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Adequate margins for random setup uncertainties in head-and-neck IMRT
Eleftheria Astreinidou1, Arjan Bel, Cornelis P J Raaijmakers
1Department of Radiotherapy, University Medical Center Utrecht, Heidelberglaan 100, 3584 CX Utrecht, The Netherlands. e.astreinidou@azu.nl
International Journal of Radiation Oncology, Biology, Physics
|February 15, 2005
Summary
Random setup uncertainties in intensity-modulated radiotherapy (IMRT) for head-and-neck cancer require specific planning target volume (PTV) margins. Margins of 1.5 mm and 3.0 mm are recommended for the clinical target volume (CTV) primary tumor based on translational deviations.
Area of Science:
- Radiation Oncology
- Medical Physics
- Cancer Treatment
Background:
- Intensity-modulated radiotherapy (IMRT) offers precise dose delivery for head-and-neck cancers.
- Accurate dose distribution is sensitive to patient setup uncertainties.
- Determining appropriate margins is crucial for effective treatment outcomes.
Purpose of the Study:
- To evaluate the impact of random setup uncertainties on IMRT dose distributions in head-and-neck cancer patients.
- To establish optimal planning target volume (PTV) margins to mitigate these uncertainties.
Main Methods:
- Simulated patient setup displacements (translations and rotations) using normally distributed errors (sigma=2mm, 4mm for translation; sigma=1 degree for rotation).
- Calculated IMRT doses for various PTV margins (0.0-5.0 mm) applied to clinical target volumes (CTV) of primary tumors and lymph nodes.
- Compared dose coverage (V95) of actual plans with static plans to assess the effect of uncertainties.
Main Results:
- Translational deviations (sigma=2mm) and rotational deviations (sigma=1 degree) had minimal impact on CTV(primary) V95.
- Higher translational deviations (sigma=4mm) reduced CTV(primary) V95 by up to 3% for smaller PTV margins.
- CTV(elective) V95 showed reductions of 1-5% with increasing uncertainties, especially for margins <5.0 mm.
- Maximal spinal cord dose increased by up to 3 Gy.
Conclusions:
- Recommended PTV margins for CTV(primary) are 1.5 mm (sigma=2mm) and 3.0 mm (sigma=4mm) to account for random setup uncertainties.
- For CTV(elective), a 5.0 mm margin is suggested to achieve at least 99% V95, considering uncertainties.