Accuracy of gross tumour volume delineation with [68Ga]-PSMA-PET compared to histopathology for high-risk prostate cancer.

BACKGROUND: The delineation of intraprostatic lesions is vital for correct delivery of focal radiotherapy boost in patients with prostate cancer (PC). Errors in the delineation could translate into reduced tumour control and potentially increase the side effects. The purpose of this study is to compare PET-based delineation methods with histopathology. MATERIALS AND METHODS: The study population consisted of 15 patients with confirmed high-risk PC intended for prostatectomy. [68Ga]-PSMA-PET/MR was performed prior to surgery. Prostate lesions identified in histopathology were transferred to the in vivo [68Ga]-PSMA-PET/MR coordinate system. Four radiation oncologists manually delineated intraprostatic lesions based on PET data. Various semi-automatic segmentation methods were employed, including absolute and relative thresholds, adaptive threshold, and multi-level Otsu threshold. RESULTS: The gross tumour volumes (GTVs) delineated by the oncologists showed a moderate level of interobserver agreement with Dice similarity coefficient (DSC) of 0.68. In comparison with histopathology, manual delineations exhibited the highest median DSC and the lowest false discovery rate (FDR) among all approaches. Among semi-automatic approaches, GTVs generated using standardized uptake value (SUV) thresholds above 4 (SUV > 4) demonstrated the highest median DSC (0.41), with 0.51 median lesion coverage ratio, FDR of 0.66 and the 95th percentile of the Hausdorff distance (HD95%) of 8.22 mm. INTERPRETATION: Manual delineations showed a moderate level of interobserver agreement. Compared to histopathology, manual delineations and SUV > 4 exhibited the highest DSC and the lowest HD95% values. The methods that resulted in a high lesion coverage were associated with a large overestimation of the size of the lesions.

Ultrahypofractionated Radiation Therapy for Prostate Cancer Including Seminal Vesicles in the Target Volume: A Treatment-planning Study Based on the HYPO-RT-PC Fractionation Schedule.

Purpose: Ultrahypofractionated (UHF) radiation therapy (RT) has become a treatment alternative for patients with localized prostate cancer. In more advanced cases, seminal vesicles (SVs) are routinely included in the target volume. The Scandinavian HYPO-RT-PC trial, which compared 42.7 Gy in 7 fractions (fr) to conventional fractionation (CF), did not include SVs in the clinical target volume. The primary objective of the present work was to implement a ultrahypofractionated-simultaneous integrated boost (UHF-SIB) for prostate cancer RT, incorporating SVs into the target volume based on this fractionation schedule. A secondary objective was to analyze the unintentional dose coverage of SVs from state-of-the-art volumetric modulated arc therapy treatments to the prostate gland only. Methods and Materials: Two different equieffective UHF-SIB treatment schedules to SVs were derived based on the CF clinical schedule (50.0 Gy/25 fr to elective SVs and 70.0 Gy/35 fr to verified SV-invasion (SVI)) using the linear quadric model with α/ß = 2 Gy and 3 Gy. The dose to the prostate was 42.7 Gy/7 fr in both schedules, with 31.2 Gy/37.8 Gy (α/ß = 2 Gy) and 32.7 Gy/40.1 Gy (α/ß = 3 Gy) to elective SV/verified SVI. Volumetric modulated arc therapy plans to the proximal 10 mm and 20 mm were optimized, and dose-volume metrics for target volumes and organs at risk were evaluated. Results: Dose metrics were overall lower for UHF-SIB compared with CF. QUANTEC-based volume criteria were 2% to 7% lower for the rectum and 2% to 4% lower for the bladder in the UHF-SIB. The D98% to elective SV was 7 to 12 Gy3 lower with UHF-SIB, and the corresponding data for verified SVI were approximately 2 to 3 Gy3. The SV(10 mm) V90%/(29.5 Gy) for prostate-only treatments (42.7 Gy) were as follows: median (IQR), 99% (87-100) and 78% (58-99) for the clinical target volume and planning target volume, respectively. Conclusions: UHF RT based on the HYPO-RT-PC fractionation schedule, with a SIB technique, to the prostate and the base of the SV can be planned with lower doses (EQD2) to organs at risk, compared with CF. The unintentional dose to the proximal parts of SVs in prostate-only treatment can be substantial.

[Treatment of non-metastatic prostate cancer]. / Behandling av icke spridd prostatacancer ­ individuellt val.

