Effect of hip prostheses on radiotherapy dose

Area of Science:

• Medical Physics
• Radiation Oncology
• Radiotherapy Planning

Background:

• A growing number of prostate cancer patients undergoing radiotherapy have hip prostheses.
• Hip prostheses can interfere with radiotherapy by shadowing the target and altering dose distribution.
• Approximately 10 such cases are treated annually at the Illawarra Cancer Care Centre.

Purpose of the Study:

• To evaluate the accuracy of different radiotherapy treatment methods for prostate cancer patients with hip prostheses.
• To analyze dose variations within the target volume considering the presence of hip implants.
• To compare the effectiveness of various beam setups in minimizing dose discrepancies.

Main Methods:

• Fixed-field measurements to assess dose reduction in the prosthesis shadow.
• Monte Carlo simulations to analyze dose distribution, including surface dose.
• Thermoluminescent dosimeters and Gafchromic film used for benchmarking.
• Planning and analysis of three beam setups: four-field brick, dual arc, and four-field oblique techniques.

Main Results:

• Fixed-field measurements showed a 52% dose reduction in the prosthesis shadow.
• Monte Carlo simulations indicated a 35% dose increase on the prosthesis's distal surface.
• The four-field brick technique resulted in a +/- 15% dose variation across the target volume.
• The dual arc technique achieved a +/- 5% dose variation.
• The four-field oblique technique provided a +/- 2% dose variation but increased rectal dose.

Conclusions:

• The dual arc and four-field oblique techniques demonstrate superior accuracy in dose distribution for prostate cancer radiotherapy with hip prostheses.
• Careful selection of beam setup is crucial to optimize target coverage and minimize dose variations.
• The four-field oblique technique, while precise, necessitates consideration of potential increased rectal dose.