ESTRO 2020 Abstract Book

S1097 ESTRO 2020

Material and Methods All procedures were performed in a dedicated MR Simulator (Magnetom Espree, Siemens, Inc). Thirteen women with gynecological cancer were enrolled on a prospective clinical trial. All received interstitial brachytherapy with active MR-tracking guiding the interstitial needle implantation. Needle placements were video recorded and per-needle implant times were extracted. A cohort of ten “conventional” (tracked using metal-susceptibility artifacts on 1x1 mm 2 resolution, 3 mm slice-width T2-weighted image sets, acquisition time 60- 80 sec/set ) interstitial patients were used for comparison using an independent samples t-test. Passively-tracked per-needle implant times were estimated from detailed electronic anesthesia time records using regression analysis. Needle utilization rates were calculated for both groups by counting interstitial catheters which were activated for dose delivery.

associated with a higher occurrence of rectal morbidities: the risk of grade 2-3 rectal morbidity was 9% for a D 0.5cm 3 of 50 Gy, versus 17% for a D 0.5cm 3 of 60 Gy. The 10% probability for grade ≥2 rectal toxicity was reached for a D 0.5cm 3 = 52 Gy. In multivariate analysis, only D 0.5cm 3 , D 1cm 3 and D 2cm 3 were identified as risk factors for rectal events (age, TRAK and the volume of 100% isodose were not significant for rectal morbidity).

Results 207 actively-tracked and 171 conventional interstitial needles were evaluated. Utilization rate improvement was statistically significant (p=0.0066) with rates of 93.4% ± 9.8% and 79.9% ± 9.3% for needles implanted using active tracking and conventional methods, respectively. Per- needle placement efficiency for actively-tracked and conventional implants was 2.0 ± 0.9 minutes/needle and 7.1 ± 3.3 minutes/needle, respectively. No organ perforations occurred in either group. Conclusion Relative to conventional MR-guided interstitial brachytherapy, active MR-tracking provides real-time needle positions within the patient which safely improves implant speed and quality. It can assist radiation oncologists achieve superior implant geometries and improve outcomes in interstitial brachytherapy while reducing procedure times. OC-1047 Dose to vaginal wall in cervical cancer brachytherapy and associated morbidity M. Serban 1 , A.A.C. De Leeuw 2 , K. Tanderup 1 , I.M. Jürgenliemk-Schulz 2 1 Aarhus University Hospital, Department of Oncology, Aarhus, Denmark ; 2 University Medical Centre Utrecht, Department of Oncology, Utrecht, The Netherlands Purpose or Objective To develop a methodology for generating vagina dose- surface maps (DSMs) in cervix cancer patients. To investigate the association of dose level and spatial distribution with vaginal stenosis and mucositis (St/Muc). Material and Methods A mono-institutional series of 31 patients, enrolled in the EMBRACE I study, with no vaginal St/Muc (CTCAE v3) at baseline were selected for analysis. Patients were divided in 3 morbidity groups: 16 had St/Muc G0/1, 8 had St G≥2 (3 of them also having Muc G≥2), 7 had Muc G≥2 (all with St ≤1) within 24 months after treatment. 16 patients had vaginal involvement at diagnosis and 10 at first BT

Conclusion To our knowledge, this is the first study showing significant dose/volume effects relationships for rectal morbidity in children treated with brachytherapy. D 0.5cm 3 appears to be the most relevant factor with a D 0.5cm 3 > 52 Gy associated with a > 10% probability for grade ≥2 rectal toxicity. Integrating these data into brachytherapy treatment planning may help to optimize the therapeutic index in these very young patients. Long-term follow-up is required to ensure that the satisfactory functional outcome in terms of rectal morbidity is maintained over time. Session: Optimising outcome in cervix BT OC-1046 Improving needle placement and efficiency with real-time 1.5T MR-tracking of interstitial implants M. Morcos 1 , J. Lee 1 , E.J. Schmidt 1,2 , A.N. Viswanathan 1 1 Johns Hopkins University, Department of Radiation Oncology and Molecular Radiation Sciences, Baltimore, USA ; 2 Johns Hopkins University, Department of Medicine Cardiology, Baltimore, USA Purpose or Objective Currently, MR-guided interstitial brachytherapy is conducted by passively visualizing the signal voids created by the needle in MR images. Passive tracking requires the physician to stop implanting so that a scan can be acquired to assess the location of the needles. Accurate and real- time localization are not possible with passive tracking and lead to long procedure times due to the iterative nature of the process. In this work we investigate implant efficiency and catheter utilization rate improvements using an active MR-tracking system that provides accurate catheter tip localization in real-time.