Patterns of Prostate Cancer Recurrence After Brachytherapy Determined by Prostate-Specific Membrane Antigen-Positron Emission Tomography and Computed Tomography Imaging

Target Volume Optimization for Localized Prostate Cancer

PURPOSE

To provide a comprehensive review of the means by which to optimize target volume definition for the purposes of treatment planning for patients with intact prostate cancer with a specific emphasis on focal boost volume definition.

METHODS

Here we conduct a narrative review of the available literature summarizing the current state of knowledge on optimizing target volume definition for the treatment of localized prostate cancer.

RESULTS

Historically, the treatment of prostate cancer included a uniform prescription dose administered to the entire prostate with or without coverage of all or part of the seminal vesicles. The development of prostate magnetic resonance imaging (MRI) and positron emission tomography (PET) using prostate-specific radiotracers has ushered in an era in which radiation oncologists are able to localize and focally dose-escalate high-risk volumes in the prostate gland. Recent phase 3 data has demonstrated that incorporating focal dose escalation to high-risk subvolumes of the prostate improves biochemical control without significantly increasing toxicity. Still, several fundamental questions remain regarding the optimal target volume definition and prescription strategy to implement this technique. Given the remaining uncertainty, a knowledge of the pathological correlates of radiographic findings and the anatomic patterns of tumor spread may help inform clinical judgement for the definition of clinical target volumes.

CONCLUSION

Advanced imaging has the ability to improve outcomes for patients with prostate cancer in multiple ways, including by enabling focal dose escalation to high-risk subvolumes. However, many questions remain regarding the optimal target volume definition and prescription strategy to implement this practice, and key knowledge gaps remain. A detailed understanding of the pathological correlates of radiographic findings and the patterns of local tumor spread may help inform clinical judgement for target volume definition given the current state of uncertainty.

Stereotactic Body Radiation Therapy Salvage for Lymph Node Recurrent Prostate Cancer in the Era of PSMA PET Imaging

PURPOSE OF REVIEW

Our understanding of patterns of prostate cancer recurrence after primary treatment of localized disease has significantly evolved since the development of positron emission tomography (PET) agents targeting prostate cancer. Previously, most biochemical recurrences were not associated with imaging correlates when restaging with computed tomography (CT), magnetic resonance imaging (MRI), or bone scintigraphy and, hence, were typically assumed to represent occult metastases. A rising prostate specific antigen (PSA) after previous local therapy prompting a PET scan showing uptake limited to regional lymph nodes is an increasingly common clinical scenario as advanced prostate cancer imaging becomes more widely utilized. The optimal management strategy for patients who have lymph node recurrent prostate cancer is both unclear and evolving, particularly in terms of local and regionally directed therapies. Stereotactic body radiation therapy (SBRT) utilizes ablative radiation doses with steep gradients to achieve local tumor control while sparing nearby normal tissues. SBRT is an attractive therapeutic modality due to its efficacy, favorable toxicity profile, and flexibility to administer elective doses to areas of potential occult involvement. The purpose of this review is to briefly describe how SBRT is being implemented in the era of PSMA PET for the management of solely lymph node recurrent prostate cancer.

RECENT FINDINGS

SBRT has been shown to effectively control individual lymph node tumor deposits within the pelvis and retroperitoneum for prostate cancer and is well-tolerated with a favorable toxicity profile. However, a major limitation thus far has been the lack of prospective trials supporting the use of SBRT for oligometastatic nodal recurrent prostate cancer. As further trials are conducted, its exact role in the treatment paradigm of recurrent prostate cancer will be better established. Although PET-guided SBRT appears feasible and potentially beneficial, there is still considerable uncertainty about the use of elective nodal radiotherapy (ENRT) in patients with nodal recurrent oligometastatic prostate cancer. PSMA PET has undoubtedly advanced imaging of recurrent prostate cancer, revealing anatomic correlates for disease recurrence that previously went undetected. At the same time, SBRT continues to be explored in prostate cancer with feasibility, a favorable risk profile, and satisfactory oncologic outcomes. However, much of the existing literature comes from the pre-PSMA PET era and integration of this novel imaging approach has led to greater focus on new and ongoing clinical trials to rigorously evaluate this approach and compare to other established treatment modalities utilized for oligometastatic, nodal recurrence of prostate cancer.

Salvage Prostate Brachytherapy in Radiorecurrent Prostate Cancer: An International Delphi Consensus Study

BACKGROUND AND PURPOSE

Local recurrences after previous radiotherapy (RT) are increasingly being identified in biochemically recurrent prostate cancer. Salvage prostate brachytherapy (BT) is an effective and well tolerated treatment option. We sought to generate international consensus statements on the use and preferred technical considerations for salvage prostate BT.

MATERIALS AND METHODS

International experts in salvage prostate BT were invited (n=34) to participate. A three-round modified Delphi technique was utilized, with questions focused on patient- and cancer-specific criteria, type and technique of BT, and follow-up. An a priori threshold for consensus of ≥ 75% was set, with a majority opinion being ≥ 50%.

RESULTS

Thirty international experts agreed to participate. Consensus was achieved for 56% (18/32) of statements. Consensus was achieved in several areas of patient selection: 1) A minimum of 2-3 years from initial RT to salvage BT; 2) MRI and PSMA PET should be obtained; and 3) Both targeted and systematic biopsies should be performed. Several areas did not reach consensus: 1) Maximum T stage/PSA at time of salvage; 2) Utilization/duration of ADT; 3) Appropriateness of combining local salvage with SABR for oligometastatic disease and 4) Repeating a second course of salvage BT. A majority opinion preferred High Dose-Rate salvage BT, and indicated that both focal and whole gland techniques could be appropriate. There was no single preferred dose/fractionation.

CONCLUSION

Areas of consensus within our Delphi study may serve as practical advice for salvage prostate BT. Future research in salvage BT should address areas of controversy identified in our study.