ESTRO 36 Abstract Book

S510 ESTRO 36 2017 _______________________________________________________________________________________________

PO-0929 Needle Migration in HDR Brachytherapy for Prostate Cancer evaluated by Serial MRI a nd Photos S. Buus 1 , M. Lizondo 2 , S. Hokland 3 , S. Rylander 3 , E. Pedersen 4 , L. Bentzen 1 , K. T anderup 3 1 Aarhus University Hospital, Department o f Oncology, Aarhus C, Denmark 2 Hospital de la Santa Creu i Sant Pau, Servei de Radiofísica i Radioprotecció, Barcelona, Spain 3 Aarhus University Hospital, Department of Medical physics, Aarhus C, Denmark 4 Aarhus University Hospital, Department of Radiology, Aarhus C, Denmark Purpose or Objective Needle migration in high dose rate brachytherapy (HDR- BT) for prostate cancer may lead to insufficient target coverage and increased dose to organs at risk. The aim of this study was to assess the magnitude of needle migration in HDR-BT with serial MRI and photos. Material and Methods 12 patients with high risk prostate cancer treated with EBRT and two separate boosts of HDR-BT were included in the study. In order to fixate the needles, a thin silicone pad was placed within the template, which was fixated to perineum with 4 sutures. Following US guided needle implant, patients were placed in supine positi on on an MRI couch on trolley for the rest of the procedure. Three MRIs were performed; one for planning (MRI1), one immediately before HDR-BT (MRI2), and one after HDR-BT (MRI3). All MRIs were a transversal T2-weighted turbo spin-echo with 2 mm slice thickness and 1.2 x 1.49 mm resolution. The position of the template was marked with indian ink on the thighs of patients, and photos of the perineum were taken after each MRI. MRI2 and MRI3 were co-registered to MRI1 to match the prostate. Coordinates of each needle tip defined on all three MRIs were used to calculate the migration for each needle. An average needle migration of ≤3 mm was considered "acceptable". On photos, movement of the template relative to the ink markings was regarded as needle migration, which was scored as either "acceptable" or "considerable" from MRI1 to MRI2 and from MRI1 to MRI3. Scoring of needle migration with MRI and photos was compared. An analysis was performed to examine whether posterior needles were more prone to migrate compared with anterior needles.

Figure 1: Difference in D90 (%) between plugged (blue) and plug-free (pink) needles in each sector. Conclusion Our study suggests that plug-free needles have the potential to improve implant quality via better spatial dose distribution within the prostate using fewer numbers of needles and reduced seed loss. Further, it provides added freedom to use any number of special loaded strands without increasing needle numbers. PO-0928 Androgen deprivation therapy influences PSA bounce rate after brachytherapy W. Burchardt 1 , M. Kanikowski 1 , J. Skowronek 1 1 Greater Poland Cancer Centre, Brachytherapy, Poznan, Poland Purpose or Objective To evaluate predictive clinical and dosimetric factor for PSA bounce (PB) after HDR and LDR brachytherapy with or without androgen deprivation therapy (ADT). PB can imitate biochemical failure and causes introduction of unnecessary diagnostics and patients’ treatment. Material and Methods We analysed data of 101 patients (age 50-81 years) with clinical localized prostate cancer (T1-T2cN0) treated with brachytherapy from June 2008 to December 2010 at Greater Poland Cancer Centre in Poznan, Poland. Neoadjuvant or adjuvant androgen deprivation therapy was applied in 33 cases. All patients underwent LDR (LDR n=41) or HDR (HDR n=53) brachytherapy with curative intent. The total doses (TD) for LDR was 145 Gy and for HDR brachytherapy 3 x 10,5 - 15 Gy. Results A total of 94 patients were followed up at our Cancer Centre. Median follow-up was 3,0 years. Average initial PSA (iPSA) value was 7,8 ng/ml +/-3,1 (SD). In the follow up the median PSA nadir 0,1 ng/ml was achieved after median 21 months. In 58 cases PSA decreased gradually without any event. In 23 cases PB was observed using 0,2 ng/ml definition. In 10 cases (11%) biochemical failure (BF) was diagnosed using nadir + 2 ng/ml definition. In 24% of patients PB was observed. Patients treated with ADT experienced fewer PB than hormone naïve patients (90 % vs. 62%, p=0,016). Patients with PB achieved later and higher PSA nadir (time to nadir 30 vs. 18 months and PSA nadir 0,3 vs. 0,1 ng/ml). Clinical stage, Gleason scale, iPSA and risk groups were not different between PB and No PB groups. Conclusion Patients after brachytherapy for low and intermediate risk prostate cancer had PB in 24 % of cases. ADT decreased the PB rate after brachytherapy what could have protected the patients from unnecessary interventions. Patients with PB had later and higher level of PSA nadir. Other clinical and dosimetric factors were not predictive for PB.

Results A median of 16 needles (14 - 21) were used for each HDR- BT procedure. Serial photos were taken in 19/24 procedures. MRI2 was performed in 24/24 procedures and MRI3 in 22/24 procedures. MRI evaluated needle migration was median 2.2 mm per needle (-0.8 - 4.4) from MRI1 to MRI2, median 2.6 mm per needle (0 - 10) from MRI2 to MRI3, and median 3.9 mm per needle (0.3 - 9.8) from MRI1 to MRI3. Needle migration evaluated by MRI was found "acceptable" in 23/24 procedures from MRI1 to MRI2, and in 7/22 procedures measured from MRI1to MRI3. Needle migration evaluated by photo was found "acceptable" in