Reduced radiation tolerance of penile structures associated with dose-escalated hypofractionated prostate radiotherapy

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.

[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.

Risk of erectile dysfunction after modern radiotherapy for intact prostate cancer

BACKGROUND

Erectile dysfunction (ED) is a prevalent side effect of prostate cancer treatment. We hypothesized that the previously reported rates of ED may have improved with the advent of modern technology. The purpose of this project was to evaluate modern external beam radiotherapy and brachytherapy techniques to determine the incidence of radiotherapy (RT) induced ED.

METHODS

A systematic review of the literature published between January 2002 and December 2018 was performed to obtain patient reported rates of ED after definitive external beam radiotherapy, ultrafractionated stereotactic radiotherapy, and brachytherapy (BT) to the prostate in men who were potent prior to RT. Univariate and multivariate analyses of radiation dose, treatment strategy, and length of follow-up were analyzed to ascertain their relationship with RT-induced ED.

RESULTS

Of 890 articles reviewed, 24 met inclusion criteria, providing data from 2714 patients. Diminished erectile function status post RT was common and similar across all studies. The median increase in men reporting ED was 17%, 26%, 23%, and 23%, 3DCRT, IMRT, low dose rate BT, and SBRT, respectively, at 2-year median follow-up.

CONCLUSION

ED is a common side effect of RT. Risk of post-RT ED is similar for both LDR brachytherapy and external beam RT with advanced prostate targeting and penile-bulb sparing techniques utilized in modern RT techniques.

Challenges in Reporting the Effect of Radiotherapy on Erectile Function

BACKGROUND

Erectile dysfunction (ED) is the most common side effect of prostate radiotherapy (RT), but reported rates over time and across modalities have varied widely.

AIM

To evaluate the published literature between 2002 and 2018 for high quality data utilizing prospectively gathered patient-reported ED, and to summarize the challenges in reporting of RT-induced ED (RIED).

METHODS

A PubMed search and literature review was performed to identify articles describing rates of ED before and after definitive external beam RT or brachytherapy without androgen deprivation.

OUTCOMES

Patient-reported ED, patient and treatment variables, and study follow-up constituted the main outcomes of this study.

RESULTS

24 articles were identified, reporting RIED rates between 17% and 90%. Variables contributing to this range included patient, treatment, and study characteristics known to impact ED reporting.

CLINICAL IMPLICATIONS

For future studies, we recommend the use of validated patient-reported questionnaires and reporting of baseline function and comorbidities, RT type and dose, and use of androgen deprivation therapy and erectile aids at the time of ED measurement. With sufficient follow-up to understand the late nature of RIED, these recommendations will improve comparison of results between studies and the applicability of results to patients undergoing pretreatment counseling regarding the risks of RIED.

STRENGTHS & LIMITATIONS

The literature search and formulation of results were based on a broad understanding of the Preferred Reporting Items for Systematic Reviews and Meta-analyses guidelines and the literature, but because of the focus on data reporting, a comprehensive systematic review of all RIED literature was not performed.

CONCLUSION

Reported rates of ED after RT vary widely due to differences in patients' baseline reported erectile function, age, comorbidities, and characteristics of the treatment delivered. The methodology of ED measurement has significant impact on the applicability and comparability of results to other studies and clinical practice. Nukala V, Incrocci L, Hunt AA, et al. Challenges in Reporting the Effect of Radiotherapy on Erectile Function. J Sex Med 2020;17:1053-1059.

Evaluation of erectile potency and radiation dose to the penile bulb using image guided radiotherapy in the CHHiP trial

BACKGROUND AND PURPOSE

The penile bulb (PB) dose may be critical in development of post prostate radiotherapy erectile dysfunction (ED). This study aimed to generate PB dose constraints based on dose-volume histograms (DVHs) in patients treated with prostate radiotherapy, and to identify clinical and dosimetric parameters that predict the risk of ED post prostate radiotherapy.

