Treatment planning for metals using an extended CT number scale

Area of Science:

• Medical Physics
• Radiotherapy
• Medical Imaging

Background:

• Metal implants in patients undergoing radiation therapy can cause artifacts and saturate standard CT (Computed Tomography) number scales.
• Accurate dose calculation is crucial for effective radiotherapy, but metal artifacts complicate this process, often requiring manual intervention by dosimetrists and physicists.

Purpose of the Study:

• To evaluate the accuracy of direct dose calculation using extended CT scale images for various metals and geometries.
• To compare the efficacy of extended CT scale imaging against standard CT methods for handling high-Z materials and artifacts in radiotherapy planning.

Main Methods:

• Dose calculations were performed directly on extended CT scale images for different metal samples and geometries.
• Gafchromic film measurements were used for experimental validation of calculated doses.
• Clinical patient treatment plans with metal implants were analyzed, comparing dose distributions from standard CT and extended CT methods.

Main Results:

• Dose calculations using the extended CT method showed agreement within 2% with film measurements and standard methods for cobalt-chromium, a strong metal attenuator.
• The maximum dose discrepancy observed in clinical patient plans between the standard and extended CT methods was 1.2%.
• Extended CT demonstrated accuracy comparable to standard methods despite its reduced HU resolution.

Conclusions:

• Direct dose calculation on extended CT scale images is a clinically viable and accurate method for patients with metal implants.
• This approach enhances the efficiency of clinical workflows by eliminating the need for manual contouring and CT number assignment for metals.
• Utilizing extended CT scale imaging reduces the potential for human error in radiotherapy dose calculations involving metal artifacts.