What is the role of radiotherapy to the prostate in metastatic prostate cancer?

Role of Radiotherapy to the Prostate in Metastatic Prostate Cancer

Radiotherapy to the primary prostate tumor is not a standard treatment for metastatic prostate cancer, but it plays important roles in palliating local symptoms and treating bone metastases. 1

Palliative Radiotherapy for Local Symptoms

• External beam radiotherapy to the prostate can effectively palliate local symptoms in patients with metastatic prostate cancer, including hematuria, urinary obstruction, rectal symptoms, and pelvic pain 2
• Short-course palliative radiotherapy (20 Gy in 5 fractions) is commonly used with response rates of up to 89% for symptom resolution at 4 months 2
• Radiotherapy for local symptoms is generally well-tolerated with minimal toxic side effects, making it suitable for patients with advanced disease 2, 3

Radiotherapy for Bone Metastases

• For painful bone metastases from castration-refractory prostate cancer, external beam radiotherapy is highly effective 4, 1
• A single 8 Gy fraction is equally effective for pain relief as multi-fraction schedules (e.g., 30 Gy in 10 fractions) for non-vertebral metastases, and is more cost-effective 1, 5
• Retreatment with a second course of radiation can induce pain responses in approximately 50% of patients 6

Radiopharmaceuticals for Widespread Bone Metastases

• Radium-223 is FDA-approved for patients with symptomatic bone metastases and no known visceral disease 4, 1
• Radium-223 significantly improves overall survival (median 14.9 vs 11.3 months) and prolongs time to first skeletal-related event compared to placebo 1
• Other radiopharmaceuticals like strontium-89 and samarium-153 should be considered for patients with painful bone metastases from castration-refractory disease 4, 1

Treatment Algorithm for Radiotherapy in Metastatic Prostate Cancer

1. For localized symptoms in the prostate:

   • Consider short-course palliative radiotherapy (20 Gy in 5 fractions) for hematuria, obstruction, or local pain 2, 3
   • Monitor for symptom relief and consider retreatment if symptoms recur 2

2. For bone metastases:

   • For limited bone metastases: Single 8 Gy fraction external beam radiotherapy 1
   • For widespread bone metastases: Consider radiopharmaceuticals 1
     • Radium-223 for patients with symptomatic bone metastases without visceral disease 4, 1
     • Strontium-89 or samarium-153 for patients with painful bone metastases 4, 1

Important Considerations and Pitfalls

• Radium-223 should not be combined with standard doses of docetaxel based on preliminary safety data 4, 1
• Patients receiving external beam radiotherapy for locally advanced disease should receive androgen suppression before, during, and after radiotherapy for at least 6 months 4
• For patients with bone pain resistant to palliative radiotherapy, intravenous bisphosphonates should be considered 4, 1
• Patients with castration-refractory disease should be managed in collaboration with dedicated palliative care services 4