There is a long history of curative treatment of prostate cancer. However, as prostate cancer often grows very slowly, and symptoms do not have time to develop during a person's lifetime, a more tentative approach has become more and more common in many cases. This may be through either watchful waiting or active surveillance. In the first case palliative hormonal treatment is given in the case of progression, in the latter curative treatment would be the choice. When treatment is deemed necessary for localized disease, surgery and radiotherapy are considered equivalent in terms of efficacy and overall risk of side effects. For locally advanced disease, radiotherapy is the recommended first-hand choice outside the SPCG 15 study. Focal treatment, which may lead to less side effects than surgery or radiotherapy, is not recommended outside trial settings due to lack of long-term follow-up data.

Evaluation of a deep learning magnetic resonance imaging reconstruction method for synthetic computed tomography generation in prostate radiotherapy.

Background and Purpose: In magnetic resonance imaging (MRI) only radiotherapy computed tomography (CT) is excluded. The method relies entirely on synthetic CT images generated from MRI. This study evaluates the compatibility of a commercial synthetic CT (sCT) with an accelerated commercial deep learning reconstruction (DLR) in MRI-only prostate radiotherapy. Materials and Methods: For a group of 24 patients (cohort 1) the effects of DLR were studied in isolation. MRI data were reconstructed conventionally and with DLR from identical k-space data, and sCTs were generated for both reconstructions. The sCT quality, Hounsfield Unit (HU) and dosimetric impact were investigated. In another group of 15 patients (cohort 2) effects on sCT generation using accelerated MRI acquisition (40 % time reduction) reconstructed with DLR were investigated. Results: sCT images from both cohorts, generated from DLR MRI data, were of clinically expected image quality. The mean dose differences for targets and organs at risks in cohort 1 were <0.06 Gy, corresponding to a 0.1 % prescribed dose difference. Similar dose differences were observed in cohort 2. Gamma pass rates for cohort 1 were 100 % for criteria 3 %/3mm, 2 %/2mm and 1 %/1mm for all dose levels. Mean error and mean absolute error inside the body, between sCTs, averaged over all cohort 1 subjects, were -1.1 ± 0.6 [-2.4 0.2] and 2.9 ± 0.4 [2.3 3.9] HU, respectively. Conclusions: DLR was suitable for sCT generation with clinically negligible differences in HU and calculated dose compared to the conventional MRI reconstruction method. For sCT generation DLR enables scan time reduction, without compromised sCT quality.

Dose-volume relationships of planned versus estimated delivered radiation doses to pelvic organs at risk and side effects in patients treated with salvage radiotherapy for recurrent prostate cancer.

Purpose: To investigate estimated delivered dose distributions using weekly cone-beam computed tomography (CBCT) scans for pelvic organs at risk (OARs) in salvage radiotherapy (SRT) after radical prostatectomy. Furthermore, to compare them with the originally planned dose distributions and analyse associations with gastrointestinal (GI) and genitourinary (GU) side effects. Methods: This study is part of a phase II trial involving SRT for recurrent prostate cancer. Treatment was personalised based on PSA response during SRT, classifying patients as PSA responders or non-responders. Estimated radiation dose distributions were obtained using deformable image registration from weekly CBCT scans. GI and GU toxicities were assessed using the RTOG toxicity scale, while patient-reported symptoms were monitored through self-assessment questionnaires. Results: The study included 100 patients, with similar treatment-related side effects observed in both responders and non-responders. Differences in dose-volume metrics between the planned and estimated delivered doses for the examined OARs were mostly modest, although generally statistically significant. We identified statistically significant associations between QUANTEC-recommended dose-volume constraints and acute bowel toxicity, as well as late urinary patient-reported symptoms, for both the estimated delivered and planned dose distributions. Conclusion: We found small but statistically significant differences between estimated delivered and planned doses to OARs. These differences showed trends toward improved associations for estimated delivered dose distributions with side effects. Enhanced registration methods and imaging techniques could potentially further enhance the assessment of truly delivered doses and yield more reliable dose-volume constraints for future therapies.

Risk of prostate cancer death after radical radiotherapy with neoadjuvant and adjuvant therapy with bicalutamide or gonadotropin-releasing hormone agonists.

