Journal of Medical Physics
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Year : 2006  |  Volume : 31  |  Issue : 4  |  Page : 262-268

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

1 Variable Energy Cyclotron Centre, 1/AF Bidhan Nagar, Kolkata, India
2 Health Physics Unit, VIP Road, Kolkata, India
3 L - 404 VIP Enclave, VIP Road, Kolkata, India
4 B-12, Adhunika Co-operative, 164/3A Lake Gardens, Kolkata, India
5 Chittaranjan National Cancer Institute, Kolkata, India
6 Department of Physics, Visva-Bharati, Santiniketan, India

Correspondence Address:
Surajit Pal
Variable Energy Cyclotron Centre, 1/AF Bidhan Nagar, Kolkata - 700 064
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/0971-6203.29196

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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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