Prostate cancer post-prostatectomy radiotherapy: CT vs MRI for vesico-urethral anastomosis target delineation

Artificial intelligence in radiotherapy: Current applications and future trends

Radiation therapy has dramatically changed with the advent of computed tomography and intensity modulation. This added complexity to the workflow but allowed for more precise and reproducible treatment. As a result, these advances required the accurate delineation of many more volumes, raising questions about how to delineate them, in a uniform manner across centers. Then, as computing power improved, reverse planning became possible and three-dimensional dose distributions could be generated. Artificial intelligence offers the opportunity to make such workflow more efficient while increasing practice homogeneity. Many artificial intelligence-based tools are being implemented in routine practice to increase efficiency, reduce workload and improve homogeneity of treatments. Data retrieved from this workflow could be combined with clinical data and omic data to develop predictive tools to support clinical decision-making process. Such predictive tools are at the stage of proof-of-concept and need to be explainatory, prospectively validated, and based on large and multicenter cohorts. Nevertheless, they could bridge the gap to personalized radiation oncology, by personalizing oncologic strategies, dose prescriptions to tumor volumes and dose constraints to organs at risk.

Development of Prostate Bed Delineation Consensus Guidelines for Magnetic Resonance Image-Guided Radiotherapy and Assessment of Its Effect on Interobserver Variability

PURPOSE

The use of magnetic resonance imaging (MRI) in radiotherapy planning is becoming more widespread, particularly with the emergence of MRI-guided radiotherapy systems. Existing guidelines for defining the prostate bed clinical target volume (CTV) show considerable heterogeneity. This study aimed to establish baseline interobserver variability (IOV) for prostate bed CTV contouring on MRI, develop international consensus guidelines, and evaluate its effect on IOV.

METHODS AND MATERIALS

Participants delineated the CTV on 3 MRI scans, obtained from the Elekta Unity MR-Linac, as per their normal practice. Radiation oncologist contours were visually examined for discrepancies, and interobserver comparisons were evaluated against simultaneous truth and performance level estimation (STAPLE) contours using overlap metrics (Dice similarity coefficient and Cohen's kappa), distance metrics (mean distance to agreement and Hausdorff distance), and volume measurements. A literature review of postradical prostatectomy local recurrence patterns was performed and presented alongside IOV results to the participants. Consensus guidelines were collectively constructed, and IOV assessment was repeated using these guidelines.

RESULTS

Sixteen radiation oncologists' contours were included in the final analysis. Visual evaluation demonstrated significant differences in the superior, inferior, and anterior borders. Baseline IOV assessment indicated moderate agreement for the overlap metrics while volume and distance metrics demonstrated greater variability. Consensus for optimal prostate bed CTV boundaries was established during a virtual meeting. After guideline development, a decrease in IOV was observed. The maximum volume ratio decreased from 4.7 to 3.1 and volume coefficient of variation reduced from 40% to 34%. The mean Dice similarity coefficient rose from 0.72 to 0.75 and the mean distance to agreement decreased from 3.63 to 2.95 mm.

CONCLUSIONS

Interobserver variability in prostate bed contouring exists among international genitourinary experts, although this is lower than previously reported. Consensus guidelines for MRI-based prostate bed contouring have been developed, and this has resulted in an improvement in contouring concordance. However, IOV persists and strategies such as an education program, development of a contouring atlas, and further refinement of the guidelines may lead to additional improvements.

Prostate-specific membrane antigen positron emission tomography detected local failure after post-prostatectomy radiation therapy: Low rates of out-of-field recurrence validates current Australian prostate bed contouring guidelines

INTRODUCTION

The Australian Faculty of Radiation Oncology Genitourinary Group (FROGG) developed prostate bed clinical target volume (CTV) contouring guidelines which were subsequently used to develop the National EviQ guidelines for adjuvant and salvage post-prostatectomy radiotherapy (PPRT). These guidelines were based mainly upon consensus agreement. With the advent of prostate-specific membrane antigen (PSMA) positron emission tomography (PET), sites of recurrence can now be detected with low prostate-specific antigen (PSA) levels following radical prostatectomy. We evaluated sites of recurrence in patients treated with FROGG/EviQ CTVs to inform upcoming modifications of these guidelines.

