Dosimetry of rhenium-188 diethylene triamine penta-acetic acid for endovascular intra-balloon brachytherapy after coronary angioplasty

To examine the possibility of using rhenium-188 diethylene triamine penta-a cetic acid (DTPA) for endovascular intra-balloon brachytherapy after angiop lasty, dose distribution around the balloon was calculated and validated by film dosimetry. Medical internal radiation dosimetry (MIRD) was calculated assuming that the balloon had ruptured and that the contents had been rele ased into the systemic circulation. Re-188-perrhenate eluate from the W-188 /Re-188 generator was concentrated using an ion column and used to label DT PA. The dose distibution around the angioplasty balloon (20 mm length, 3 mm diameter cylinder) was estimated by Monte Carlo simulation using the EGS4 code. The time required for 17.6 Gy to be absorbed at 1 mm from the balloon 's surface following application of 3700 MBq/ml Of Re-188 was found to be 2 78 s. Fifty percent of the energy was deposited in the first millimetre of the vessel wall from the balloon's surface. The calculated radiation absorb ed dose agreed with that measured by film dosimetry, which was performed us ing a water phantom, with errors ranging from 9.4% to 17%. Upon balloon rup ture the total amount of Re-188-DTPA was presumed to enter the systemic cir culation. The resulting radiation absorbed dose was calculated using the MI RDOSE3 program and residence times obtained from dogs and amounted to 0.005 6 mGy/MBq to the whole body and 4.56 mGy/MBq to the urinary bladder. The ab sorbed dose of 188Re-DTPA to the whole body was one-tenth of that of Re-188 -perrhenate. A window-based program was developed to calculate the exposure time and the radiation dose absorbed as a function of the Re-188 concentra tion and the arbitrary distance from the balloon to the surrounding tissues . We conclude that Re-188-DTPA is easy to prepare, safe to use and suitable for intra-balloon brachytherapy after coronary angioplasty.