Simultaneous Focal Boost With Stereotactic Radiation Therapy for Localized Intermediate- to High-Risk Prostate Cancer: Primary Outcomes of the SPARC Phase 2 Trial

PURPOSE

Dose-escalated radiation therapy is associated with better biochemical control at the expense of toxicity. Stereotactic body radiation therapy (SBRT) with dose escalation to the dominant intraprostatic lesion (DIL) provides a logical approach to improve outcomes in high-risk disease while limiting toxicity. This study evaluated the toxicity and quality of life (QoL) with CyberKnife-based SBRT and simultaneous integrated boost in localized prostate cancer.

METHODS AND MATERIALS

Eligible participants included newly diagnosed, biopsy-proven unfavorable intermediate- to high-risk localized prostate cancer (at least 1 of the following: Gleason ≥4+3, magnetic resonance imaging(MRI)-defined T3a N0, prostate-specific antigen ≥20) with up to 2 MRI-identified DILs. Participants received 36.25 Gy in 5 fractions on alternative days with a simultaneous boost to DIL up to 47.5 Gy as allowed by organ-at-risk constraints delivered by CyberKnife. All participants received androgen deprivation therapy. The primary outcome measure was acute grade 2+ genitourinary toxicity. Acute and late genitourinary and gastrointestinal toxicity using Radiation Therapy Oncology Group scoring, biochemical parameters, International Prostate Symptom Score, International Index of Erectile Function 5, and EQ-5D QoL outcomes were assessed.

RESULTS

Between 2013 and 2023, 20 participants were enrolled with a median follow-up of 30 months. The median D95 dose to DIL was 47.43 Gy. Cumulative acute grade 2+ genitourinary and gastrointestinal toxicity were 25% and 30%, respectively. One patient developed acute grade 3 genitourinary toxicity (5%). There is no late grade 3 genitourinary or gastrointestinal toxicity to date. International Prostate Symptom Score and urinary QoL scores recovered to baseline by 6 months. Patient-reported outcomes showed no significant change in EQ-5D QoL scores at 12 weeks and 1 year. There are no cases of biochemical relapse reported to date.

CONCLUSIONS

CyberKnife SBRT-delivered dose of 36.25 Gy to the prostate with a simultaneous integrated boost up to 47.5 Gy is well tolerated. Acute and late genitourinary and gastrointestinal toxicity rates are comparable to other contemporary SBRT trials and series with focal boost.

The impact of transportation mode, socioeconomic deprivation and rurality on travel times to radiotherapy and surgical services for patients with prostate cancer: A national population-based evaluation

BACKGROUND

The distances that patients have to travel can influence their access to cancer treatment. We investigated the determinants of travel time, separately for journeys by car and public transport, to centres providing radical surgery or radiotherapy for prostate cancer.

METHODS

Using national cancer registry records linked to administrative hospital data, we identified patients who had radical surgery or radiotherapy for prostate cancer between January 2017 and December 2018 in the English National Health Service. Estimated travel times from the patients' residential area to the nearest specialist surgical or radiotherapy centre were estimated for journeys by car and by public transport.

RESULTS

We included 13,186 men who had surgery and 26,581 who had radiotherapy. Estimated travel times by public transport (74.4 mins for surgery and 69.4 mins for radiotherapy) were more than twice as long as by car (33.4 mins and 29.1mins, respectively). Patients living in more socially deprived neighbourhoods in rural areas had the longest travel times to the nearest cancer treatment centres by car (62.0 mins for surgery and 52.1 mins for radiotherapy). Conversely patients living in more affluent neighbourhoods in urban conurbations had the shortest (18.7 mins for surgery and 17.9 mins for radiotherapy).

CONCLUSION

Travel times to cancer centres vary widely according to mode of transport, socioeconomic deprivation, and rurality. Policies changing the geographical configuration of cancer services should consider the impact on the expected travel times both by car and by public transport to avoid enhancing existing inequalities in access to treatment and patient outcomes.

Joint radial trajectory correction for accelerated T2 * mapping on an MR-Linac

BACKGROUND

T2 * mapping can characterize tumor hypoxia, which may be associated with resistance to therapy. Acquiring T2 * maps during MR-guided radiotherapy could inform treatment adaptation by, for example, escalating the dose to resistant sub-volumes.

PURPOSE

The purpose of this work is to demonstrate the feasibility of the accelerated T2 * mapping technique using model-based image reconstruction with integrated trajectory auto-correction (TrACR) for MR-guided radiotherapy on an MR-Linear accelerator (MR-Linac).

MATERIALS AND METHODS

The proposed method was validated in a numerical phantom, where two T2 * mapping approaches (sequential and joint) were compared for different noise levels (0,0.1,0.5,1) and gradient delays ([1, -1] and [1, -2] in units of dwell time for x- and y-axis, respectively). Fully sampled k-space was retrospectively undersampled using two different undersampling patterns. Root mean square errors (RMSEs) were calculated between reconstructed T2 * maps and ground truth. In vivo data was acquired twice weekly in one prostate and one head and neck cancer patient undergoing treatment on a 1.5 T MR-Linac. Data were retrospectively undersampled and T2 * maps reconstructed, with and without trajectory corrections were compared.

RESULTS

Numerical simulations demonstrated that, for all noise levels, T2 * maps reconstructed with a joint approach demonstrated less error compared to an uncorrected and sequential approach. For a noise level of 0.1, uniform undersampling and gradient delay [1, -1] (in units of dwell time for x- and y-axis, respectively), RMSEs for sequential and joint approaches were 13.01 and 9.32 ms, respectively, which reduced to 10.92 and 5.89 ms for a gradient delay of [1, 2]. Similarly, for alternate undersampling and gradient delay [1, -1], RMSEs for sequential and joint approaches were 9.80 and 8.90 ms, respectively, which reduced to 9.10 and 5.40 ms for gradient delay [1, 2]. For in vivo data, T2 * maps reconstructed with our proposed approach resulted in less artifacts and improved visual appearance compared to the uncorrected approach. For both prostate and head and neck cancer patients, T2 * maps reconstructed from different treatment fractions showed changes within the planning target volume (PTV).

CONCLUSION

Using the proposed approach, a retrospective data-driven gradient delay correction can be performed, which is particularly relevant for hybrid devices, where full information on the machine configuration is not available for image reconstruction. T2 * maps were acquired in under 5 min and can be integrated into MR-guided radiotherapy treatment workflows, which minimizes patient burden and leaves time for additional imaging for online adaptive radiotherapy on an MR-Linac.

Radium-223 in metastatic castration-resistant prostate cancer: whole-body diffusion-weighted magnetic resonance imaging scanning to assess response

BACKGROUND

Radium-223 is a bone-seeking, ɑ-emitting radionuclide used to treat men with bone metastases from castration-resistant prostate cancer. Sclerotic bone lesions cannot be evaluated using Response Evaluation Criteria in Solid Tumors. Therefore, imaging response biomarkers are needed.

METHODS

We conducted a phase 2 randomized trial to assess disease response to radium-223. Men with metastatic castration-resistant prostate cancer and bone metastases were randomly allocated to 55 or 88 kBq/kg radium-223 every 4 weeks for 6 cycles. Whole-body diffusion-weighted magnetic resonance imaging (DWI) was performed at baseline, at cycles 2 and 4, and after treatment. The primary endpoint was defined as a 30% increase in global median apparent diffusion coefficient.

RESULTS

Disease response on DWI was seen in 14 of 36 evaluable patients (39%; 95% confidence interval = 23% to 56%), with marked interpatient and intrapatient heterogeneity of response. There was an association between prostate-specific antigen response and MRI response (odds ratio = 18.5, 95% confidence interval = 1.32 to 258, P = .013). Mean administered activity of radium-223 per cycle was not associated with global MRI response (P = .216) but was associated with DWI response using a 5-target-lesion evaluation (P = .007). In 26 of 36 (72%) patients, new bone metastases, not present at baseline, were seen on DWI scans during radium-223 treatment.

CONCLUSIONS

DWI is useful for assessment of disease response in bone. Response to radium-223 is heterogeneous, both between patients and between different metastases in the same patient. New bone metastases appear during radium-223 treatment.The REASURE trial is registered under ISRCTN17805587.