MATERIALS AND METHODS

Penile bulb DVHs were generated for 276 patients treated within the randomised IGRT substudy of the multicentre randomised trial, CHHiP. Incidence of ED in relation to dose and randomised IGRT groups were evaluated using Wilcoxon rank sum, Chi-squared test and atlases of complication incidence. Youden index was used to find dose-volume constraints that discriminated for ED. Multivariate analysis (MVA) of effect of dosimetry, clinical and patient-related variables was performed.

RESULTS

Reduced treatment margins using IGRT (IGRT-R) produced significantly reduced mean PB dose compared with standard margins (IGRT-S) (median: 25 Gy (IGRT-S) versus 11 Gy (IGRT-R); p < 0.0001). Significant difference in both mean (median: 23 Gy (ED) vs. 18 Gy (no ED); p = 0.011) and maximum (median: 59 Gy (ED) vs. 52 Gy (no ED); p = 0.018) PB doses between those with and without clinician reported ED were identified. Mean PB dose cut-point for ED was derived at around 20 Gy. On MVA, PB mean dose and age predicted for impotence.

CONCLUSION

PB dose appears predictive of post-radiotherapy ED with calculated threshold mean dose of around 20 Gy, substantially lower than published recommendations. IGRT-R enables favourable PB dosimetry and can be recommended provided prostate coverage is not compromised.

Erectile Dysfunction and Absorbed Dose to Penile Base Structures in a Randomized Trial Comparing Ultrahypofractionated and Conventionally Fractionated Radiation Therapy for Prostate Cancer

PURPOSE

To study the relationships between absorbed dose to penile base structures and erectile dysfunction (ED) in patients treated with ultrahypofractionated (UHF) radiation therapy (RT) or conventionally fractionated (CF) RT for prostate cancer.

METHODS AND MATERIALS

This dose-response study comprises 673 patients (57%) of the 1180 per-protocol patients included in the HYPO-RT-PC trial (median follow-up 5, years), where patients were randomized to CF (39 × 2.0 Gy, 8 weeks) or UHF (7 × 6.1 Gy, 2.5 weeks). No androgen deprivation therapy was allowed. Only patients with erectile function sufficient for intercourse at baseline and complete RT data were included in this study. Erectile function was assessed by physician at regular follow-ups. The main endpoint was severe ED (ED_s). The penile bulb (PB) and crus were retrospectively delineated on the treatment planning computed tomography scans. Dose-volume descriptors were derived from EQD2 converted dose matrices (α/β = 3 Gy). Univariable and multivariable Cox proportional hazard regression and logistic regression were used to find predictors for ED_S.

RESULTS

No significant difference in ED_s was found between CF and UHF. During the follow-up period, ED_s occurred in 27% of the patients in both treatment groups. Average (median) PB mean dose, D_mean, was 24.5 (20.2) in CF and 18.7 (13.1) Gy₃ in UHF. Age was the only significant predictor for ED_s in Cox analyses. All dose-volume variables contributed significantly in univariable logistic regression at 2-year follow-up. Age and near maximum dose (D_2%) were significant predictors for ED_s in multivariable logistic regression analyses at both 1 and 2 years.

CONCLUSIONS

The frequency of ED_S was similar in the CF and UHF treatment groups. Age at radiation therapy was the strongest predictor for ED_s, followed by dose to PB, and was most evident for younger patients. We propose D_{2 %} <50 Gy₃ and D_mean <20 Gy₃ to the PB as the primary objectives to be applied in the treatment planning process.

[Moderate or extreme hypofractionation and localized prostate cancer: The times are changing]

There are many treatment options for localized prostate cancers, including active surveillance, brachytherapy, external beam radiotherapy, and radical prostatectomy. Quality of life remains a primary objective in the absence of superiority of one strategy over another in terms of specific survival with similar long-term biochemical control rates. Despite a significant decrease in digestive and urinary toxicities thanks to IMRT and IGRT, external radiotherapy remains a treatment that lasts approximately 2 months or 1.5 months, when combined with a brachytherapy boost. Given the specific radiosensitivity of this tumor, several randomized studies have shown that a hypofractionated scheme is not inferior in terms of biochemical control and toxicities, allowing to divide the number of fractions by a factor 2 to 8. Given that SBRT becomes a validated therapeutic option for a selected population of patients with localized prostate cancer, extreme hypofractionation is becoming a strong challenger of conventional external radiotherapy or brachytherapy.

