Tadalafil in Preventing Erectile Dysfunction in Patients With Prostate Cancer Treated With Radiation Therapy

Prostate Cancer Clinical Trial

Official title:

A Randomized, Double-blind, Placebo-controlled Phase III Trial to Evaluate the Effectiveness of a Phosphodiesterase 5 Inhibitor, Tadalafil, in Prevention of Erectile Dysfunction in Patients Treated With Radiotherapy for Prostate Cancer

Clinical Trial Details — Status: Completed

Administrative data

• NCT number: NCT00931528
• Other study ID #: RTOG 0831
• Secondary ID: CDR0000647146NCI
• Status: Completed
• Phase: Phase 3
• First received: June 30, 2009
• Last updated: January 18, 2018
• Start date: November 2009
• Est. completion date: November 2014

Study information

• Verified date: January 2018
• Source: Radiation Therapy Oncology Group
• Contact: n/a
• Is FDA regulated: No
• Study type: Interventional

Clinical Trial Summary

RATIONALE: Tadalafil may help prevent erectile dysfunction (ED) in patients with prostate cancer that has been treated with radiation therapy. It is not yet known whether tadalafil is more effective than a placebo in preventing erectile dysfunction.

PURPOSE: This randomized phase III trial is studying tadalafil to see how well it works compared with a placebo in preventing erectile dysfunction in patients with prostate cancer treated with radiation therapy.

Description:

OBJECTIVES:

Primary

• To determine whether tadalafil maintains spontaneous (off-drug) erectile function, as measured by the International Index of Erectile Function (IIEF) as compared to placebo at weeks 28-30 after initiation of radiotherapy in patients with prostate cancer.

Secondary

• Determine the difference in spontaneous (off-drug) erectile function between tadalafil and placebo at 1 and 2 years.

• Determine the difference in overall sexual function as measured by the IIEF between tadalafil and placebo at weeks 28-30 and at 1 and 2 years.

• Determine differences in patient and partner overall sexual satisfaction as measured by the Sexual Adjustment Questionnaire (SAQ) between tadalafil and placebo at weeks 28-30 and at 1 and 2 years.

• Determine differences in patient and partner marital adjustment as measured by Locke's Marital Adjustment Test (LMAT) between tadalafil and placebo at weeks 28-30 and at 1 and 2 years.

• Determine associations between patient and partner overall sexual satisfaction as measured by SAQ and patient and partner marital adjustment as measured by LMAT at weeks 28-30 and at 1 and 2 years.

• Determine patient-related factors (i.e., age, pretreatment sexual response, tobacco use, and comorbidities) that may predict response to tadalafil therapy at weeks 28-30 and at 1 and 2 years.

• Determine the difference in adverse events between tadalafil and placebo as assessed by Common Toxicity Criteria for Adverse Effects (CTCAE) v3.0 criteria.

Tertiary

• Characterization of preference and erectile function among patients who choose to stay on (or if on placebo, to start) tadalafil, a phosphodiesterase type 5 (PDE5) inhibitor other than tadalafil, a non-PDE5-inhibitor erectile aide, or no PDE5 inhibitor or erectile aide at 28-30 weeks and at 1 and 2 years.

• Identification of radiotherapy factors (i.e., modality, prescribed total dose, planning target volume margin, penile bulb dose-volume parameters) associated with erectile function.

• Evaluation of the number of patients screened for eligibility, the number eligible that are presented the study, the number who refuse, and the number who are accrued.

OUTLINE: This is a multicenter study. Patients are stratified according to age (≤ 65 years vs > 65 years) and radiotherapy treatment (external beam radiation therapy vs brachytherapy*). Patients are randomized to 1 of 2 treatment arms.

Note: * Radiotherapy start date for brachytherapy patients is the date of the procedure.

All patients undergo either external beam radiotherapy alone to the prostate ± seminal vesicles only or low-dose rate permanent brachytherapy alone.

• Arm I: Beginning ≤ 7 days after the start of radiotherapy, patients receive oral tadalafil once daily for 24 weeks in the absence of disease progression or unacceptable toxicity.

• Arm II: Beginning ≤ 7 days after the start of radiotherapy, patients receive oral placebo once daily for 24 weeks in the absence of disease progression or unacceptable toxicity.

