC) and extensive disease (ES-SCLC). Patients were divided into groups based on baseline brain MRI prior to chemotherapy and PCI. The primary endpoint was time to symptomatic BM. Secondary endpoints were overall survival (OS), and progression-free survival (PFS). RESULTS: In patients with LS-SCLC staged with brain MRI the probability of developing symptomatic BM at one year was 4% vs. 22% (p < 0.05), median OS was 55 vs. 24 months (p < 0.05), and median PFS was 30 vs. 10 months (p < 0.05) with and without PCI, respectively. No differences in probability of symptomatic BM and survival outcomes were observed in ES-SCLC. In a multivariate regression analysis, no variables were statistically significant associated with the risk of developing symptomatic BM in patients with LS-SCLC and ES-SCLC. For patients with ES-SCLC staged with brain MRI, PS (HR = 3.33, CI; 1.41-7.89, p < 0.05) was associated with poor survival. CONCLUSION: This study found that PCI in LS-SCLC patients staged with brain MRI had lower incidence of symptomatic BM and improved survival outcomes suggesting PCI as standard of care. Similar benefit of PCI in patients with ES-SCLC was not found.

Patient, Family Caregiver, and Nurse Involvement in End-of-Life Discussions During Palliative Chemotherapy: A Phenomenological Hermeneutic Study.

The aim of this study was to investigate current nursing practice related to end-of-life discussions with incurable lung cancer patients and their family caregivers from the perspectives of patients, family caregivers, and nurses in an oncology outpatient clinic. This phenomenological hermeneutic study included nine patients, eight family caregivers, and 11 nurses. Data were collected using participant observation, informal and semi-structured individual or joint interviews with patients and family caregivers, and focus group interviews with nurses. A Ricoeur-inspired approach was used to analyze the data. Three themes were identified: (a) content of end-of-life discussions, (b) timing of end-of-life discussions, and (c) challenges in end-of-life discussions. End-of-life discussions were seldom initiated; when they were, it was often too late. Discussions addressed treatment, place of care, practical/economic concerns, and existential matters. The physical environment at the outpatient clinic, lack of continuity, and nurses' instrumental task workloads and time pressure posed challenges to initiating end-of-life discussions.

Online adaptive radiotherapy potentially reduces toxicity for high-risk prostate cancer treatment.

BACKGROUND AND PURPOSE: With daily, MR-guided online adapted radiotherapy (MRgART) it may be possible to reduce the PTV in pelvic RT. This study investigated the potential reduction in normal tissue complication probability (NTCP) of MRgART compared to standard radiotherapy for high-risk prostate cancer. MATERIALS AND METHODS: Twenty patients treated with 78 Gy to the prostate and 56 Gy to elective pelvic lymph nodes were included. VMAT plans were generated with standard clinical PTV margins. Additionally to the planning MR, patients had three MRI scans during treatment to simulate an MRgART. A reference plan with PTV margins determined for MRgART was created per patient and adapted to each of the following MRs. Adapted plans were warped to the planning MR for dose accumulation. The standard plan was rigidly registered to each adaptation MR before it was warped to the planning MR for dose accumulation. Dosimetric impact was compared by DVH analysis and potential clinical effects were assessed by NTCP modeling. RESULTS: MRgART yielded statistically significant lower doses for the bladder wall, rectum and peritoneal cavity, compared to the standard RT, which translated into reduced median risks of urine incontinence (ΔNTCP 2.8%), urine voiding pain (ΔNTCP 2.8%) and acute gastrointestinal toxicity (ΔNTCP 17.4%). Mean population accumulated doses were as good or better for all investigated OAR when planned for MRgART as standard RT. CONCLUSION: Online adapted radiotherapy may reduce the dose to organs at risk in high-risk prostate cancer patients, due to reduced PTV margins. This potentially translates to significant reductions in the risks of acute and late adverse effects.

Tumour motion analysis from planning to end of treatment course for a large cohort of peripheral lung SBRT targets.

