ESTRO 37 Abstract book

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ESTRO 37

that can be widely disseminated to BT clinics for real- time treatment verification. Material and Methods We have manufactured miniature ISDs based on ruby (Al 2 O 3 :Cr), Y 2 O 3 :Eu, YVO 4 :Eu, ZnSe:O or CsI:Tl. The ISDs consisted of a 1 mm-size scintillator that was optically coupled to a 1 mm-diameter and 15 m-long fiber-optic cable. The ISDs were connected to a charge-coupled device camera or a spectrometer spectrograph, and placed in a water phantom during experiments with a 192 Ir BT source, to measure their emission spectra, scintillation intensities and influences of the stem signal, photoluminescence and time-dependent luminescence properties. The ISDs were compared with detectors based on the commonly used organic scintillators BCF-12 and BCF-60. A new in vivo dosimetry system based on ISDs was developed using photodetector and data acquisition components that matched the luminescence characteristics of the ISDs. The new system was tested in water phantom experiments to determine its dynamic range and signal-to-noise ratio. Results The scintillation intensities of the ISDs were between 20 and 900 times greater than the intensity of the BCF-12 based detector (Figure 1). The large scintillation intensity of the ZnSe:O and CsI:Tl based ISDs made it possible to develop an in vivo dosimetry system based on low-cost photodetector and data acquisition components. The final detector system (Figures 2A and B) measured dose rates with <0.2% precision for source-to-detector distances up to 10 cm (Figure 2C and D). The stem signal was <0.5% of the total signal for the ZnSe:O and CsI:Tl based ISDs, and up to 5% and 3% for the ruby and Y 2 O 3 :Eu and YVO 4 :Eu based ISDs, respectively. The photoluminescence background was up to 1% for the ruby based ISD and <0.5% for the other ISDs. All ISDs exhibited stable scintillation during constant irradiation and negligible afterglow.

Conclusion High-intensity ISD materials, e.g. ZnSe:O and CsI:Tl, make it possible to develop low-cost in vivo dosimetry systems with 1 mm-size detector volumes that exhibit large signal-to-noise ratios and negligible stem and photoluminescence backgrounds. The new ISD system makes it possible to precisely monitor BT treatments at a low cost and can therefore facilitate dissemination of real-time treatment verification technology for BT. OC-0173 Intensity modulated brachytherapy system for dynamic modulation of shielded catheters G. Famulari 1 , S.A. Enger 1,2,3 1 McGill University, Medical Physics Unit, Montreal, Canada 2 McGill University Health Centre, Research Institute of the McGill University Health Centre, Montreal, Canada 3 McGill University, Oncology, Montreal, Canada Purpose or Objective Conventional brachytherapy often results in les s than ideal tumor dose conformity due to the non-symmetrical shape of the tumors, resulting in dose spillage to radiation sensitive organs at risk (OARs). Intensity modulated brachytherapy (IMBT) can dynamically direct the radiation towards the tumor and away from OARs by incorporating metallic shields inside within brachytherapy We propose a novel delivery system for IMBT which can dynamically control the rotation of shielded catheters. To modulate the intensity of the source, the device combines a custom made 169 Yb source with thin platinum shields (maximum thickness of 0.8 mm) within the catheter. The source has an active core with a diameter of 0.6 mm and a length of 3 mm. The device can be connected to any commercial afterloader as an add-on device, and is compatible with both interstitial and intracavitary applicators. The device is divided in three main systems: a rotating system, a link assembly and a shield assembly (Fig. 1). The rotation of the shield is controlled through a series of moving panels with an interlock system. Each panel is connected to a stepper motor which handles the rotation of a subset of needles. The shielded needles are connected to the rotating mechanism through flexible locking luers that will allow the opportunity to implant the needles at an angle. As in conventional brachytherapy, the afterloader is responsible for the motion of the source through the source guide and within the catheter. Controller sensors will read the actual position of the shield and provide feedback to the stepper motor system. As a proof of principle, an IMBT treatment plan for a prostate cancer case was simulated using a Monte Carlo based treatment planning system to show the potential advantages of IMBT. needles/applicators. Material and Methods