Use of Focal Radiotherapy Boost for Prostate Cancer and Perceived Barriers toward its Implementation: A Survey

PURPOSE/OBJECTIVE(S)

In a recent phase III randomized control trial (FLAME), delivering a focal radiotherapy (RT) boost to tumors visible on MRI was shown to improve outcomes for prostate cancer patients without increasing toxicity. The aim of this study was to assess how widely this technique is being applied in current practices worldwide as well as physicians' perceived barriers toward its implementation.

MATERIALS/METHODS

An online survey assessing the use of intraprostatic focal boost was conducted in December 2022 and February 2023. The survey link was distributed to radiation oncologists worldwide via email list, group text platform, and social media. Survey questions included how many prostate cancer cases participants treat in a typical month; how often they use focal boost, if at all; the degree to which their practice is genitourinary (GU)-subspecialized; main barriers to implementing focal boost more often in their practice; and demographic information. Subgroup analyses were also conducted for participants from high-income or low-to-middle-income countries, as defined by the World Bank.

RESULTS

The survey initially collected 205 responses from various countries over a two-week period in December 2022. The survey was then reopened for one week in February 2023 to allow for more participation, leading to a total of 263 responses. The highest-represented countries were the United States (42%), Mexico (13%), and the United Kingdom (8%). The majority of respondents worked at an academic medical center (52%) and considered their practice to be at least partially GU-subspecialized (74%). 57% of participants overall reported not routinely using intraprostatic focal boost. Even among complete subspecialists, a substantial proportion (39%) do not routinely use focal boost. Less than half of participants in both high-income and low-to-middle-income countries were shown to routinely use focal boost. Perceived barriers to implementation are shown in Table 1.

CONCLUSION

Despite the promising level 1 results of the FLAME trial, many radiation oncologists worldwide are not routinely offering focal RT boost. Adoption of this technique might be accelerated by increased access to high-quality MRI, better registration algorithms of MRI to CT simulation images, physician education on benefit-to-harm ratio, automated planning algorithms, and physician training on contouring prostate lesions on MRI.

The Association between Acute and Late Genitourinary and Gastrointestinal Toxicities: An Analysis of the PACE B Study

PURPOSE/OBJECTIVE(S)

Acute gastrointestinal (GI) and genitourinary (GU) toxicity after prostate radiotherapy (RT) has been shown to be associated with late toxicity with 3D conformal RT. However, whether this association is present with modern approaches, such as stereotactic body radiotherapy (SBRT), remains unclear. We analyzed patients treated within the international phase III non-inferiority randomized control trial, PACE-B, to assess the association between acute and late toxicity following SBRT and conventional/moderately hypofractionated radiotherapy (CRT). We hypothesize that acute toxicity is significantly associated with equivalent late toxicity following prostate SBRT and CRT.

MATERIALS/METHODS

We analyzed patients with GI and GU Common Terminology Criteria for Adverse Events (CTCAE) measurements in the acute (≤12 weeks post-RT) and late period (6-24 months post-RT). Using logistic regression, we analyze the association between G2+ acute GI and GU toxicities with equivalent late toxicities. Lasso variable selection was used to determine patient, tumor and treatment variables to include in the multivariable model. The area under the receiver operator characteristics curve (AUC) was used to evaluate the model's predictive performance.

RESULTS

Of patients included in this analysis (n = 842), 414 were treated with SBRT and 428 with CRT. In univariable analysis (UVA), G2+ acute GU toxicity was significantly associated with developing G2+ late GU toxicity after SBRT (OR 4.63, 95% CI (2.96-7.25), p<0.0001) and CRT (OR 2.83, 95% CI (1.69-4.71), p<0.0001). This association remained significant in multivariable analysis (MVA). The models AUC for predicting G2+ late GU toxicity after SBRT was 0.73 (95% CI, 0.67-0.78) and 0.66 (95% CI, 0.59-0.73) following CRT. In UVA, G2+ acute GI toxicity was associated with developing G2+ late GI toxicity after SBRT (OR 3.67, 95% CI (1.91-7.03), p <0.0001) and CRT (OR 4.4, 95% CI (2.04-9.47), p<0.0001). This association also remained significant in MVA. The models AUC for predicting G2+ late GI toxicity after SBRT was 0.66 (0.95% CI, 0.57-0.75) and 0.64 (95% CI, 0.57-0.72) following CRT. In UVA analysis, G2+ baseline GU symptoms were also associated with developing G2+ late GU toxicity after SBRT (OR 7.59, 95% CI (2.72-21.19, p<0.0001) and CRT (OR 7.98, 95% CI (3.03-20.96), p<0.0001), and this continued to be significant in MVA. Acute toxicity remained associated with persistent late toxicity (≥2 G2+ late events) and late toxicity 12-24 months.

CONCLUSION

Our study demonstrates an independent association between acute and late GU/GI toxicity in patients treated with SBRT and CRT for localized prostate cancer. Recognizing those at risk of late toxicity can provide an opportunity for early intervention to improve outcomes. G2+ acute toxicity should be considered an essential variable for predicting late GI/GU toxicity after prostate RT.

Validating a Simple Urethra Surrogate Model to Facilitate Dosimetric Analysis to Predict Genitourinary Toxicity

PURPOSE/OBJECTIVE(S)

The urethra may be a critical structure in prostate radiotherapy planning as some studies have shown that higher urethral dose correlates with worse genitourinary (GU) toxicity. Identifying the urethra requires an MRI planning scan or foley catheter insertion at CT planning. Most surrogates have been developed and validated against the urethra identified by a foley catheter. However, the urethral position can shift with catheter placement. We, therefore, aim to validate a simple urethra surrogate model against MRI-defined urethra. The surrogate model can be used to correlate urethra dose-volume parameters (DVP) with late GU toxicity and to apply urethral constraints in those with a CT-only based workflow.

MATERIALS/METHODS

Thirty-nine MRI-defined urethras from patients in the PACE-C trial were assessed to determine the average position of the urethra in the midline sagittal prostate plane along the ¼ gland, midgland, ¾ gland, apex and 3mm below apex. Using these average positions, a Python script was developed, which places a 10mm diameter circle in the 1/4 gland, midgland, ¾ gland, apex and 3mm below the apex. The observer manually contours a 10mm circle at the prostate base (prostate-bladder neck interface) to infer the urethra position and interpolates the contours. The urethra surrogate model was compared against 20 MRI-defined urethras (within the treatment PTV) in patients treated with 36.25Gy in 5 fractions as part of the PACE-B trial. To assess the surrogate's geometric performance, the Dice similarity coefficient (DSC), Hausdorff distance (HD), mean surface distance to agreement (MDTA) and the percentage of MRI-defined urethra outside the surrogate (UOS) were calculated. The surrogate model's dosimetric performance was assessed by comparing the mean D99, D98, average dose, D50, D2 and D1 using a paired t-test. The D(n) is the dose (Gy) to (n)% of the urethra.

RESULTS

The median results were: DSC 0.36 (IQR 0.28-0.42), HD 0.88cm (IQR, 0.70-1.04), MDTA 0.24cm (IQR, 0.21-0.28), UOS 29% (IQR, 17-52%). When comparing DVP between the MRI-defined urethra and surrogate urethra, the mean D99, D98 and D95 as 38.8Gy vs 39.1Gy (p = 0.17), 39.3Gy vs 39.5Gy (p = 0.23), 40.1Gy vs 40.4Gy (p = 0.21), respectively. The mean D50, average dose, D2 and D1 was 41.8Gy vs 41.9Gy (p = 0.03), 41.7 vs 41.8Gy (p = 0.04), 42.9Gy vs 43.0Gy (p = 0.05) and 43.0Gy vs 43.1Gy (p = 0.03), respectively.

CONCLUSION

While there were geometric differences between the surrogate urethra and MRI-defined urethra, there was no statistically significant difference between most urethral dose-volume parameters (D99, D98, D95, and D1). Similarly, the actual differences in urethra DVP were not clinically significant. This surrogate model could be validated in a larger cohort and then used to estimate the urethra position on CT planning scans for dosimetric analysis in those without an MRI planning scan or urinary catheter.

Individual Patient Data Analysis of 17 Randomized Trials vs. Real-World Data for Men with Localized Prostate Cancer Receiving Radiotherapy

PURPOSE/OBJECTIVE(S)

Prior work has demonstrated poor correlation between the results of randomized controlled trials (RCTs) and real-world evidence (RWD). However, patients enrolled in RCTs are often considered to poorly represent the real-world population. Herein, we utilize multiple large data repositories to determine differences in baseline characteristics and long-term outcomes between patients enrolled in RCTs and RWD that received radiotherapy for localized prostate cancer.

