Dosimetric feasibility of neurovascular bundle-sparing stereotactic body radiotherapy with periprostatic hydrogel spacer for localized prostate cancer to preserve erectile function

Sexual Structure Sparing for Prostate Cancer Radiotherapy: A Systematic Review

CONTEXT

Erectile dysfunction represents a major side effect of prostate cancer (PCa) treatment, negatively impacting men's quality of life. While radiation therapy (RT) advances have enabled the mitigation of both genitourinary and gastrointestinal toxicities, no significant improvement has been showed in sexual quality of life over time.

OBJECTIVE

The primary aim of this review was to assess sexual structures' dose-volume parameters associated with the onset of erectile dysfunction.

EVIDENCE ACQUISITION

We searched the PubMed database and ClinicalTrials.gov until January 4, 2023. Studies reporting the impact of the dose delivered to sexual structures on sexual function or the feasibility of innovative sexual structure-sparing approaches were deemed eligible.

EVIDENCE SYNTHESIS

Sexual-sparing strategies have involved four sexual organs. The mean penile bulb doses exceeding 20 Gy are predictive of erectile dysfunction in modern PCa RT trial. Maintaining a D100% of ≤36 Gy on the internal pudendal arteries showed preservation of erectile function in 88% of patients at 5 yr. Neurovascular bundle sparing appears feasible with magnetic resonance-guided radiation therapy, yet its clinical impact remains unanswered. Doses delivered to the testicles during PCa RT usually remain <2 Gy and generate a decrease in testosterone levels ranging from -4.6% to -17%, unlikely to have any clinical impact.

CONCLUSIONS

Current data highlight the technical feasibility of sexual sparing for PCa RT. The proportion of erectile dysfunction attributable to the dose delivered to sexual structures is still largely unknown. While the ability to maintain sexual function over time is impacted by factors such as age or comorbidities, only selected patients are likely to benefit from sexual-sparing RT.

PATIENT SUMMARY

Technical advances in radiation therapy (RT) made it possible to significantly lower the dose delivered to sexual structures. While sexual function is known to decline with age, the preservation of sexual structures for prostate cancer RT is likely to be beneficial only in selected patients.

One-year clinical outcomes of MR-guided stereotactic body radiation therapy with rectal spacer for patients with localized prostate cancer

BACKGROUND AND PURPOSE

This prospective study aimed to investigate adaptive magnetic resonance (MR)-guided stereotactic body radiation therapy (MRgSBRT) with rectal spacer for localized prostate cancer (PC) and report 1-year clinical outcomes.

MATERIALS AND METHODS

Thirty-four consecutive patients with low- to high-risk localized PC that underwent 5-fraction adaptive MRgSBRT with rectal spacer were enrolled. The dosimetric comparison was performed on a risk- and age-matched cohort treated with MRgSBRT but without a spacer at a similar timepoint. Clinician-reported outcomes were based on Common Terminology Criteria for Adverse Events. Patient-reported outcomes were based on the Expanded Prostate Cancer Index Composite (EPIC) questionnaire at baseline, acute (1-3 months), subacute (4-12 months), and late (> 12 months) phases.

RESULTS

The median follow-up was 390 days (range 28-823) and the median age was 70 years (range 58-82). One patient experienced rectal bleeding soon after spacer insertion that subsided before MRgSBRT. The median distance between the midline of the prostate midgland and the rectum after spacer insertion measured 7.8 mm (range 2.6-15.3), and the median length of the spacer was 45.9 mm (range 16.8-62.9) based on T2-weighted MR imaging. The use of spacer resulted in significant improvements in target coverage (V100% > 95% = 98.6% [range 93.4-99.8] for spacer vs. 97.8% [range 69.6-99.7] for non-spacer) and rectal sparing (V95% < 3 cc = 0.7 cc [range 0-4.6] for spacer vs. 4.9 cc [range 0-12.5] for non-spacer). Nine patients (26.5%) experienced grade 1 gastrointestinal toxicities, and no grade ≥ 2 toxicities were observed. During the 1-year follow-up period, EPIC scores for the bowel domain remained stable and were the highest among all other domains.