Patients complete the International Index of Erectile Function (IIEF), the Sexual Adjustment Questionnaire (SAQ), the Locke's Marital Adjustment Test (LMAT) (if applicable), and the Expanded Prostate Cancer Index Composite Sexual Medications and Devices Evaluations Supplement questionnaires periodically. Partners or spouses complete the SAQ-Partner, LMAT (if applicable), and IIEF questionnaires periodically.

After completion of study treatment, patients are followed at 28-30 weeks, and annually for up to 2 years.

Recruitment information / eligibility

• Status: Completed
• Enrollment: 242
• Est. completion date: November 2014
• Est. primary completion date: December 2012
• Accepts healthy volunteers: Accepts Healthy Volunteers
• Gender: Male
• Age group: 18 Years to 120 Years

Eligibility

Inclusion Criteria:

1. Clinical stage T1b-T2b (AJCC, 6th ed.) adenocarcinoma of the prostate within 6 months of registration

2. Clinically negative lymph nodes as established by imaging (pelvic ± abdominal CT or MR), nodal sampling, or dissection within 3 months prior to registration. Patients with lymph nodes equivocal or questionable by imaging are eligible if the nodes are = 1.5 cm. Lymph node assessment is optional, and at investigator discretion, for patients with Gleason Score <7.

3. No evidence of bone metastases (M0) on bone scan within 3 months prior to registration. Equivocal bone scan findings are allowed if plain films are negative for metastasis. Bone metastases assessment is optional, and at investigator discretion, for patients with Gleason Score <7.

4. Baseline serum prostatic specific antigen (PSA) value performed with an FDA-approved assay (e.g., Abbott, Hybritech) within 3 months prior to registration.

-4.1 Any of the following combinations of factors (NOTE: tumor found in 1 or both lobes on biopsy, but not palpable, will not alter T stage):

• T1b-T2b disease, Gleason Score <7 and serum total PSA that is <20 ng/ml or

• T1b-T2b disease, Gleason Score =7 and PSA that is <15 ng/ml

5. Serum total testosterone level prior to the initiation of radiation therapy (RT) within normal range according to institutional guidelines

6. Zubrod Performance Status 0 or 1 (Appendix III)

7. Age = 18 years

8. Treatment that will consist of either external beam RT alone to the prostate ± seminal vesicles only at a dose between 75 Gy and 79.2 Gy or brachytherapy alone (NOTE: treatment with combined external RT and brachytherapy excludes patient participation)

9. Pretreatment (before starting prostate cancer treatment) erectile function as measured by IIEF Question 1, "How often were you able to get an erection during sexual activity?" - with responses of:

• "sometimes (about half the time)" [response 3] or

• "most times (much more than half the time)" [response 4] or

• "almost always/always" [response 5]

10. History of prior tadalafil use: Document usual dosage per sexual encounter, date of last dose, and patient's response (No; Yes—Unsatisfactory Response; Yes—Satisfactory Response). Regardless of past experience, the patient is eligible if he agrees to adhere to protocol and take only tadalafil or placebo prescribed on study.

11. Although patients with partners are targeted for recruitment, patients without partners or without partners willing to participate are eligible. Patients (and spouses/partners, if willing to participate) must be able to provide study-specific informed consent.

Exclusion Criteria:

1. The patient's participation in another medical research study that involves the treatment of ED

2. Previous or concomitant invasive cancer (American Joint Committee on Cancer [AJCC] Stage >0), other than localized basal cell or squamous cell skin carcinoma (AJCC Stage 0-II), or a hematological malignancy (e.g., leukemia, lymphoma, myeloma) unless continually disease free for at least 5 years

3. History of myocardial infarction within the last year

4. Heart failure in the last 6 months

5. Uncontrolled arrhythmias, hypotension (<90/50mm Hg), or uncontrolled hypertension (>170/100 mm Hg)

6. Stroke within the last 6 months

7. Use of luteinizing hormone-releasing hormone (LHRH) agonist androgen suppression (e.g., Lupron, Zoladex), anti-androgen (e.g., Casodex, Eulexin, Nilandron), or estrogenic (e.g., diethylstilbestrol) agents within the last 6 months

