Brachytherapy involves the placement of either temporary catheter with radioactive source material inside or permanent radioactive seeds in the resection bed at the time of surgery. These sources are spaced at even intervals to cover the area of potential tumour spread. Brachytherapy may be used as a sole treatment modality, or in conjunction with external beam radiation. An advantage of brachytherapy is that the sources used have steeper dose gradients than those for external beam radiation therapy, minimizing exposure of adjacent tissues to substantial radiation. Besides, treatment durations are generally shorter with brachytherapy than with external beam radiotherapy.