BACKGROUND: The aim is to quantify and analyse tumour motion during a course of treatment for lung SBRT patients. MATERIAL AND METHODS: Peak-to-peak motion of 483 tumours in 441 patients treated with peripheral lung SBRT at a single institution over a two year period was measured on planning CT and at all treatment fractions. Planning 4D-CT scans were analysed using our clinical workflow involving deformable propagation of the delineated target to all phases. Similarly, acquisition of the 4D-CBCT data followed the clinical workflow based on XVI 5.0 available on Elekta linacs. Differences and correlations of the peak-to-peak motion on the planning CT and at treatment were analysed. RESULTS: On the planning CT, a total of 81.4% of the tumours had a peak-to-peak motion <10 mm, and 96.1% had <20 mm. The largest motion was observed in the CC direction, with largest amplitude for tumours located in the caudal posterior part of the lung. The difference in amplitude in CC between planning CT and first fraction had a mean and standard deviation of 0.3 mm and 3.5 mm, respectively, and the largest differences were observed in the caudal posterior part of the lung. Patients with a difference in tumour motion amplitude exceeding two standard deviations (>7 mm) at the first fraction were evaluated individually, and they all had poor 4DCT image quality. The difference between the first and second/third fractions had a mean and standard deviation of 0.4 mm/0.5 mm and 2.0 mm/1.9 mm. CONCLUSION: Tumour motion at first treatment was similar to motion at planning, and motion at subsequent treatments was very similar to motion at first treatment. Large tumour motions are located towards the caudal posterior tumour locations. Patients with poor 4D-CT image quality should be closely followed at the first treatment to verify the motion.

[Challenges in cancer treatment for the elderly].

About half of all Danish cancer patients are 70 years or older at diagnosis. The incidence is expected to increase further over the coming years because of an increasing longevity. Therefore, this review recommends that the Danish health care system develops and implement models to ensure optimal care for older adults with cancer. We are still in need of knowledge about the optimal treatment, rehabilitation, palliation and care for older adults with cancer. We encourage the Danish health authorities to formulate a national strategy for this area.

Combination of the G-8 Screening Tool and Hand-Grip Strength to Predict Long-Term Overall Survival in Non-Small Cell Lung Cancer Patients Undergoing Stereotactic Body Radiotherapy.

The Geriatric 8 (G-8) is a known predictor of overall survival (OS) in older cancer patients, but is mainly based on nutritional aspects. This study aimed to assess if the G-8 combined with a hand-grip strength test (HGST) in patients with NSCLC treated with stereotactic body radiotherapy can predict long-term OS better than the G-8 alone. A total of 46 SBRT-treated patients with NSCLC of stage T1-T2N0M0 were included. Patients were divided into three groups: fit (normal G-8 and HGST), vulnerable (abnormal G-8 or HGST), or frail (abnormal G-8 and HGST). Statistically significant differences were found in 4-year OS between the fit, vulnerable, and frail groups (70% vs. 46% vs. 25%, p = 0.04), as well as between the normal and abnormal G-8 groups (69% vs. 39%, p = 0.02). In a multivariable analysis of OS, being vulnerable with a hazard ratio (HR) of 2.03 or frail with an HR of 3.80 indicated poorer OS, but this did not reach statistical significance. This study suggests that there might be a benefit of adding a physical test to the G-8 for more precisely predicting overall survival in SBRT-treated patients with localized NSCLC. However, this should be confirmed in a larger study population.

Evolution of the gross tumour volume extent during radiotherapy for glioblastomas.

BACKGROUND AND PURPOSE: Tumour growth during radiotherapy may lead to geographical misses of the target volume. This study investigates the evolution of the tumour extent and evaluates the need for plan adaptation to ensure dose coverage of the target in glioblastoma patients. MATERIALS AND METHODS: The prospective study included 29 patients referred for 59.4 Gy in 33 fractions. Magnetic resonance imaging (MRI) was performed at the time of treatment planning, at fraction 10, 20, 30, and three weeks after the end of radiotherapy. The gross tumour volume (GTV) was defined as the T1w contrast-enhanced region plus the surgical cavity on each MRI set. The relative GTV volume and the maximum distance (Dmax) of the extent of the actual GTV outside the original GTV were measured. Based on the location of the actual GTV during radiotherapy and the original planned dose, a prospective clinical decision was made whether to adapt the treatment. RESULTS: Dose coverage of the GTV during radiotherapy was not compromised, and none of the radiotherapy plans was adapted. The median Dmax (range) was 5.7 (2.0-18.9) mm, 8.0 (2.0-27.4) mm, 8.0 (1.9-27.3) mm, and 8.9 (1.9-34.4) mm at fraction 10, 20, 30, and follow-up. The relative GTV volume and Dmax observed at fraction 10 were correlated with the values observed at follow-up (R = 0.74, p < 0.001 and R = 0.79, p < 0.001, respectively). CONCLUSION: Large variations in the GTV extent were observed, and changes often occurred early in the treatment. Plan adaptation for geographical misses was not performed in our cohort due to sufficient CTV margins.

