Inter-centre variability of CT-based stopping-power prediction in particle therapy: Survey-based evaluation

Area of Science:

• Medical Physics
• Radiation Oncology
• Medical Imaging

Background:

• Stopping-power ratios (SPRs) are crucial for calculating particle range in particle therapy.
• The heuristic CT-to-SPR conversion (Hounsfield Look-Up-Table, HLUT) is essential for treatment planning.
• HLUT derivation depends on CT scan, reconstruction parameters, and HLUT definition, leading to potential inter-center variability.

Purpose of the Study:

• To assess inter-center differences in CT scan parameters and HLUT definitions used for SPR derivation.
• To evaluate the current practices in particle therapy centers regarding CT-based SPR calculations.
• To identify areas for standardization in CT-to-SPR conversion for improved treatment planning.

Main Methods:

• A survey questionnaire was distributed to twelve particle therapy centers (ten in Europe, two in the USA).
• The questionnaire gathered details on CT scanners, image acquisition/reconstruction, HLUT definition, body-region specific HLUT selection, beam-hardening investigations, and experimental HLUT validations.
• Technological improvements' potential to enhance SPR accuracy was rated.

Main Results:

• Significant variations were observed in scan parameters and HLUT definitions across centers.
• The stoichiometric method was used by eight centers, while three used tissue-substitute-only HLUTs; one center combined both.
• HLUT line segments varied widely (2-11), and validation schemes differed substantially among centers that performed experimental validations. Dual-energy CT was considered promising.

Conclusions:

• Substantial inter-center variability exists in CT scan implementation, image reconstruction, and CT-to-SPR conversion specification.
• Standardization is recommended to reduce institution-specific efforts and variations in treatment quality.
• Due to parameter interdependencies, conclusions on the accuracy and variability of derived SPRs could not be drawn from this study.