CONCLUSIONS

MRgSBRT with rectal spacer for localized PC showed exceptional tolerability with minimal gastrointestinal toxicities and satisfactory patient-reported outcomes. Improvements in dosimetry, rectal sparing, and target coverage were achieved with a rectal spacer. Randomized trials are warranted for further validation.

Dosimetric correlates of toxicities and quality of life following two-fraction stereotactic ablative radiotherapy (SABR) for prostate cancer

PURPOSE

There is no evidence-based data to guide dose constraints in two-fraction prostate stereotactic ablative radiotherapy (SABR). Using individual patient-data from two prospective trials, we aimed to correlate dosimetric parameters with toxicities and quality of life (QoL) outcomes.

MATERIALS AND METHODS

We included 60 patients who had two-fraction prostate SABR in the 2STAR (NCT02031328) and 2SMART (NCT03588819) trials. The prescribed dose was 26 Gy to the prostate+/-32 Gy boost to the dominant intraprostatic lesions. Toxicities and QoL data were prospectively collected using CTCAEv4 and EPIC-26 questionnaire. The outcomes evaluated were acute and late grade ≥ 2 toxicities, and late minimal clinical important changes (MCIC) in QoL domains. Dosimetric parameters for bladder, urethra, rectum, and penile bulb were evaluated.

RESULTS

The median follow-up was 56 months (range: 39-78 months). The cumulative incidence of grade ≥ 2 genitourinary (GU), gastrointestinal (GI), and sexual toxicities were 62%, 3%, and 17% respectively in the acute setting (<3 months), and 57%, 15%, and 52% respectively in late setting (>6 months). There were 36%, 28%, and 29% patients who had late MCIC in urinary, bowel and sexual QoL outcomes respectively. Bladder 0.5 cc was significant predictor for late grade ≥ 2 GU toxicities, with optimal cut-off of 25.5 Gy. Penile bulb D5cc was associated of late grade ≥ 2 sexual toxicities (no optimal cut-off was identified). No dosimetric parameters were identified to be associated with other outcomes.

CONCLUSION

Using real-life patient data from prospective trials with medium-term follow-up, we identified additional dose constraints that may mitigate the risk of late treatment-related toxicities for two-fraction prostate SABR.

[Relationship between doses to anatomical structures and erectile dysfunction after radiotherapy for prostate cancer: A systematic review]

PURPOSE

During prostatic radiotherapy, damage to several anatomical structures could be the cause of erectile dysfunction: corpora cavernosa, internal pudendal arteries, penile bulb, and neurovascular bundles. Numerous studies have analysed the correlations between the dose received by these structures and erectile function. The objective of this article is to make a systematic review on current knowledge.

MATERIALS AND METHODS

A systematic review was performed in the Medline database using the search engine PubMed. Keywords for the search included: erectile dysfunction, penile bulb, corpora cavernosa, cavernosum, neurovascular bundles, radiation therapy, cancer, prostate cancer. The selected articles must study a correlation between erectile dysfunction and the dose received by anatomical structures. A total of 152 articles were identified. Of these 152 articles, 45 fulfilled the defined selection criteria.

RESULTS

For corpora cavernosa, seven studies were identified, only two studies demonstrated a significant correlation between the dose received by corpora cavernosa and the occurrence of erectile dysfunction. For penile bulb, only 15 of 23 studies showed a correlation. A mean dose on the penile bulb greater than 20Gy was found to be predictive of erectile dysfunction. None of the eight trials concerning neurovascular bundles succeeded to show a correlation between dose and erectile dysfunction. Only one study evaluated the relationship between the dose received by internal pudendal arteries and erectile dysfunction but was found to be negative. However, vessels-sparing studies showed good results on erectile function preservation without compromising the target volume.

CONCLUSION

We currently have little data to show a correlation between erectile dysfunction and sexual structures. It would be necessary to have additional prospective studies evaluating the impact of an optimization on these sexual structures on erectile dysfunction.