A Systematic Post-QUANTEC Review of Tolerance Doses for Late Toxicity After Prostate Cancer Radiation Therapy

PURPOSE

The aims of this study were to systematically review tolerance doses for late distinct gastrointestinal (GI), genitourinary (GU), and sexual dysfunction (SD) symptoms after external beam radiation therapy (EBRT) alone and treatments involving brachytherapy (BT) for prostate cancer after Quantitative Analysis of Normal Tissue Effects in the Clinic (QUANTEC) and ultimately to perform quantitative syntheses of identified dose/volume tolerances represented by dose-volume histogram (DVH) thresholds, that is, statistically significant (P ≤ .05) cutoff points between symptomatic and asymptomatic patients in a certain study.

METHODS AND MATERIALS

PubMed was scrutinized for full-text articles in English after QUANTEC (January 1, 2010). The inclusion criteria were randomized controlled trials, case-control studies, or cohort studies with tolerance doses for late distinct symptoms ≥3 months after primary radiation therapy for prostate cancer (N > 30). All DVH thresholds were converted into equivalent doses in 2-Gy fractions (EQD2α/β) and were fitted with a linear or linear-quadratic function (goodness of fit, R2). The review was registered on PROSPERO (CRD42016042464).

RESULTS

From 33 identified studies, which included 36 to 746 patients per symptom domain, the majority of dose/volume tolerances were derived for GI toxicity after EBRT alone (GI, 97 thresholds; GU, 8 thresholds; SD, 1 threshold). For 5 symptoms (defecation urgency, diarrhea, fecal incontinence, proctitis, and rectal bleeding), relationships between dose/volume tolerances across studies (R2 = 0.93 [0.82-1.00]), and across symptoms, leading to a curve for overall GI toxicity (R2 = 0.98), could be determined. For these symptoms, mainly rectal thresholds were found throughout low and high doses (10 Gy ≤ equivalent dose in 2-Gy fractions using α/β = 3Gy (EQD23) ≤ 50 Gy and 55 Gy ≤ EQD23 ≤ 78 Gy, respectively). For BT with or without EBRT, dose/volume tolerances were also mainly identified for GI toxicity (GI, 14 thresholds; GU, 4 thresholds; SD, 2 thresholds) with the largest number of DVH thresholds concerning rectal bleeding (5 thresholds).

CONCLUSIONS

Updated dose/volume tolerances after QUANTEC were found for 17 GI, GU, or SD symptoms. A DVH curve described the relationship between dose/volume tolerances across 5 GI symptoms after EBRT alone. Restricting treatments for EBRT alone using the lower boundaries of this curve is likely to limit overall GI toxicity, but this should be explored prospectively. Dose/volume tolerances for GU and SD toxicity after EBRT alone and after BT with or without EBRT were scarce and support further research including data-sharing initiatives to untangle the dose/volume relationships for these symptoms.

Association between EBRT dose volume histograms and quality of life in prostate cancer patients

Aim

To evaluate the association between dose-volume histogram (DVH) values in organs at risk (OAR) and patient-reported HRQoL outcomes.

Background

Data on the association between DVHs and health-related quality of life (HRQoL) in prostate cancer (PCa) patients are limited.

Materials and methods

Five-year follow-up study of 154 patients with organ-confined (stage T1/T2) PCa treated with EBRT between January 2003 and November 2005. HRQoL was evaluated with the Expanded Prostate Cancer Index (EPIC). DVH for OARs (penile bulb, rectum and bladder) were created for all patients for whom data were available (119/154; 77%). The functional data analysis (FDA) statistical method was used. HRQoL data was collected prospectively and data analysis was performed retrospectively.

Results

Worsening of urinary incontinence and obstructive symptoms correlated with higher DVH dose distributions at 24 months. Increased rectal bleeding at months 24 and 60 correlated with higher DVH dose distributions in the 40-70 Gy range. Patients with deterioration in rectal incontinence presented a higher DVH distribution range than patients without rectal incontinence. Penile bulb DVH values and erectile dysfunction were not significantly associated.