BACKGROUND: Oncological outcome after radical radiotherapy (RRT) combined with neoadjuvant and adjuvant androgen suppression therapy (AST) may differ according to type of AST. The aim of this nationwide register-based study was to investigate risk of prostate cancer (Pca) death after different neoadjuvant and adjuvant ASTs; (i) bicalutamide, (ii) gonadotropin-releasing hormone agonists (GnRH) or (iii) combined bicalutamide and GnRH (CAB), together with RRT. MATERIALS AND METHODS: Data for 6882 men diagnosed with high-risk Pca between 2007 and 2020 and treated with primary RRT was retrieved from Prostate Cancer data Base Sweden (PCBaSe) 5.0. Time to Pca death according to type of neoadjuvant and adjuvant AST was assessed by use of Kaplan-Meier plots and Cox proportional hazard models adjusted for putative confounders. RESULTS: Data were stratified by RRT type since the effect of AST in risk of Pca death differed according to type of RRT. Compared with the reference RRT combined with neoadjuvant CAB/adjuvant GnRH, risk of Pca death for men treated with CAB/bicalutamide and conventionally fractionated external beam radiotherapy (CF-EBRT) was hazard ratio (HR) 0.73 (95% CI: 0.50-1.04), hypofractionated EBRT (HF-EBRT), HR 1.35 (95% CI: 0.65-2.81) and EBRT with high dose rate brachytherapy (EBRT-HDRBT), HR 0.85 (95% CI: 0.37-1.95). Risk of Pca death for men treated with bicalutamide/bicalutamide and: (i) CF-EBRT was HR 2.35 (95% CI: 1.42-3.90), (ii) HF-EBRT, HR 0.70 (95% CI: 0.26-1.85), (iii) HF-EBRT, HR 4.07 (95% CI: 1.88-8.77) vs the reference. CONCLUSION: In this observational study, risk of Pca death between men receiving different combinations of AST varied according to RRT type. No difference was found in risk of Pca death for men treated with bicalutamide or GnRH as adjuvant therapy to RRT following neoadjuvant CAB. Risk of Pca death was increased for men with monotherapy neo-/adjuvant bicalutamide in combination with CF-EBRT or EBRT-HDRBT.

MRI-only radiotherapy from an economic perspective: Can new techniques in prostate cancer treatment be cost saving?

Background and Purpose: The aim of this study was to analyze a magnetic resonance imaging (MRI)-only radiotherapy workflow from an economic perspective in terms of reduced time, costs and systematic uncertainties. Material/Methods: A documented Swedish clinical implementation of MRI-only radiotherapy was used as template for cost assessments compared to a combined computed tomography (CT)/MRI workflow. The costs were taken from official regional price lists from 2021. MRI-only specific quality assurance (QA) was assumed necessary in an initial phase. Treatment plans for target volumes with margins of 5-10 mm were created for ten prostate cancer patients prescribed 78 Gy in 39 fractions. The risk of Grade ≥ 2 rectal toxicity or rectal bleeding was calculated using the QUANTEC recommended NTCP model and costs estimated based on subsequent diagnostic examinations. Results: The exclusion of the CT-examination and faster target delineation were the main contributors to cost reductions. Additional QA procedures limited the initial cost reduction to 14 EUR/patient. Long-term MRI-only reduced the costs by 209 EUR/patient. Reducing margins resulted in Grade ≥ 2 rectal toxicity or rectal bleeding probability of 9.7 % for 7 mm margin and 6.0 % for 5 mm margin. This margin reduction resulted in an additional cost reduction of 46 EUR/patient. Conclusion: An MRI-only workflow implementation is associated with reduced costs when the workflow tasks are more time efficient and side effects are reduced as a result of margin reduction. The short-term economic benefits are limited due to extra costs of QA procedures. The economic benefits of MRI-only will make impact first when the workflow is well established, and margin reduction has been included.

A prospective phase II study of prostate-specific antigen-guided salvage radiotherapy and 68Ga-PSMA-PET for biochemical relapse after radical prostatectomy - The PROPER 1 trial.

Background and purpose: The treatment of biochemical recurrence (BCR) after prostatectomy is challenging as the site of the recurrence is often undetectable. Our aim was to test a personalised treatment concept for BCR based on PSA kinetics during salvage radiotherapy (SRT) combined with prostate-specific membrane antigen positron emission tomography (PSMA-PET). Materials and methods: This phase II trial included 100 patients with BCR. PSMA-PET was performed at baseline. PSA was measured weekly during SRT. Initially, 70 Gy in 35 fractions was prescribed to the prostate bed. Radiotherapy was adapted after 50 Gy. Non-responders (PSA still ≥ 0.15 ng/mL) received sequential lymph node irradiation with a boost to PSMA-PET positive lesions, while responders (PSA < 0.15 ng/mL) continued SRT as planned. PET-findings were only taken into consideration for treatment planning in case of PSA non-response after 50 Gy. Results: Data from 97 patients were eligible for analysis. Thirty-four patients were classified as responders and 63 as non-responders. PSMA-PET was positive in 3 patients (9%) in the responder group and in 22 (35%) in the non-responder group (p = 0.007). The three-year failure-free survival was 94% for responders and 68% for non-responders (median follow-up 38 months). There were no significant differences in physician-reported urinary and bowel toxicity. Patient-reported diarrhoea at end of SRT was more common among non-responders. Conclusion: This new personalised treatment concept with intensified SRT based on PSA response demonstrated a high tumour control rate in both responders and non-responders. These results suggest a clinically significant effect with moderate side effects in a patient group with otherwise poor prognosis. PSMA-PET added limited value. The treatment approach is now being evaluated in a phase III trial.Clinical trial registration numbers: NCT02699424&ISRCTN45905321.

