Effect of reconstruction methods of HDR brachytherapy gynecological applicator on the prescription and reference points

ABSTRACT

This Paper demonstrate the effect of reconstruction methods on the prescription and reference points for HDR brachytherapy using Fletcher-Suit-Delclos applicator. To evaluate the effect of reconstruction methods on the prescription points for HDR brachytherapy, the gynecological applicator [Fletcher-Suit-Delclos] is used ovoid and different angles in uterine tube. Three different methods of applicator reconstruction were investigated, first reconstruction method was used electronic simulator image as 2 orthogonal pairs of A-P and lateral films. Second reconstruction method was used 150 slice image of CT as manual and automated reconstruction. All applications are used 22 dwell positions as 7 cm tandem contained 14 dwell positions and the ovoids each 4 dwell positions. All dwell positions are separated by 5 mm. The definition of prescription and reference point was related to Manchester technique. From 150 slices image of CT the applicator was reconstructed manually in TPS using 2cm ovoid and different angles in uterine tube. The dose to the prescription points A Rt and Lt were 500 cGy for all angles in uterine tube. While the dose to the reference points B Rt and Lt were slightly changed 137.1, 132.2 cGy, 144.3, 132.1 cGy and 136.2, 135.2 cGy for angles in uterine tube 15°, 30° and 45° respectively. By comparing CT automated and simulator reconstruction data in relation to the CT manual reconstruction the data illustrate that the difference in dose fore point A between manual and automated reconstruction was approximately 0.2, 2.1 and 6% for angles in uterine tubs 15°, 30° and 45° respectively. On the other hand the difference in dose tore point A between manual and simulator reconstruction was approximately 1.3, 4.3 and 8.6% for angles in uterine tube 15°, 30° and 45° respectively. This study has highlighted the effect of reconstruction methods on the prescription and reference points for HDR brachytherapy. While the differences were minimal on the reference point B it becomes highly considerable prescription point A. As the angle of tandem increases the dose to point A is highly dependent in the reconstruction. The difference in dose fore reference point B between manual and automated reconstruction was minimal approximately less than 1% for all angles in uterine tube. Our recomendation is the CT manual reconstruction is the best reconstruction method to reconstruct the applicator and to determine the accurate position of prescription point A and reference point B as will as bladder and rectum for patients