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Published on: May 9, 2014
A study on beam homogeneity for a Siemens Primus linac
F Cutanda Henriquez1, S T Vargas-Castrillón
1NW Medical Physics, Christie Hospital NHS Trust, Withington, Manchester, UK. francisco.cutanda@physics.cr.man.ac.uk
Australasian Physical & Engineering Sciences in Medicine
|August 9, 2007
Summary
Highly asymmetric offset fields used in radiotherapy show significant dose inhomogeneity near the beam edge. This beam characteristic, stemming from linear accelerator design, makes them unsuitable for patient treatment and causes discrepancies with treatment planning systems.
Area of Science:
- Medical Physics
- Radiation Oncology
- Radiotherapy Technology
Background:
- Asymmetric offset fields are crucial in modern radiotherapy.
- Assessing the dose homogeneity of these fields is essential for treatment efficacy and patient safety.
Purpose of the Study:
- To evaluate the dose homogeneity of highly asymmetric offset fields on a Siemens PRIMUS clinical linear accelerator.
- To investigate the impact of linear accelerator design, specifically the flattening filter and primary collimator, on beam uniformity.
Main Methods:
- Measured dose profiles and absolute dose for 10 cm x 10 cm fields with extreme offset.
- Analyzed beam characteristics related to the flattening filter radius and primary collimator aperture.
- Compared experimental results with calculations from Philips Pinnacle v6.3 treatment planning system.
Main Results:
- Measured profiles exhibited a marked decreasing dose gradient towards the beam edge.
- Beam inhomogeneities were observed, particularly in large and asymmetric fields, linked to the flattening filter and collimator design.
- Significant discrepancies were found between measured data and treatment planning system calculations.
Conclusions:
- Highly asymmetric offset fields, as implemented in the studied linear accelerator, demonstrate dose inhomogeneities rendering them unsuitable for clinical radiotherapy.
- The design of the primary collimator and flattening filter assembly critically influences beam homogeneity.
- Current treatment planning systems may not accurately model these beam inhomogeneities, potentially impacting treatment accuracy.
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