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Hip prostheses during pelvic irradiation: effects and corrections.
M B Hazuka1, G S Ibbott, J J Kinzie
1Division of Radiation Oncology, Presbyterian/Saint Luke's Medical Center, Denver, CO 80218.
Summary
Hip prostheses can alter radiation therapy dose distribution in pelvic cancer treatment. This study provides correction factors for metal alloys, improving accuracy in computer-aided treatment planning.
Area of Science:
- Medical Physics
- Radiation Oncology
- Biomedical Engineering
Background:
- Pelvic malignancy treatment often involves radiation fields that intersect with hip prostheses.
- Metal hip implants can significantly perturb radiation dose distribution, impacting treatment efficacy and patient safety.
- Accurate dose calculations require accounting for the presence and material properties of these implants.
Purpose of the Study:
- To determine and report correction factors for metal-based hip prostheses used in radiation therapy.
- To compare measured photon transmission data with computed correction factors using the ratio of tissue-maximum ratios (TMRs) method.
- To provide data on relative electron densities for artificial hip alloys to aid computer-aided treatment planning.
Main Methods:
- Acquired prostheses made from common metal alloys.
- Measured the transmission of 4MV and 10MV photons through these prostheses.
- Compared measured data with computed correction factors derived from physical and relative electron densities.
- Investigated the impact of scattered radiation on dose computations and adjusted electron densities accordingly.
Main Results:
- Correction factors determined using relative electron densities showed better agreement with measured data compared to physical density.
- The ratio of TMRs algorithm required adjustments to relative electron density at lower X-ray energies due to unaddressed scattered radiation.
- Satisfactory agreement was achieved for higher energy X-rays without adjustment.
- Provided relative and adjusted electron densities for commonly used hip prosthesis alloys.
Conclusions:
- Relative electron densities are crucial for accurate dose perturbation calculations in the presence of hip prostheses.
- Adjustments to electron density may be necessary for lower energy X-ray beams to account for scattered radiation.
- The findings facilitate improved computer-aided treatment planning for pelvic malignancies in patients with hip implants.