Response on DCE-MRI predicts outcome of salvage radiotherapy for local recurrence after radical prostatectomy

Prostate-Specific Membrane Antigen Positron Emission Tomography/Computed Tomography-Based Clinical Target Volume Delineation Guideline for Postprostatectomy Salvage Radiation Therapy: The PERYTON Guideline

PURPOSE

Prostate-specific membrane antigen positron emission tomography/computed tomography (PSMA PET/CT) scan is the standard imaging procedure for biochemical recurrent prostate cancer postprostatectomy because of its high detection rate at low serum prostate-specific antigen levels. However, existing guidelines for clinical target volume (CTV) in prostate bed salvage external beam radiation therapy (sEBRT) are primarily based on experience-based clinical consensus and have been validated using conventional imaging modalities. Therefore, this study aimed to optimize CTV definition in sEBRT by using PSMA PET/CT-detected local recurrences (LRs).

METHODS AND MATERIALS

Patients with suspected LR on PSMA PET/CT postprostatectomy were retrospectively enrolled in 9 Dutch centers. Anonymized scans were centrally reviewed by an expert nuclear medicine physician. Each boundary of the CTV guideline from the Groupe Francophone de Radiothérapie en Urologie (GFRU) was evaluated and adapted to improve the accuracy and coverage of the area at risk of LR (CTV) on PSMA PET/CT. The proposed CTV adaptation was discussed with the radiation oncologists of the participating centers, and final consensus was reached. To assess reproducibility, the participating centers were asked to delineate 3 new cases according to the new PERYTON-CTV, and the submitted contours were evaluated using the Dice similarity coefficient (DSC).

RESULTS

After central review, 93 LRs were identified on 83 PSMA PET/CTs. The proposed CTV definition improved the coverage of PSMA PET/CT-detected LRs from 67% to 96% compared with the GFRU-CTV, while reducing the GFRU-CTV by 25%. The new CTV was highly reproducible, with a mean DSC of 0.82 (range, 0.81-0.83).

CONCLUSIONS

This study contributes to the optimization of CTV definition in postprostatectomy sEBRT by using the pattern of LR detected on PSMA PET/CT. The PERYTON-CTV is highly reproducible across the participating centers and ensures coverage of 96% LRs while reducing the GFRU-CTV by 25%.

Multi-parametric MRI for radiotherapy simulation

Magnetic resonance imaging (MRI) has become an important imaging modality in the field of radiotherapy (RT) in the past decade, especially with the development of various novel MRI and image-guidance techniques. In this review article, we will describe recent developments and discuss the applications of multi-parametric MRI (mpMRI) in RT simulation. In this review, mpMRI refers to a general and loose definition which includes various multi-contrast MRI techniques. Specifically, we will focus on the implementation, challenges, and future directions of mpMRI techniques for RT simulation.

The Prognostic Value of DCE-MRI Findings before Salvage Radiotherapy after Radical Prostatectomy

BACKGROUND

To investigate the predictive role of dynamic contrast-enhanced-magnetic resonance imaging (DCE-MRI) findings before salvage radiotherapy after radical prostatectomy (RP).

METHODS

This retrospective study selected patients with biochemical failure (BF) after RP restaged with DCE-MRI. Patients underwent sRT in 30 fractions delivering 66-69 Gy and 73.5 Gy to the prostatic fossa and to the local failure as per DCE-MRI, respectively. Pelvic nodes were treated to 54 Gy in selected patients. The endpoint was BF after sRT.

RESULTS

In total, 236 patients were analyzed and 146 (61.9%) had presumed local failure at DCE-MRI: 54.8%, 23.8% and 21.4% were found at the vesico-urethral anastomosis (VUA), the bladder neck and the retro-vesical space, respectively. The presence of a local failure at DCE-MRI halved the risk of BF; VUA-only location and lesion volume were independently correlated with survival without evidence of biochemical failure (bNED) at multivariable analysis. For patients with VUA-only disease up to 0.4 cc, the 4-year-bNED was 94.6% (95%CI: 80.2-98.6%) as opposed to 80.9% (95%CI: 71.6-87.4%) and 73.7% (95%CI: 63.1-81.8%) for other lesions and no macrodisease, respectively.

CONCLUSIONS

DCE-MRI at restaging for BF after RP provides predictive and therapeutic information. Patients with small lesions at the VUA have an excellent prognosis after sRT.

Mapping of Local Recurrences After Radical Prostatectomy Using 68-Gallium-Prostate-Specific Membrane Antigen Positron Emission Tomography/Computed Tomography: Implications for Postprostatectomy Radiation Therapy Clinical Target Volumes

PURPOSE

Our objective is to describe the distribution of local recurrences after radical prostatectomy (RP) as delineated using 68-Gallium-prostate-specific membrane antigen positron emission tomography/computed tomography (⁶⁸Ga-PSMA PET/CT) to identify areas where current consensus guideline clinical target volumes (CTVs) are insufficient or excessive and to identify predictors of recurrence location within the fossa.

