Can knees with prosthetic replacements be treated with radiation therapy?

Radiation Therapy for Knees with Prosthetic Replacements

Radiation therapy can be safely administered to patients with knee prostheses, but requires special treatment planning to account for dose distribution alterations caused by the metal components.

Effects of Prosthetic Knee Components on Radiation Therapy

Knee prostheses significantly impact radiation dose distribution during radiotherapy due to their metallic composition:

• Metal prostheses with high density and atomic number cause major changes in radiation scattering and attenuation 1
• Different prosthetic materials produce varying effects on dose distribution:
  • Cobalt-chromium-molybdenum alloy: Up to 6.8% dose increase and 41.18% dose reduction
  • Steel: Up to 6.1% dose increase and 40.66% dose reduction
  • Titanium: Up to 4.29% dose increase and 37.51% dose reduction
  • Titanium alloy: Up to 4% dose increase and 37.76% dose reduction 1

Treatment Planning Considerations

When planning radiation therapy for patients with knee prostheses:

1. Material composition matters: Titanium and titanium alloy prostheses cause less dose perturbation than cobalt-chromium-molybdenum or steel 1

2. Dosimetric calculations: Treatment planning must account for:

   • Increased dose anterior to the prosthesis (due to backscatter)
   • Decreased dose posterior to the prosthesis (due to attenuation)
   • Potential cold spots in target volumes behind the prosthesis

3. Imaging considerations:

   • Standard radiographs are essential for initial evaluation of prosthesis position and alignment 2
   • CT imaging may be needed for treatment planning but will have significant artifact around the prosthesis 2

Clinical Applications and Evidence

Radiation therapy has been successfully used in patients with knee prostheses for specific conditions:

1. Heterotopic ossification (HO) prophylaxis:

   • HO occurs in 42% of patients after total knee arthroplasty
   • Postoperative radiotherapy has been used to prevent recurrence after surgical resection of symptomatic HO 3

2. Painful degenerative joint disorders:

   • While less common now, radiotherapy has shown efficacy for pain reduction in osteoarthritis
   • Treatment protocol example: Two series of 6 x 1 Gy (total 12 Gy) with 3 weekly fractions 4

3. Soft tissue sarcomas:

   • Radiation therapy remains an important component of local therapy for soft tissue sarcomas
   • The presence of a knee prosthesis requires special consideration in treatment planning 2

Potential Complications and Monitoring

Patients with knee prostheses receiving radiation therapy should be monitored for:

1. Implant longevity: A history of radiation therapy may impact outcomes after total knee arthroplasty, with some studies showing increased risk of prosthetic joint infection at 1-year in cancer patients who received radiation therapy (OR: 1.5,95% CI: 1.1-2.0) 5

2. Dose homogeneity: Regular imaging during treatment may be necessary to ensure proper dose delivery

3. Tissue effects: Radiation has clinically significant short- and long-term risks including edema, fibrosis, and potential for second malignancies 2

Follow-up Recommendations

After radiation therapy in patients with knee prostheses:

• Regular radiographic follow-up is recommended to assess prosthesis stability and alignment
• Standard radiographic examination should include standing anteroposterior (AP), lateral, and axial views of the knee 2, 6
• More frequent follow-up is indicated if there are signs of failure, decreased periprosthetic bone quality, or history of prior revision 2

In conclusion, while radiation therapy can be administered to patients with knee prostheses, it requires careful treatment planning to account for dose perturbations caused by the metallic components. Titanium-based prostheses are preferred when possible due to their lesser impact on dose distribution.