Use of GammaPlan convolution algorithm for dose calculation on CT and cone-beam CT images
Prabhakar Ramachandran1, Ben Perrett1, Orrie Dancewicz1
1Department of Radiation Oncology, Princess Alexandra Hospital, Brisbane, Australia.
Radiation Oncology Journal
|October 8, 2021
Summary
Cone-beam computed tomography (CBCT) images from Leksell Gamma Knife (LGK) Icon systems can generate electron density data for treatment planning. However, artifacts and Hounsfield value variations necessitate cautious use of this data for dose calculations.
Area of Science:
- Medical Physics
- Radiotherapy
- Image Processing
Background:
- Accurate electron density information is crucial for radiation dose calculation in Leksell GammaPlan Treatment Planning System (TPS).
- Cone-beam computed tomography (CBCT) offers onboard imaging capabilities, but its suitability for electron density generation requires evaluation.
Purpose of the Study:
- To assess the suitability of Leksell Gamma Knife (LGK) Icon system's CBCT images for generating electron density data.
- To evaluate the impact of using CBCT-derived electron density on dose calculation within the Leksell GammaPlan (LGP) convolution algorithm.
Main Methods:
- A retrospective analysis of 30 Leksell Gamma Knife (LGK) treatment plans for multiple metastases.
- Comparison of plan quality metrics (coverage, selectivity, gradient index, beam-on time) using convolution with CBCT (convCBCT) and planning CT (convCT) data versus the TMR10 algorithm.
Main Results:
- Convolution using CBCT data (convCBCT) resulted in slightly increased beam-on times compared to the TMR10 algorithm.
- Minimal differences were observed in coverage, selectivity, and gradient index between TMR10 and convCBCT.
- Higher beam-on times for convCBCT were linked to Hounsfield value variations dependent on field-of-view position.
Conclusions:
- Artifacts and Hounsfield unit variations in CBCT images must be considered for dose calculation.
- Electron density data derived from onboard CBCT imaging should be used with caution in LGP treatment planning.
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