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Updated: Jan 25, 2026
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High-resolution In Vivo Manual Segmentation Protocol for Human Hippocampal Subfields Using 3T Magnetic Resonance Imaging
Published on: November 10, 2015
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Fluence-weighted average subfield size in helical TomoTherapy.
Simon Howitz1, Tilo Wiezorek2, Andrea Wittig2
1University Hospital Jena, Department of Radiation Oncology, Germany; Institute for Medical Physics and Radiation Protection IMPS, University of Applied Science - THM, Giessen, Germany; Philipps-University, Marburg, Germany.
Zeitschrift Fur Medizinische Physik
|May 7, 2019
Summary
This study defines average subfield size for helical TomoTherapy, finding no correlation between field size and dose deviation with the Delta4 system. Planning parameters significantly influence subfield size, impacting dose distribution.
Area of Science:
- Medical Physics
- Radiation Oncology
- Radiotherapy Technology
Background:
- Helical TomoTherapy offers conformal dose distribution but faces dosimetric uncertainties due to small field sizes.
- IAEA provides correction factors for static TomoTherapy fields (TRS483).
- Investigating average subfield size in helical plans is crucial for accuracy.
Purpose of the Study:
- Define and investigate the fluence-weighted average subfield size in helical TomoTherapy.
- Assess the impact of planning parameters on average subfield size.
- Evaluate dosimetric reliability using Delta4 measurements in relation to subfield size.
Main Methods:
- Defined fluence-weighted average subfield size.
- Extracted subfield sizes from RT-plan files of 30 clinical plans (prostate, H&N).
- Varied modulation factor, iterations, and pitch; verified with Delta4 Phantom+ measurements.
Main Results:
- Average subfield sizes were similar for prostate (2.75±0.14cm) and H&N (2.70±0.16cm) plans (2.5cm jaw width).
- No correlation found between field size and measured dose deviation with Delta4.
- Increased modulation factor and iterations reduced subfield size and improved dose distribution.
Conclusions:
- A method to determine average subfield size for helical TomoTherapy was established.
- Delta4 system showed no field size dependence within the studied range.
- Further investigation is needed for other dosimetry systems' response to subfield sizes.
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