Journal of Medical Physics (Jan 2006)

Empirical formula for the prediction of off axis ratios and isodose curves for a treatment planning system

  • Pal Surajit,
  • Ravishankar R,
  • Sharma R,
  • Muthukrishnan G,
  • Ray Dilip,
  • Roy S,
  • Srivastava D

Journal volume & issue
Vol. 31, no. 4
pp. 262 – 268

Abstract

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A mathematical model has been developed for prediction of off axis ratio (OAR), using Wood - Saxon term used to represent nuclear potential. This method has been satisfactorily applied for predicting OAR in case of 60Co γ -rays and high energy X-rays. Investigations are considered upto a depth of 25 cm in the case of 4MV LINAC for which measurements were carried out in our laboratory using indigenously developed Radiation Field Analyzer. For 60Co γ-rays as well as 6 and 18MV LINAC beams we could get off-axis profiles only upto 20 cm. The shift δ between measured and predicted OAR is within ±2 mm except for 20 cm depth near the falling edge of the penumbra, where it is 2.80 mm. Software has been developed in Visual Basic 6 on Windows platform to plot Isodose curves, which is based on the mathematical modeling of OAR and central axis percentage depth dose.

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