Automatic segmentation of neurovascular bundle on mri using deep learning based topological modulated network

PURPOSE

Radiation damage on neurovascular bundles (NVBs) may be the cause of sexual dysfunction after radiotherapy for prostate cancer. However, it is challenging to delineate NVBs as organ-at-risks from planning CTs during radiotherapy. Recently, the integration of MR into radiotherapy made NVBs contour delineating possible. In this study, we aim to develop an MRI-based deep learning method for automatic NVB segmentation.

METHODS

The proposed method, named topological modulated network, consists of three subnetworks, that is, a focal modulation, a hierarchical block and a topological fully convolutional network (FCN). The focal modulation is used to derive the location and bounds of left and right NVBs', namely the candidate volume-of-interests (VOIs). The hierarchical block aims to highlight the NVB boundaries information on derived feature map. The topological FCN then segments the NVBs inside the VOIs by considering the topological consistency nature of the vascular delineating. Based on the location information of candidate VOIs, the segmentations of NVBs can then be brought back to the input MRI's coordinate system.

RESULTS

A five-fold cross-validation study was performed on 60 patient cases to evaluate the performance of the proposed method. The segmented results were compared with manual contours. The Dice similarity coefficient (DSC) and 95th percentile Hausdorff distance (HD95 ) are (left NVB) 0.81 ± 0.10, 1.49 ± 0.88 mm, and (right NVB) 0.80 ± 0.15, 1.54 ± 1.22 mm, respectively.

CONCLUSION

We proposed a novel deep learning-based segmentation method for NVBs on pelvic MR images. The good segmentation agreement of our method with the manually drawn ground truth contours supports the feasibility of the proposed method, which can be potentially used to spare NVBs during proton and photon radiotherapy and thereby improve the quality of life for prostate cancer patients.

Advanced hydrogels: New expectation for the repair of organic erectile dysfunction

Organic erectile dysfunction (ED) is a type of sexual disorder in men that is usually associated with illness, surgical injury, normal aging and has a high incidence across the globe. And the essence of penile erection is a neurovascular event regulated by a combination of factors. Nerve and vascular injury are the main causes of erectile dysfunction. Currently, the main treatment options for ED include phosphodiesterase type 5 inhibitors (PDE5Is), intracorporeal injections and vacuum erection devices (VEDs), which are ineffective. Therefore, it is essential to find an emerging, non-invasive and effective treatment for ED. The histopathological damage causing ED can be improved or even reversed with hydrogels, in contrast to current therapies. Hydrogels have many advantages, they can be synthesized from various raw materials with different properties, possess a definite composition, and have good biocompatibility and biodegradability. These advantages make hydrogels an effective drug carrier. In this review, we began with an overview of the underlying mechanisms of organic erectile dysfunction, discussed the dilemmas of existing treatments for ED, and described the unique advantages of hydrogel over other approaches. Then emphasizing the progress of research on hydrogels in the treatment of ED.

Contouring lumbosacral plexus nerves with MR neurography and MR/CT deformable registration technique

Purpose

It is difficult to contour nerve structures with the naked eye due to poor differentiation between the nerve structures with other soft tissues on CT images. Magnetic resonance neurography (MRN) has the advantage in nerve visualization. The purpose of this study is to identify one MRN sequence to better assist the delineation of the lumbosacral plexus (LSP) nerves to assess the radiation dose to the LSP using the magnetic resonance (MR)/CT deformable coregistration technique.

Methods

A total of 18 cases of patients with prostate cancer and one volunteer with radiation-induced lumbosacral plexopathy (RILSP) were enrolled. The data of simulation CT images and original treatment plans were collected. Two MRN sequences (Lr_NerveVIEW sequence and Cs_NerveVIEW sequence) were optimized from a published MRN sequence (3D NerveVIEW sequence). The nerve visualization ability of the Lr_NerveVIEW sequence and the Cs_NerveVIEW sequence was evaluated via a four-point nerve visualization score (NVS) scale in the first 10 patients enrolled to determine the better MRN sequence for assisting nerve contouring. Deformable registration was applied to the selected MRN sequence and simulation CT images to get fused MR/CT images, on which the LSP was delineated. The contouring of the LSP did not alter treatment planning. The dosimetric data of the LSP nerve were collected from the dose–volume histogram in the original treatment plans. The data of the maximal dose (Dmax) and the location of the maximal radiation point received by the LSP structures were collected.

