ESTRO 2023 - Abstract Book

S411

Sunday 14 May 2023

ESTRO 2023

Purpose or Objective The purpose of this study was to review brachytherapy planning statistics from a single centre with an active cervix brachytherapy service over the last nine years. Over this time period, the planning technique has evolved from simple library planning using CT to conformal MR-guided brachytherapy with interstitial needles. Materials and Methods Brachytherapy dose statistics from 191 Cervical Cancer patients treated between 2013 and 2022 were compared to the dose aims and limits from the EmbraceII trial. The only patients excluded from the study were those who could not complete the treatment course. All patients included in the study had Organs at Risk (OARs) outlined on CT or MRI and were planned using Oncentra Masterplan. Patients from 2015 onwards had a High Risk Clinical Target Volume (HRCTV) defined using MRI. Annual reviews during this time were used to improve the planning aims and techniques. The impact of treatment technique, interstitial needle use and HRCTV volume on the dose statistics achieved was considered. Results Conformal and interstitial planning was introduced in the centre in 2016 and in 2017 the planning method was reviewed and changed to prioritise HRCTV coverage over achieving optimal dose aims for OARs. The review shows that the hard limits for HRCTV dose have been consistently met in approximately 70% of cases since 2017. Optimal HRCTV dose constraints have been consistently met in 50%-60% of cases from 2018 onwards. Since the introduction of conformal planning the hard limits have been met for all OARs in more than 90% of cases, whereas with standard plans OAR doses only met the limits in 40%-60% of cases for the sigmoid and 78%-95% of cases for the bladder. The optimal OAR constraints have been met in around 40% of cases each year since 2017. Needle usage has increased since introduction in 2016 and 45% of all eligible patients in this time have been treated with interstitial needles. Limited follow up data was available from 68 patients treated between 2015 -2019, this was analysed and compared to the dose statistics achieved. There was a marginal increase in three year survival rates for conformal planned patients compared to standard planning. The incidence of toxicity was comparable, with a slight reduction in complications to the bladder, bowel and rectum from conformal planning but a small increase in vaginal toxicity; this will be investigated further. Conclusion Annual reviews of dose statistics have facilitated audit of the treatment delivered to patients, to discuss outlying cases and to improve patient treatments by understanding what is being achieved and allowing strategies for improvement. The impact of these improvements on local control and toxicity has been seen in the move from standard to conformal planning. Techniques have continued to improve since 2019 and the OAR doses have been reduced; follow up data from this period will be reviewed to see if complication rates have also reduced. PD-0503 A pre-clinical, phantom based study for real time source position monitoring in HDR brachytherapy A. Sipahi 1 , J. Strotmann 2,3 , N. Chofor 4 , I. Simiantonakis 1 , A. Patil 5 , A.A. Schönfeld 4 1 Heinrich Heine University, Department of Radiation Oncology, Duesseldorf, Germany; 2 Carl von Ossietzky University, University Clinic of Medical Radiation Physics, Oldenburg, Germany; 3 University Clinic of Medical Radiation Physics, Medical Campus Pius-Hospital, Oldenburg, Germany; 4 Sun Nuclear, A Mirion Medical Company, Research & Development, Melbourne, USA; 5 Mirion Technologies, Inc., Research & Development, Meriden, USA Purpose or Objective In high dose rate brachytherapy, technical malfunctions of the equipment or unexpected complications during the therapeutic intervention can lead to misapplication of the dose and thus to severe consequences for the patient and personnel. In this project we performed a pre-clinical phantom investigation of a prototype gamma-camera system for real time source localization under clinical circumstances. Materials and Methods The prototype HDR-Vue© (Mirion Technologies, Atlanta, USA) consists of a gamma camera and an optical video camera. By co-registering both datasets in real-time, a source position indicator is superimposed onto the optical camera’s image. The system was tested using a CBCT electron density phantom (Sun Nuclear, A Mirion Medical Company, Norfolk, USA) to simulate attenuation and scatter within a patient. A stainless steel applicator probe of a GammaMedplus iX afterloader (Varian Medical Systems, Palo Alto, USA) was positioned inside the phantom and the phantom was placed in the center of the HDR-Vue's FOV at a source-to-camera distance of 50 cm. The Iridium-192 source had 20 stopping positions with dwell times of 5 seconds each and a step width of 5 mm. Results The HDR-Vue was able to visualize the real-time position of the Iridium-192 source during the radiation. A red circle in the live image indicates the localized real-time position of the radioactive source at any moment of the radiation. Figure 1 shows a composition of three images recorded when the source was at positions 1, 10 and 20.