8. Current use of any organic nitrate or as needed nitrates (e.g., use of nitroglycerin)

9. Current use of cimetidine, ketoconazole, itraconazole, erythromycin, or ritonavir

10. Known moderate to severe renal insufficiency or end-stage renal disease

11. Known severe hepatic impairment

12. Use of mechanical (vacuum) devices, intracorporeal, intraurethral, topical, or oral (sildenafil, tadalafil, vardenafil) agents as therapy for ED or supplements to enhance sexual function within 5-7 days prior to the start of RT. Patients who discontinue these therapies remain eligible if they can meet eligibility criteria

13. Pretreatment (before starting prostate cancer treatment) ED as measured by IIEF Question 1, "How often were you able to get an erection during sexual activity?" - with responses of:

• "no sexual activity" [response 0] or

• "almost never/never" [response 1] or

• "a few times (much less than half the time)" [response 2]

14. Prior penile implant or history of bilateral orchiectomy

15. Prior prostatectomy, prostatic cryosurgery or high-intensity focused ultrasound (HIFU), radionuclide prostate brachytherapy, or chemotherapy for prostate cancer

16. Prior or anticipated combined external RT and brachytherapy

17. Prior or anticipated external RT to the pelvic ± para-aortic lymph nodes

18. Acquired Immune Deficiency Syndrome (AIDS) based upon current Centers for Disease Control and Prevention (CDC) definition; note, however, that HIV testing is not required for entry into this protocol. The need to exclude patients with AIDS from this protocol is necessary because the treatments involved in this protocol may be significantly immunosuppressive. Protocol-specific requirements may also exclude immunocompromised patients.

19. Anatomical genital abnormalities or concurrent conditions that in the estimation of the physician would prohibit sexual intercourse or prevent study completion

20. Major medical or psychiatric illness which, in the opinion of the investigator, would prevent completion of treatment or would interfere with follow-up

Related Conditions & MeSH terms

• Erectile Dysfunction
• Prostate Cancer
• Prostatic Neoplasms
• Sexual Dysfunction

Intervention

Drug:
• Tadalafil
Beginning = 7 days after the start of radiotherapy, patients receive oral tadalafil 5mg once daily for 24 weeks.

Other:
• Placebo
Beginning = 7 days after the start of radiotherapy, patients receive oral placebo once daily for 24 weeks.

