Online Prostate-Specific Membrane Antigen and Positron Emission Tomography-Guided Radiation Therapy for Oligometastatic Prostate Cancer

Stereotactic body radiotherapy as metastasis-directed therapy in oligometastatic prostate cancer: a systematic review and meta-analysis of randomized controlled trials

BACKGROUND

The use of stereotactic body radiotherapy (SBRT) to definitively treat oligometastases in prostate cancer has drawn large clinical and research interests within radiation oncology. However, the evidence is considered in its early stages and there is currently no systematic review of randomized controlled trials (RCTs) in this field. We aimed to evaluate the efficacy and safety of SBRT as metastasis-directed therapy (MDT) in oligometastatic prostate cancer (OMPC) compared to no MDT reported in RCTs.

METHODS

MEDLINE, Embase, CINAHL Complete, and Cochrane Library were searched on October 28, 2023. Eligible studies were RCTs comparing SBRT as MDT with no MDT in extracranial OMPC, without restrictions on follow-up time, publication status, language, or year. Participant subsets fulfilling the eligibility criteria were included. Critical outcomes were overall survival and grade ≥ 3 toxicity, and additional important outcomes were progression-free survival (PFS), local control, grade 5 toxicity, health-related quality of life, and systemic therapy-free survival. Meta-analyses were planned. Risk of bias was assessed using the Cochrane risk-of-bias tool version 2, and the quality of evidence using the Grading of Recommendations Assessment, Development, and Evaluation.

RESULTS

In total, 1825 unique study reports were identified and seven phase II RCTs with 559 eligible participants were included. Four trials included multiple types of primary cancer. Outcome definitions were heterogeneous except for overall survival and toxicity. For overall survival, only one study reported events in both arms. Meta-analysis of the grade ≥ 3 toxicity results from two trials showed no difference (pooled risk ratio 0.78, 95% confidence interval 0.37-1.65, p = 0.52). Four trials reported significantly longer PFS, with a pooled hazard ratio of 0.31 (95% confidence interval 0.21-0.45, p < 0.00001). Risk of bias was of some concerns or high. Quality of evidence was low or moderate.

CONCLUSIONS

Phase II trials have shown promising improvements in PFS for several OMPC states without excess toxicity. Overall survival comparisons are immature. In future confirmatory phase III trials, adequately large sample sizes, blinding of outcome assessors, and/or increased adherence to assigned intervention could improve the quality of evidence. PROSPERO registration number: CRD42021230131.

The potential of biology-guided radiation therapy in thoracic cancer: A preliminary treatment planning study

Purpose

We investigated the feasibility of biology-guided radiotherapy (BgRT), a technique that utilizes real-time positron emission imaging to minimize tumor motion uncertainties, to spare nearby organs at risk.

Methods

Volumetric modulated arc therapy (VMAT), intensity-modulated proton (IMPT) therapy, and BgRT plans were created for a paratracheal node recurrence (case 1; 60 Gy in 10 fractions) and a primary peripheral left upper lobe adenocarcinoma (case 2; 50 Gy in four fractions).

Results

For case 1, BgRT produced lower bronchus V40 values compared to VMAT and IMPT. For case 2, total lung V20 was lower in the BgRT case compared to VMAT and IMPT.

Conclusions

BgRT has the potential to reduce the radiation dose to proximal critical structures but requires further detailed investigation.

Narrative Review of Synergistics Effects of Combining Immunotherapy and Stereotactic Radiation Therapy

Stereotactic radiotherapy (SRT) has become an attractive treatment modality in full bloom in recent years by presenting itself as a safe, noninvasive alternative to surgery to control primary or secondary malignancies. Although the focus has been on local tumor control as the therapeutic goal of stereotactic radiotherapy, rare but intriguing observations of abscopal (or out-of-field) effects have highlighted the exciting possibility of activating antitumor immunity using high-dose radiation. Furthermore, immunotherapy has revolutionized the treatment of several types of cancers in recent years. However, resistance to immunotherapy often develops. These observations have led researchers to combine immunotherapy with SRT in an attempt to improve outcomes. The benefits of this combination would come from the stimulation and suppression of various immune pathways. Thus, in this review, we will first discuss the immunomodulation induced by SRT with the promising results of preclinical studies on the changes in the immune balance observed after SRT. Then, we will discuss the opportunities and risks of the combination of SRT and immunotherapy with the preclinical and clinical data available in the literature. Furthermore, we will see that many perspectives are conceivable to potentiate the synergistic effects of this combination with the need for prospective studies to confirm the encouraging data.

Utility of Biology-Guided Radiotherapy to De Novo Metastases Diagnosed During Staging of High-Risk Biopsy-Proven Prostate Cancer

Background

Biology-guided radiotherapy (BgRT) uses real-time functional imaging to guide radiation therapy treatment. Positron emission tomography (PET) tracers targeting prostate-specific membrane antigen (PSMA) are superior for prostate cancer detection than conventional imaging. This study aims at describing nodal and distant metastasis distribution from prostate cancer and at determining the proportion of metastatic lesions suitable for BgRT.

