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In vivo dose measurements for high-dose-rate brachytherapy using a new scintillating fiber dosimetry system: A prostate phantom study
Oral Presentations / Brachytherapy 8 (2009) 105e180 Conclusions: Interfractional catheter displacement along the cranio-caudal axis occurs in a substantial proportion of patients. The dosimetric consequences of not re-planning the second fraction for prostate HDR implants may result in dosimetric deviations and suboptimal dose distributions. Catheter adjustment with planning before each fraction resulted in higher quality dosimetry parameters.
OR21 Presentation Time: 3:50 PM In vivo dose measurements for high-dose-rate brachytherapy using a new scintillating fiber dosimetry system: A prostate phantom study Francois Therriault-Proulx, M.Sc.,1,2 Maxime Villeneuve, B.Sc.,1 Andre-Guy Martin, M.D., MSc,1 Luc Gingras, Ph.D.,1 Sam A. Beddar, Ph.D.,2 Luc Beaulieu, Ph.D.1 1Radio-oncologie, Centre Hospitalier Universitaire de Quebec, Quebec City, QC, Canada; 2Radiation Physics, The University of Texas M.D. Anderson Cancer Center, Houston, TX. Purpose: The goal of this study was to develop a scintillating fiber dosimeter and verify its suitability in assessing the dose deposited during brachytherapy high-dose-rate (HDR) treatments. As a first step toward in vivo dosimetry, it has been decided to conduct a full process, from planning to treatment, using a prostate phantom. Methods and Materials: The scintillating fiber dosimeter proposed in this study for in vivo dose measurements is based on the use of RGB photodiode (MCS3AT) to detect the light emitted by a scintillator (BCF-60) optically coupled to an optical fiber. A connectors system has been developed to ensure proper alignment between the fiber and the photodiode. The temperature of the photodiode was controlled for better stability and noise reduction. The output from photodiode went through an amplification stage before being acquired with a NI DAQPaD-6015 acquisition card. The signal was then recorded and processed to obtain the dose deposited during treatment. The Cerenkov component was subtracted in real-time following a proper calibration. A prostate phantom (CIRS Model 053 G) has been used to conduct the study using the Nucletron HDR 192Ir brachytherapy system (Nucletron B.V., Veenendaal, The Netherlands). An ultrasound-guided catheter insertion procedure was performed by a radiation oncologist at our institution. A total of 13 catheters were inserted to cover the entire target volume. Following the insertion, a CT scan of the phantom was then obtained. A radio-opaque marker was used in one of the catheter during the scan to indicate the position of the dosimeter, thus leaving 12 catheters for planning purpose. The prostate and urethra were contoured and treatment planning was performed according to our prostate clinical protocol on a PLATO workstation (Nucletron). The marker was removed and the dosimeter was inserted in the phantom. The plan was delivered using a microSelectron V2 192Ir afterloader. Results: As represented in figure 1, the scintillating fiber dosimeter allowed to record the dose rate as function of time during the treatment. Each peak on the figure represents the irradiation in a specific catheter. The measured dose rate is function of distance between the dosimeter and the dwell-positions as
115
well as dwell-times for a given distance. Cerenkov contamination depends on the scintillator volume and distance. It constitutes up to 7% of the signal. Integration of the dose rate, after Cerenkov radiation subtraction, is performed to determine the total dose deposited during treatment. The dose measured was within 2% of the dose predicted by the planning system. Conclusions: A simple scintillating fiber dosimeter has been presented. It provides an accurate method to assess dose deposited to targets and organs at risk during HDR brachytherapy. It has been demonstrated that dose rates measured with such a system allow real-time quality assurance of treatment delivery for each catheter and for the total delivered dose. The measured total dose is in very good agreement with what is expected by the planning system. Measurements have been done in a prostate phantom, but its potential for a variety of clinical sites is obvious.