Accuracy of automatic structure propagation for daily magnetic resonance image-guided head and neck radiotherapy.

BACKGROUND AND PURPOSE: Deformable image registration (DIR) and contour propagation are used in daily online adaptation for hybrid MRI linac (MRL) treatments. The accuracy of the propagated contours may vary depending on the chosen workflow (WF), affecting the amount of required manual corrections. This study investigated the impact of three different WFs of contour propagations produced by a clinical treatment planning system for a high-field MRL on head and neck cancer patients. METHODS: Seventeen patients referred for curative radiotherapy for oropharyngeal cancer underwent standard CT-based dose planning and MR scans in the treatment position for planning (pMR), and at the 10th (MR10), 20th (MR20) and 30th (MR30) fraction (±2). The primary tumour, a metastatic lymph node and 8 organs at risk were manually delineated on each set of T2 weighted images. Delineations were repeated one month later on the pMR by the same observer to determine the intra-observer variation (IOV). Three WFs were used to deform images in the treatment planning system for the high-field MRL: In WF1, only the planning image and contours were used as a reference for DIR and propagation to MR10,20,30. The most recently acquired image set prior to the daily images was deformed and uncorrected (WF2) versus manually corrected (WF3) structures propagated to the session image. Dice similarity coefficient (DSC), mean surface distance (MSD) and Hausdorff distance (HD) were calculated for each structure in each model. RESULTS: Population median DSC, MSD and HD for WF1 and WF3 were similar and slightly better than for WF2. WF3 provided higher accuracy than WF1 for structures that are likely to shrink. All DIR workflows were less accurate than the IOV. CONCLUSIONS: WF1 and WF3 provide higher accuracy in structure propagation than WF2. Manual revision and correction of propagated structures are required for all evaluated workflows.

Patients and family caregivers report high treatment expectations during palliative chemotherapy: a longitudinal prospective study.

BACKGROUND: When discussing treatment options and future care, it is important to understand the expectations of patients and family caregivers related to palliative chemotherapy and to identify patterns in patients' quality of life. The study aims were to evaluate differences in treatment expectations and quality of life between patients with thoracic cancer (non-small-cell lung cancer, small-cell lung cancer and mesothelioma) who were < 70 and ≥ 70 years of age and receiving palliative chemotherapy and to assess family caregivers' treatment expectations. METHODS: A prospective longitudinal study included patients with thoracic cancer receiving outpatient palliative chemotherapy at a university hospital in Denmark and their family caregivers. Patients' treatment expectations and quality of life were assessed three times during treatment with a survey of treatment expectations and the Functional Assessment of Cancer Therapy - General questionnaire. Family caregivers' treatment expectations were assessed once. RESULTS: A total of 48 patients and 36 family caregivers participated between 2018 and 2019. No statistically significant age-related differences in treatment expectations and quality of life were identified. 28% of patients aged < 70 years and 7% of those aged ≥70 years expected a cure. Among family caregivers, 36% expected a cure. Across both age groups, mean total quality of life scores significantly decreased from 73.2 at first palliative chemotherapy cycle to 70.5 at third cycle (p = 0.02). No meaningful changes were found in quality of life within either age group. A subgroup analysis found no significant between-group differences in quality of life. Mean physical well-being score for all patients decreased from 20.3 at first cycle to 18.4 at third cycle (p = 0.03) and mean emotional well-being score decreased from 15.4 at first cycle to 14.6 at third cycle (p = 0.04). CONCLUSION: This study emphasizes the importance of initiating conversations about treatment expectations and paying attention to expectations that may differ by the age of the patient and between patients and family caregivers. Addressing treatment expectations among patients and family caregivers and monitoring quality of life among patients is important in clinical practice.

Prospectively scored pulmonary toxicities in non-small cell lung cancer: Results from a randomized phase II dose escalation trial.

