ESTRO 38 Abstract book

S586 ESTRO 38

Conclusion We have developed a fast method to solve the assignment problem between two seed datasets which does not need any adjustable parameter to work. This allows us to calculate some metrics to assess the quality of the implant. PO-1052 Is there a clinically meaningful change in anatomy during planning of US HDR prostate brachytherapy? A. David 1 , V. Brennan 2 , G. Cohen 1 , A. Damato 1 1 Memorial Sloan Kettering Cancer Center, Medical Physics, New York, USA ; 2 Memorial Sloan Kettering Cancer Center, Radiation Oncology, New York, USA Purpose or Objective To investigate the role of anatomical and implant geometry changes during planning time in final delivered dose for US-based HDR prostate brachytherapy Material and Methods The record of 13 patients who received US-based HDR prostate brachytherapy at our institution was retrospectively reviewed. All patients receive a single dose fraction brachytherapy boost treatment, 2 weeks before external beam treatment. Gold fiducial markers were positioned at the apex and base of the prostate at the beginning of the procedure. A set of static US images were acquired using transverse transducer pre-treatment (pre-Tx) after needle insertion and used for contouring, final digitization, and dose optimization. Post-treatment (post-Tx) transverse images were acquired immediately after treatment delivery. Targets were re-contoured and the clinical plans (dwell pattern and times on the newly digitized catheters) was replicated on the post-Tx images. The DICOM plans were analyzed using MATLAB routines to assess catheter shift (average distances between reciprocal dwell source positions pre- and post- treatment after rigid registration between all dwell positions is performed) and implant expansion (average of the difference between the distances from each dwell source position to the center of mass of the dwell sources system). Superior-inferior swelling (difference between the post- and pre-Tx distance between fiducial markers) was assessed on 10 patients. Differences in target volumes are also reported. Results The number of needles (average ± 1 standard deviation) was 13 ± 2 needles. No meaningful catheter shift (0.08 ± 0.03 cm), implant expansion (0.003 ± 0.02 cm) and sup-inf swelling (-0.01 ± 0.09) were observed. Changes in target volume, were 0.26 ± 3.41 cm 3 .

Conclusion Geometric assessment of single catheter shift, implant expansion and superior-inferior swelling indicate that no clinical meaningful change occurred in the time between planning scan and treatment. Further analysis will be performed to assess the role of contouring uncertainty on the patient-by-patient results. More patients and dose distributions are being analyzed to validate these results, which suggest high fidelity between planned and delivered dose. PO-1053 Efficacy/toxicity after high dose rate brachytherapy as monotherapy for localized prostate cancer S. Novikov 1 , S. Kanaev 1 , M. Gotovchikova 1 , R. Novikov 1 , D. Ilin 1 , M. Girshovitch 1 1 Prof. N.N. Petrov Research Institute of Oncology, Radiotherapy, St. Petersburg, Russian Federation Purpose or Objective to present toxicity profile and biochemical control rates of a prospective single center trial comparing 2 fractions of 13 Gy and three fractions of 11.5 Gy high dose rate brachytherapy as sole treatment for localized prostate cancer. Material and Methods Between 01.06.2013 and 01.06.2017, 198 men with clinically localized prostate cancer T1-T3aN0M0, Gleason score below 8 and PSA less than 20 ng/ml were included in the study. Sixty-seven patients received TRUS guided HDR brachytherapy in 2 fractions of 13 Gy, 131 men – in 3 fractions of 11.5 Gy. Qmax below 10 ml/sec and IPSS above 20 were excluding criteria. Biochemical failure was registered according to the Phoenix definition, and toxicity was scored according CTCAE-5. Results Median follow-up was 40.9 (range 15.1-71.1) months. The 36 month's biochemical control (BC) was 95.5% for 121 patients with follow-up of 36-56 months: 100% - in low- risk, 94.2% - in intermediate risk and 90.5% - in high risk groups. We found comparable BC rates for patients that received 2 fractions (BC-93.2%) and 3 fractions (BC-98.5%) HDR-BT. Grade 2 late genitourinary toxicity manifested by urgency in 4 (2%) cases; grade 3 late toxicity was detected in 2 (1%) men with urethral stenosis and another 1 (0.5%) - with severe urgency. Median International Prostate Symptom Score raised from 8 [4; 12] (0-21) (before HDR-BT) to 12 [7;16] (1,0-28,0) 3 months after the treatment with subsequent decrease to 10 [9;16] (1-25) and 7 [7;8] (6-12) after 12 and 36 months of follow-up (р=0,001). In the same manner median Q maх decreased from 15,0 [12,7;18,0] (9,0-36,0) ml/sec to 14,3 [12,0; 17,0] (7,0- 30,0) ml/cec 3 months after treatment (р=0,001) and subsequently reached 14,9 [13,1;17,0] (7,0-25,0) and 14,1 [13,0;16,0] (6,0-29,0) ml/sec 1 and 3 years after the end of HDR-BT. Poster: Brachytherapy: Prostate