MATERIALS/METHODS

Meta-Analysis of Randomized trials in Cancer of the Prostate (MARCAP) Consortium was leveraged, and 17 phase III randomized trials were included. RWD were accessed through the Staging Collaboration for Cancer of the Prostate (STAR-CAP) cohort, a cohort that is comprised of >60 centers across the United States and Europe. Additionally, RWD was assessed via the Surveillance, Epidemiology, and End Results (SEER) database. MARCAP and STAR-CAP both contain outcomes for distant metastasis (DM), metastasis-free survival (MFS), prostate cancer-specific mortality (PCSM), and overall survival (OS). SEER only contains PCSM and OS. Wilcoxon signed-rank test and chi-square test were used to compare continuous and categorical variables, respectively. Inverse probability of treatment weighting (IPTW) analysis was conducted, balancing for age, PSA, Gleason score, T stage, and treatment year in the three cohorts. Cox and Fine-Gray regression models were used to compare disease outcomes between RCTs vs. RWD.

RESULTS

Data from 10,666 patients from RCTs, 6,530 patients in STAR-CAP, and 117,586 patients in SEER were included. SEER patients were slightly younger (p<0.001, median age 68 (IQR 62-73) than those in RCTs (70, IQR 65-74) and in STAR-CAP (70, IQR 64-74). 10-year OS in RCTs was 65.4%, STAR-CAP 70.2%, SEER 64.1%. OS was superior in STAR-CAP (RCTs as reference; HR 0.91, 95% CI 0.85-0.96, p<0.0001), but there was no significant difference between SEER and RCTs (HR 0.96, 95% CI 0.91-1.02, p = 0.22). 10-year PCSM cumulative incidence was 7.4% in RCTs, 8.1% in STAR-CAP, and 11.0% in SEER. There was no significant difference in PCSM between STAR-CAP RWD and RCTs (HR 0.88, 95% CI 0.78-1.01, p = 0.08), whereas PCSM was worse in SEER than RCTs (HR 1.37, 95% CI 1.21-1.55, p<0.0001). There was no significant difference in DM between STAR-CAP RWD and RCTs (HR 0.93, 95% CI 0.83-1.04, p = 0.2).

CONCLUSION

While baseline differences exist in patients enrolled on localized prostate cancer RCTs and real-world datasets, there were small if any significant relative differences in oncologic outcomes. This provides reassurance that RCT results are generally applicable to patients in routine practice.

Quality of Life in Prostate Cancer Patients Undergoing Daily Adaptive Versus Non-Adaptive Radiation Therapy Utilizing A 1.5 Tesla MR-Linac

PURPOSE/OBJECTIVE(S)

Using adaptive radiation therapy (ART) physicians can re-contour normal organs (such as bladder and rectum) before each fraction. While ART may result in more reliable dosimetry to regional organs at risk, the process is time consuming and more expensive than non-ART. We evaluated differences in patient reported quality of life (PR-QOL) between daily ART and non- ART.

MATERIALS/METHODS

Patients with prostate cancer from 3 centers in the Netherlands and United States were treated using a 1.5 Tesla MR Linear accelerator. Patients consented to the Multiple Outcome Evaluation of Radiation Therapy Using the MR-Linac Study (MOMENTUM, NCT04075305) between 2019 and 2022. PR-QOL was prospectively collected using the EORTC QLQ-C30 and PR-25 at baseline (before RT), and at 3 and 6 months after RT. Patients without complete QOL data were excluded. QOL differences were compared between patients undergoing daily ART vs. non-ART. A linear mixed effect model was performed to account for repeated measurements. Analyses were performed using R Studio.

RESULTS

One hundred thirty-six patients underwent RT with QOL were analyzed. Median follow up was 13 months (6-26 months). Patients were treated without daily ART (n = 94) or with daily ART (n = 42). The median age was 70 (range 53-83) years and 65.4% had intermediate risk disease, 35% of patients received hormonal therapy. Fractionation schedules included 36 Gy/6 (n = 16), 36.25 Gy/5 (n = 103), 60 Gy/20 (n = 6), 62 Gy/20 (n = 8), and 70 Gy/28 (n = 3). Compared to baseline scores, EORTC QLQ C30 diarrhea scores at 6 months post-treatment were significantly worse for patients treated without daily ART compared to those treated with daily ART (p < 0.05). Other QLQ PR25 bowel scores were not significantly different at 3 or 6 months. Both PR25 urinary and treatment-related symptoms were improved with daily ART compared to non-ART at the 3 (p < 0.001 and p < 0.01, respectively) and 6 (p < 0.01 and p < 0.001, respectively) month time points. Magnitude of improvements can be found in Table 1.

CONCLUSION

Among prostate cancer patients treated using 1.5 Tesla MRI-guided RT, daily ART was associated with improved PR-QOL in urinary and bowel domains compared to non-ART. These hypotheses generating preliminary results provide the first indications (to our knowledge) that adapting contours to daily anatomy may improve short-term urinary and bowel PR-QOL. Updated results will be presented at ASTRO 2023.

Evolution of the MOMENTUM Study for Evidence-Based Implementation of MR-Guided Radiotherapy Using the 1.5 Tesla MR-Linac

PURPOSE/OBJECTIVE(S)

The international prospective 'Multiple Outcome Evaluation of Radiation Therapy Using the MR-Linac' (MOMENTUM) study (NCT04075305) was initiated in 2019 by seven hospitals and industry partner precision radiation medicine company, with the aim to facilitate evidence-based implementation of magnetic resonance (MR) guided radiotherapy using the 1.5 Tesla (T) MR-linear accelerator (Linac). Over the last four years, MOMENTUM has expanded to other institutions and the design and organization of MOMENTUM have evolved. Herein, we give an overview of the current status of MOMENTUM and study innovations that have been implemented to accelerate development and assessment of the 1.5T MR-Linac.

MATERIALS/METHODS

We summarized operational outputs of MOMENTUM, including site participation, data aggregation, academic output, and study design elements that have been introduced since 2019.

RESULTS

As of January 2023, 17 sites have joined and 10 sites are actively enrolling patients in MOMENTUM. The MOMENTUM infrastructure, which consists of prospectively collected clinical and technical patient data and patient reported outcomes, is increasingly being used for predicate studies, technical development studies, safety and early clinical evaluation, and hypothesis testing studies according to R-IDEAL. Over 3500 patients who received treatment for 33 different tumor sites have provided informed consent for using their data for scientific research and product development. The technical database currently includes over 190.000 items, including approximately 98,000 MRI scans and 33,800 dose plans. A total of 38 data requests have been accepted (2019: n = 1; 2020: n = 5; 2021: n = 10; 2022: n = 22), including technical studies focused on algorithmic development. The MOMENTUM infrastructure is also hosting prospective clinical studies, including the randomized HERMES trial (NCT04595019) and prospective UNITED study (NCT04726397). Recently, the 'Trials within Cohorts' (TwiCs) design has been implemented, which is well suited to perform pragmatic randomized trials. MOMENTUM has partnered with Kaiku Health, an electronic patient-reported outcomes application, to facilitate collection of patient reported toxicity.

CONCLUSION

Over the past four years, the MOMENTUM study has evolved into a unique platform, whose infrastructure is increasingly being used by clinicians, researchers, physicists and industry. Continuous efforts are being made to encourage the participation of new sites and the development of innovative tools to facilitate the conduct of well-designed trials that are expected to transform daily clinical practice.

Is the Motion Causing a Commotion? Two-Fraction Prostate SBRT on the MR-Linac

PURPOSE/OBJECTIVE(S)

In HERMES (NCT04595019) men with localized prostate cancer are treated on the Unity MR-Linac platform (MRL, Elekta AB, Stockholm) and randomized between stereotactic body radiotherapy (SBRT) with 36.25 Gy in 5 fractions and 24 Gy in 2 fractions. Patients randomized to two fractions receive 24 Gy to the high risk PTV, 20 Gy to the low risk PTV and a boost of 27 Gy to the dominant intraprostatic lesion. This study explores dose received by the target and organs at risk (OARs) when considering intrafraction motion in two fraction SBRT.

