Dynamic Anatomy: The Three Sides of the Bermuda Triangle

Abstract

Dynamic anatomy is a descriptive term for changes in position, size, shape, and relationship of a target or critical organ at risk during a brachytherapy procedure. We have previously reported the discrepancy between seed to rectum distance by Ultrasound (US) at completion versus seed distance to rectum on CT day 1 and 21. This effect is due in part to recoil of the rectum after probe removal, resuming its former position adjacent and below the apex. We refer to this as the rectal side of the Bermuda triangle (BT). The opposite side is the prostate and 2 factors influencing rectal row position are 1) variable acute swelling affecting the relationship of the rectal row to prostate, and 2) whole prostate shift superior on the grid due to massive RU bleeding(rare). All these effects contribute to closer proximity of seeds to rectum. The recoil effect outcome cannot be fully predicted but is compensated by a variety of strategies. It is possible to monitor the prostate side of the BT by checking in real time the urethra shift and whole prostate shift (urethra and posterior prostate both rise) superior on the grid.