OR22 Presentation Time: 4:00 PM Inverse-planned image-guided robotic brachytherapy: Preclinical proofs of principle J. Adam M. Cunha, Ph.D.,1 Jean Pouliot, Ph.D.,1 I-Chow J. Hsu, M.D.,1 Dan Stoianovici, Ph.D.,2 John Kurhanewicz, Ph.D.,3 Galen D. Reed, B.S.,3 Mack Roach III, M.D.1 1Radiation Oncology, University of California (UCSF), San Francisco, CA; 2Urology, Johns Hopkins University, Baltimore, M.D; 3Radiology, University of California (UCSF), San Francisco, CA. Purpose: To establish proofs of principle necessary for the deployment of Inverse-Planned Image-Guided Robotic Brachytherapy in the clinic. The specific objective is to integrate the robot into the image/plan/deliver (IPD) workflow (Figure). We will also show that a robotic device can augment the IPD workflow into a fully adaptive procedure: image/plan/ begin-delivery/image/plan/finish delivery. Methods and Materials: We used MRBot, an MR-stealth brachytherapy delivery device, in (1) a closed-bore 3 T MRI using sagittal SPGR T1weighted sequences, TR 5 16.5 ms, TE 5 3.32 ms, flip angle 5 12 degrees and (2) a clinical brachytherapy suite equipped with a Nucletron Simulix-Evolution cone beam CT (CBCT) with an amorphous Si flat panel detector. Targets included ceramic dummy seeds, MR-spectroscopy-sensitive matobolite, and a prostate phantom. Acquired DICOM images were exported to Nucletron’s Oncentra planning software to register the robot coordinates in the imager’s frame, contour, verify target locations, create dose plans, and export needle and seed positions to the robot. To demonstrate adaptive dose planning, a CBCT of a prostate-region phantom was acquired and contoured. IPSA was used to generate a seed placement plan. Coordinates for 10 needles and 29 seeds were transferred to the robot. After every two needles placed, an image of the phantom was acquired. The already-placed seeds were identified and validated prior to placing the seeds in the next two needles. Results: The coordination of each system element (imaging device, brachytherapy planning system, robot control, robot) was validated with a seed delivery to within 1 mm of a targetda ceramic seed in both a phantom and bovine soft tissue (a non-homogeneous environment). An adaptive image guided delivery workflow was demonstrated by acquiring MRI/CBCT images after needle insertion and prior to seed deposition. This allows for adjustment if the needle is in the wrong position. We demonstrated the ability to robotically deliver seeds to locations determined by IPSA, and the ability of the system to incorporate novel (non-rectangular-template-based) seed/needle patterns that can avoid penetrating sensitive organs (e.g. penile bulb, rectum, urethra) and circumvent the pubic arch. Conclusions: We have shown that a robotic device can be incorporated into the clinical brachytherapy workflow by demonstrating the following proofs of concept: (a) Link multiple coordinate systems; (b) Guide a needleplacement robot using MR spectroscopy; (c) Use an MR-guided robot to
OR21 Presentation Time: 3:50 PM In vivo dose measurements for high-dose-rate brachytherapy using a new scintillating fiber dosimetry system: A prostate phantom study Francois Therriault-Proulx, M.Sc.,1,2 Maxime Villeneuve, B.Sc.,1 Andre-Guy Martin, M.D., MSc,1 Luc Gingras, Ph.D.,1 Sam A. Beddar, Ph.D.,2 Luc Beaulieu, Ph.D.1 1Radio-oncologie, Centre Hospitalier Universitaire de Quebec, Quebec City, QC, Canada; 2Radiation Physics, The University of Texas M.D. Anderson Cancer Center, Houston, TX. Purpose: The goal of this study was to develop a scintillating fiber dosimeter and verify its suitability in assessing the dose deposited during brachytherapy high-dose-rate (HDR) treatments. As a first step toward in vivo dosimetry, it has been decided to conduct a full process, from planning to treatment, using a prostate phantom. Methods and Materials: The scintillating fiber dosimeter proposed in this study for in vivo dose measurements is based on the use of RGB photodiode (MCS3AT) to detect the light emitted by a scintillator (BCF-60) optically coupled to an optical fiber. A connectors system has been developed to ensure proper alignment between the fiber and the photodiode. The temperature of the photodiode was controlled for better stability and noise reduction. The output from photodiode went through an amplification stage before being acquired with a NI DAQPaD-6015 acquisition card. The signal was then recorded and processed to obtain the dose deposited during treatment. The Cerenkov component was subtracted in real-time following a proper calibration. A prostate phantom (CIRS Model 053 G) has been used to conduct the study using the Nucletron HDR 192Ir brachytherapy system (Nucletron B.V., Veenendaal, The Netherlands). An ultrasound-guided catheter insertion procedure was performed by a radiation oncologist at our institution. A