METHODS

At our institution, we use the FROGG/EviQ guidelines for PPRT. From 2015, patients with PSA failure following PPRT have been re-staged using PSMA PET imaging. We identified patients with PET-avid local, nodal, and distant recurrences, fusing them with original treatment plans to determine whether recurrences were within or outside the prostate bed CTV. Regional nodal failures were reviewed to determine if they were within current elective node contouring guidelines.

RESULTS

Ninety-four patients had positive PSMA PET following PPRT. Nine (9.6%) recurrences were local, seven being local-only. One local recurrence (1.1%) was just superior to the contoured prostate bed CTV, located within the vas deferens. Seventy-three (77.7%) patients had a component of node failure, with 56 (59.6%) having node-only failure. Sites of nodal relapses were covered by standard contouring guidelines 60.3% of the time.

CONCLUSION

The low recurrence rate outside of current prostate bed CTV contouring guidelines is consistent with other studies using contemporary contouring, and validates the efficacy of the current FROGG/EviQ prostate bed CTV definition.

ESTRO ACROP guideline on prostate bed delineation for postoperative radiotherapy in prostate cancer

Purpose/Objective

Radiotherapy to the prostate bed is a potentially curative salvage option after radical prostatectomy. Although prostate bed contouring guidelines are available in the literature, important variabilities exist. The objective of this work is to provide a contemporary consensus guideline for prostate bed delineation for postoperative radiotherapy.

Methods

An ESTRO-ACROP contouring consensus panel consisting of 11 radiation oncologists and one radiologist, all with known subspecialty expertise in prostate cancer, was established. Participants were asked to delineate the prostate bed clinical target volumes (CTVs) in 3 separate clinically relevant scenarios: adjuvant radiation, salvage radiation with PSA progression, and salvage radiation with persistently elevated PSA. These cases focused on the presence of positive surgical margin, extracapsular extension, and seminal vesicles involvement. None of the cases had radiographic evidence of local recurrence on imaging. A single computed tomography (CT) dataset was shared via FALCON platform and contours were performed using EduCaseTM software. Contours were analyzed qualitatively using heatmaps which provided a visual assessment of controversial regions and quantitatively analyzed using Sorensen-Dice similarity coefficients. Participants also answered case-specific questionnaires addressing detailed recommendations on target delineation. Discussions via electronic mails and videoconferences for final editing and consensus were performed.

Results

The mean CTV for the adjuvant case was 76 cc (SD = 26.6), salvage radiation with PSA progression was 51.80 cc (SD = 22.7), and salvage radiation with persistently elevated PSA 57.63 cc (SD = 25.2). Compared to the median, the mean Sorensen-Dice similarity coefficient for the adjuvant case was 0.60 (SD 0.10), salvage radiation with PSA progression was 0.58 (SD = 0.12), and salvage radiation with persistently elevated PSA 0.60 (SD = 0.11). A heatmap for each clinical scenario was generated. The group agreed to proceed with a uniform recommendation for all cases, independent of the radiotherapy timing. Several controversial areas of the prostate bed CTV were identified based on both heatmaps and questionnaires. This formed the basis for discussions via videoconferences where the panel achieved consensus on the prostate bed CTV to be used as a novel guideline for postoperative prostate cancer radiotherapy.