Conclusions

DVH parameters and post-radiotherapy HRQoL appear to be closely correlated, underscoring the importance of assessing DVH values prior to initiating EBRT to determine the risk of developing HRQoL related adverse effects. Advanced treatment modalities may be appropriate in high risk cases to minimize treatment-related toxicity and to improve treatment outcomes and HRQoL. Future studies are needed to better elucidate the association between pre-treatment DVH parameters in organs at risk and subsequent HRQoL.

Influence of inhomogeneous radiosensitivity distributions and intrafractional organ movement on the tumour control probability of focused IMRT in prostate cancer

PURPOSE

To evaluate the influence of radioresistance and intrafractional movement on the tumour control probability (TCP) in IMRT prostate treatments using simultaneous integrated boosts to PSMA-PET/CT-delineated GTVs.

MATERIALS AND METHODS

13 patients had PSMA-PET/CT prior to prostatectomy and histopathological examination. Two GTVs were available: GTV-PET and GTV-histo, which is the true cancer volume. Focused IMRT plans delivering 77 Gy in 35 fractions to the prostate and 95 Gy to PTV-PET were produced. For random portions of the true cancer volume, α and α/β were uniformly changed to represent different radiosensitivity reductions. TCP was calculated (linear quadratic model) for the true cancer volume with and without simulated intrafractional movement.

RESULTS

Intrafractional movement increased the TCP by up to 10.2% in individual cases and 1.2% averaged over all cases for medium radiosensitivity levels. At lower levels of radiosensitivity, movement decreased the TCP. Radiosensitivity reductions of 10-20% led to TCP reductions of 1-24% and 10-68% for 1% and 5% affected cancer volume, respectively. There is no linear correlation but a sudden breakdown of TCPs within a small range of radiosensitivity levels.

CONCLUSION

TCP drops significantly within a narrow range of radiosensitivity levels. Intrafractional movement can increase TCP when the boost volume is surrounded by a sufficiently high dose plateau.

Evaluation of intensity modulated radiation therapy dose painting for localized prostate cancer using 68Ga-HBED-CC PSMA-PET/CT: A planning study based on histopathology reference

PURPOSE

To demonstrate the feasibility and to evaluate the tumour control probability (TCP) and normal tissue complication probability (NTCP) of IMRT dose painting using ⁶⁸Ga-HBED-CC PSMA PET/CT for target delineation in prostate cancer (PCa).

METHODS AND MATERIALS

10 patients had PSMA PET/CT scans prior to prostatectomy. GTV-PET was generated on the basis of an intraprostatic SUVmax of 30%. Two IMRT plans were generated for each patient: Plan⁷⁷ which consisted of whole-prostate IMRT to 77Gy, and Plan⁹⁵ which consisted of whole-prostate IMRT to 77Gy and a simultaneous integrated boost to the GTV-PET up to 95Gy (35 fractions). The feasibility of these plans was judged by their ability to adhere to the FLAME trial protocol. TCP-histo/-PET were calculated on co-registered histology (GTV-histo) and GTV-PET, respectively. NTCPs for rectum and bladder were calculated.

RESULTS

All plans reached prescription doses whilst adhering to dose constraints. In Plan⁷⁷ and Plan⁹⁵ mean doses in GTV-histo were 75.8±0.3Gy and 96.9±1Gy, respectively. Average TCP-histo values for Plan⁷⁷ and Plan⁹⁵ were 70% (range: 15-97%), and 96% (range: 78-100%, p<0.0001). Average TCP-PET values for Plan⁷⁷ and Plan⁹⁵ were 55% (range: 27-82%), and 100% (range: 99-100%, p<0.0001). There was no significant difference between TCP-PET and TCP-histo in Plan⁹⁵ (p=0.25). There were no significant differences in rectal (p=0.563) and bladder (p=0.3) NTCPs.

CONCLUSIONS

IMRT dose painting using PSMA PET/CT was technically feasible and resulted in significantly higher TCPs without higher NTCPs.