Limitations of the straight-line assumption for endobronchial HDR brachytherapy treatments.

It is useful to expedite high dose rate brachytherapy endobronchial treatments by using standardized dwell weights and worksheets, avoiding computerized planning where possible. Such methods assume the treatment catheter is straight. This study uses inverse-square considerations to quantify the curvature that invalidates the straight-line approximation. The ratio of the distance between end dwell positions and the active length can be used as a measure of the curvature. The variation in mean dose and maximum dose at the prescription points is presented as a function of active length and curvature, allowing the planner to determine quickly when a pre-treatment computer plan is necessary.