MATERIALS/METHODS

Targets and OARs were delineated and a reference plan generated on Monaco v5.40.01 (Elekta). An Adapt-to-Shape (ATS) workflow was used. Contours were propagated to the session MRI (MRIsession) and edited accordingly. Prior to delivery, a verification MRI (MRIverif) was acquired with baseline shifts corrected for using the Adapt-to-Position (ATP-of-ATS) workflow. A post treatment MRI (MRIpost) was acquired after delivery. Men in the 2-fraction arm received each fraction in 2 sub-fractions sequentially on the same day, to mitigate intrafraction motion. The plans of 5 men receiving 2 fraction SBRT were analyzed. The targets, urethra, bladder and rectum were recontoured on the MRIverif and MRIpost. Delivered plans were recalculated on the corresponding MRIverif and MRIpost. The percentage of optimal and mandatory target dose constraints met were calculated. Accumulated OAR doses were calculated by averaging their respective dose statistics across all sub-fractions, conservatively assuming that the same area of the OAR receives the maximum dose each fraction. Analysis was carried out separately for MRIverif and MRIpost as the true 'delivered dose' most likely lies between these two estimates.

RESULTS

There was good coverage across all fractions. The mandatory constraints of CTVpsv V24.0 Gy > 95% and CTVsv V20.0 Gy > 95% were met in 100% of fractions and V2700cGy > 95% in 90% on the MRIpost. Table 3 shows OAR dose.

CONCLUSION

This work demonstrates that target coverage is good, even for the GTV where no margin is applied. With our conservative dose calculation approach, we found dose constraints are exceeded for some patients. However, treatment has been well tolerated, suggesting that that our current dose constraints may be cautious. Once Elekta's True Tracking and automated gating software is implemented at our center we will be able to further improve OAR clinical goal compliance.

Recommendations for improved reproducibility of ADC derivation on behalf of the Elekta MRI-linac consortium image analysis working group

BACKGROUND AND PURPOSE

The apparent diffusion coefficient (ADC), a potential imaging biomarker for radiotherapy response, needs to be reproducible before translation into clinical use. The aim of this study was to evaluate the multi-centre delineation- and calculation-related ADC variation and give recommendations to minimize it.

MATERIALS AND METHODS

Nine centres received identical diffusion-weighted and anatomical magnetic resonance images of different cancerous tumours (adrenal gland, pelvic oligo metastasis, pancreas, and prostate). All centres delineated the gross tumour volume (GTV), clinical target volume (CTV), and viable tumour volume (VTV), and calculated ADCs using both their local calculation methods and each of the following calculation conditions: b-values 0-500 vs. 150-500 s/mm2, region-of-interest (ROI)-based vs. voxel-based calculation, and mean vs. median. ADC variation was assessed using the mean coefficient of variation across delineations (CVD) and calculation methods (CVC). Absolute ADC differences between calculation conditions were evaluated using Friedman's test. Recommendations for ADC calculation were formulated based on observations and discussions within the Elekta MRI-linac consortium image analysis working group.

RESULTS

The median (range) CVD and CVC were 0.06 (0.02-0.32) and 0.17 (0.08-0.26), respectively. The ADC estimates differed 18% between b-value sets and 4% between ROI/voxel-based calculation (p-values < 0.01). No significant difference was observed between mean and median (p = 0.64). Aligning calculation conditions between centres reduced CVC to 0.04 (0.01-0.16). CVD was comparable between ROI types.

CONCLUSION

Overall, calculation methods had a larger impact on ADC reproducibility compared to delineation. Based on the results, significant sources of variation were identified, which should be considered when initiating new studies, in particular multi-centre investigations.

PACE-A: An international phase 3 randomised controlled trial (RCT) comparing stereotactic body radiotherapy (SBRT) to surgery for localised prostate cancer (LPCa)—Primary endpoint analysis

298

Background: People presenting with early-stage LPCa have several treatment options. There is therapeutic equipoise with lack of randomised evidence for superiority of radiotherapy or surgery. PACE-A aimed to determine if there is improved quality of life (QoL) following SBRT compared to surgery. Methods: PACE (NCT01584258) is a phase 3 open-label multiple-cohort RCT. In PACE-A, people with LPCa, T1-T2, Gleason≤3+4, PSA≤20ng/mL & suitable for surgery were randomised (1:1) to SBRT or surgery. SBRT dose was 36.25Gy/5 fractions in 1-2 weeks; surgery was laparoscopic or robotically assisted prostatectomy. Androgen deprivation was not permitted. Co-primary endpoints were patient reported outcomes (PROs) of Expanded Prostate Index Composite (EPIC-26) questionnaire number of absorbent pads per day & EPIC bowel subdomain score at 2 years. Target sample size was 234 participants (pts) to detect 9% difference in urinary incontinence (80% power, 5% 2-sided alpha) & 5-point difference in mean bowel subdomain score (90% power, 5% 2-sided alpha) with higher EPIC score (range 0-100) indicating better QoL. Secondary endpoints included clinician reported toxicity and additional PROs (1% significance level). Analysis is by treatment received. Results: From Aug 2012 to Feb 2022, 123 men from 10 UK centres were randomised. The IDMC advised stopping recruitment after a 2-year gap in during COVID. Pts had median age 66years (IQR: 61, 69), median PSA 8ng/ml (6, 11) with 52% tumours ≥T2b and 79% Gleason 3+4; 93% pts were of white race. 58/63 pts received SBRT as allocated (2 received surgery, 2 unknown, 1 withdrawn); 48/60 received surgery as allocated (1 received SBRT, 3 received CRT, 2 unknown, 6 withdrawn). 8 laparoscopic and 42 robotic assisted operations were performed. Median follow-up is 50 months (IQR 41, 74). At 2 years, fewer SBRT pts reported use of urinary pads: 2/43 (4.5%) vs 15/32 (46.9%), p<0.001. SBRT pts had significantly worse bowel subdomain score (mean (SD) 88.4 (12.7) vs 97.3 (5.5), p<0.001). 7/45 (15.6%) SBRT and 0/31 (0%) surgery pts reported moderate/big problem with bowel symptoms (p=0.04). SBRT pts reported less EPIC sexual subdomain score (58.0 (31.9) vs 29.3 (20.5), p<0.001); there was no evidence of a difference in urinary subdomain score (85.5 (19.8) vs 80.5 (20.8), p=0.29). At 2 years, CTCAE genitourinary grade 2 or higher(G2+) toxicity was seen in 5/54 (9.3%) SBRT vs 4/42 (9.5%) surgery pts (p=0.97); there was no G2+ gastrointestinal (GI) events seen in either group. Conclusions: PACE-A contributes the first randomised data to the comparison of SBRT with surgery in LPCa providing PRO data relevant to informed decision making. Compared to surgery, pts receiving SBRT had better urinary continence & sexual bother score; clinician reported GI toxicity was low but SBRT pts reported more bowel bother at 2 years. Clinical trial information: NCT01584258 .

10-Year efficacy and co-morbidity outcomes of a phase III randomised trial of conventional vs. hypofractionated high dose intensity modulated radiotherapy for prostate cancer (CHHiP; CRUK/06/016)