Results

The Cs_NerveVIEW sequence gained lower NVS scores than the Lr_NerveVIEW sequence (Z=-2.887, p=0.004). The LSP structures were successfully created in 18 patients and one volunteer with MRN (Lr_NerveVIEW)/CT deformable registration techniques, and the LSP structures conformed with the anatomic distribution. In the patient cohort, the percentage of the LSP receiving doses exceeding 50, 55, and 60 Gy was 68% (12/18), 33% (6/18), and 17% (3/18), respectively. For the volunteer with RILSP, the maximum irradiation dose to his LSP nerves was 69 Gy.

Conclusion

The Lr_NerveVIEW MRN sequence performed better than the Cs_NerveVIEW sequence in nerve visualization. The dose in the LSP needs to be measured to understand the potential impact on treatment-induced neuropathy.

Better preservation of erectile function in localized prostate cancer patients with modern proton therapy: Is it cost-effective?

BACKGROUND

Stereotactic body radiation therapy (SBRT) has gradually been recognized as favorable curative treatment for localized prostate cancer (PC). However, the high rate of erectile dysfunction (ED) after traditional photon-based SBRT remains an ongoing challenge that greatly impacts the quality of life of PC survivors. Modern proton therapy allows higher conformal SBRT delivery and has the potential to reduce ED occurrence but its cost-effectiveness remains uninvestigated.

METHODS

A Markov decision model was designed to evaluate the cost-effectiveness of proton SBRT versus photon SBRT in reducing irradiation-related ED. Base-case evaluation was performed on a 66-year-old (median age of PC) localized PC patient with normal pretreatment erectile function. Further, stratified analyses were performed for different age groups (50, 55, 60, 65, 70, and 75 years) and threshold analyses were conducted to estimate cost-effective scenarios. A Chinese societal willingness-to-pay (WTP) threshold (37,653 US dollars [$])/quality-adjusted life-year [QALY]) was adopted.

RESULTS

For the base case, protons provided an additional 0.152 QALY at an additional cost of $7233.4, and the incremental cost-effectiveness ratio was $47,456.5/QALY. Protons was cost-effective for patients ≤62-year-old at the WTP of China (≤66-year-old at a WTP of $50,000/QALY; ≤73-year-old at a WTP of $100,000/QALY). For patients at median age, once the current proton cost ($18,000) was reduced to ≤$16,505.7 or the patient had a life expectancy ≥88 years, protons were cost-effective at the WTP of China.

CONCLUSIONS

Upon assumption-based modeling, the results of current study support the use of proton SBRT in younger localized PC patients who are previously potent, for better preservation of erectile function. The findings await further validation using data from future comparative clinical trials.

Ejaculatory Function Following Stereotactic Body Radiation Therapy for Prostate Cancer

BACKGROUND

Ejaculatory dysfunction is an important male quality of life issue which has not yet been studied in the setting of prostate stereotactic body radiation therapy (SBRT).

AIM

The purpose of this study is to evaluate ejaculatory function following SBRT for prostate cancer.

METHODS

Two hundred and thirty-one patients on a prospective quality of life study with baseline ejaculatory capacity treated with prostate SBRT from 2013 to 2019 were included in this analysis. Ejaculation was assessed via the Ejaculation Scale (ES-8) from the Male Sexual Health Questionnaire. Patients completed the questionnaire at 1, 3, 6, 9, 12, 18, and 24 months post-SBRT. Elderly patients (Age > 70) and those who received hormonal therapy were excluded from analysis. Patients were treated to 35-36.25 Gy in 5 fractions delivered with the CyberKnife Radiosurgical System (Accuray).

