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Monte Carlo treatment planning for stereotactic radiosurgery
T D Solberg1, J J DeMarco, F E Holly
1Department of Radiation Oncology, Jonsson Comprehensive Cancer Center, UCLA School of Medicine, University of California, Los Angeles 90095-6951, USA.
Summary
Radiosurgery dose calculations are often simplified, but ignoring tissue variations significantly alters dose distributions. Monte Carlo simulations reveal that heterogeneities broaden beams, impacting treatment accuracy.
Area of Science:
- Medical Physics
- Radiation Oncology
Background:
- Current radiosurgery treatment planning often assumes homogeneous target volumes, using simplified dose algorithms.
- These algorithms, typically a product of tissue-maximum ratios, off-axis ratios, and output factors, may be inadequate for small photon beams due to lack of scatter equilibrium.
Purpose of the Study:
- To develop and employ advanced Monte Carlo techniques for more accurate radiosurgical dose distribution calculations.
- To investigate the impact of tissue heterogeneities and contour variations on dose distributions in radiosurgery.
Main Methods:
- Utilized a Monte Carlo system to simulate radiation transport through patient-specific computed tomography data.
- Accounted for perturbations from external contours and internal tissue heterogeneities.
- Incorporated multi-beam, multi-arc stereotactic delivery simulation.
Main Results:
- Calculations demonstrated substantial differences when tissue homogeneity was not assumed.
- Tissue heterogeneities caused lateral beam broadening.
- Higher isodose levels (80-90%) encompassed smaller volumes, while lower isodose levels (<50%) treated larger volumes.
Conclusions:
- The assumption of homogeneity in radiosurgery treatment planning can lead to inaccurate dose distributions.
- Further investigation and refinement of radiosurgery dose algorithms are necessary to account for tissue heterogeneities.