Faster and more accurate patient positioning with surface guided radiotherapy for ultra-hypofractionated prostate cancer patients.

INTRODUCTION: The aim of this study was to evaluate if surface guided radiotherapy (SGRT) can decrease patient positioning time for localized prostate cancer patients compared to the conventional 3-point localization setup method. The patient setup accuracy was also compared between the two setup methods. MATERIALS AND METHODS: A total of 40 localized prostate cancer patients were enrolled in this study, where 20 patients were positioned with surface imaging (SI) and 20 patients were positioned with 3-point localization. The setup time was obtained from the system log files of the linear accelerator and compared between the two methods. The patient setup was verified with daily orthogonal kV images which were matched based on the implanted gold fiducial markers. Resulting setup deviations between planned and online positions were compared between SI and 3-point localization. RESULTS: Median setup time was 2:50 min and 3:28 min for SI and 3-point localization, respectively (p < 0.001). The median vector offset was 4.7 mm (range: 0-10.4 mm) for SI and 5.2 mm for 3-point localization (range: 0.41-17.3 mm) (p = 0.01). Median setup deviation in the individual translations for SI and 3-point localization respectively was: 1.1 mm and 1.9 mm in lateral direction (p = 0.02), 1.8 and 1.6 mm in the longitudinal direction (p = 0.41) and 2.2 mm and 2.6 mm in the vertical direction (p = 0.04). CONCLUSIONS: Using SGRT for positioning of prostate cancer patients provided a faster and more accurate patient positioning compared to the conventional 3-point localization setup.

Investigation of the clinical inter-observer bias in prostate fiducial marker image registration between CT and MR images.

BACKGROUND AND PURPOSE: Inter-modality image registration between computed tomography (CT) and magnetic resonance (MR) images is associated with systematic uncertainties and the magnitude of these uncertainties is not well documented. The purpose of this study was to investigate the potential uncertainty of gold fiducial marker (GFM) registration for localized prostate cancer and to estimate the inter-observer bias in a clinical setting. METHODS: Four experienced observers registered CT and MR images for 42 prostate cancer patients. Manual GFM identification was followed by a landmark-based registration. The absolute difference between observers in GFM identification and the displacement of the clinical target volume (CTV) was investigated. The CTV center of mass (CoM) vector displacements, DICE-index and Hausdorff distances for the observer registrations were compared against a clinical baseline registration. The time allocated for the manual registrations was compared. RESULTS: Absolute difference in GFM identification between observers ranged from 0.0 to 3.0 mm. The maximum CTV CoM displacement from the clinical baseline was 3.1 mm. Displacements larger than or equal to 1 mm, 2 mm and 3 mm were 46%, 18% and 4%, respectively. No statistically significant difference was detected between observers in terms of CTV displacement. Median DICE-index and Hausdorff distance for the CTV, with their respective ranges were 0.94 [0.70-1.00] and 2.5 mm [0.7-8.7]. CONCLUSIONS: Registration of CT and MR images using GFMs for localized prostate cancer patients was subject to inter-observer bias on an individual patient level. A CTV displacement as large as 3 mm occurred for individual patients. These results show that GFM registration in a clinical setting is associated with uncertainties, which motivates the removal of inter-modality registrations in the radiotherapy workflow and a transition to an MRI-only workflow for localized prostate cancer.

Adaptive sequential plan-on-plan optimization during prostate-specific antigen response guided radiotherapy of recurrent prostate cancer.

BACKGROUND: Treatment adaptation based on tumour biomarker response during radiotherapy of prostate cancer, could be used for both escalation and de-escalation of radiation doses and volumes. To execute an adaptation involving extension of treatment volumes during radiation can however be restricted by the doses already delivered. The aim of this work was to develop a treatment planning method that addresses this challenge. MATERIAL AND METHODS: A volumetric-modulated-arc-therapy (VMAT) planning method with sequential plan-on-plan optimization was developed for a prospective phase II trial including 100 patients on salvage radiotherapy (SRT) for prostate cancer recurrence. A treatment adaptation was performed after five weeks of SRT based on prostate-specific antigen response during this phase of the treatment. This involved extension of treatment volumes for non-responders (n = 64) to include pelvic lymph nodes and boost to 68Gallium-Prostate-Specific-Membrane-Antigen-Positron-Emission-Tomography positive lesions. This method was evolved by introducing an EQD2 (equivalent dose in 2.0 Gy fractions) correction of the base plan for improved dose coverage. RESULTS: All dose-volume criteria for target coverage were met for the non-responders when based on physical dose. An EQD2 correction of the base plan for non-responders, implemented for the final 29 patients, led to a statistically significant improvement in dose coverage as compared to the 35 patients treated without EQD2 correction. CONCLUSIONS: This is to our knowledge the only study presented on biomarker-guided sequential VMAT radiotherapy using a plan-on-plan technique in the pelvis. By using a biologically adapted technique an improved target coverage was achieved without compromising doses to organs at risk.