Locations

Country	Name	City	State
Canada	Tom Baker Cancer Centre	Calgary	Alberta
Canada	Cross Cancer Institute	Edmonton	Alberta
Canada	Juravinski Cancer Centre at Hamilton Health Sciences	Hamilton	Ontario
Canada	BCCA-Cancer Centre for the Southern Interior	Kelowna	British Columbia
Canada	London Regional Cancer Program	London	Ontario
Canada	CHUQ - Pavilion Hotel-Dieu de Quebec	Quebec City	Quebec
Canada	Allan Blair Cancer Centre	Regina	Saskatchewan
Canada	BCCA-Fraser Valley Cancer Centre	Surrey	British Columbia
Canada	BCCA-Vancouver Cancer Centre	Vancouver	British Columbia
United States	Abington Memorial Hospital	Abington	Pennsylvania
United States	Summa Akron City Hospital/Cooper Cancer Center	Akron	Ohio
United States	New York Oncology Hematology PC - Albany	Albany	New York
United States	University of New Mexico Cancer Center	Albuquerque	New Mexico
United States	Saint Vincent Anderson Regional Hospital/Cancer Center	Anderson	Indiana
United States	Appleton Medical Center	Appleton	Wisconsin
United States	Mission Hospital-Memorial Campus	Asheville	North Carolina
United States	Sutter Cancer Centers Radiation Oncology Services-Auburn	Auburn	California
United States	University of Colorado Cancer Center - Anschutz Cancer Pavilion	Aurora	Colorado
United States	Johns Hopkins University/Sidney Kimmel Comprehensive Cancer Center	Baltimore	Maryland
United States	Saint Agnes Hospital	Baltimore	Maryland
United States	University of Maryland/Greenebaum Cancer Center	Baltimore	Maryland
United States	Summa Barberton Hospital	Barberton	Ohio
United States	Mary Bird Perkins Cancer Center	Baton Rouge	Louisiana
United States	Bronson Battle Creek	Battle Creek	Michigan
United States	Southside Hospital	Bay Shore	New York
United States	Alta Bates Summit Medical Center-Herrick Campus	Berkeley	California
United States	Lourdes Hospital	Binghamton	New York
United States	University of Alabama at Birmingham	Birmingham	Alabama
United States	IU Health Bloomington	Bloomington	Indiana
United States	Saint Alphonsus Cancer Care Center-Boise	Boise	Idaho
United States	Veteran Affairs New York Harbor Healthcare System-Brooklyn Campus	Brooklyn	New York
United States	Bryn Mawr Hospital	Bryn Mawr	Pennsylvania
United States	Roswell Park Cancer Institute	Buffalo	New York
United States	Cooper Hospital University Medical Center	Camden	New Jersey
United States	Sutter Cancer Centers Radiation Oncology Services-Cameron Park	Cameron Park	California
United States	Mercy San Juan Medical Center	Carmichael	California
United States	University of Virginia	Charlottesville	Virginia
United States	Advocate Illinois Masonic Medical Center	Chicago	Illinois
United States	Enloe Medical Center	Chico	California
United States	University of Cincinnati	Cincinnati	Ohio
United States	Clackamas Radiation Oncology Center	Clackamas	Oregon
United States	Case Western Reserve University	Cleveland	Ohio
United States	Cleveland Clinic Cancer Center/Fairview Hospital	Cleveland	Ohio
United States	Cleveland Clinic Foundation	Cleveland	Ohio
United States	Penrose-Saint Francis Healthcare	Colorado Springs	Colorado
United States	Central Maryland Radiation Oncology in Howard County	Columbia	Maryland
United States	Arthur G. James Cancer Hospital and Solove Research Institute at Ohio State University Medical Center	Columbus	Ohio
United States	John B Amos Cancer Center	Columbus	Georgia
United States	Ohio State University Medical Center	Columbus	Ohio
United States	Huron Valley-Sinai Hospital	Commerce	Michigan
United States	Concord Hospital	Concord	New Hampshire
United States	Danville Regional Medical Center	Danville	Virginia
United States	Atlanta VA Medical Center	Decatur	Georgia
United States	Broward Health North	Deerfield Beach	Florida
United States	Texas Oncology-Denton South	Denton	Texas
United States	Henry Ford Hospital	Detroit	Michigan
United States	Saint John Hospital and Medical Center	Detroit	Michigan
United States	Wayne State University/Karmanos Cancer Institute	Detroit	Michigan
United States	Wentworth-Douglass Hospital	Dover	New Hampshire
United States	Delaware County Memorial Hospital	Drexel Hill	Pennsylvania
United States	Saint Luke's Hospital of Duluth	Duluth	Minnesota
United States	Duke University Medical Center	Durham	North Carolina
United States	Willamette Valley Cancer Center	Eugene	Oregon
United States	Exeter Hospital	Exeter	New Hampshire