OUTCOMES

Ejaculatory function was assessed by ES-8 scores (range 4-40) with lower values representing increased interference or annoyance.

RESULTS

Median age at the time of treatment was 65 years. Median follow up was 24 months (IQR 19-24.5 months). 64.5% of patients had ED at baseline (SHIM < 22). The 2-year anejaculation rate was 15%. Mean composite ES-8 scores showed a decline in the first month following treatment then stabilized: 30.4 (start of treatment); 26.5 (1 month); 27.6 (3 month); 27.0 (6 month); 26.2 (9 month); 25.4 (12 month); 25.0 (18 month) and 25.4 (24 month). White race, higher pre-treatment SHIM (≥22), and higher ES-8 (≥31) at treatment start were significantly associated with a decreased probability of a clinically significant decline. Patient-reported ejaculate volume was significantly reduced at all time points post-SBRT. Ejaculatory discomfort peaked at 1 month and 9 months post-SBRT. Prior to treatment, 8.0% of men reported that they were very to extremely bothered by their ejaculatory dysfunction. The number of patients reporting this concern increased to 14.4% at one year and dropped to 11% at 24-months post-SBRT.

CLINICAL TRANSLATION

Patients undergoing prostate SBRT may experience meaningful changes in ejaculatory function and should be counseled on the trajectory of these side effects.

STRENGTHS & LIMITATIONS

This was a retrospective analysis of a prospectively maintained database. Subjective questionnaire responses captured limited aspects of ejaculatory function in this cohort.

CONCLUSION

The high incidence of moderate to extreme bother in ejaculatory function before and after SBRT suggests a need for novel approaches to improving ejaculation. Sholklapper T, Creswell M, Cantalino J, et al. Ejaculatory Function Following Stereotactic Body Radiation Therapy for Prostate Cancer. J Sex Med 2022;19:771-780.

Characterization of an Iodinated Rectal Spacer for Prostate Photon and Proton Radiation Therapy

PURPOSE

Conventional rectal spacers (nonI-SPs) are low-contrast on computed tomography (CT), often necessitating magnetic resonance imaging for accurate delineation. A new formulation of spacers (I-SPs) incorporates iodine to improve radiopacity and CT visualization. We characterized placement, stability, and plan quality of I-SPs compared to nonI-SPs.

METHODS AND MATERIALS

Patients with intact prostate cancer (n = 50) treated with I-SPs and photons were compared to randomly selected patients (n = 50) with nonI-SPs (photon or proton therapy). The I-SP was contoured on the planning CT and cone beam CTs at 3 timepoints: first, middle, and final treatment (n = 200 scans). I-SPs Hounsfield units (HU), volume, surface area (SA), centroid position relative to prostate centroid, and distance between prostate/rectum centroids were compared on the planning CTs between each cohort. I-SP changes were evaluated on cone beam CTs over courses of treatment. Dosimetric evaluations of plan quality and robustness were performed. I-SP was tested in a phantom to characterize its relative linear stopping power for protons.

RESULTS

I-SPs yielded a distinct visible contrast on planning CTs compared to nonI-SPs (HU 138 vs 12, P < .001), allowing delineation on CT alone. The delineated volume and SA of I-SPs were smaller than nonI-SPs (volume 8.9 vs 10.6 mL, P < .001; SA 28 vs 35 cm², P < .001), yet relative spacer position and prostate-rectal separation were similar (P = .79). No significant change in HU, volume, SA, or relative position of the I-SPs hydrogel occurred over courses of treatment (all P > .1). Dosimetric analysis concluded there were no significant changes in plan quality or robustness for I-SPs compared to nonI-SPs. The I-SP relative linear stopping power was 1.018, necessitating HU override for proton planning.

CONCLUSIONS

I-SPs provide a manifest CT contrast, allowing for delineation on planning CT alone with no magnetic resonance imaging necessary. I-SPs radiopacity, size, and relative position remained stable over courses of treatment from 28 to 44 fractions. No changes in plan quality or robustness were seen comparing I-SPs and nonI-SPs.