Conclusion

Variability was observed in a group formed by experienced genitourinary radiation oncologists and a radiologist. A single contemporary ESTRO-ACROP consensus guideline was developed to address areas of dissonance and improve consistency in prostate bed delineation, independent of the indication.There is important variability in existing contouring guidelines for postoperative prostate bed (PB) radiotherapy (RT) after radical prostatectomy. This work aimed at providing a contemporary consensus guideline for PB delineation. An ESTRO ACROP consensus panel including radiation oncologists and a radiologist, all with known subspecialty expertise in prostate cancer, delineated the PB CTV in 3 scenarios: adjuvant RT, salvage RT with PSA progression, and salvage RT with persistently elevated PSA. None of the cases had evidence of local recurrence. Contours were analysed qualitatively using heatmaps for visual assessment of controversial regions and quantitatively using Sorensen-Dice coefficient. Case-specific questionnaires were also discussed via e-mails and videoconferences for consensus. Several controversial areas of the PB CTV were identified based on both heatmaps and questionnaires. This formed the basis for discussions via videoconferences. Finally, a contemporary ESTRO-ACROP consensus guideline was developed to address areas of dissonance and improve consistency in PB delineation, independent of the indication.

A rapid review of influential factors and appraised solutions on organ delineation uncertainties reduction in radiotherapy

Background and purpose.Accurate volume delineation plays an essential role in radiotherapy. Contouring is a potential source of uncertainties in radiotherapy treatment planning that could affect treatment outcomes. Therefore, reducing the degree of contouring uncertainties is crucial. The role of utilized imaging modality in the organ delineation uncertainties has been investigated. This systematic review explores the influential factors on inter-and intra-observer uncertainties of target volume and organs at risk (OARs) delineation focusing on the used imaging modality for these uncertainties reduction and the reported subsequent histopathology and follow-up assessment.Methods and materials.An inclusive search strategy has been conducted to query the available online databases (Scopus, Google Scholar, PubMed, and Medline). 'Organ at risk', 'target', 'delineation', 'uncertainties', 'radiotherapy' and their relevant terms were utilized using every database searching syntax. Final article extraction was performed following Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guideline. Included studies were limited to the ones published in English between 1995 and 2020 and that just deal with computed tomography (CT) and magnetic resonance imaging (MRI) modalities.Results.A total of 923 studies were screened and 78 were included of which 31 related to the prostate 20 to the breast, 18 to the head and neck, and 9 to the brain tumor site. 98% of the extracted studies performed volumetric analysis. Only 24% of the publications reported the dose deviations resulted from variation in volume delineation Also, heterogeneity in studied populations and reported geometric and volumetric parameters were identified such that quantitative synthesis was not appropriate.Conclusion.This review highlightes the inter- and intra-observer variations that could lead to contouring uncertainties and impede tumor control in radiotherapy. For improving volume delineation and reducing inter-observer variability, the implementation of well structured training programs, homogeneity in following consensus and guidelines, reliable ground truth selection, and proper imaging modality utilization could be clinically beneficial.

Vesico-urethral anastomosis sampling: a forgotten tool for guiding salvage radiation after radical prostatectomy

OBJECTIVE

To review the utility of vesicourethral anastomosis (VUA)-directed biopsy in the setting of biochemical recurrence (BCR) after radical prostatectomy (RP) for prostate cancer (PCa) in patients who have undergone evaluation by gallium-68 prostate-specific membrane antigen positron emission tomography with computed tomography (⁶⁸ Ga-PSMA PET/CT).

METHODS

We completed a retrospective review of a prospectively maintained dataset from January 2015 to August 2020. Patient demographics were recorded for those who experienced BCR, as defined by a rise in prostate-specific antigen (PSA) level to above 0.2 ng/mL, who had a ⁶⁸ Ga-PSMA PET/CT that did not demonstrate recurrence within the prostate bed, and who subsequently underwent a transperineal ultrasonography (TPUS)-guided biopsy directed at the VUA. Histological reporting of the biopsies was undertaken in order to determine whether the benefits of salvage radiation therapy (SRT) could be justified by the presence of cancer cells.

RESULTS

Eighteen patients who had a ⁶⁸ Ga-PSMA PET/CT and underwent VUA-directed biopsy were identified as having BCR. ⁶⁸ Ga-PSMA PET/CT scans demonstrated avidity at the VUA in none of the patients, although two out of 18 patients showed avidity in the seminal vesicles and two out of 18 patients showed avidity within regional lymph nodes. Histology from the TPUS-guided, VUA-directed biopsies demonstrated no prostatic tissue in six out of 18 and presence of prostatic tissue in 12 out of 18 of patients, respectively. In 7 out of 18 cases, there was histological evidence of recurrent PCa at the VUA in the absence of a positive ⁶⁸ Ga-PSMA PET/CT scan.

