K M Alexander

Delivery validation of VMAT stereotactic ablative body radiotherapy at commissioning

Dosimetric validation of two volumetric modulated arc therapy (VMAT) stereotactic ablative radiotherapy (SABR) plans was completed as part of the commissioning process of this technique in our clinic. Static and dynamic ion chamber, EBT3 film and leuco crystal violet (LCV) micelle gel measurements were acquired using a motion phantom with appropriate inserts for each dosimeter. The results show good agreement between measured and calculated plan dose.

Leuco-crystal-violet micelle gel dosimeters: I. Influence of recipe components and potential sensitizers

Radiochromic leuco crystal violet (LCV) micelle gel dosimeters are promising three-dimensional radiation dosimeters because of their spatial stability and suitability for optical readout. The effects of surfactant type and surfactant concentration on dose sensitivity of LCV micelle gels are tested, demonstrating that dose sensitivity and initial colour of the gel increases with increasing Triton x-100 (Tx100) concentration. Using Cetyl Trimethyl Ammonium Bromide (CTAB) in place of Tx100 produces gels that are nearly colourless prior to irradiation, but reduces the dose sensitivity. The separate effects of Tri-chloro acetic acid concentration and pH are investigated, revealing that controlling the pH near 3.6 is crucial for achieving high dose sensitivity. The sensitizing effect of chlorinated species on dose sensitivity is tested using 2,2,2-trichloroethanol (TCE), chloroform, and 1,1,1-trichloro-2-methyl-2-propanol hemihydrate. TCE gives the largest improvement in dose sensitivity and is recommended for use in micelle gel dosimeters because it is less volatile and safer to use than chloroform. Preliminary experiments on a new gel containing CTAB as the surfactant and TCE show that this new gel gives a dose sensitivity that is 24% higher than that of previous LCV micelle gels and is nearly colourless prior to irradiation.

Leuco-crystal-violet micelle gel dosimeters: II. Recipe optimization and testing

In this study, recipe optimization of Leuco Crystal Violet (LCV) micelle gels made with the surfactant Cetyl Trimethyl Ammonium Bromide (CTAB) and the chemical sensitizer 2,2,2-trichloroethanol (TCE) was aided by a two-level three-factor designed experiment. The optimized recipe contains 0.75 mM LCV, 17.0 mM CTAB, 120 mM TCE, 25.0 mM tri-chloro acetic acid (TCAA), 4 wt% gelatin and ~96 wt% water. Dose sensitivity of the optimized gel is 1.5 times higher than that of Jordans standard LCV micelle gel. Spatial integrity of the 3D dose distribution information in 1L phantoms filled with this recipe is maintained for >120 d. Unfortunately, phantoms made using the optimized recipe showed dose-rate dependence (14% difference in optical attenuation at the peak dose using electron beam irradiations at 100 and 400 MU min(-1)). Further testing suggests that the surfactant CTAB is the cause of this dose rate behaviour.

Stereotactic body radiation therapy delivery validation

This work describes the use of a motion phantom and 1D, 2D, and 3D ion chamber, EBT3 film, electronic portal imaging device (EPID) and FXG gel measurements for dosimetric validation of a stereotactic ablative radiation therapy (SBRT) technique in our clinic. Results show good agreement between the measurements and calculated treatment plan dose.

Implementation of an efficient workflow process for gel dosimetry using 3D Slicer

One challenge in gel dosimetry is the manipulation and analysis of complex data sets from different systems. In this paper, we describe a simple and fast gel dosimetry analysis tool for radiation therapy dose deliveries. Using the open source medical imaging software 3D Slicer, an extension was designed and implemented for the purpose of importing treatment planning system dose, CT imaging from simulation and at treatment, and optical CT gel dosimeter data. The extension also allows for calibration of gel dosimeter data, registration, and comparison of 3D dose distributions. The development of an open source gel dosimetry processing environment may help adoption of gels in the clinic.