METHODS AND MATERIALS

Retrospective review of databases from 2 tertiary referral centers was performed to identify patients who underwent ⁶⁸Ga-PSMA PET/CT for biochemical recurrence after RP. Those with a component of local recurrence were included for further analysis. The epicenter of each recurrence was defined relative to reference points in 3 axes, categorized into 1 of 7 levels in the superior/inferior axis relative to the vesicourethral anastomosis, and recorded as within or outside the Faculty of Radiation Oncology Genito-urinary Group (FROGG) and Radiation Therapy Oncology Group consensus CTVs. Univariate and multivariate analysis was performed to identify predictors of recurrence location based on clinical and histopathologic variables.

RESULTS

One thousand forty-nine ⁶⁸Ga-PSMA PET/CT scans were reviewed. One hundred forty sites of local recurrence were identified on 132 scans. Relative to the vesicourethral anastomosis, 13 (9%), 31 (22%), 17 (12%), 24 (17%), 27 (19%), 20 (14%), and 8 (6%) recurrences occurred >5 mm inferior; within 5 mm above or below; and 6 to 15 mm, 16 to 25 mm, 26 to 35 mm, 36 to 45 mm, and >45 mm superiorly, respectively. Thirteen (9%) and 2 (1.4%) recurrences occurred beyond the FROGG and Radiation Therapy Oncology Group consensus CTVs, respectively, with all below the inferior CTV margin.

CONCLUSIONS

In the largest study to date mapping local recurrences after RP in 3-dimensions, we provide several insights to inform future contouring guidelines; in particular, 9% of recurrences occurred inferior to the FROGG CTV.

Comparison of rigid and deformable coregistration between mpMRI and CT images in radiotherapy of prostate bed cancer recurrence

PURPOSE

To evaluate the accuracy of rigid coregistration between multiparametric magnetic resonance (mpMR) and computed tomography (CT) images for radiotherapy of prostate bed cancer recurrence.

MATERIALS AND METHOD

Fifty-three patients (59 nodules) accrued in a prospective study on salvage radiotherapy for prostatic bed recurrence were suitable for the analysis. Patients underwent a pre radiotherapy mpMR exam and a planning CT in the same treatment position and with control of organ filling. The site of recurrence was delineated on mpMR images and contours transferred on planning CT images using both rigid and deformable registrations. Coregistrations were evaluated by mathematical operators that quantify deformation (Jacobian determinant and vector curl) and similarity indices (Dice and Jaccard coefficients). Dose coverage was evaluated.

RESULTS

Deformable registration did not change volumes, (p = 0.92 MW test). The Jacobian coefficient and the vector curl revealed no important image deformations. Dice and Jaccard coefficients indicated dislocation of the nodule volumes. Dislocation magnitude was d = (5.6 ± 3.1) mm. Organ filling was not correlated with deformation or dislocation. Volumes were covered by the 95% isodose in 96% of cases when rigid registration was performed versus 75% of cases when deformed.

CONCLUSIONS

Rigid image coregistration is sufficiently accurate in this setting. The results indicate that the deformable registration tends to shrink the voxels and to dislocate the ROI, the adopted expansion for the recurrence volume adequately accounts for the observed deformation and dislocation, provided that organ filling is controlled.

A Prospective Study Assessing the Post-Prostatectomy Detection Rate of a Presumed Local Failure at mpMR with Either 64CuCl2 or 64CuPSMA PET/CT

Simple Summary

The role of PET/CT with two novel tracers was investigated in prostate cancer patients with both a biochemical failure after surgery and a presumed local failure at multiparametric MR. Overall, both PET tracers detected only about 50% of local failures. Therefore, multiparametric MR remains the exam of choice to investigate the prostatic fossa in patients who fail surgery.

Abstract

Background: We aimed assess the detection rate (DR) of positron emission tomography/computed tomography with two novel tracers in patients referred for salvage radiotherapy (sRT) with a presumed local recurrence at multiparametric magnetic resonance (mpMR) after radical prostatectomy (RP). Methods: The present prospective study was conducted at a single institution between August 2017 and June 2020. Eligibility criteria were undetectable PSA after RP; subsequent biochemical recurrence (two consecutive PSA rises to 0.2 ng/mL or greater); a presumed local failure at mpMR; no distant metastases at ¹⁸F-fluorocholine PET/CT (CH/PET); no previous history of androgen deprivation therapy. Patients were offered both ⁶⁴CuCl₂ PET/CT (CU/PET) and ⁶⁴Cu-PSMA PET/CT (PSMA/PET) before sRT. After image co-registration, PET findings were compared to mpMR ones in terms of DR and independent predictors of DR investigated at logistic regression. Results: A total of 62 patients with 72 nodules at mpMR were accrued. Compared to mpMR (DR = 100%, 95%CI: 94.9–100%), DRs were 47.2% (95%CI: 36.1–58.6%) and 54.4% (95%CI: 42.7–65.7%) for CU/PET and PSMA/PET, respectively (p < 0.001 for both). Both experimental PET/CT performed particularly poorly at PSA levels consistent with early sRT. Conclusions: The two novel radiotracers are inferior to mpMR in restaging the prostatic fossa for sRT planning purposes, particularly in the context of early salvage radiotherapy.