Effect of planning margin on dosimetric quality in 131Cs permanent prostate brachytherapy

It is shown that the planning margin has minimal effect on dosimetric quality because of 131Cs's gradual dose fall-off. Thus, it is possible to reduce or even eliminate planning margin using 131Cs. The modest benefits in reducing the planning margin, such as lower total activity (lower integral dose), dose reduction to surrounding healthy tissues and reduced likelihood of seeds migration, can be achieved while adequate coverage is maintained.