304

Background: Five-year results from the CHHiP trial indicated that moderate hypofractionation of 60 Gray (Gy)/20 fractions (f) was non-inferior to 74Gy/37f (Lancet Oncology, 2016). Reporting of long-term efficacy and side effects is essential in a patient population that remain at risk of recurrence years after treatment. Here we report specific co-morbidity data collected at 10 years and an update of efficacy. Methods: Between October 2002 and June 2011, 3216 men with node negative T1b-T3a localised prostate cancer with risk of seminal vesical involvement ≤30% were randomised (1:1:1 ratio) to 74Gy/37f (control), 60Gy/20f or 57Gy/19f. Patients received 3-6 months of androgen deprivation prior to radiotherapy. The primary endpoint was time to biochemical failure (Phoenix consensus guidelines) or clinical failure (BCF). The non-inferiority design specified a critical hazard ratio (HR) of 1.208 for each hypofractionated schedule compared to control. Data on specific radiotherapy related co-morbidities were collected at 10-year follow-up and are presented as frequency and percentages. Analysis was by intention-to-treat; HRs quoted are unadjusted. Results: With a median follow up of 12.1 years, 10-year BCF-free rates (95% CI) were 74Gy: 76.0% (73.1%, 78.6%); 60Gy: 79.8% (77.1%, 82.3%) and 57Gy: 73.4% (70.5%, 76.1%). For 60Gy/20f, non-inferiority was confirmed: HR60=0.84 (90% CI 0.72, 0.97) with borderline significance for superiority (HR=0.84 (95% CI 0.70, 1.00). As in the primary analysis, for 57Gy/19f, non-inferiority could not be declared: HR57=1.13 (90% CI 0.98, 1.30). 10-year overall survival (95% CI) was 78.5% (75.9%, 81.0%), 82.9% (80.4%, 85.0%) and 79.9% (77.3%, 82.2%) in the 74Gy, 60Gy and 57Gy groups. Bone fractures were reported in 2% (15/700), 2% (19/771) and 3% (22/719) of patients in the 74Gy, 60Gy and 57Gy groups respectively at 10 years. The most common intervention reported was a sigmoidoscopy with 12% (79/681), 8% (60/739) and 9% (65/702) in the 74Gy, 60Gy and 57Gy groups respectively. Of those patients who underwent a sigmoidoscopy it was due to symptoms for 81% (63/78) 81% (48/59) and 85% (55/65) of patients in the 74Gy, 60Gy and 57Gy group respectively. Frequencies of all other pre-specified co-morbidities or related interventions (ureteric obstruction, bowel strictures, trans-urethral resection of prostate, urethrotomy, urethral dilatation or long term catheterisation or treatment of proctopathy with steroid, sucralfate, formalin, laser coagulation or rectal diversion) were <1% in all groups. Conclusions: With a median follow-up of 12 years, oncological outcomes following 60Gy/20f continue to be non-inferior to those with 74Gy/37f. Late co-morbidities were very low across all treatment groups. These data support the long-term safety of moderate hypofractionation. Clinical trial information: 97182923 .

Impact of centralization of prostate cancer services on the choice of radical treatment

OBJECTIVE

To assess the impact of centralization of prostate cancer surgery and radiotherapy services on the choice of prostate cancer treatment.

PATIENTS AND METHODS

This national population-based study used linked cancer registry data and administrative hospital-level data for all 16 621 patients who were diagnosed between 1 January 2017 and 31 December 2018 with intermediate-risk prostate cancer and who underwent radical prostatectomy (RP) or radical radiation therapy (RT) in the English National Health Service (NHS). Travel times by car to treating centres were estimated using a geographic information system. We used logistic regression to assess the impact of the relative proximity of alternative treatment options on the type of treatment received, with adjustment for patient characteristics.

RESULTS

Of the 78 NHS hospitals that provide RT or RP for prostate cancer, 41% provide both, 36% provide RT and 23% provide RP. Compared to patients who had both treatment options available at their nearest centre where overall 57% of patients received RT and 43% RP, patients were less likely to receive RT if their nearest centre offered RP only and the extra travel time to a hospital providing RT was >15 min (52% of patients received RT and 48% RP%, odds ratio [OR] 0.70 (0.58-0.85); P < 0.001). Conversely, patients were more likely to receive RT if their nearest centre offered RT and the extra travel time to a hospital providing RP was >15 min (63% of patients received RT and 37% RP, OR 1.23 (1.08-1.40); P < 0.001). There was a negligible impact on the type of treatment received if centres providing alternative treatment options were ≤15-min travel time from each other.

CONCLUSION

The relative proximity of prostate cancer treatment options to a patient's residence is an independent predictor for the type of radical treatment received. Centralization policies for prostate cancer should not focus on one treatment modality but should consider all treatments to avoid a negative impact on treatment choice.

MRI-guided adaptive radiotherapy for prostate cancer: When do we need to account for intra-fraction motion?

A shift of the daily plan can mitigate target position changes that occur between daily MR acquisition and treatment for MR-linac radiotherapy, but increases the session time. We demonstrated that our workflow strategy and decision-making process, to determine whether a subsequent shift is necessary, is appropriate.

PEARLS - A multicentre phase II/III trial of extended field radiotherapy for androgen sensitive prostate cancer patients with PSMA-avid pelvic and/or para-aortic lymph nodes at presentation

PEARLS is a multi-stage randomised controlled trial for prostate cancer patients with pelvic and/or para-aortic PSMA-avid lymph node disease at presentation. The aim of the trial is to determine whether extending the radiotherapy field to cover the para-aortic lymph nodes (up to L1/L2 vertebral interspace) can improve outcomes for this patient group.

Nonrandomized Comparison of Efficacy and Side Effects of Bicalutamide Compared With Luteinizing Hormone-Releasing Hormone (LHRH) Analogs in Combination With Radiation Therapy in the CHHiP Trial

PURPOSE

CHHiP is a randomized trial evaluating moderately hypofractionated radiation therapy for treatment of localized prostate cancer. Of all participants, 97% of them had concurrent short-course hormone therapy (HT), either luteinizing hormone-releasing hormone analog (LHRHa) or 150 mg of bicalutamide daily. This exploratory analysis compares efficacy and side effects in a nonrandomized comparison.

METHODS AND MATERIALS

In our study, 2700 patients received LHRHa and 403 received bicalutamide. The primary endpoint was biochemical/clinical failure. Groups were compared with Cox regression adjusted for various prognostic factors and stratified by radiation therapy dose. A key secondary endpoint was erectile dysfunction (ED) assessed by clinicians (using scores from Late Effects on Normal Tissues: Subjective/Objective/Management [LENT-SOM] subjective erectile function for vaginal penetration) and patients (single items within the University of California-Los Angeles Prostate Cancer Index [UCLA PCI] and Expanded Prostate Cancer Index Composite [EPIC]-50 questionnaires) at 2 years and compared between HT regimens by χ2 trend test.

RESULTS

Bicalutamide patients were significantly younger (median 67 vs 69 years LHRHa). Median follow-up was 9.3 years. There was no difference in biochemical or clinical failure with an adjusted hazard ratio or 0.97 (95% confidence interval, 0.77-1.23; P = .8). At 2 years, grade ≥2 LENT-SOM ED was reported in significantly more LHRHa patients (313 out of 590; 53%) versus bicalutamide (17 out of 68; 25%) (P < .0001). There were no differences in ED seen with UCLA-PCI and EPIC-50 questionnaires.

CONCLUSIONS

In this nonrandomized comparison, there was no evidence of a difference in efficacy according to type of HT received. Bicalutamide preserved clinician assessed (LENT-SOM) erectile function at 2 years but patient-reported outcomes were similar between groups.

UK 2022 Consensus on Normal Tissue Dose-Volume Constraints for Oligometastatic, Primary Lung and Hepatocellular Carcinoma Stereotactic Ablative Radiotherapy

The use of stereotactic ablative radiotherapy (SABR) in the UK has expanded over the past decade, in part as the result of several UK clinical trials and a recent NHS England Commissioning through Evaluation programme. A UK SABR Consortium consensus for normal tissue constraints for SABR was published in 2017, based on the existing literature at the time. The published literature regarding SABR has increased in volume over the past 5 years and multiple UK centres are currently working to develop new SABR services. A review and update of the previous consensus is therefore appropriate and timely. It is hoped that this document will provide a useful resource to facilitate safe and consistent SABR practice.

MR-guided radiotherapy for prostate cancer: state of the art and future perspectives

Advances in radiotherapy technology have increased precision of treatment delivery and in some tumour types, improved cure rates and decreased side effects. A new generation of radiotherapy machines, hybrids of an MRI scanner and a linear accelerator, has the potential to further transform the practice of radiation therapy in some cancers. Facilitating superior image quality and the ability to change the dose distribution online on a daily basis (termed "daily adaptive replanning"), MRI-guided radiotherapy machines allow for new possibilities including increasing dose, for hard to treat cancers, and more selective sparing of healthy tissues, where toxicity reduction is the key priority.These machines have already been used to treat most types of cancer, although experience is still in its infancy. This review summarises the potential and current evidence for MRI-guided radiotherapy, with a predominant focus on prostate cancer. Current advantages and disadvantages are discussed including a realistic appraisal of the likely potential to improve patient outcomes. In addition, horizon scanning for near-term possibilities for research and development will hopefully delineate the potential role for this technology over the next decade.