Methods

A single-institution patient subset from the ProPSMA trial (ID ACTRN12617000005358) was analysed. Gross tumour volumes (GTV) were delineated on the CT component of a PSMA PET/CT scan. To determine the suitability of BgRT tracking zones, the normalized SUV (nSUV) was calculated as the ratio of SUVmax inside the GTV to the SUVmean of adjacent three-dimensional shells of thickness 5 mm/10 mm/20 mm as a measure of signal to background contrast. Targets were suitable for BgRT if (1) nSUV was larger than an nSUV threshold and (2) non-tumour tissue inside adjacent shell was free of PET-avid uptake.

Results

Of this cohort of 84 patients, 24 had at least one pelvic node or metastatic site disease, 1 to 13 lesions per patient, with a total of 98 lesions (60 pelvic nodes/38 extra-pelvic nodal diseases and haematogenous metastases). Target volumes ranged from 0.08 to 9.6 cm³ while SUVmax ranged from 2.1 to 55.0. nSUV ranged from 1.9 to 15.7/2.4 to 25.7/2.5 to 34.5 for the 5 mm/10 mm/20 mm shell expansion. Furthermore, 74%/68%/34% of the lesions had nSUV ≥ 3 and were free of PSMA PET uptake inside the GTV outer shell margin expansion of 5 mm/10 mm/20 mm. Adjacent avid organs were another lesion, bladder, bowel, ureter, prostate, and liver.

Conclusions

The majority of PSMA PET/CT-defined radiotherapy targets would be suitable for BgRT by using a 10-mm tracking zone in prostate cancer. A subset of lesions had adjacent non-tumour uptake, mainly due to the proximity of ureter or bladder, and may require exclusion from emission tracking during BgRT.

Prostate specific membrane antigen positron emission tomography for lesion-directed high-dose-rate brachytherapy dose escalation

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This paper evaluated lesion-directed prostatic high dose rate brachytherapy.

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Lesions defined by prostate specific membrane antigen positron emission tomography.

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Dose escalation was confirmed using whole-mount digital histology.

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Targeting lesions led to significantly higher dose to high-grade histologic cancer.

Background and purpose

Prostate specific membrane antigen positron emission tomography imaging (PSMA-PET) has demonstrated potential for intra-prostatic lesion localization. We leveraged our existing database of co-registered PSMA-PET imaging with cross sectional digitized pathology to model dose coverage of histologically-defined prostate cancer when tailoring brachytherapy dose escalation based on PSMA-PET imaging.

Materials and methods

Using a previously-developed automated approach, we created segmentation volumes delineating underlying dominant intraprostatic lesions for ten men with co-registered pathology-imaging datasets. To simulate realistic high-dose-rate brachytherapy (HDR-BT) treatments, we registered the PSMA-PET-defined segmentation volumes and underlying cancer to 3D trans-rectal ultrasound images of HDR-BT cases where 15 Gray (Gy) was delivered. We applied dose/volume optimization to focally target the dominant intraprostatic lesion identified on PSMA-PET. We then compared histopathology dose for all high-grade cancer within whole-gland treatment plans versus PSMA-PET-targeted plans. Histopathology dose was analyzed for all clinically significant cancer with a Gleason score of 7or greater.

Results

The standard whole-gland plans achieved a median [interquartile range] D98 of 15.2 [13.8–16.4] Gy to the histologically-defined cancer, while the targeted plans achieved a significantly higher D98 of 16.5 [15.0–19.0] Gy (p = 0.007).

Conclusion

This study is the first to use digital histology to confirm the effectiveness of PSMA-PET HDR-BT dose escalation using automatically generated contours. Based on the findings of this study, PSMA-PET lesion dose escalation can lead to increased dose to the ground truth histologically defined cancer.

Oligometastatic prostate cancer treatment

Oligometastatic prostate cancer is an intermediate state between localized disease and widespread metastasis. Its biological and clinical peculiarities are still to be elucidated. New imaging techniques contribute to the detection of patients with oligometastatic disease. PET/CT scanning with prostate-specific membrane antigen can improve the selection of men with true early, low-volume oligometastatic disease, who are candidates for metastasis-directed therapy. Clinical studies demonstrated that androgen deprivation therapy can be delayed in oligometastatic patients with a low tumor burden, although no survival benefit has been demonstrated at present. This article presents available evidence on the treatment strategies for oligometastatic prostate cancer.

