title: Empirical formula for the prediction of off axis ratios and isodose curves for a treatment planning system.
abstract: 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 (60)Co 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 (60)Co 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.
authors.affiliation: Variable Energy Cyclotron Centre, 1/AF Bidhan Nagar, Kolkata, India.
authors.forename: Surajit
authors.initials: S
authors.lastname: Pal
authors.forename: R
authors.initials: R
authors.lastname: Ravishankar
authors.forename: R P
authors.initials: RP
authors.lastname: Sharma
authors.forename: G
authors.initials: G
authors.lastname: Muthukrishnan
authors.forename: Dilip Kr
authors.initials: DK
authors.lastname: Ray
authors.forename: S N
authors.initials: SN
authors.lastname: Roy
authors.forename: D K
authors.initials: DK
authors.lastname: Srivastava