PEARLS: A multicenter phase II/III trial of extended field radiotherapy for androgen-sensitive prostate cancer patients with PSMA‐avid pelvic and para-aortic lymph nodes at presentation

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Background: Optimal management for lymph node (LN) positive prostate cancer has not yet been determined. With the emerging role of PSMA-PET/CT in diagnostic staging, identification of this disease status is increasing. The superior border for prostate nodal radiotherapy is variable across different centres. PEARLS (CRUK/19/016) aims to show that extending the radiotherapy field to cover the para-aortic LN (up to L1/L2 vertebral interspace) can improve outcomes for prostate cancer patients with PSMA-avid pelvic LN at presentation. The trial is registered: ISRCTN36344989. Methods: PEARLS is a multi‐stage randomised controlled trial. Men with histologically confirmed prostate cancer with PSMA‐avid nodal disease within the pelvis +/‐ para‐aortic region receiving androgen deprivation therapy +/‐ androgen receptor targeted therapy or docetaxel chemotherapy are eligible. Two cohorts defined by extent of LN disease determined by PSMA‐PET/CT will be recruited: cohort A (pelvic LN at or below the L4/L5 vertebral interspace) and cohort B (para-aortic LN below L1/L2 vertebral interspace). Patients are randomly allocated (1:1) to standard field (dependent on cohort) intensity modulated radiotherapy (IMRT) (control) or extended-field IMRT (experimental) in 20 fractions over 4 weeks. In the control group, cohort A will receive 60Gy to the prostate and 44Gy to the pelvis with an integrated boost of 51Gy to PSMA-avid LN and cohort B will receive 60Gy to the prostate only. In the experimental group, participants in both cohorts will receive 60Gy to the prostate and 44Gy to the pelvis and para‐aortic region with an integrated boost of 51Gy to involved LN. In phase II, the primary endpoint is lower gastrointestinal RTOG grade 2+ toxicity at week 18 from start of radiotherapy. Assuming acceptable toxicity in the first 75 participants receiving extended-field IMRT, the study will move to phase III where the primary endpoint is metastasis‐free survival. The trial aims to recruit 714 patients with pelvic LN to detect a hazard ratio of 0.62 in favour of extended-field IMRT and a further 179 patients with para‐aortic LN disease. The trial was launched in the UK on 25 June 2021. Phase II will be conducted in 20 NHS Trusts across the UK. Clinical trial information: ISRCTN36344989.

Magnetic resonance linear accelerator technology and adaptive radiation therapy: An overview for clinicians

Radiation therapy (RT) continues to play an important role in the treatment of cancer. Adaptive RT (ART) is a novel method through which RT treatments are evolving. With the ART approach, computed tomography or magnetic resonance (MR) images are obtained as part of the treatment delivery process. This enables the adaptation of the irradiated volume to account for changes in organ and/or tumor position, movement, size, or shape that may occur over the course of treatment. The advantages and challenges of ART maybe somewhat abstract to oncologists and clinicians outside of the specialty of radiation oncology. ART is positioned to affect many different types of cancer. There is a wide spectrum of hypothesized benefits, from small toxicity improvements to meaningful gains in overall survival. The use and application of this novel technology should be understood by the oncologic community at large, such that it can be appropriately contextualized within the landscape of cancer therapies. Likewise, the need to test these advances is pressing. MR-guided ART (MRgART) is an emerging, extended modality of ART that expands upon and further advances the capabilities of ART. MRgART presents unique opportunities to iteratively improve adaptive image guidance. However, although the MRgART adaptive process advances ART to previously unattained levels, it can be more expensive, time-consuming, and complex. In this review, the authors present an overview for clinicians describing the process of ART and specifically MRgART.

Fracture Risk in Men with Metastatic Prostate Cancer Treated With Radium-223

BACKGROUND

Radium-223 is a bone-seeking, alpha-emitting radionuclide used in metastatic castration-resistant prostate cancer (mCRPC). Radium-223 increases the risk of fracture when used in combination with abiraterone and prednisolone. The risk of fracture in men receiving radium-223 monotherapy is unclear.

PATIENTS AND METHODS

This was a prospective, multicenter phase II study of radium-223 in 36 men with mCRPC and a reference cohort (n = 36) matched for fracture risk and not treated with radium-223. Bone fractures were assessed using whole-body magnetic resonance imaging. The primary outcome was risk of new fractures.

RESULTS

Thirty-six patients were treated with up to six 4-week cycles of radium-223. With a median follow-up of 16.3 months, 74 new fractures were identified in 20 patients. Freedom from fracture was 56% (95% confidence interval, 35.3-71.6) at 12 months. On multivariate analysis, prior corticosteroid use was associated with risk of fracture. In the reference cohort (n = 36), 16 new fractures were identified in 12 patients over a median follow-up of 24 months. Across both cohorts, 67% of all fractures occurred at uninvolved bone.

CONCLUSIONS

Men with mCRPC, and particularly those treated with radium-223, are at risk of fracture. They should receive a bone health agent to reduce the risk of fragility fractures.

Imaging features of the evolving patterns of metastatic prostate cancer

The pattern of metastases in prostate cancer (PC) is evolving. Increased use of imaging, newer imaging techniques with higher sensitivity for disease detection and patients receiving multiple lines of novel therapies with increased life expectancy are likely to be contributory. Awareness of metastatic disease patterns improves early diagnosis, accurate staging, and initiation of appropriate therapy, and can inform prognostic information and anticipate potential disease complications. The aim of this review is to document the spectrum of metastases in PC including emerging and unusual patterns, and to highlight the role of novel imaging including prostate-specific membrane antigen (PSMA)-positron-emission tomography (PET) and whole-body magnetic resonance imaging (WB-MRI) to improve diagnostic and response assessment accuracy.

Longitudinal cohort analysis of patients with metastatic penile cancer treated in a large quaternary academic centre

Objective:

This study aimed to provide real-world data on the multidisciplinary management of metastatic penile squamous-cell carcinoma (mpSCC) patients and their survival outcomes, particularly those who receive best supportive care (BSC).

Methods:

A retrospective analysis of 1720 patients, managed via a supra-regional penile-specialist multidisciplinary team was conducted between January 2006 and May 2020.

Results:

A total of 101 patients (median age 63 years; interquartile range 56–72 years; 73% ECOG 0/1) were included. Of these, 32% (32/101) had previously received adjuvant chemotherapy prior to metastatic recurrence, 58% (59/101) received chemotherapy and 42% (42/101) received BSC. Further, 17% (17/101) received second-line systemic therapy, and 3% (3/101) received third-line systemic therapy. For first-line systemic-therapy, there was a 46% (27/59) clinical benefit rate (CBR), with 9% (5/59) complete response, 15% (9/59) partial response and 22% (13/59) stable disease. Patients receiving second-line therapy ( n=17) had a 29% (5/17) CBR. Median progression-free survival for first- and second-line treatment was 3.2 and 2.2 months, respectively. Median overall survival (mOS) for all patients was 6.2 months. mOS for first-line chemotherapy, second-line chemotherapy and BSC patients was 7.2, 4.5 and 2.0 months, respectively.

Conclusions:

First-line platinum-based chemotherapy is associated with notable response rates in mpSCC patients. Agents with better response rates are needed urgently potentially in combination with platinum-based chemotherapy.

Level of evidence:

Level 2b.

ESTRO-ACROP recommendations on the clinical implementation of hybrid MR-linac systems in radiation oncology

Online magnetic resonance-guided radiotherapy (oMRgRT) represents one of the most innovative applications of current image-guided radiation therapy (IGRT). The revolutionary concept of oMRgRT systems is the ability to acquire MR images for adaptive treatment planning and also online imaging during treatment delivery. The daily adaptive planning strategies allow to improve targeting accuracy while avoiding critical structures. This ESTRO-ACROP recommendation aims to provide an overview of available systems and guidance for best practice in the implementation phase of hybrid MR-linac systems. Unlike the implementation of other radiotherapy techniques, oMRgRT adds the MR environment to the daily practice of radiotherapy, which might be a new experience for many centers. New issues and challenges that need to be thoroughly explored before starting clinical treatments will be highlighted.

