AN EQUATION TO QA CHECK THE TOTAL TREATMENT TIME FOR SINGLE-CATHETER HDR BRACHYTHERAPY

Purpose: To develop a simple equation that can be used to quickly QA c heck the total treatment time needed for straight or moderately bendin g, single-catheter implants from the treatment length and dose-prescri ption depth. A method to quickly check the total treatment time is use ful for high dose rate (HDR) treatments, but may be most useful for in travascular patients that are catheterized while planning the treatmen t. Methods and Materials: Nucletron-Oldelft treatment planning softwar e was used to plan treatments with treatment lengths from 50 to 200 mm , and dose-prescription depths from 2 to 14 mm. For each plan, dose po ints were defined at a fixed depth away from the catheter. Doses were calculated, normalized, and optimized using the dose points. From thes e plans, a single equation was developed for the total treatment time as a function of treatment length and dose-prescription depth. Results : Total treatment time increases linearly with treatment length and su pra-linearly with dose-prescription depth. A difference of 3% or more between the treatment time determined by the QA check equation and by the treatment planning software will alert the clinician and physicist to check for potential errors in dose prescription, prescription dept h, source activity, treatment length, or inadvertent modifications to physics parameters used in the treatment planning software. Conclusion : The simple equation that is developed can be used to quickly and acc urately QA check the total treatment time needed for straight or moder ately bending, single-catheter implants. (C) 1998 Elsevier Science Inc .