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Evaluation of Dosimetric Effect in Vaginal Cylindrical Application Using HDR Brachy Therapy

D Palani*, B Arun, S Prasath, T Selvan, D Gowardan, R Achari

SU-E-T-587 Sunday 3:00PM - 6:00PM Room: Exhibit Hall

Purpose: This study is to quantify the amount of dose reduction on the tip of the dome in vaginal application due to the source self attenuation and inverse square law(ISL)along the longitudinal axis of the source during the Iridium-192 high dose rate brachytherapy using different source dwell step size.

Methods: This brachytherapy dosimetric study was carried out in Varian HDR brachytherapy unit having single(Ir-192)source. The appropriate vaginal cylinder with applicator was chosen for the patients. 1.5 mm CT slice thickness of CT scan was taken, then exported to Eclipse and reconstructed the applicator. Two normalization lines were created one on the surface and other on 5mm distance from the surface of cylindrical dome. Four plans were made with the combination of 2.5 mm and 5mm of source step size with normalization on the surface and 5mm from surface of cylindrical dome for each case for 10 patients. Thus the doses were compared to study the influence due to source self attenuation and ISL.

Results:
In the case of surface normalisation, the Percentage of dose reduction using 2.5 mm and 5mm step size are -13.22% and -7.6% respectively. Similarly for the case of normalization at 0.5 cm distance from surface , the Percentage of dose reduction using 2.5 mm and 5mm step size are -33.02% and -28.15% respectively.

Conclusion:The deviation of dose delivered at reference points with respect to the prescription is more with the 2.5 mm step size when compared to that of the 5 mm step size in both the cases namely prescription at the surface of the dome as well as the prescription at the 0.5 cm away from the surface of the dome. It is concluded that by using 5mm step size, the dose reduction due to above mentioned effects can be minimized by 5 %.

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