total of 13 catheters were inserted to cover the entire target volume. Following the insertion, a CT scan of the phantom was then obtained. A radio-opaque marker was used in one of the catheter during the scan to indicate the position of the dosimeter, thus leaving 12 catheters for planning purpose. The prostate and urethra were contoured and treatment planning was performed according to our prostate clinical protocol on a PLATO workstation (Nucletron). The marker was removed and the dosimeter was inserted in the phantom. The plan was delivered using a microSelectron V2 192Ir afterloader. Results: As represented in figure 1, the scintillating fiber dosimeter allowed to record the dose rate as function of time during the treatment. Each peak on the figure represents the irradiation in a specific catheter. The measured dose rate is function of distance between the dosimeter and the dwell-positions as
115
well as dwell-times for a given distance. Cerenkov contamination depends on the scintillator volume and distance. It constitutes up to 7% of the signal. Integration of the dose rate, after Cerenkov radiation subtraction, is performed to determine the total dose deposited during treatment. The dose measured was within 2% of the dose predicted by the planning system. Conclusions: A simple scintillating fiber dosimeter has been presented. It provides an accurate method to assess dose deposited to targets and organs at risk during HDR brachytherapy. It has been demonstrated that dose rates measured with such a system allow real-time quality assurance of treatment delivery for each catheter and for the total delivered dose. The measured total dose is in very good agreement with what is expected by the planning system. Measurements have been done in a prostate phantom, but its potential for a variety of clinical sites is obvious.
OR22 Presentation Time: 4:00 PM Inverse-planned image-guided robotic brachytherapy: Preclinical proofs of principle J. Adam M. Cunha, Ph.D.,1 Jean Pouliot, Ph.D.,1 I-Chow J. Hsu, M.D.,1 Dan Stoianovici, Ph.D.,2 John Kurhanewicz, Ph.D.,3 Galen D. Reed, B.S.,3 Mack Roach III, M.D.1 1Radiation Oncology, University of California (UCSF), San Francisco, CA; 2Urology, Johns Hopkins University, Baltimore, M.D; 3Radiology, University of California (UCSF), San Francisco, CA. Purpose: To establish proofs of principle necessary for the deployment of Inverse-Planned Image-Guided Robotic Brachytherapy in the clinic. The specific objective is to integrate the robot into the image/plan/deliver (IPD) workflow (Figure). We will also show that a robotic device can augment the IPD workflow into a fully adaptive procedure: image/plan/ begin-delivery/image/plan/finish delivery. Methods and Materials: We used MRBot, an MR-stealth brachytherapy delivery device, in (1) a closed-bore 3 T MRI using sagittal SPGR T1weighted sequences, TR 5 16.5 ms, TE 5 3.32 ms, flip angle 5 12 degrees and (2) a clinical brachytherapy suite equipped with a Nucletron Simulix-Evolution cone beam CT (CBCT) with an amorphous Si flat panel detector. Targets included ceramic dummy seeds, MR-spectroscopy-sensitive matobolite, and a prostate phantom. Acquired DICOM images were exported to Nucletron’s Oncentra planning software to register the robot coordinates in the imager’s frame, contour, verify target locations, create dose plans, and export needle and seed positions to the robot. To demonstrate adaptive dose planning, a CBCT of a prostate-region phantom was acquired and contoured. IPSA was used to generate a seed placement plan. Coordinates for 10 needles and 29 seeds were transferred to the robot. After every two needles placed, an image of the phantom was acquired. The already-placed seeds were identified and validated prior to placing the seeds in the next two needles. Results: The coordination of each system element (imaging device, brachytherapy planning system, robot control, robot) was validated with a seed delivery to within 1 mm of a targetda ceramic seed in both a phantom and bovine soft tissue (a non-homogeneous environment). An adaptive image guided delivery workflow was demonstrated by acquiring MRI/CBCT images after needle insertion and prior to seed deposition. This allows for adjustment if the needle is in the wrong position. We demonstrated the ability to robotically deliver seeds to locations determined by IPSA, and the ability of the system to incorporate novel (non-rectangular-template-based) seed/needle patterns that can avoid penetrating sensitive organs (e.g. penile bulb, rectum, urethra) and circumvent the pubic arch. Conclusions: We have shown that a robotic device can be incorporated into the clinical brachytherapy workflow by demonstrating the following proofs of concept: (a) Link multiple coordinate systems; (b) Guide a needleplacement robot using MR spectroscopy; (c) Use an MR-guided robot to