United States	Saint Anne's Hospital	Fall River	Massachusetts
United States	McLaren-Flint	Flint	Michigan
United States	Parkview Hospital Randallia	Fort Wayne	Indiana
United States	Radiation Oncology Associates PC	Fort Wayne	Indiana
United States	The Klabzuba Cancer Center	Fort Worth	Texas
United States	Saint Agnes Medical Center	Fresno	California
United States	Fox Chase Cancer Center Buckingham	Furlong	Pennsylvania
United States	University of Florida	Gainesville	Florida
United States	University of Texas Medical Branch at Galveston	Galveston	Texas
United States	Adams Cancer Center	Gettysburg	Pennsylvania
United States	Tate Cancer Center	Glen Burnie	Maryland
United States	IU Health Goshen Center for Cancer Care	Goshen	Indiana
United States	Mercy Health Saint Mary's	Grand Rapids	Michigan
United States	Spectrum Health at Butterworth Campus	Grand Rapids	Michigan
United States	Three Rivers Community Hospital	Grants Pass	Oregon
United States	Saint Vincent Hospital	Green Bay	Wisconsin
United States	Cherry Tree Cancer Center	Hanover	Pennsylvania
United States	High Point Regional Hospital	High Point	North Carolina
United States	Queen's Medical Center	Honolulu	Hawaii
United States	The Cancer Center of Hawaii-Liliha	Honolulu	Hawaii
United States	University of Hawaii Cancer Center	Honolulu	Hawaii
United States	Cape Cod Hospital	Hyannis	Massachusetts
United States	Cleveland Clinic Cancer Center Independence	Independence	Ohio
United States	Baptist Cancer Institute	Jacksonville	Florida
United States	Cancer Specialists of North Florida-Baptist South	Jacksonville	Florida
United States	Cancer Specialists of North Florida-Southside	Jacksonville	Florida
United States	Mayo Clinic in Florida	Jacksonville	Florida
United States	University of Florida Health Science Center	Jacksonville	Florida
United States	Cancer Specialists of North Florida-Beaches	Jacksonville Beach	Florida
United States	West Michigan Cancer Center	Kalamazoo	Michigan
United States	Good Samaritan Hospital	Kearney	Nebraska
United States	Academic Urology Prostate Center	King Of Prussia	Pennsylvania
United States	Gundersen Lutheran	La Crosse	Wisconsin
United States	Mayo Clinic Health System-Franciscan Healthcare	La Crosse	Wisconsin
United States	Memorial Medical Center - Las Cruces	Las Cruces	New Mexico
United States	Central Maine Medical Center	Lewiston	Maine
United States	Baptist Health Lexington	Lexington	Kentucky
United States	Saint Elizabeth Regional Medical Center	Lincoln	Nebraska
United States	Veterans Administration Long Beach Medical Center	Long Beach	California
United States	Elliot Hospital	Manchester	New Hampshire
United States	Bay Area Medical Center	Marinette	Wisconsin
United States	Toledo Clinic Cancer Centers-Maumee	Maumee	Ohio
United States	Hillcrest Hospital Cancer Center	Mayfield Heights	Ohio
United States	Providence Medford Medical Center	Medford	Oregon
United States	Rogue Valley Medical Center	Medford	Oregon
United States	Lake University Ireland Cancer Center	Mentor	Ohio
United States	University of Miami Miller School of Medicine-Sylvester Cancer Center	Miami	Florida
United States	Southwest General Health Center Ireland Cancer Center	Middleburg Heights	Ohio
United States	Aurora Saint Luke's Medical Center	Milwaukee	Wisconsin
United States	Clement J. Zablocki VA Medical Center	Milwaukee	Wisconsin
United States	Providence Hospital	Mobile	Alabama
United States	The Coleman Radiation Center-Carteret General Hospital	Morehead City	North Carolina
United States	Intermountain Medical Center	Murray	Utah
United States	CarolinaEast Health System-Medical Center	New Bern	North Carolina
United States	The Hospital of Central Connecticut	New Britain	Connecticut
United States	Long Island Jewish Medical Center	New Hyde Park	New York
United States	Ochsner Clinic CCOP	New Orleans	Louisiana
United States	Columbia University Medical Center	New York	New York
United States	Christiana Care Health System-Christiana Hospital	Newark	Delaware
United States	Northridge Hospital Medical Center	Northridge	California
United States	Kaiser Permanente Oakland-Broadway	Oakland	California
United States	Oconomowoc Memorial Hospital-ProHealth Care Inc	Oconomowoc	Wisconsin
United States	West Texas Cancer Center	Odessa	Texas
United States	University of Oklahoma Health Sciences Center	Oklahoma City	Oklahoma
