Injection of hyaluronic acid (HA) to better preserve the rectal wall in prostate hypofractionated radiotherapy (HFR).

202 Background: Several studies are in favor of an α/β ratio of less than 3Gy for prostate (P) cancer, encouraging HFR. However, the development of such radiation patterns can only be done if the risk of rectal toxicity is well controlled. The objective of the present study was to evaluate the contribution of an injection of HA between the rectum and the P to reduce the risk of rectal toxicity in a HFR approach. Methods: A phase II study of HFR at 62Gy in 20 fractions (BED = 84Gy; α / β = 1.5Gy) is currently conducted. A transperineal injection of 10cc of HA (NASHA Spacer gel, Q-Med AB, Uppsala, Sweden) is systematically performed, between the rectum and the P, under local anesthesia and under ultrasound guidance. A dosimetric CT scan is performed before (CT1) and after injection (CT2). Patients are treated with a 7 beams IMRT plan, optimized on the CT2. For the first 10 patients included in the study, the same treatment plan was optimized on CT1. The rectum was empty on the 2 CTs and defined from 2cm above the seminal vesicles to 2 cm below the P. The rectal wall was defined by an internal expansion of 5 mm. The volumes of rectum irradiated, with and without HA, were compared on the following dosimetric parameters: maximum dose (D max), dose to 2.5cc (D2.5), 5cc (D5) and 10cc (D10) of rectal wall and volume of rectum receiving 90% (V90), 80% (V80) and 70% (V70) of the prescribed dose of 62Gy. To limit a potential impact of variation of rectal volume between the two CT, all results are given in cc and not in % of volume. Results: The mean P volume was 52.4cc (30cc - 93.8cc) on the CT1 and 52cc (32.5 - 92.7) on the CT2. The injection of HA reduced the mean D max value to the rectal wall of 4.5Gy (57.5Gy vs 62 Gy). The mean values of V90, V80, and V70 are reduced by 69% (1.9cc vs 6.1cc), 46% (4.5cc vs 8.4cc) and 32% (7.4cc vs 10.9cc). Same way, the average values of D2.5, D5 and D10 are reduced by 6.2 Gy (54.6Gy vs 60.8Gy) 9.3Gy (49.0Gy vs 58.3Gy) and 7.8Gy (39.7Gy vs 47.5Gy). Conclusions: In this study, the injection of HA limited the doses to the rectal wall. These results suggest that late toxicities could be significantly reduced. A phase II study is underway to assess the rate of late rectal toxicities when a HFR at 62Gy in 20 fractions is combined with an injection of HA.

Multiple forms of acetylcholinesterase from pig brain

1. A number of methods of solubilization of pig brain acetylcholinesterase (EC 3.1.1.7) were studied. The multiple enzymic forms of the resultant preparations were examined by polyacrylamide-gel electrophoresis. 2. Butanol extraction, Nagarase treatment and ultrasonication proved unsuitable as preparatory methods, but detergent treatment (Triton X-100, Triton X-100–KCl and lysolecithin) gave good yields. 3. Separation of soluble enzyme in three systems of polyacrylamide-gel electrophoresis were compared and the relative advantages are discussed. 4. By using a 6% (w/v) gel and continuous buffer system two forms of acetylcholinesterase were detected in Triton X-100-solubilized enzyme, but the incorporation of a sample and spacer gel and a discontinuous buffer system resolved this into four components. The forms of the soluble enzyme extracted by different methods differed in mobility. 5. With gradient polyacrylamide-gel electrophoresis between two and six forms were detected, depending on the method used for extraction. The average molecular weights of the five forms most frequently found were 60000, 130000, 198000, 266000 and 350000. 6. Treatment of the Triton X-100-extracted enzyme with 2.5m-urea altered the pattern and evidence of dissociation was observed. 7. The results are discussed in the light of present theories on the molecular structure of acetylcholinesterase.