Long-Term Risk of Hip Complications After Radiation Therapy for Prostate Cancer: A Dose-Response Study.

PURPOSE: The aim of the present study was to analyze the long-term incidence of hip complications after external beam radiation therapy compared with age-matched controls from the general population. We also investigated whether there were any dose-response associations. METHODS AND MATERIALS: A total of 349 patients with prostate cancer treated to curative dose with external beam radiation therapy between 1997 and 2002 were included in the study. Physical and fractionation-corrected dose-volume descriptors were derived for the femoral heads, pubic bone, and sacrum. Information on skeletal events was collected for the patients and 1661 matched controls through the Prostate Cancer database Sweden. Uni- and multivariable Cox proportional hazard regressions were used to analyze the time to event. RESULTS: Data from 346 patients were available for analysis. The median mean physical dose and corresponding equivalent 2-Gy/fraction dose (EQD2) to the femoral heads were 35.5 Gy and 28.7 Gy, respectively. The median follow-up time was 16.0 years. During the follow up, 12 hip fractures occurred. Hip osteoarthritis was diagnosed in 36 cases, with 29 cases leading to replacement surgery. No increased risk of hip fractures was found. Hip osteoarthritis was the only event for which a statistically significant difference was found between the irradiated cohort and the controls (cause-specific hazard ratio: 1.56; 95% confidence interval, 1.07-2.26; P = .02). The cumulative incidence of osteoarthritis at 10 years was 8.1% and 4.9% in the irradiated cohort and the controls, respectively. A significant relationship between osteoarthritis and the volume of the femoral head receiving ≥40 Gy (ie, EQD2) was found. CONCLUSIONS: In this study of 346 patients treated with conventional radiation therapy, we found no increased risk of hip fracture but an increased risk of clinically relevant osteoarthritis at long-term follow up. Our results indicate a dose-response relationship between osteoarthritis and the volume of the femoral head receiving an EQD2 dose of ≥40 Gy.

Ultra-hypofractionated versus conventionally fractionated radiotherapy for prostate cancer (HYPO-RT-PC): patient-reported quality-of-life outcomes of a randomised, controlled, non-inferiority, phase 3 trial.

