Dosimetry and Medical Internal Radiation Dose of Re-188-DTPA for Endovascular Balloon Brachytherapy Against Restenosis after Coronary Angioplasty / 대한핵의학회잡지

PURPOSE: Liquid beta emitter filled in angioplasty balloon could be used to perform endovascular balloon brachytherapy to prevent coronary artery restenosis. We investigated the dosimetry for Re-188-DTPA liquid-filled balloon and medical internal radiation dosimetry in case of balloon leakage. MATERIALS AND METHODS: We estimated radiation dose from an angioplasty balloon (20 mm lengfh, 3 mm diameter cylinder) to the adjacent vessel wall using Monte Carlo EGS4 code. We obtained time-activity curves of kidneys in normal dog and calculated Tmax, T1/2. Using MIRDOSE3 program, we estimated absorbed doses to the major organs (kidneys, bladder) and the whole body when we assumed that balloon leaked all the isotope contained. RESULTS: The radiation dose was 17.5 Gy at the balloon surface when we applied 3,700 MBq/ml of Re-188 for 100 seconds. Fifty percent of the energy deposited within 1 mm from the balloon surface. The estimated internal dose to the whole body was 0.005 mGy/MBq and 18.5 mGy for the spillage of 3,700 MBq of Re-188. CONCLUSION: We suggest that Re-188-DTPA can be used for endovascular balloon brachytherapy to inhibit coronary artery restenosis after angioplasty with tolerable whole body radiation dose in case of balloon rupture.

The Heterogeneity of Flow Distribution and Partition Coefficient in Myocardium Positron Emission Tomography / 대한핵의학회잡지

For estimation of regional myocardial blood flow with O-15 water PET, a few modifications considering partial volume effect based on single compartment model have been proposed. In this study, we attempted to quantify the degree of heterogeneity and to show the effect of tissue flow heterogeneity on partition coefficient(lamda) and to find the relation between perfusable tissue index(PTI) and (lamda) by computer simulation using two modified models. We simulated tissue curves for the regions with homogeous and heterogenous blood flow over a various flow range(0.2-4.0ml/g/min).Simulated heterogeneous tissue composed of 4 subregions of the same or different size of block which have different homogeneous flow and different degree of slope of distribution of blood flow. We measured the index representing heterogeneity of distribution of blood flow for each heterogeneous tissue by the constitution heterogeneity(CH). For model I, we assumed that tissue recovery coefficient (FMME) was the product of partial volume effect(FMMF) and PTI. Using model I, PTI, flow, and FMM were estimated. For model II, we assumed that partition coefficient was another variable which could represent tissue characteristics of heterogeneity of flow distribution. Using model II PTI, flow and (lamda) were estimated. For the simulated tissue with homogeneous flow, both models gave exactly the same estimates of three parameters. For the simulated tissue with heterogeneous flow distribution, in model I, flow and FMM were correctly estimated as CH was increased moderately. In model II, flow and (lamda) were decreased curvi-linearly as CH was increased. The degree of underestimation of (lamda) obtained using model II, was correlated with CH. The degree of underestimation of flow was dependent on the degree of underestimation of (lamda). PTI was somewhat overestimated and did not change according to CH. We conclude that estimated (lamda) reflect the degree of tissue heterogeneity of flow distribution. We could use the degree of underestimation of (lamda) to find the characteristic heterogeneity of tissue flow and use (lamda) to recover the underestimated flow.

Labeling and Biodistribution of Re-188-DTPA ( Diethylenetriaminepentaacetic acid ) / 대한핵의학회잡지

Re-188 is useful candidate for therapeutic radionuclide because it has a physical half life of 17 hours, contains beta ernissions suitable for therapy(maximum energy 2.12MeV) and emits a garnma ray that is suitable for quantitative diagnostic scanning(155keV). To use He-188 as a radionuclide compound of angioplasty balloon radiotherapy, we investigated the labelling method and biodistribution of Re-188- DTPA. We postulated that labeled Re-188-DTPA is preferable because it would be excreted via urinary system more easily than other compounds. To label Re-188 with DTI'A, 1ml of 222MBqI(6mCi) of Re-188 was added to DTPA solution(DTPA 20mg, SnC4 2HsO 10mg, pH 3.5) and boiled at 100C for 120min in water bath. pH was adjuted to 5 with 2.3Fo sodium acetate. I.abeling efficiency was measured using TLC-SG(acetone, saline). We evaluated biodistribution of Re-188-DTPA in sacrificed mice at 10 and 60 minutes after injection. We acquired images of kidneys, and drew tirne-activity r.urves in normal dogs and rats and calculated Trnax and Tl/2 in rats. The labelling efficiency was 95.7Yo on average. Labelling of Re-188-DTPA was stable(90% after 5hours) in vitro at room temperature. According to time-activity curves of dogs and rats, it took 15 to 20 minutes after injection for Re-188-DTPA to be washed out through kidneys. In conclusion, Re-188-DTPA was successfully labeled, Re-188-DTPA was stable in vitro and was excreted early via kidneys in animals. We could recornmend Re-188-DTPA as radionuclide of potential use in angioplasty balloon radiotherapy.