The effect of pull back technique on dose distribution in the junction region for 90Sr/90Y intravascular brachytherapy sources

The aim of this work is to investigate the effect of pull back technique on dose distribution in the junction region for intravascular brachytherapy (IVBT) with beta source train. In this purpose, the five positions which were created with 0 cm gap, 2.5, 5 mm gap and 2.5, 5 mm overlap between active seeds were studied. The measurement for IVBT beta source train (Novoste Beta Cath) with 40 mm active source length were performed using radiochromic film dosimetry. Radiochromic film measurements were performed using a specially manufactured phantom, which was made of a white polystyrene material in our department. Radiochromic films were calibrated using 60Co beams with 50, 100, 150, 200 Gy doses at 5 cm depth within solid water phantom in the same day. In the presence of a 2.5 mm (1 seed) and 5 mm (2 seed) gap, the dose in the middle of junction region can be decreased to 44% and 23%, respectively. On the other hand, in the presence of a 2.5 mm (1 seed) and 5 mm (2 seed) overlap, the dose can be increased as to much as 62% and 74%, respectively. In an IVBT application using pull back technique, the best dose distribution in the junction region was obtained with a perfect end-to-end match and our results show that significant underdose or overdose regions in the junction can occur in the presence of gap or overlap. Therefore, to create a perfect end-to-end match in an IVBT application using pull back technique, all movements of balloon should be recorded and the sources have been carefully placed to irradiate the injured vessel part with sufficient radiation doses.