A narrative review of oligometastatic prostate cancer-an evolving paradigm

There has been growing interest in oligometastatic prostate cancer (OMPC) with a mounting body of evidence to suggest that it is a distinct disease state, both biologically and prognostically, when compared to polymetastatic prostate cancer. Three subgroups have been recognised; de novo synchronous, metachronous/oligorecurrent and oligoprogressive disease. The belief that patients with OMPC can be treated more aggressively to improve survival is transforming patient care. Identifying these patients poses the first challenge, and we explore the imaging modalities currently utilised and those that are promising. For patients with de novo synchronous OMPC, both early systemic treatment in addition to androgen deprivation therapy (ADT) and radiotherapy to the prostate increase overall survival (OS), and both are increasingly being integrated into routine clinical practice. Metastasis-directed therapy (MDT) has predominantly been delivered using stereotactic body radiotherapy (SBRT) in prostate cancer and studies have shown SBRT is well-tolerated, provides excellent local control and can be used to delay ADT in the metachronous setting. We discuss the current management strategies in OMPC, review the evidence supporting the use of SBRT and outline ongoing trials.

Factors affecting accuracy and precision in ultrasound guided radiotherapy

BACKGROUND AND PURPOSE

Transperineal ultrasound (TPUS) is used clinically for directly assessing prostate motion. Factors affecting accuracy and precision in TPUS motion estimation must be assessed to realise its full potential.

METHODS AND MATERIALS

Patients were imaged using volumetric TPUS during the Clarity-Pro trial (NCT02388308). Prostate motion was measured online at patient set-up and offline by experienced observers. Cone beam CT with markers was used as a comparator and observer performance was also quantified. The influence of different clinical factors was examined to establish specific recommendations towards efficacious ultrasound guided radiotherapy.

RESULTS

From 330 fractions in 22 patients, offline observer random errors were 1.5 mm, 1.3 mm, 1.9 mm (left-right, superior-inferior, anteroposterior respectively). Errors increased in fractions exhibiting poor image quality to 3.3 mm, 3.3 mm and 6.8 mm. Poor image quality was associated with inconsistent probe placement, large anatomical changes and unfavourable imaging conditions within the patient. Online matching exhibited increased observer errors of: 3.2 mm, 2.9 mm and 4.7 mm. Four patients exhibited large systematic residual errors, of which three had poor quality images. Patient habitus showed no correlation with observer error, residual error, or image quality.

CONCLUSIONS

TPUS offers the unique potential to directly assess inter- and intra-fraction motion on conventional linacs. Inconsistent image quality, inexperienced operators and the pressures of the clinical environment may degrade precision and accuracy. Experienced operators are essential and cross-centre standards for training and QA should be established that build upon current guidance. Greater use of automation technologies may further minimise uncertainties.

Prevalence of oligoprogression in metastatic hormone-resistant prostate cancer patients on androgen targeted therapies: Could targeted radiotherapy improve patient outcomes?

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Background: Androgen receptor-targeted therapies (ART) such as Abiraterone and Enzalutamide have shifted the management paradigm of metastatic castrate-resistant prostate cancer (mCRPC). These treatments are well-tolerated with less toxicities compared to chemotherapy, therefore methods to delay chemotherapy are beneficial to patients. Patients eventually become resistant to ARTs, and some patients will progress in a limited number of sites. This study investigated the prevalence of oligoprogressive disease (OPD) amenable to Stereotactic-body radiotherapy (SBRT). OPD is defined as ≤3 metastatic lesions which are progressing or new whilst all other sites of disease are well-controlled by ART. Methods: Retrospective analysis of electronic patient records and imaging studies of 95 patients treated with ART for mCRPC between April 2015 – 2017 from a single centre was undertaken. Data was analysed at the time of first tumour progression on ART. Results: The median (IQR) age of patients was 78.8 (74.4-83.6) years. OPD was found in 27 (28%) patients, 18 (19%) had lesions suitable for SBRT (Table). Seventeen (63%) patients were treated with abiraterone, 10 (27%) patients with enzalutamide. Median (IQR) time from starting ART to OPD was 16.4 (8.6-19.9) months. Five (19%) patients had 3 sites of OPD, 8 (29%) patients had 2 sites of OPD and 14 (52%) patients had 1 site of OPD. Nineteen patients continued ART beyond OPD for ≥3months. OPD was diagnosed using CT scan (56%), whole body diffusion-weighted MRI (22%), choline PET/CT (19%) and bone scan (3%). Six (22%) patients were treated with radiotherapy for OPD, 3 as participants of the TRAP trial (NCT03644303). Median time to subsequent progression after OPD for the 3 patients treated off trial with radiotherapy was 20.5 months. The OPD lesions treated with radiotherapy included the prostate (2 patients, 30 Gy in 5 and 24 Gy in 4 fractions) and para-aortic lymph node (1 patient, 30 Gy in 5 fractions). Median time to subsequent progression after OPD for those who did not receive radiotherapy was 6.4 months. There was no significant difference between median overall survival between patients with OPD and those who progressed with > 3 lesions (7 vs 9.2 years, P= 0.54). Ten (66%) patients who progressed after initial OPD on continuation of ART progressed with further OPD (≤3 lesions including original OPD lesion). Conclusions: OPD is prevalent in patients on ART for mCRPC. The most frequent site of OPD was in bone and majority of patients had only 1 site of OPD at presentation. These results identify a cohort of patients who may benefit from SBRT to maximise ART treatment. Fourteen (14%) patients met entry criteria for TRAP trial which is currently testing the role of SBRT to sites of OPD in mCRPC. [Table: see text]

Analysis of rectal dose during prostate stereotactic body radiotherapy in MR-guided radiotherapy

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Background: The Unity MR-Linac combines a 7-MV Linac with 1.5T magnetic resonance (MR) imaging capability and it enables adaptive radiotherapy, whereby the target and organs at risk are recontoured and a plan is optimised daily. During treatment a session MR image is taken first, on which the target and organs-at-risk are contoured, and a plan created. A verification image is taken prior to dose delivery to identify intra-fractional changes. If present, the daily treatment plan is shifted to reflect the anatomy. A post-treatment image is acquired at the end of treatment. This study evaluates the dosimetric changes to the rectum caused by intra-fractional changes during treatment delivery for prostate stereotactic body radiotherapy (SBRT) calculated on the verification and post-treatment images. Methods: The first five patients treated on the MR-Linac with 5-fraction SBRT to the prostate are included in this study. For each patient, the rectum was contoured on the verification and post-treatment MR images for each of the five fractions. The dose delivered to the rectum with the original treatment plan was then calculated on each image and the V36Gy rectal dose constraint was noted. Results: Out of the 25 fractions, a post treatment image was not performed in one fraction; 24 fractions were therefore analysed in total. The rectal V36Gy dose constraint exceeded the mandatory target of 2cc on 50% of the verification images and 46% of the post-treatment images. In 6 fractions the rectal V36Gy was greater than 2cc on both the verification and post-treatment images suggesting this rectal constraint was exceeded throughout treatment. In 17% of patients, the volume of rectum receiving 36Gy increased at each timepoint an image was taken during the treatment workflow. Conclusions: The rectal V36Gy dose constraint is susceptible to minor changes in rectal filling, which may often lead to higher than the accepted dose constraint. Thus, a single planning CT scan is unlikely to be representative of dose delivered. Adaptive radiotherapy can reduce this uncertainty somewhat, but intra-fraction dose re-optimisation would be required to ensure the rectal V36Gy remains acceptable at all times.

Feasibility of MR-guided ultrahypofractionated radiotherapy in 5, 2 or 1 fractions for prostate cancer

The drive towards hypofractionated prostate radiotherapy is motivated by a low alpha/beta ratio for prostate cancer (1 to 3 Gy) compared to surrounding organs at risk, implying an improved therapeutic ratio with increasing dose per fraction. Early evidence from studies of ultrahypofractionated (UHF) prostate HDR brachytherapy has shown good tolerability in terms of normal tissue toxicities and clinical outcomes similar to conventional fractionation schedules. MR-guided stereotactic body radiotherapy (SBRT) with online plan adaptation and real-time tumour imaging may enable UHF doses to be delivered to the prostate safely, without the invasiveness of brachytherapy. The feasibility of UHF prostate treatment planning for the Unity MR-Linac (MRL, Elekta AB, Stockholm) was investigated for target prescriptions and planning constraints derived from the HDR brachytherapy and SBRT literature. Monaco 5.40 (Elekta) was used to generate MRL step-and-shoot IMRT plans for three dose fractionation protocols (5, 2 and 1 fractions), for ten randomly selected previously treated prostate cancer patients. Of the ten plans per UHF scheme, all clinical goals were met in all cases for 5 fractions, and in six cases for both 2 and 1 fraction schemes. PTV D95% was compromised by up to 6.4% and 3.9% of the associated target dose for 2 and 1 fraction plans respectively. There were two cases of PTV D95% compromise greater than a 5% dose decrease for the 2 fraction plans. The study suggests feasibility of the UHF treatment planning approaches if combined with real-time motion mitigation strategies.