CONCLUSION

This study highlights the potential value of VUA-directed biopsy. We are reminded that a negative ⁶⁸ Ga-PSMA PET/CT does not exclude local recurrence and that the addition of a VUA-directed biopsy may aid in the decision-making process for patients with BCR following RP, especially when ⁶⁸ Ga-PSMA PET/CT is locally negative. When the result of both ⁶⁸ Ga-PSMA PET/CT and VUA-directed biopsy are negative, it should encourage clinicians to share decision-making in regard to undertaking SRT vs continuing BCR surveillance. This may delay the possible side effects associated with SRT, despite its excellent PSA failure-free survival rate.

[Modern radiation therapy planning and image-guided radiotherapy using the example of prostate cancer]

CLINICAL/METHODICAL ISSUE

Optimizing radiotherapy demands precise delineation of the target structure, not only before but also during the course of radiotherapy.

STANDARD RADIOLOGICAL METHODS

For many years, planning of external radiation treatment planning has been based on computer tomography data.

METHODOLOGICAL INNOVATIONS

With the advent of image-guided radiotherapy (IGRT), magnetic resonance imaging (MRI) and functional hybrid imaging are increasingly being integrated into radiation treatment planning. The development of the MR-linac can be seen as an innovation.

PERFORMANCE

The integration of MRI and hybrid imaging (positron emission tomography [PET]/CT, PET/MRI) in the treatment planning process enables more precise treatment planning due to the better morphological and functional information. The integration of MRI data on the MR-linac in daily position control enables adaptation of the irradiation plan to the current conditions.

ACHIEVEMENTS

Technical innovation such as the MR-linac as well as increasing use of hybrid imaging contribute to the objective of further individualization within (radio)oncology.

PRACTICAL RECOMMENDATIONS

Using the example of prostate cancer, the application of prostate-specific membrane antigen (PSMA) ligands and hybrid imaging offers great potential for individualized strategic treatment decisions. The MR-linac appears to be particularly suitable for radiation therapy of prostate cancer. Special attention must be paid to the technical aspects of positioning and data acquisition for the purpose of radiation treatment planning.

Multiparametric MRI for prostate cancer: a national survey of patterns of practice among radiation oncologists in Spain

PURPOSE

To investigate patterns of practice among Spanish radiation oncologists in the use of multiparametric magnetic resonance imaging (mpMRI) for the treatment of prostate cancer (PCa). We evaluated (1) access to mpMRI, (2) current clinical practices, and (3) physician expectations of mpMRI.

METHODS

Cross-sectional survey of 118 radiation oncologists at 75 Radiation Oncology (RO) departments in Spain.

RESULTS

A total of 55 radiation oncologists from 52 RO departments (52/75; 69%) completed the survey. Prostate mpMRI is performed at 94.5% of the centres that provided data. The most common indications for mpMRI in routine clinical practice were: (1) detection/localization of the tumour prior to second biopsy (82.7%), (2) cancer staging (80.8%), and (3) detection of recurrence after definitive treatment (80.8%). Most respondents (72.7%) reported modifying the primary radiotherapy treatment when mpMRI findings indicate a more advanced T stage with a resultant change in the risk group. Most respondents (90.5%) treat macroscopic local recurrence after prostatectomy with high doses, ranging from 71 to 83 Gy; in 37.7% of cases, the full dose is delivered to the entire prostate bed. In pelvic nodal recurrence, more than half (59.3%) of the respondents reported performing elective pelvic radiotherapy, including the prostate bed, with a boost to the involved nodes.

CONCLUSIONS

This survey shows that prostate mpMRI is routinely used by radiation oncologists in Spain in a wide range of clinical scenarios. The findings reported here underscore the need to standardize treatment protocols for definitive and salvage radiotherapy in patients evaluated with mpMRI.