BACKGROUND: The HYPO-RT-PC trial compared conventionally fractionated radiotherapy with ultra-hypofractionated radiotherapy in patients with localised prostate cancer. Ultra-hypofractionation was non-inferior to conventional fractionation regarding 5-year failure-free survival and toxicity. We aimed to assess whether patient-reported quality of life (QOL) differs between conventional fractionation and ultra-hypofractionation up to 6 years after treatment in the HYPO-RT-PC trial. METHODS: HYPO-RT-PC is a multicentre, open-label, randomised, controlled, non-inferiority, phase 3 trial done in 12 centres (seven university hospitals and five county hospitals) in Sweden and Denmark. Inclusion criteria were histologically verified intermediate-to-high-risk prostate cancer (defined as T1c-T3a with one or two of the following risk factors: stage T3a; Gleason score ≥7; and prostate-specific antigen 10-20 ng/mL with no evidence of lymph node involvement or distant metastases), age up to 75 years, and WHO performance status 0-2. Participants were randomly assigned (1:1) to conventional fractionation (78·0 Gy in 39 fractions, 5 days per week for 8 weeks) or ultra-hypofractionation (42·7 Gy in seven fractions, 3 days per week for 2·5 weeks) via a minimisation algorithm with stratification by trial centre, T-stage, Gleason score, and prostate-specific antigen. QOL was measured using the validated Prostate Cancer Symptom Scale (PCSS) and European Organization for Research and Treatment of Cancer Quality-of-Life Questionnaire (EORTC QLQ-C30) at baseline, the end of radiotherapy, months 3, 6, 12, and 24 after radiotherapy, every other year thereafter up to 10 years, and at 15 years. The primary endpoint (failure-free survival) has been reported elsewhere. Here we report QOL, a secondary endpoint analysed in the per-protocol population, up to 6 years after radiotherapy. The HYPO-RT-PC trial is registered with the ISRCTN registry, ISRCTN45905321. FINDINGS: Between July 1, 2005, and Nov 4, 2015, 1200 patients were enrolled and 1180 were randomly assigned (conventional fractionation n=591, ultra-hypofractionation n=589); 1165 patients (conventional fractionation n=582, ultra-hypofractionation n=583) were included in this QOL analysis. 158 (71%) of 223 patients in the conventional fractionation group and 146 (66%) of 220 in the ultra-hypofractionation group completed questionnaires at 6 years. The median follow-up was 48 months (IQR 25-72). In seven of ten bowel symptoms or problems the proportion of patients with clinically relevant deteriorations at the end of radiotherapy was significantly higher in the ultra-hypofractionation group than in the conventional fractionation group (stool frequency [p<0·0001], rush to toilet [p=0·0013], flatulence [p=0·0013], bowel cramp [p<0·0001], mucus [p=0·0014], blood in stool [p<0·0001], and limitation in daily activity [p=0·0014]). There were no statistically significant differences in the proportions of patients with clinically relevant acute urinary symptoms or problems (total 14 items) and sexual functioning between the two treatment groups at end of radiotherapy. Thereafter, there were no clinically relevant differences in urinary, bowel, or sexual functioning between the groups. At the 6-year follow-up there was no difference in the incidence of clinically relevant deterioration between the groups for overall urinary bother (43 [33%] of 132 for conventional fractionation vs 33 [28%] of 120 for ultra-hypofractionation; mean difference 5·1% [95% CI -4·4 to 14·6]; p=0·38), overall bowel bother (43 [33%] of 129 vs 34 [28%] of 123; 5·7% [-3·8 to 15·2]; p=0·33), overall sexual bother (75 [60%] of 126 vs 59 [50%] of 117; 9·1% [-1·4 to 19·6]; p=0·15), or global health/QOL (56 [42%] of 134 vs 46 [37%] of 125; 5·0% [-5·0 to 15·0]; p=0·41). INTERPRETATION: Although acute toxicity was higher for ultra-hypofractionation than conventional fractionation, this long-term patient-reported QOL analysis shows that ultra-hypofractionation was as well tolerated as conventional fractionation up to 6 years after completion of treatment. These findings support the use of ultra-hypofractionation radiotherapy for intermediate-to-high-risk prostate cancer. FUNDING: The Nordic Cancer Union, the Swedish Cancer Society, and the Swedish Research Council.

Dosimetric effects of adaptive prostate cancer radiotherapy in an MR-linac workflow.

BACKGROUND: The purpose was to evaluate the dosimetric effects in prostate cancer treatment caused by anatomical changes occurring during the time frame of adaptive replanning in a magnetic resonance linear accelerator (MR-linac) workflow. METHODS: Two MR images (MR1 and MR2) were acquired with 30 min apart for each of the 35 patients enrolled in this study. The clinical target volume (CTV) and organs at risk (OARs) were delineated based on MR1. Using a synthetic CT (sCT), ultra-hypofractionated VMAT treatment plans were created for MR1, with three different planning target volume (PTV) margins of 7 mm, 5 mm and 3 mm. The three treatment plans of MR1, were recalculated onto MR2 using its corresponding sCT. The dose distribution of MR2 represented delivered dose to the patient after 30 min of adaptive replanning, omitting motion correction before beam on. MR2 was registered to MR1, using deformable registration. Using the inverse deformation, the structures of MR1 was deformed to fit MR2 and anatomical changes were quantified. For dose distribution comparison the dose distribution of MR2 was warped to the geometry MR1. RESULTS: The mean center of mass vector offset for the CTV was 1.92 mm [0.13 - 9.79 mm]. Bladder volume increase ranged from 12.4 to 133.0% and rectum volume difference varied between -10.9 and 38.8%. Using the conventional 7 mm planning target volume (PTV) margin the dose reduction to the CTV was 1.1%. Corresponding values for 5 mm and 3 mm PTV margin were 2.0% and 4.2% respectively. The dose to the PTV and OARs also decreased from D1 to D2, for all PTV margins evaluated. Statistically significant difference was found for CTV Dmin between D1 and D2 for the 3 mm PTV margin (p < 0.01). CONCLUSIONS: A target underdosage caused by anatomical changes occurring during the reported time frame for adaptive replanning MR-linac workflows was found. Volume changes in both bladder and rectum caused large prostate displacements. This indicates the importance of thorough position verification before treatment delivery and that the workflow needs to speed up before introducing margin reduction.

PSA decay during salvage radiotherapy for prostate cancer as a predictor of disease outcome - 5 year follow-up of a prospective observational study.

