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The effect of source-axis distance on integral dose: implications for IMRT.
1Department of Radiation Oncology, Virginia Commonwealth University Health System, Richmond 23298-0058, USA. pjkeall@vcu.edu
Australasian Physical & Engineering Sciences in Medicine
|January 5, 2002
Summary
Increasing source-axis distance (SAD) in conformal arc therapy increases integral dose, particularly at higher photon energies. Body size and PTV position also influence this relationship, impacting treatment planning for IMRT machines.
Area of Science:
- Medical Physics
- Radiation Oncology
- Radiotherapy Physics
Background:
- Source-axis distance (SAD) is a critical design parameter in radiation therapy machines, influencing integral dose, dose rate, and patient clearance.
- Understanding SAD's impact is crucial for optimizing Intensity-Modulated Radiation Therapy (IMRT) machine characteristics.
Purpose of the Study:
- To investigate the effect of source-axis distance (SAD) on integral dose for conformal arc therapy.
- To determine the sensitivity of SAD to beam energy, planning target volume (PTV) size, body size, and PTV position in conformal arc therapy.
Main Methods:
- Calculations were performed assuming dose equals terma.
- Integral Dose Ratio (IDR) was used to quantify the dosimetric results.
- The study analyzed the influence of SAD, photon energy, PTV size, body size, and PTV position.
Main Results:
- Integral Dose Ratio (IDR) increases with both SAD and photon energy; this dependence lessens at higher energies.
- PTV size had a negligible effect on the SAD-IDR relationship.
- Body size and PTV position significantly affect the SAD-IDR relationship.
Conclusions:
- Larger SAD generally improves dose distribution from a dosimetric perspective.
- A very large SAD can increase IDR by approximately 5% compared to a 100 cm SAD.
- A 100 cm SAD results in approximately 5% higher IDR than a 50 cm SAD.