A radiotherapy technique to improve dose homogeneity around bone prostheses

Area of Science:

• Oncology
• Radiation Oncology
• Medical Physics

Background:

• Limb-sparing surgery for bone and soft tissue sarcomas often necessitates post-operative radiotherapy.
• Metal prostheses used in these surgeries can cause dose reduction (approx. 10%) in their shadow during radiotherapy with opposed fields.
• This under-dosing increases the risk of local recurrence in the critical area around the prosthesis.

Purpose of the Study:

• To describe and evaluate a technique for boosting radiation dose in the under-dosed region caused by metal prostheses.
• To improve target dose homogeneity in patients undergoing radiotherapy after limb-sparing surgery with metallic implants.
• To ensure adequate radiation dose intensity at the site most at risk of local recurrence.

Main Methods:

• A custom-made keyhole cutout was designed to deliver a boost dose to the area shadowed by the metal prosthesis.
• The degree of radiation attenuation by the prosthesis was estimated to calculate the necessary boost dose.
• Exit thermoluminescent dosimetry (TLD) was employed to verify dose calculations and individualize treatment plans.

Main Results:

• The custom boost technique successfully delivered higher radiation doses to the under-dosed areas.
• Exit TLD confirmed patient-specific variations in dose attenuation, highlighting the need for individualized treatment.
• The method improved overall dose homogeneity within the target volume.

Conclusions:

• A boost field technique using custom keyhole cutouts is effective in overcoming under-dosage caused by metal prostheses during post-operative radiotherapy.
• This method enhances dose homogeneity and ensures adequate radiation intensity around the prosthesis, crucial for minimizing local recurrence.
• Individualized treatment planning with exit dosimetry is essential for optimizing radiotherapy in these complex cases.