United States	Nebraska Methodist Hospital	Omaha	Nebraska
United States	21st Century Oncology-Orange Park	Orange Park	Florida
United States	UHHS-Chagrin Highlands Medical Center	Orange Village	Ohio
United States	21st Century Oncology-Palatka	Palatka	Florida
United States	Advocate Lutheran General Hospital.	Park Ridge	Illinois
United States	Arizona Center for Cancer Care-Peoria	Peoria	Arizona
United States	Albert Einstein Medical Center	Philadelphia	Pennsylvania
United States	Fox Chase Cancer Center	Philadelphia	Pennsylvania
United States	Providence Portland Medical Center	Portland	Oregon
United States	Providence Saint Vincent Medical Center	Portland	Oregon
United States	Western Oncology Research Consortium	Portland	Oregon
United States	Utah Valley Regional Medical Center	Provo	Utah
United States	Rapid City Regional Hospital	Rapid City	South Dakota
United States	Mayo Clinic	Rochester	Minnesota
United States	Sutter Cancer Centers Radiation Oncology Services-Roseville	Roseville	California
United States	William Beaumont Hospital-Royal Oak	Royal Oak	Michigan
United States	Mercy General Hospital Radiation Oncology Center	Sacramento	California
United States	Radiological Associates of Sacramento	Sacramento	California
United States	Saint Mary's of Michigan	Saginaw	Michigan
United States	Cancer Specialists of North Florida-Saint Augustine	Saint Augustine	Florida
United States	Coborn Cancer Center at Saint Cloud Hospital	Saint Cloud	Minnesota
United States	Dixie Medical Center Regional Cancer Center	Saint George	Utah
United States	Barnes-Jewish West County Hospital	Saint Louis	Missouri
United States	Washington University School of Medicine	Saint Louis	Missouri
United States	United Hospital	Saint Paul	Minnesota
United States	Siteman Cancer Center - Saint Peters	Saint Peters	Missouri
United States	Cancer Care Center, Incorporated	Salem	Ohio
United States	Huntsman Cancer Institute/University of Utah	Salt Lake City	Utah
United States	Utah Cancer Specialists-Salt Lake City	Salt Lake City	Utah
United States	University of Texas Health Science Center	San Antonio	Texas
United States	California Pacific Medical Center	San Francisco	California
United States	UCSF-Mount Zion	San Francisco	California
United States	Lewis Cancer and Research Pavilion at Saint Joseph's/Candler	Savannah	Georgia
United States	Maine Medical Center- Scarborough Campus	Scarborough	Maine
United States	Arizona Oncology Services Foundation	Scottsdale	Arizona
United States	Mayo Clinic in Arizona	Scottsdale	Arizona
United States	Virginia Mason CCOP	Seattle	Washington
United States	Texas Cancer Center-Sherman	Sherman	Texas
United States	Memorial Hospital of South Bend	South Bend	Indiana
United States	Northern Indiana Cancer Research Consortium	South Bend	Indiana
United States	Kaiser Permanente Cancer Treatment Center	South San Francisco	California
United States	Spartanburg Regional Medical Center	Spartanburg	South Carolina
United States	Saint John's Hospital	Springfield	Illinois
United States	Door County Cancer Center	Sturgeon Bay	Wisconsin
United States	Texas Oncology Cancer Center Sugar Land	Sugar Land	Texas
United States	South Atlantic Radiation Oncology	Supply	North Carolina
United States	Flower Hospital	Sylvania	Ohio
United States	Arizona Oncology Associates-West Orange Grove	Tucson	Arizona
United States	Tyler Cancer Center	Tyler	Texas
United States	Carle Cancer Center	Urbana	Illinois
United States	Sutter Cancer Centers Radiation Oncology Services-Vacaville	Vacaville	California
United States	Sutter Solano Medical Center	Vallejo	California
United States	Compass Oncology Vancouver	Vancouver	Washington
United States	MD Anderson Cancer Center at Cooper-Voorhees	Voorhees	New Jersey
United States	Washington Hospital Center	Washington	District of Columbia
United States	Waukesha Memorial Hospital - ProHealth Care	Waukesha	Wisconsin
United States	Aurora West Allis Medical Center	West Allis	Wisconsin
United States	UHHS-Westlake Medical Center	Westlake	Ohio
United States	Coastal Carolina Radiation Oncology	Wilmington	North Carolina
United States	New Hanover Regional Medical Center	Wilmington	North Carolina
United States	Cancer Treatment Center	Wooster	Ohio
United States	Cleveland Clinic Wooster Specialty Center	Wooster	Ohio
United States	Lankenau Medical Center	Wynnewood	Pennsylvania
United States	WellSpan Health-York Hospital	York	Pennsylvania