PURPOSE: Prospectively scored radiation pneumonitis (RP) observed in a national, randomized phase II dose-escalation trial for patients with locally advanced non-small cell lung cancer (NSCLC) was investigated. METHODS: Patients with stage IIB-IIIB histologically proven NSCLC were treated with concomitant chemo-radiotherapy (oral Vinorelbine 3times/week) at 60 Gy/30fx (A-59pts) and 66 Gy/33fx (B-58pts) from 2009 to 2013 at five Danish RT centers. Grade 2 RP (CTCAEv3.0) was investigated with univariate analysis for association with clinical and dosimetric parameters, including dyspnea and cough at baseline and during RT. Multivariable logistic regression and Cox regression with regularization were used to find a multivariable model for RP ≥ G2. RESULTS: Despite a tendency of higher mean lung dose in the high-dose arm (median[range] A = 14.9 Gy[5.8,23.1], B = 17.5 Gy[8.6,24.8], p = 0.075), pulmonary toxicities were not significantly different (RP ≥ G2 41%(A) and 52%(B), p = 0.231). A Kaplan Meier analysis of the time to RP ≥ G2 between the two arms did not reach statistical significance (p = 0.180). Statistically significant risk factors for RP ≥ G2 were GTV size (OR = 2.091/100 cm3, p = 0.002), infection at baseline or during RT (OR = 8.087, p = 0.026), dyspnea at baseline (OR = 2.184, p = 0.044) and increase of cough during RT (OR = 2.787, p = 0.008). In the multivariable logistic regression and the Cox regression analysis, the deviances of the most predictive models were within one standard deviation of the null model. CONCLUSION: No statistical difference between the high- and low dose arm was found in the risk of developing RP. The univariate analysis identified target volume, infection, dyspnea at baseline, and increase of cough during RT as risk factors for RP. The number of patients was too small to establish a statistically sound multivariable model.

Long-term follow-up 3 years after a randomized rehabilitation study among radiated prostate cancer survivors.

PURPOSE: In the Rehabilitation of Prostate Cancer (RePCa) study, the intervention reduced early adverse effects in prostate cancer 6 months after radiotherapy. This 3-year follow-up study assesses late adverse effects, evaluates rehabilitative long-term effects and identifies patients who benefit the most. DESIGN: RePCa was a randomized clinical trial with multidisciplinary rehabilitation (n = 79) or usual care (n = 82). The intervention during the first 6 months consisted of consultations by nurses and physiotherapists focusing on psychosocial support and physical activity, respectively. Here we report the 3-year follow-up. Data consisted of disease-specific quality of life (EPIC-26), general quality of life (SF-12) and pelvic floor strength measured by electromyography. RESULTS: One hundred forty-three patients (92%) responded. The primary outcome urinary irritative sum-score was no longer significantly different between groups. In patients with moderate-severe urinary problems at baseline, we observed a significant long-term effect on the urinary irritative sum-score in favour of the intervention (+ 13.4 points P = .014). More patients had moderate-severe bowel problems in the control group (n = 10; 14%) compared to the intervention group (n = 2; 3%) (P = .016). Pelvic floor strength deteriorated significantly in both groups. CONCLUSION: The short-term rehabilitation was beneficial but of limited benefit in the long term for all patients. A significant and clinically relevant effect was found in irradiated prostate cancer patients with moderate-severe urinary problems at baseline. In both groups, pelvic floor strength was weakened during follow-up. IMPACT FOR CANCER SURVIVORS: Prior research showed patients benefit from early rehabilitation. Identification of patients with moderate-severe urinary problems followed by a focused rehabilitation during the first 6 months after radiotherapy results in long-term improvement. Radiated patients have to be aware of their pelvic floor strength. IMPLICATIONS FOR CANCER SURVIVORS: Patients can be informed that they benefit from early rehabilitation, and they cannot expect larger changes in adverse effects within the first years, but they have to be aware of their pelvic floor strength. Future rehabilitation studies could be applied mainly to patients with assessed rehabilitation needs after radiotherapy and intensified with long-term follow-up.

Accuracy of automatic deformable structure propagation for high-field MRI guided prostate radiotherapy.

BACKGROUND: In this study we have evaluated the accuracy of automatic, deformable structure propagation from planning CT and MR scans for daily online plan adaptation for MR linac (MRL) treatment, which is an important element to minimize re-planning time and reduce the risk of misrepresenting the target due to this time pressure. METHODS: For 12 high-risk prostate cancer patients treated to the prostate and pelvic lymph nodes, target structures and organs at risk were delineated on both planning MR and CT scans and propagated using deformable registration to three T2 weighted MR scans acquired during the treatment course. Generated structures were evaluated against manual delineations on the repeated scans using intra-observer variation obtained on the planning MR as ground truth. RESULTS: MR-to-MR propagated structures had significant less median surface distance and larger Dice similarity index compared to CT-MR propagation. The MR-MR propagation uncertainty was similar in magnitude to the intra-observer variation. Visual inspection of the deformed structures revealed that small anatomical differences between organs in source and destination image sets were generally well accounted for while large differences were not. CONCLUSION: Both CT and MR based propagations require manual editing, but the current results show that MR-to-MR propagated structures require fewer corrections for high risk prostate cancer patients treated at a high-field MRL.