Intrakoronare Brachytherapie mit Strontium/Yttrium-90

Abstract

Restenosis after PTCA is still an unresolved problem and occurs in approximately 30% of our patients despite a stent implantation rate of up to 63%. Intracoronary brachytherapy has the potential to counteract the proliferative component of restenosis as well as to prevent shrinking of the coronary artery. Two years ago, we applied for the license to use the Novoste Beta-Cath system. This is the first report of its use in Germany. Attaining the license was complicated by the facts that this device did not yet have CE-certification (MPG section 17), that brachytherapy is not yet an approved method of treatment (StrSchV section 41), the report of the BfS and the approval by an accredited ethical committee. The application becomes even more complicated by the amount demanded by the LfU for insurance: 1 Million DM for each individual patient (AtDeckV section 15). The final local inspection needs to be performed by an expert from the LfAS (StrSchV section 76). Strontium-90 decays into Yttrium-90 with a half-life time of approximately 28 years. Yttrium-90, too, is a pure beta-emitter with a shorter half-life time of approximately 64 hours and a considerably higher electron energy of maximum 2.27 MeV. Yttrium-90 is the therapeutic agent. The radiation source of the Beta-Cath system consists of 12 single, separate cylinders (pellets, seeds) with a total length of 3 cm. The activity of the total train is approximately 1.3 to 1.5 GBq (35 to 40 mCi). For verification of the dose rate provided by the manufacturer, we performed a check using the GafChromic film. The test dose (exactly 2 mm from the center of the long axis of the activity train) was 150 Gy. We obtained the following results for the optical density: reference source: 0.29 +/- 0.01, source C: 0.318 +/- 0.013 and source D: 0.317 +/- 0.028. For a dose rate of e.g. 0.083 Gy/s, the radiation times are 169 s for a dose of 14 Gy (vessel diameter 2.7 to 3.35 mm) or 217 s for 18 Gy (vessel diameter 3.36 to 4.0 mm), respectively. In our cath lab, the following dose rates were measured: at the lead container: 20 microSv/h, surface of the transfer device: 400 microSv/h, surface of the phantom: 20 microSv/h and surface of the bail out box: 100 microSv/h. Because moving the source train to the tip of the catheter takes only approximately 1 s, the exposure to other tissues or organs is negligible. However, inappropriate handling of the device could cause significant radiation of other organs. Therefore, the importance of intensive training cannot be overemphasized. The results of the currently ongoing multicenter trials (Beta-Cath system trial in the USA and the BRIE trial in Europe) are being anxiously awaited and will have a decisive impact on the medical acceptance of intracoronary radiation for prophylaxis and/or therapy of restenosis.

Dosimetry of a W‐188/Re‐188 beta line source for endovascular brachytherapy

“…One of the disadvantages of the higher energy ␤-emitters is their relatively short half-life. One way to overcome this is to use a parent/daughter nuclide tandem such as has been done with 90 Sr/ 90 Y, 4,5 where the radiation of the parent nuclide has no significant influence on the depth-dose profile distribution. With the 90 Sr/ 90 Y pair, the half-life of the parent isotope 90 Sr is 27 years.…”