Sponsors (3)

Lead Sponsor	Collaborator
Radiation Therapy Oncology Group	National Cancer Institute (NCI), NRG Oncology

Countries where clinical trial is conducted

United States,  Canada, 

Outcome

Type	Measure	Description	Time frame	Safety issue
Other	Radiotherapy Factors Associated With Spontaneous (Off-drug) EF at Weeks 28-30 and Years 1 and 2 After Initiation of RT		Baseline, week 30 and years 1 and 2 after the start of treatment
Other	Patient Follow-up Treatment for Erectile Dysfunction at Weeks 28-30 and Years 1 and 2 After Initiation of RT		Baseline, week 30 and years 1 and 2 after the start of treatment
Primary	Percentage of Patients Maintaining Spontaneous (Off-drug) Erectile Function (EF) at Weeks 28-30 After Initiation of Radiation Therapy (RT)	EF is measured by Question 1 of the International Index of Erectile Function (IIEF). The IIEF is a validated 15-item for measuring patient-reported erectile function. Question 1 asks "How often were you able to get an erection during sexual activity?" Responses ranged from 0=no sexual activity, to 5=Almost always or always. Higher scores indicated better functioning. All patients have erectile function prior to initiation of RT, indicated by a score of 3, 4, or 5 on IIEF Q1. Patients with a lower IIEF Q1 score at weeks 28-30 than at baseline will have less erectile function and be categorized as nonresponders. Patients with similar or improved erectile function will be categorized as responders (maintaining). Patient-related predictors of at erectile function at this time point are also reported with this outcome measure.	Baseline and 30 weeks from the start of radiation therapy
Secondary	Percentage of Patients Maintaining Spontaneous (Off-drug) EF at Years 1 and 2 After Initiation of RT	The International Index of Erectile Function (IIEF) is a validated 15-item for measuring patient-reported erectile function. Question 1 asks "How often were you able to get an erection during sexual activity?" Responses ranged from 0=no sexual activity, to 5=Almost always or always. Higher scores indicated better functioning. All patients have erectile function prior to initiation of RT, indicated by a score of 3, 4, or 5. Patients with a lower IIEF Q1 score at weeks 28-30 than at baseline will have less erectile function and be categorized as nonresponders. Patients with similar or improved erectile function will be categorized as responders (maintaining). Patient-related predictors of at erectile function at Years 1 and 2 are also reported with this outcome measure.	Baseline, 1 and 2 years from the start of tadalafil or placebo
Secondary	Overall Sexual Function as Measured by Change From Baseline in the International Index of Erectile Function (IIEF)	The IIEF is a validated 15-item for measuring patient-reported erectile function. A score of 0-5 is given to each of the 15 questions that examine 5 main domains of male sexual function: erectile function, orgasmic function, sexual desire, intercourse satisfaction, and overall satisfaction. Domain scores are the sum of each item. The erectile function domain has 5 items with a score range of 1-30, orgasmic function has 2 items with a score range of 0-10, sexual desire has 2 items with a score range of 0-10, intercourse satisfaction has 3 items with a score range of 0-15, and overall satisfaction has 2 items with a score range of 2-10. Total score ranges from 0-70, with higher scores indicated better functioning. Change from baseline is calculated by subtracting baseline score from score at the time point of interest.	Baseline, week 30, and years 1 and 2 from start of treatment
Secondary	Overall Patient Sexual Satisfaction as Measured by Change From Baseline in the Sexual Adjustment Questionnaire (SAQ) Score	The Sexual Adjustment Questionnaire (SAQ) is a 20-item questionnaire with an overall score range between 8 and 100 including the following domains: desire, ranging between 5 and 30; dysfunction, 0 and 25; activity, 0 and 10; satisfaction, 1 and 10; and fatigue, 1 and 5. The change in SAQ score is calculated by subtracting the baseline score from the follow-up score. A positive change indicates an improvement in sexual well-being.	Baseline, week 30 and years 1 and 2 after the start of treatment
Secondary	Overall Partner Sexual Satisfaction as Measured by Change From Baseline in the Sexual Adjustment Questionnaire-Partner (SAQ-P) Score	The SAQ-P is an 18-item questionnaire with an overall score range between 0 and 90 including the following domains: desire, dysfunction, activity, satisfaction, and fatigue. The change in SAQ score is calculated by subtracting the baseline score from the follow-up score. A positive change indicates an improvement in sexual well-being.	Baseline, week 30 and years 1 and 2 after the start of treatment
Secondary	Patient Marital Adjustment as Measured by the Locke's Marital Adjustment Test	The Locke Marital Adjustment Test (LMAT) is a 16-item questionnaire with scores ranging from 48 to 138 for participants. Higher scores indicate greater sexual function, sexual wellbeing, or marital adjustment. The change in LMAT score is calculated by subtracting the baseline score from the follow-up score.	Baseline, week 30 and years 1 and 2 after the start of treatment
Secondary	Partner Marital Adjustment as Measured by the Locke's Marital Adjustment Test	The Locke Marital Adjustment Test (LMAT) is a 16-item questionnaire with scores ranging from 48 to 138 for participants. Higher scores indicate greater sexual function, sexual wellbeing, or marital adjustment. The change in LMAT score is calculated by subtracting the baseline score from the follow-up score.	Baseline, week 30 and years 1 and 2 after the start of treatment