Manually Fine-Tuning the Calibraton

Introduction

After the automated optimization and surface annealing processes are complete you will need to manually fine tune the model parameters.

Click the Calibrate Manually tab. Adjust the parameters using the sliders followed by the bumper arrows to minimize the RMS% error of the fit of the central axis profile to the measured data over the range 0..10 mm.

  1. Manual fine-tuning is an iterative process. Begin by adjusting the Dose Calibration slider until the dose profile curve passes through the 5 mm measurement point.

  2. Next, adjust the Crossover slider to minimize the RMS error in the range 0..5 mm.
  3. Next, adjust the Nearfield slope slider to minimize the RMS error in the range 0..5 mm.
  4. Next, adjust the Anisotropy shift slider to minimize the RMS error in the range 0..5 mm.
  5. Next, adjust the Anisotropy threshold slider to minimize the RMS error in the range 0..5 mm.
  6. Next, adjust the Farfield power slider to minimize the RMS error in the range 0..10 mm.
  7. Next, adjust the Farfield threshold slider to minimize the RMS error in the range 0..10 mm.
  8. Next, adjust the Dose Calibration slider to minimize the RMS error in the range 0..5 mm.

  9. Repeat steps 2-8 until the RMS error over the range 0..10 mm can no longer be reduced. Optional: try varying the order of the steps to see if any further reduction is possible.
  10. Lastly, adjust the Anisotropy bias slider to further minimize the RMS error in the range 0..5 mm.
  11. Repeat steps 2-10 until the RMS error in the range 0..10 mm can no longer be reduced.
  12. It is typically possible to achieve a central axis RMS error of under 2% over the range 0..10 mm.
  13. You may optionally return to the Surface Measurements section and repeat the simulated annealing followed by repeated manual fine-tuning to see if the RMS error between calculated and surface measurements can be further reduced.

  14. Click the Save File As... button to save the plaque file.

Final Result

For this example, simulated annealing of the surface strength distribution, followed by manual fine tuning, eventually achieved a near-surface RMS % error of about 8.2 and a central axis RMS % error of about 1.7 over the range 0..10 mm between the patch source model calculations and measurements.

CGD282PlaqueWindow
CGD282FinalSurface
CGD282FinalManual
CGD282FinalDoseProfile
CGD282Setup

Sample isodose calculations on the retina are illustrated for this plaque.

CGD282SetupDose

Note that the BEBIG points are normalized to a value of 100 at the center whereas the PS isodose lines are normalized to 1.0.

CGD282Isodose

All dosimetry has been normalized to 1.0 on the central axis of the plaque at 1 mm from the surface of the plaque, the same normalization point as the BEBIG near-surface measurements.

CGD282MeridianDose

Normalized isodose distribution on the meridian plane which passes through the plaque center.

CGD282RetinaDose

Normalized isodose distribution on the retinal diagram.