ESTRO 36 Abstract Book

S97 ESTRO 36 _______________________________________________________________________________________________

Results

PV-0189 Ring applicator source path determination using a high resolution ionisation chamber array M. Gainey 1,2 , M. Kollefrath 1 , D. Baltas 1 1 University Medical Centre, Division of Medical Physics- Department of Radiation Oncology, Freiburg, Germany 2 German Cancer Consortium DKTK, Partner Site Freiburg, Freiburg, Germany Purpose or Objective Commissioning brachytherapy applicators can be very time consuming. Brachytherapy has recently seen efforts to perform array based QA (Espinoza et al. 2013, Espinoza et al. 2015, Kollefrath 2015, Gainey 2015). Previously we described a technique for determining one source dwell position per measurement using the OD1000 (PTW-Freiburg) analogous to film measurements (Kollefrath 2015). In this work we employ a time resolved high spatial resolution dose measurement with OD1000 to determine the entire source path for each interstitial ring applicator (Elekta AB, Sweden), available in three diameters (R26, R30, R34), within a single measurement. Material and Methods Two microSelectron (Elekta AB, Sweden) v2 afterloaders (AL1, AL2) were employed to perform all measurements with 192Ir. A special PMMA jig consisting of a base plate and a central insert was constructed to mount onto the OD1000 array. A time resolved (100ms per frame) dose measurement of the entire source path within the respective ring applicator was contrived: a single plan for each ring diameter consisting of 5.0 s dwell time for each position (associated source strength 42000U). The resulting data was analysed using an in-house MATLAB script (version 8.4.0, The Mathworks NA). Typically three measurements were repeated for both (blue and green) clinically commissioned rings and for a number of source exchanges.

Mechanical uncertainties (type B) of PMMA jig position relative to OD1000 array were estimated to be 0.2mm. Repeated measurements with different afterloaders (without dismantling set-up) are plotted in figure 2. The maximum standard deviation was found to be 0.6mm for R26, 0.5mm for R30 ring. A non-linear least squares fit was made (Gander et al. 1994) to the mean positions R26 and R30 rings resulting in a radius of 13.2mm and 14.9mm, geometric centre location of (0.15,0.13) and (0.20,0.10) respectively. Conclusion Initial results indicate that the measurement technique is robust and reproducible. Repeated measurements with different afterloaders indicate a maximum standard deviation of 0.6mm (R26), 0.5mm (R30). Other central inserts can be devised for other applicators, and afterloader systems. Thus the technique is versatile but requires an high resolution 2D array and specialized measurement jig. Moreover our technique is currently limited to 2D source path determination viz. in the measurement plane, parallel to the ring plane. PV-0190 The analysis of prostate cancer with median lobe hyperplasia treated I-125 brachytherapy K. Muraki 1 , H. Suefuji 1 , E. Ogo 1 , H. Eto 1 , C. Tsuji 1 , C. Hattori 1 , Y. Miyata 1 , H. Himuro 1 , T. Abe 1 , S. Hayashi 2 , K. Chikui 2 , M. Nakiri 2 , T. Igawa 2 1 Kurume University, Radiology, Kurume, Japan 2 Kurume University, Urinology, Kurume, Japan Purpose or Objective Most patients with median lobe hyperplasia (MLH) have a large-volume prostate and severe dysuria. Prostate cancer with MLH is a relative contraindication of permanent prostate brachytherapy (PPB), because of the increased risk of post-implant urination disorder and the technical difficulties of stability while implanting intravesical tissue. We examined that the treatment outcome, seed migration, urination disorder after treatment in MLH patients who received PPB. The purpose of our research concerns is to what degree could MLH implant be stabilized.