Defining radio-recurrent intra-prostatic target volumes using PSMA-targeted PET/CT and multi-parametric MRI

Re-irradiation to the prostate using stereotactic body radiotherapy (SBRT) after initial definitive radiotherapy - A systematic review and meta-analysis of recent trials

Background

There is increasing data on re-irradiation to the prostate using stereotactic body radiotherapy (SBRT) after definitive radiotherapy for prostate cancer, with increasing evidence on prostate re-irradiation using a C-arm LINAC or an MR LINAC in recent years. We therefore conducted this systematic review and meta-analysis on prostate re-irradiation including studies published from 2020 to 2023, to serve as an update on existing meta-analysis.

Methods

We searched the PubMed and Embase databases in October 2023 with queries including combinations of "repeat", "radiotherapy", "prostate", "re-irradiation", "reirradiation", "re treatment", "SBRT", "retreatment". Publication date was set to be from 2020 to 2023. There was no limitation regarding language. We adhered to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) recommendations. After data extraction, heterogeneity testing was done by calculating the I2. A random effects model with a restricted maximum likelihood estimator was used to estimate the combined effect. Funnel plot asymmetry was assessed visually and using Egger's test to estimate the presence of publication and/or small study bias.

Results

14 publications were included in the systematic review. The rates of acute ≥ grade 2 (G2) genitourinary (GU) and gastrointestinal (GI) toxicities reported in the included studies ranged from 0.0-30.0 % and 0.0-25.0 % respectively. For late ≥ G2 GU and GI toxicity, the ranges are 4.0-51.8 % and 0.0-25.0 %. The pooled rate of acute GU and GI toxicity ≥ G2 were 13 % (95 % CI: 7-18 %) and 2 % (95 % CI: 0-4 %). For late GU and GI toxicity ≥ G2 the pooled rates were 25 % (95 % CI: 14-35 %) and 5 % (95 % CI: 1-9 %). The pooled 2-year biochemical recurrence-free survival was 72 % (95 % CI: 64-92 %).

Conclusions

SBRT in the re-irradiation of radiorecurrent prostate cancer is safe and effective. Further prospective data are warranted.

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.

Importance of magnetic resonance imaging and prostate-specific membrane antigen PET-CT in patients treated with salvage radical prostatectomy for radiorecurrent prostate cancer

BACKGROUND

Accurate staging and identification of optimal candidates for local salvage therapy, such as salvage radical prostatectomy (SRP), is necessary to ensure optimal care in patients with radiorecurrent prostate cancer (PCa). We aimed to analyze performance of magnetic resonance imaging (MRI) and prostate-specific membrane antigen (PSMA)-positron emission tomography (PET)/computed tomography (CT) for predicting pathologic nonorgan confined disease (pT3) and lymph node involvement (pN+) in patients treated with SRP for radiorecurrent PCa.

METHODS

We retrospectively reviewed the institutional database to identify patients who underwent MRI or ⁶⁸ Ga-PSMA-PET/CT before SRP for radiorecurrent PCa. The diagnostic estimates of MRI and PSMA-PET/CT for pT3 and pN+, were calculated.

RESULTS

We identified 113 patients with radiorecurrent PCa who underwent preoperative MRI followed by SRP; 53 had preoperative ⁶⁸ Ga-PSMA-PET/CT. For the detection of pT3 disease, the overall accuracy of MRI was 70% (95% confidence interval [CI] 61-78), sensitivity 40% (95% CI 26-55) and specificity 94% (95% CI 85-98); PSMA-PET/CT had slightly higher accuracy of 77% (95% CI 64-88), and higher sensitivity of 90% (95% CI 68-99), but lower specificity of 70% (95% CI 51-84). For pN+ disease, MRI had poor sensitivity of 14% (95% CI 3-36), specificity of 50 (95% CI 39-61) and total accuracy of 43% (95% CI 34-53); PSMA-PET/CT had an accuracy of 85% (95% CI 72-93), sensitivity of 27% (95% CI 6-61), and specificity of 100% (95% CI 92-100).

CONCLUSION

In patients with radiorecurrent PCa, both, MRI, and ⁶⁸ Ga-PSMA PET/CT are valuable tools for the pre-SRP staging and should be integrated into the standard workup. For lymph node metastases, ⁶⁸ Ga-PSMA PET/CT is a strong rule-in test with nearly perfect specificity; in contrast MRI had a low accuracy for lymph node metastases.

A Prospective Study of MR-Guided Focal Salvage High Dose-Rate Brachytherapy for Radiorecurrent Prostate Cancer: Updated Results of 30 Patients

PURPOSE

Limited prospective data on focal salvage high dose-rate (HDR) prostate brachytherapy are available. We sought to explore the toxicities, health related quality of life (HRQOL) and efficacy of focal salvage HDR brachytherapy in a prospective clinical trial. This report represents updated results of previously published data.

MATERIALS AND METHODS

Patients with locally recurrent prostate cancer after previous external beam radiotherapy and/or brachytherapy were enrolled. Patients received MRI-guided, ultrasound-based focal HDR brachytherapy delivered over two fractions of 13.5 Gy delivered 1-2 weeks apart. Androgen deprivation therapy (ADT) was not used.

RESULTS

Thirty patients were treated between 2012-2019. At a median follow-up of 39 months, the three-year biochemical failure-free rate was 61.8% (95% CI 44.0-86.6%), and three-year ADT/salvage therapy-free rate was 86.0% (95% CI 74.1-99.8%). Seventeen patients experienced subsequent biochemical failure, 9 have received ADT and/or further local salvage, and no patients have died from prostate cancer. Of the 28 patients who had a post-treatment MRI, 26 had a local treatment response. No acute grade ≥ 3 GU/GI toxicity was observed. One temporary late grade 3 GU toxicity event occurred, and no late grade ≥ 3 GI toxicity was seen. No significant decline in urinary or bowel HRQOL was observed.

CONCLUSIONS

Focal salvage HDR brachytherapy has a favourable side effect profile, no significant decline in HRQOL and 3-year biochemical control rates in line with other salvage options. While early MRI response at the treated site is common, this does not preclude subsequent biochemical failure.

Imaging Biomarkers in Prostate Stereotactic Body Radiotherapy: A Review and Clinical Trial Protocol

Advances in imaging have changed prostate radiotherapy through improved biochemical control from focal boost and improved detection of recurrence. These advances are reviewed in the context of prostate stereotactic body radiation therapy (SBRT) and the ARGOS/CLIMBER trial protocol. ARGOS/CLIMBER will evaluate 1) the safety and feasibility of SBRT with focal boost guided by multiparametric MRI (mpMRI) and ¹⁸F-PSMA-1007 PET and 2) imaging and laboratory biomarkers for response to SBRT. To date, response to prostate SBRT is most commonly evaluated using the Phoenix Criteria for biochemical failure. The drawbacks of this approach include lack of lesion identification, a high false-positive rate, and delay in identifying treatment failure. Patients in ARGOS/CLIMBER will receive dynamic ¹⁸F-PSMA-1007 PET and mpMRI prior to SBRT for treatment planning and at 6 and 24 months after SBRT to assess response. Imaging findings will be correlated with prostate-specific antigen (PSA) and biopsy results, with the goal of early, non-invasive, and accurate identification of treatment failure.