Future Directions in the Use of SAbR for the Treatment of Oligometastatic Cancers

The role of local therapy as a sole therapy or part of a combined approach in treating metastatic cancer continues to evolve. The most obvious requirements for prudent implementation of local therapies like stereotactic ablative radiotherapy (SAbR) to become mainstream in treating oligometastases are (1) Clear guidance as to what particular patients might benefit, and (2) Confirmation of improvements in outcome after such treatments via clinical trials. These future directional requirements are non-negotiable. However, innovation and research offer many more opportunities to understand and improve therapy. Identifying candidates and personalizing their therapy can be afforded via proteomic, genomic and epigenomic characterization techniques. Such molecular profiling along with liquid biopsy opportunities will both help select best therapies and facilitate ongoing monitoring of response. Technologies both to find targets and help deliver less-toxic therapy continue to improve and will be available in the marketplace. These technologies include molecular-based imaging (eg, PET-PSMA), FLASH ultra-high dose rate platforms, Grid therapy, PULSAR adaptive dosing, and MRI/PET guided linear accelerators. Importantly, a treatment approach beyond oligometastastic could evolve including a rationale for using SAbR in the oligoprogressive, oligononresponsive, oligobulky and oligolethal settings as well as expansion beyond oligo- toward even plurimetastastic disease. In any case, lessons learned and experiences required by the implementation of using SAbR in oligometastatic cancer will be revisited.

Peripheral androgen blockade in men with castrate-sensitive biochemical recurrent prostate cancer

The aim of the study was to evaluate the feasibility of utilizing peripheral androgen blockade in men with biochemical recurrent castrate-sensitive prostate cancer. A registration study to track outcomes of men with biochemical recurrent castrate-sensitive prostate cancer treated with peripheral androgen blockade utilizing concomitant administration of finasteride and bicalutamide. Men were on intermittent peripheral blockade for a median 20.2 months, continuous peripheral blockade for a median 6.8 months, intermittent triple dose peripheral androgen blockade for a median 10.7 months, and continuous triple dose peripheral androgen blockade for 4.4 months before failing therapy. Six men (21%) had additional therapies during treatment that included metastasis-directed therapy (5/37, 14%), systemic Lu-177 (2/37, 5%), and salvage RT (1/37, 3%). The median time to progression, which includes time from initiation through all therapies to the initiation of ADT, was 37.6 months (IQR 20-74.7). From the start of PAB, median time to castrate resistance was 49.8 months (IQR 40.9-NR). After starting ADT, median time to castrate resistance was 8.8 months (IQR 4.6-17.7). Our data support the exploration of PAB as a treatment option in carefully selected patients who present with biochemical recurrence after failure of definitive local therapy for prostate cancer.

Biology-guided radiotherapy: redefining the role of radiotherapy in metastatic cancer

The emerging biological understanding of metastatic cancer and proof-of-concept clinical trials suggest that debulking all gross disease holds great promise for improving patient outcomes. However, ablation of multiple targets with conventional external beam radiotherapy systems is burdensome, which limits investigation and utilization of complete metastatic ablation in the majority of patients with advanced disease. To overcome this logistical hurdle, technical innovation is necessary. Biology-guided radiotherapy (BgRT) is a new external beam radiotherapy delivery modality combining positron emission tomography-computed tomography (PET-CT) with a 6 MV linear accelerator. The key innovation is continuous response of the linear accelerator to outgoing tumor PET emissions with beamlets of radiotherapy at subsecond latency. This allows the deposited dose to track tumors in real time. Multiple new hardware and algorithmic advances further facilitate this low-latency feedback process. By transforming tumors into their own fiducials after intravenous injection of a radiotracer, BgRT has the potential to enable complete metastatic ablation in a manner efficient for a single patient and scalable to entire populations with metastatic disease. Future trends may further enhance the utility of BgRT in the clinic as this technology dovetails with other innovations in radiotherapy, including novel dose painting and fractionation schemes, radiomics, and new radiotracers.

Targeting Stereotactic Body Radiotherapy on Metabolic PET- and Immuno-PET-Positive Vertebral Metastases

(1) Background: Stereotactic body radiotherapy (SBRT) for vertebral metastases (VM) allows the delivery of high radiation doses to tumors while sparing the spinal cord. We report a new approach to clinical target volume (CTV) delineation based on anti-carcinoembryonic antigen (CEA) positron emission tomography (pretargeted immuno-PET; “iPET”) in patients with metastatic breast cancer (BC) or medullary thyroid cancer (MTC). (2) Methods: All patients underwent iPET, spine magnetic resonance imaging (MRI), and positron emission tomography-computed tomography (PET-CT) using ¹⁸F-deoxyglucose (FDG) for BC or ¹⁸F-dihydroxy-phenylalanine (F-DOPA) for MTC. Vertebrae locations and vertebral segments of lesions were recorded and the impact on CTV delineation was evaluated. (3) Results: Forty-six VM eligible for SBRT following iPET were evaluated in eight patients (five BC, three MTC). Eighty-one vertebral segments were detected using MRI, 26 with FDG or F-DOPA PET/CT, and 70 using iPET. iPET was able to detect more lesions than MRI for vertebral bodies (44 vs. 34). iPET-based delineation modified MRI-based CTV in 70% (32/46) of cases. (4) Conclusion: iPET allows a precise mapping of affected VM segments, and adds complementary information to MRI in the definition of candidate volumes for VM SBRT. iPET may facilitate determining target volumes for treatment with stereotactic body radiotherapy in metastatic vertebral disease.