Prostate Cancer Radiation Therapy Recommendations in Response to COVID-19

PURPOSE

During a global pandemic, the benefit of routine visits and treatment of patients with cancer must be weighed against the risks to patients, staff, and society. Prostate cancer is one of the most common cancers radiation oncology departments treat, and efficient resource utilization is essential in the setting of a pandemic. Herein, we aim to establish recommendations and a framework by which to evaluate prostate radiation therapy management decisions.

METHODS AND MATERIALS

Radiation oncologists from the United States and the United Kingdom rapidly conducted a systematic review and agreed upon recommendations to safely manage patients with prostate cancer during the COVID-19 pandemic. A RADS framework was created: remote visits, and avoidance, deferment, and shortening of radiation therapy was applied to determine appropriate approaches.

RESULTS

Recommendations were provided by the National Comprehensive Cancer Network risk group regarding clinical node-positive, postprostatectomy, oligometastatic, and low-volume M1 disease. Across all prostate cancer stages, telemedicine consultations and return visits were recommended when resources/staff available. Delays in consultations and return visits of between 1 and 6 months were deemed safe based on stage of disease. Treatment can be avoided or delayed until safe for very low, low, and favorable intermediate-risk disease. Unfavorable intermediate-risk, high-risk, clinical node-positive, recurrence postsurgery, oligometastatic, and low-volume M1 disease can receive neoadjuvant hormone therapy for 4 to 6 months as necessary. Ultrahypofractionation is preferred for localized, oligometastatic, and low-volume M1, and moderate hypofractionation is preferred for postprostatectomy and clinical node positive disease. Salvage is preferred to adjuvant radiation.

CONCLUSIONS

Resources can be reduced for all identified stages of prostate cancer. The RADS (remote visits, and avoidance, deferment, and shortening of radiation therapy) framework can be applied to other disease sites to help with decision making in a global pandemic.

Stereotactic radiotherapy with focal boost for intermediate and high-risk prostate cancer: Initial results of the SPARC trial

INTRODUCTION

Dose escalation to dominant intraprostatic lesions (DILs) is a novel method to increase the therapeutic ratio in localised prostate cancer. The Stereotactic Prostate Augmented Radiotherapy with Cyberknife (SPARC) trial was designed to determine the feasibility of a focal boost defined with multiparametric magnetic resonance imaging (mpMRI) using stereotactic ablative body radiotherapy (SABR).

MATERIALS AND METHODS

Patients were included with newly diagnosed intermediate to high risk prostate cancer with at least one of: Gleason score 4 + 3, stage T3a, or PSA > 20 ng/ml. Visible disease on mpMRI was mandatory and up to 2 separate nodules were allowed. All patients received androgen deprivation. Patients received 36.25 Gy in 5 fractions using CyberKnife® and the DIL received a simultaneous boost to a maximum of 47.5 Gy, as allowed by OAR constraints. Genitourinary (GU) and gastrointestinal (GI) toxicity was reported using the RTOG scoring criteria. International Index of Erectile Function (IIEF) and EQ-5D global health scores were regularly captured.

RESULTS

An interim safety analysis was performed on the first 8 patients, recruited between July 2013 and December 2015. Median follow up was 56 months (range 50-74). Median D95 values for the prostate PTV and boost volume were 36.55 Gy (range 35.87-36.99) and 46.62 Gy (range 44.85-48.25) respectively. Of the dose constraints, 10/80 were not achieved but all were minor dose variations. Grade 2+ acute GU and GI toxicities were 37.5% respectively while grade 2+ late GU and GI toxicities were 12.5% and 0% respectively. IIEF and quality of life scores recovered over time and all patients remain in biochemical remission.

CONCLUSION

The first patients have been successfully treated with prostate SABR and focal boost on the SPARC trial, with excellent adherence to the planning protocol. Toxicity and efficacy results are promising and further recruitment is underway.

PIVOTALboost: A phase III randomised controlled trial of prostate and pelvis versus prostate alone radiotherapy with or without prostate boost (CRUK/16/018)

•PIVOTALboost evaluates benefits/toxicity of pelvic node RT and focal boost dose escalation.•Unfavourable intermediate/high risk and bulky local disease are most likely to benefit.•Functional MRI imaging is used to select patients for different types of dose escalation.•HDR brachytherapy or focal dose escalation with IMRT are used as options.•Training and support is provided to reduce variations of contouring and radiotherapy planning.•The trial is recruiting patients in 38 radiotherapy centres through the UK.

Prostate Cancer Radiation Therapy Recommendations in Response to COVID-19

PURPOSE

During a global pandemic, the benefit of routine visits and treatment of patients with cancer must be weighed against the risks to patients, staff, and society. Prostate cancer is one of the most common cancers radiation oncology departments treat, and efficient resource utilization is essential in the setting of a pandemic. Herein, we aim to establish recommendations and a framework by which to evaluate prostate radiation therapy management decisions.

METHODS AND MATERIALS

Radiation oncologists from the United States and the United Kingdom rapidly conducted a systematic review and agreed upon recommendations to safely manage patients with prostate cancer during the COVID-19 pandemic. A RADS framework was created: remote visits, and avoidance, deferment, and shortening of radiation therapy was applied to determine appropriate approaches.

RESULTS

Recommendations were provided by the National Comprehensive Cancer Network risk group regarding clinical node-positive, postprostatectomy, oligometastatic, and low-volume M1 disease. Across all prostate cancer stages, telemedicine consultations and return visits were recommended when resources/staff available. Delays in consultations and return visits of between 1 and 6 months were deemed safe based on stage of disease. Treatment can be avoided or delayed until safe for very low, low, and favorable intermediate-risk disease. Unfavorable intermediate-risk, high-risk, clinical node-positive, recurrence postsurgery, oligometastatic, and low-volume M1 disease can receive neoadjuvant hormone therapy for 4 to 6 months as necessary. Ultrahypofractionation is preferred for localized, oligometastatic, and low-volume M1, and moderate hypofractionation is preferred for postprostatectomy and clinical node positive disease. Salvage is preferred to adjuvant radiation.

CONCLUSIONS

Resources can be reduced for all identified stages of prostate cancer. The RADS (remote visits, and avoidance, deferment, and shortening of radiation therapy) framework can be applied to other disease sites to help with decision making in a global pandemic.

Daily adaptive radiotherapy for patients with prostate cancer using a high field MR-linac: Initial clinical experiences and assessment of delivered doses compared to a C-arm linac

INTRODUCTION

MR-guided adapted radiotherapy (MRgART) using a high field MR-linac has recently become available. We report the estimated delivered fractional dose of the first five prostate cancer patients treated at our centre using MRgART and compare this to C-Arm linac daily Image Guided Radiotherapy (IGRT).

METHODS

Patients were treated using adapted treatment plans shaped to their daily anatomy. The treatments were recalculated on an MR image acquired immediately prior to treatment delivery in order to estimate the delivered fractional dose. C-arm linac non-adapted VMAT treatment plans were recalculated on the same MR images to estimate the fractional dose that would have been delivered using conventional radiotherapy techniques using a daily IGRT protocol.

RESULTS

95% and 93% of mandatory target coverage objectives and organ at risk dose constraints were achieved by MRgART and C-arm linac delivered dose estimates, respectively. Both delivery techniques were estimated to have achieved 98% of mandatory Organ At Risk (OAR) dose constraints whereas for the target clinical goals, 86% and 80% were achieved by MRgART and C-arm linac delivered dose estimates.

CONCLUSIONS

Prostate MRgART can be delivered using the a high field MR-linac. Radiotherapy performed on a C-arm linac offers a good solution for prostate cancer patients who present with favourable anatomy at the time of reference imaging and demonstrate stable anatomy throughout the course of their treatment. For patients with critical OARs abutting target volumes on their reference image we have demonstrated the potential for a target dose coverage improvement for MRgART compared to C-arm linac treatment.