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Dose variations with varying calculation grid size in head and neck IMRT
Heeteak Chung1, Hosang Jin, Jatinder Palta
1Department of Nuclear and Radiological Engineering, University of Florida, Gainesville, 32611-8300, USA.
Physics in Medicine and Biology
|September 21, 2006
Summary
Treatment planning system grid size significantly impacts radiation dose accuracy. Smaller grid sizes are crucial for precise dose calculations in radiation therapy, especially for head and neck treatments.
Area of Science:
- Medical Physics
- Radiation Oncology
Background:
- Treatment planning systems (TPS) are essential for radiation therapy.
- Dose calculation grid size remains a significant source of uncertainty in TPS.
- This uncertainty persists even with advanced 3D conformal and intensity-modulated radiation therapy (IMRT) techniques.
Purpose of the Study:
- To investigate the impact of calculation grid size on dose accuracy in radiation therapy planning.
- To quantify dose uncertainties introduced by varying grid sizes in head and neck phantom and clinical cases.
Main Methods:
- A head and neck phantom was created using solid water slabs with radiochromic film for dose measurement.
- Philips Pinnacle(3) TPS was used to generate treatment plans with prescribed doses of 5,400 cGy.
- Calculations were performed using grid sizes of 1.5, 2, 3, and 4 mm for shallow and deep targets.
Main Results:
- Dose differences up to 5.6% were observed in the phantom study due to grid size variations.
- Shifting the calculation grid origin introduced dose variations up to 3.8%.
- Increased relative dose gradient range correlated with higher relative dose differences; local effects were noted in dose difference maps.
Conclusions:
- Calculation grid size is a critical factor affecting dose accuracy in radiation therapy planning.
- Smaller grid sizes are recommended for improved precision, particularly in complex treatment sites like the head and neck.
- These findings highlight the need for careful consideration of grid size settings in TPS to minimize dose uncertainty.
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