ESTRO 36 Abstract Book

S509 ESTRO 36 2017 _______________________________________________________________________________________________

24.3% cases. Only in 24.3% observations D90 was above 100% (table 1). In addition, in 18% of these cases D10 for urethra was between 116% and 189%.

Conclusion post-implantation correction of prostate, urethra, bladder and rectum volumes with subsequent postimplantation planning of dose distribution must be considered as obligatory part of safe and accurate prostate brachytherapy. PO-0927 Plug-free needles provide dosimetric advantages over plugged needles in I-125 prostate brachytherapy A.B. Mohamed Yoosuf 1 , L. Sarri 1 , M. Byrne 1 , G. Workman 1 , D. Mitchell 2 , S. Jain 2 1 Northern Ireland Cancer Centre, Radiotherapy Medical Physics Service, Belfast, United Kingdom 2 Northern Ireland Cancer Centre, Department of Clinical Oncology, Belfast, United Kingdom Purpose or Objective To compare the dosimetric outcome of plugged and plug- free implant needles in permanent prostate brachytherapy (PPB) using global and multi-sector post implant dosimetric analysis. Material and Methods 70 consecutive men treated with I-125 PPB using either plugged (group 1, n=35) or plug-free (Group 2, n=35) had their post implant (CT) dosimetry compared. For global analysis, dosimetric quality indicators evaluated between two groups included: prostate volume (CT), number of needles per unit volume, the minimum dose delivered to 90% of prostate volume (D 90 ) and dose to 0.1 cm 3 of the rectum (D 0.1cc ). Twelve sectors of the post-implant CT was analysed for each case by dividing the prostate base, mid gland and apex into four sectors each and D 90 was compared for both groups. Results The mean prostate volume for Group 2 (40.38 cc ± 8.0 cc) was significantly larger (p < 0.05) than Group 1 (36.45 cc ± 8.5 cc) but fewer needles were required per unit volume (Group 2 - 0.59 ± 0.12 cm -3 vs Group 1 - 0.72 ± 0.18 cm -3 ; p < 0.001). Global dosimetry was similar for both groups however seed loss was significantly reduced in Group 2 (p < 0.05). Sector analysis, for Group 2, indicated increased D 90 in the posterior mid-gland and apex regions (p < 0.05) and a trend towards increased dose in the base sector as shown in Figure 1. The mean rectal D 0.1cc was higher in Group 2 than Group 1 (124.73% ± 12.2% vs 122.54% ± 10.3%; p = 0.4) which reflected the increased dose in the posterior mid-gland. However, these remained within recommended tolerances.

Poster: Brachytherapy: Prostate

PO-0926 Interstitial HDR prostate brachytherapy: comparison of pre- and post-implant dose distribution. S. Novikov 1 , S. Kanaev 1 , N. Ilin 1 , R. Novikov 1 , M. Girshovich 1 1 Prof. N.N. Petrov Research Institute of Oncology, Radiation Oncology, St. Petersburg, Russian Federation Purpose or Objective Prospective planning of interstitial high dose rate brachytherapy (HDRBT) for prostate cancer permit high accuracy of dose delivery to the tumour and\or prostate with excellent sparing of normal organs. On line correction of post-implant changes of prostate and normal tissues volumes is the key factor of precious dose delivery. The aim of the study was to evaluate possible uncertainties in dose distribution in cases when brachytherapy procedure is based only on pre-implant planning with dose distribution after HDRB with post- implant correction of dose distributiion. Material and Methods in 70 primary patients with prostate cancer we analyzed dosimetric plans that were obtained during the first session of HDRBT. Pretreatment planning was performed according to standard procedure with calculation of the following dosimetric parameters: V100, D90 – for prostate, D2cc – for rectum and D10 – for urethra. According to standard HDRBT procedure after the end of needle insertion we performed final US 3D-scanning with post implant correction of prostate, urethra, bladder and rectal volumes and subsequent post-implant optimization of treatment plan. During the study we also performed fusion of pre-implant and post-implant images. Fusion was based on needle and base-plan topography. After that we calculated dose distribution according to the model when pre-implant plan was used in patients with post-implant prostate and normal organs volumes. Results Analysis of treatment plans with post-I mplantation correction of the contours demonstrated h igh precision and excellent dosimetric parameters: mean V100 - 94.1% (V100 more than 90% in 97.2% cases), mean D90 – 104.3% (D90 more than 100% in 95.7% observations). On the contrary, after fusion of non-corrected plans and post- implant volumes we mentioned high discrepancies between preplanned and real dose distribution: V100 was below 80% in 38.6% observations; D90 was below 80% in