BACKGROUND AND PURPOSE: Biochemical recurrence after prostatectomy is commonly treated with salvage radiotherapy (SRT). In this prospective observational study we investigated the PSA decay rate, determined by predefined serial PSA measurements during SRT, as a predictor for treatment outcome. MATERIALS AND METHODS: Between 2013 and 2016, 214 patients were included in the study. The prescribed dose to the prostate bed was 70 Gy in 35 fractions (7 weeks) without hormonal treatment. PSA was measured weekly during SRT. Assuming first order kinetics, a PSA decay-rate constant (k) was calculated for 196 eligible patients. The ability of k to predict disease progression was compared with known clinical prediction parameters using Cox regression, logistic regression and ROC analyses. Disease progression was defined as continuously rising PSA after SRT, PSA increase by ≥0.2 ng/ml above nadir after SRT, hormonal treatment or clinical progression. RESULTS: After a median follow up of 4.7 years the estimated failure-free survival at 5 years was 56%. The PSA decay-rate constant (k) was found to be the strongest predictor of disease progression in both uni-and multivariable analyses. CONCLUSION: The addition of k to established clinical variables significantly improves the possibility to predict treatment outcome after SRT and could be used to personalize future therapies.

Comparative Effectiveness of Different Radical Radiotherapy Treatment Regimens for Prostate Cancer: A Population-Based Cohort Study.

BACKGROUND: It is unclear which radiotherapy technique and dose fractionation scheme is most effective in decreasing the risk of prostate cancer death. METHODS: We conducted a population-based cohort study among 15 164 men in the Prostate Cancer database Sweden (version 4.0) treated with primary radical radiotherapy for prostate cancer in Sweden from 1998 to 2016. We calculated hazard ratios with 95% confidence intervals (CIs) of the association between the following exposure groups and outcome: conventionally fractionated external beam radiotherapy (EBRT) to 78 Gy (39 × 2 Gy), EBRT combined with high dose-rate brachytherapy (HDR-BT) (25 × 2 Gy + 2 × 10 Gy), conventionally fractionated EBRT to 70 Gy (35 × 2 Gy), and moderately hypofractionated (M-HF) dose-escalated EBRT (29 × 2.5 Gy or 22 × 3 Gy). RESULTS: Of the men, 7296 received conventionally fractionated EBRT to 78 Gy, 4657 EBRT combined with HDR-BT, 1672 conventionally fractionated EBRT to 70 Gy, and 1539 M-HF EBRT. Using EBRT to 78 Gy as the reference, the multivariable hazard ratios (95% CIs) of prostate cancer death was 0.64 (0.53 to 0.78) for EBRT combined with HDR-BT, 1.00 (0.80 to 1.27) for EBRT to 70 Gy, and 1.51 (0.99 to 2.32) for M-HF EBRT. The multivariable hazard ratios (95% CIs) for death from any cause were 0.79 (0.71 to 0.88), 0.99 (0.87 to 1.14), and 1.12 (0.88 to 1.42), respectively. The lower risk of prostate cancer death comparing EBRT combined with HDR-BT with conventionally fractionated EBRT to 78 Gy was more pronounced for men with high-risk or poorly differentiated tumors. CONCLUSIONS: In this study, EBRT combined with HDR-BT was the most effective radiotherapy treatment regimen, especially for poorly differentiated tumors. Randomized trials comparing EBRT combined with HDR-BT with dose-escalated EBRT should be a priority.

Patterns of recurrence in anal cancer: a detailed analysis.

BACKGROUND: Anal cancer is a rare disease, which might be the reason for the "one size fits all" approach still used for radiotherapy target contouring. To refine and individualize future guidelines, detailed and contemporary pattern of recurrence studies are needed. METHODS: Consecutive anal cancer patients, all treated with curative intent intensity-modulated radiotherapy (IMRT), were retrospectively studied (n = 170). Data was extracted from medical records and radiological images. Radiotherapy planning CT's and treatment plans were reviewed, and recurrences were mapped and categorized according to radiation dose. RESULTS: The mean dose to the primary tumor was 59.0 Gy. With a median follow-up of 50 months (range 14-117 months), 5-year anal cancer specific survival was 86.1%. Only 1 of 20 local recurrences was located outside the high dose (CTVT) volume. More patients experienced a distant recurrence (n = 34; 20.0%) than a locoregional recurrence (n = 24; 14.1%). Seven patients (4.2%) had a common iliac and/or para-aortic (CI/PA) recurrence. External iliac lymph node involvement (P = 0.04), and metastases in ≥3 inguinal or pelvic lymph node regions (P = 0.02) were associated with a 15-18% risk of CI/PA recurrence. Following chemoradiotherapy, 6 patients with recurrent or primary metastatic CI/PA lymph nodes were free of recurrence at last follow-up. The overall rate of ano-inguinal lymphatic drainage (AILD) recurrence was 2 of 170 (1.2%), and among patients with inguinal metastases at initial diagnosis it was 2 of 65 (3.1%). CONCLUSIONS: We conclude that other measures than increased margins around the primary tumor are needed to improve local control. Furthermore, metastatic CI/PA lymph nodes, either at initial diagnosis or in the recurrent setting, should be considered potentially curable. Patients with certain patterns of metastatic pelvic lymph nodes might be at an increased risk of harboring tumor cells also in the CI/PA lymph nodes.

