Focal Radiation Therapy for the Treatment of Low or Intermediate-Risk Prostate Cancer

This phase II trial studies how well focal radiation therapy with stereotactic body radiation therapy (SBRT) or high-dose rate (HDR) brachytherapy works in treating patients with low or intermediate-risk prostate cancer. Stereotactic body radiation therapy uses special equipment to position a patient and deliver radiation to tumors with high precision. This method may kill tumor cells with fewer doses over a shorter period and cause less damage to normal tissue. Brachytherapy, also known as internal radiation therapy, uses radioactive material placed directly into or near a tumor to kill tumor cells. HDR brachytherapy uses high doses of radiation to target these tumor cells. Giving focal radiation therapy with SBRT or HDR brachytherapy may target dominant tumor cells while sparing the reminder of the prostate or surrounding normal organs and ultimately reduce side effects while maintaining disease control.

PRIMARY OBJECTIVES:

I. Evaluate biochemical progression free survival (bPFS) using the Phoenix definition.

II. Changes in quality of life. IIa. Prostate-Quality of Life (PR-QOL). IIb. Expanded Prostate Cancer Index Composite (EPIC).

SECONDARY OBJECTIVES:

I. Prostate-specific antigen (PSA) response at 3, 6, 12, and 24 months. II. Clinical progression free survival. IIa. Including phoenix definition, local progression by Response Evaluation Criteria in Solid Tumors (RECIST), regional progression, distant metastasis, or death.

III. Distant metastasis free survival. IV. Development of castration-resistant disease. V. Overall survival.

OUTLINE: Patients are assigned to 1 of 2 arms.

ARM I: Patients undergo SBRT in 5 fractions over 14 days in the absence of disease progression or unacceptable toxicity.

ARM II: Patients undergo HDR brachytherapy on day 1 and a second fraction within 14 days in the absence of disease progression or unacceptable toxicity.

After completion of study treatment, patients are followed up for 6 weeks, every 3 months for up to 24 months, every 6 months for up to 60 months, and then every 8-12 months until 120 months.

Eligibility Criteria:
Inclusion Criteria:

* Histologically confirmed diagnosis of prostate adenocarcinoma within 90 days prior to registration via systematic biopsy and with the following low/intermediate-risk features:

  * cT1c - T2b
  * PSA =\< 15
  * \< 50% cores positive
  * Gleason score (GS) =\< 7 (3+4 and 4+3 included)
* Multiparametric magnetic resonance imaging (MRI) (mp-MRI) confirmed lesion(s) with only one lobe involvement of the prostate
* Unilateral disease on systematic biopsy
* No distant or locally advanced disease on standard staging exams as indicated

  * Bone scan and abdominopelvic computed tomography (CT)/MRI OR
  * Prostate specific membrane antigen (PSMA) positron emission tomography (PET)
* Eastern Cooperative Oncology Group (ECOG)/Zubrod performance status 0/1 within 60 days prior to enrollment

Exclusion Criteria:

* Gleason score \>= 8
* Gross extracapsular extension
* Seminal vesicle invasion
* Radiographic nodal or distant metastatic disease
* Androgen deprivation therapy within 90 days of enrollment
* Lesion(s) comprising \> 40% of total prostate volume
* Lesion \< 0.5 cm from urethra
* Prior radical prostatectomy
* Prior radiotherapy to the pelvis