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Optimization of Dose Distribution for Different Vaginal Cylinders of HDR Brachytherapy


S.A Syam Kumar

s kumar*, A Silpa, C Suja, B Resmi, Malabar Cancer Centre, Kannur, Kerala

PO-BPC-Exhibit Hall-16 Saturday  Room: Exhibit Hall

Purpose:
Optimization of dose distribution for different vaginal cylinders of HDR Brachytherapy using different optimization methods namely Iterative, Geometric and Equal time.

Methods:
Four different vaginal cylinders with diameters ranging from 2. 6 to 4 cm is selected and dose reference points on the surface of the cylinders have been defined to optimize a dose of 6Gy for a treatment length of 6cm. Three optimization methods available in the TPS have been used to calculate the dose distribution. Apex points at the tip of the dome of the applicator and along the curvature of the dome was defined as dose reference points (DRP) and optimization was repeated with these points included. Comparison has been made between the dose distribution obtained with and without these apex points.

Results:
whenever we specify apex points as dose reference points, the minimum and maximum variation of dose with respect to the mean dose is higher than the variations compared to calculations made when apex points are not specified. When apex points are defined, the treatment volume increased by 8% and area only by 2% in case of 3cm diameter cylinder. Treatment volume increases by 14% and area increases by 2% is observed in case of 3.5 cm diameter cylinder, when apex points are included in optimization. But with 4cm diameter cylinder both the treatment volume and area increases by 9%.

Conclusion:
The dose reference points to be defined at the apex of the cylinder to deliver adequate dose at the dome of the cylinder. Even through the variation in doses between apex points and points along the cylinder is maximum, adequate dose is delivered at the vault thereby reducing the frequency of recurrences in these types of treatments.

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