MR-PROTECT: Clinical feasibility of a prostate MRI-only radiotherapy treatment workflow and investigation of acceptance criteria.

BACKGROUND: Retrospective studies on MRI-only radiotherapy have been presented. Widespread clinical implementations of MRI-only workflows are however limited by the absence of guidelines. The MR-PROTECT trial presents an MRI-only radiotherapy workflow for prostate cancer using a new single sequence strategy. The workflow incorporated the commercial synthetic CT (sCT) generation software MriPlanner™ (Spectronic Medical, Helsingborg, Sweden). Feasibility of the workflow and limits for acceptance criteria were investigated for the suggested workflow with the aim to facilitate future clinical implementations. METHODS: An MRI-only workflow including imaging, post imaging tasks, treatment plan creation, quality assurance and treatment delivery was created with questionnaires. All tasks were performed in a single MR-sequence geometry, eliminating image registrations. Prospective CT-quality assurance (QA) was performed prior treatment comparing the PTV mean dose between sCT and CT dose-distributions. Retrospective analysis of the MRI-only gold fiducial marker (GFM) identification, DVH- analysis, gamma evaluation and patient set-up verification using GFMs and cone beam CT were performed. RESULTS: An MRI-only treatment was delivered to 39 out of 40 patients. The excluded patient was too large for the predefined imaging field-of-view. All tasks could successfully be performed for the treated patients. There was a maximum deviation of 1.2% in PTV mean dose was seen in the prospective CT-QA. Retrospective analysis showed a maximum deviation below 2% in the DVH-analysis after correction for rectal gas and gamma pass-rates above 98%. MRI-only patient set-up deviation was below 2 mm for all but one investigated case and a maximum of 2.2 mm deviation in the GFM-identification compared to CT. CONCLUSIONS: The MR-PROTECT trial shows the feasibility of an MRI-only prostate radiotherapy workflow. A major advantage with the presented workflow is the incorporation of a sCT-generation method with multi-vendor capability. The presented single sequence approach are easily adapted by other clinics and the general implementation procedure can be replicated. The dose deviation and the gamma pass-rate acceptance criteria earlier suggested was achievable, and these limits can thereby be confirmed. GFM-identification acceptance criteria are depending on the choice of identification method and slice thickness. Patient positioning strategies needs further investigations to establish acceptance criteria.

Erectile Dysfunction and Absorbed Dose to Penile Base Structures in a Randomized Trial Comparing Ultrahypofractionated and Conventionally Fractionated Radiation Therapy for Prostate Cancer.

PURPOSE: To study the relationships between absorbed dose to penile base structures and erectile dysfunction (ED) in patients treated with ultrahypofractionated (UHF) radiation therapy (RT) or conventionally fractionated (CF) RT for prostate cancer. METHODS AND MATERIALS: This dose-response study comprises 673 patients (57%) of the 1180 per-protocol patients included in the HYPO-RT-PC trial (median follow-up 5, years), where patients were randomized to CF (39 × 2.0 Gy, 8 weeks) or UHF (7 × 6.1 Gy, 2.5 weeks). No androgen deprivation therapy was allowed. Only patients with erectile function sufficient for intercourse at baseline and complete RT data were included in this study. Erectile function was assessed by physician at regular follow-ups. The main endpoint was severe ED (EDs). The penile bulb (PB) and crus were retrospectively delineated on the treatment planning computed tomography scans. Dose-volume descriptors were derived from EQD2 converted dose matrices (α/ß = 3 Gy). Univariable and multivariable Cox proportional hazard regression and logistic regression were used to find predictors for EDS. RESULTS: No significant difference in EDs was found between CF and UHF. During the follow-up period, EDs occurred in 27% of the patients in both treatment groups. Average (median) PB mean dose, Dmean, was 24.5 (20.2) in CF and 18.7 (13.1) Gy3 in UHF. Age was the only significant predictor for EDs in Cox analyses. All dose-volume variables contributed significantly in univariable logistic regression at 2-year follow-up. Age and near maximum dose (D2%) were significant predictors for EDs in multivariable logistic regression analyses at both 1 and 2 years. CONCLUSIONS: The frequency of EDS was similar in the CF and UHF treatment groups. Age at radiation therapy was the strongest predictor for EDs, followed by dose to PB, and was most evident for younger patients. We propose D2 % <50 Gy3 and Dmean <20 Gy3 to the PB as the primary objectives to be applied in the treatment planning process.