Performing radiation therapy research using the open-source SlicerRT toolkit

Radiation therapy (RT) is a common treatment option for a wide variety of cancer types. Despite significant improvements in this technique over the past years, software tools for research in RT are limited to either expensive, closed, proprietary applications or heterogeneous sets of open-source software packages with limited scope, reliability, and user support. Our SlicerRT toolkit aspires to overcome these limitations by providing an extensive set of RT research tools leveraging the advanced visualization and image analysis features of its base platform 3D Slicer.

SU-E-T-231: Cross-Validation of 3D Gamma Comparison Tools

Purpose: Moving the computational analysis for 3D gel dosimetry into the 3D Slicer (www.slicer.org) environment has made gel dosimetry more clinically accessible. To ensure accuracy, we cross-validate the 3D gamma comparison module in 3D Slicer with an independently developed algorithm using simulated and measured dose distributions. Methods: Two reference dose distributions were generated using the Varian Eclipse treatment planning system. The first distribution consisted of a four-field box irradiation delivered to a plastic water phantom and the second, a VMAT plan delivered to a gel dosimeter phantom. The first reference distribution was modified within Eclipse to create an evaluated dose distribution by spatially shifting one field by 3mm, increasing the monitor units of the second field, applying a dynamic wedge for the third field, and leaving the fourth field unchanged. The VMAT plan was delivered to a gel dosimeter and the evaluated dose in the gel was calculated from optical CT measurements. Results from the gamma comparison tool built into the SlicerRT toolbox were compared to results from our in-house gamma algorithm implemented in Matlab (via MatlabBridge in 3D Slicer). The effects of noise, resolution and the exchange of reference and evaluated designations on the gamma comparison were also examined. Results: Perfect agreement was found between the gamma results obtained using the SlicerRT tool and our Matlab implementation for both the four-field box and gel datasets. The behaviour of the SlicerRT comparison with respect to changes in noise, resolution and the role of the reference and evaluated dose distributions was consistent with previous findings. Conclusion: Two independently developed gamma comparison tools have been cross-validated and found to be identical. As we transition our gel dosimetry analysis from Matlab to 3D Slicer, this validation serves as an important test towards ensuring the consistency of dose comparisons using the 3D Slicer environment.

Opportunities for improving the performance of LCV micelle gel dosimeters: II. Recipe optimization

Designed experiments and empirical models are used to optimize a Leuco Crystal Violet (LCV) micelle gel recipe to improve dose sensitivity and initial colour. The optimized recipe contains 0.75 mM LCV, 17.0 mM Cetyl Trimethyl Ammonium Bromide (CTAB), 120 mM 2,2,2-trichloroethanol (TCE), 25.0 mM tri-chloro acetic acid (TCAA), 4 wt% gelatin and ~96 wt% water. Dose sensitivity of the optimized gel is 1.5 times higher than Jordans standard LCV gel. Spatial integrity of the 3D dose distribution information in 1L jar phantoms made using this recipe is maintained for more than two weeks.

Dosimetric impact of a change in breathing period on VMAT stereotactic ablative body radiotherapy

The dosimetric impact of a change in breathing period during treatment was assessed for a volumetric modulated arc therapy (VMAT) stereotactic ablative radiotherapy (SABR) lung plan optimized according to our centres planning protocol. Plan delivery was evaluated at three breathing rates ranging from 7 to 23 breaths-per-minute (BPM) against the planning anatomy (15 BPM) calculated dose. Dynamic ion chamber, EBT3 film and Fricke-xylenol orange-gelatin (FXG) gel measurements were acquired using a motion phantom with appropriate inserts for each dosimeter. The results show good agreement between measured and calculated plan dose within the internal gross tumour volume (IGTV) target.

Development of 3D Slicer based film dosimetry analysis

Radiochromic film dosimetry has been widely adopted in the clinic as it is a convenient option for dose measurement and verification. Film dosimetry analysis is typically performed using expensive commercial software, or custom made scripts in Matlab. However, common clinical film analysis software is not transparent regarding what corrections/optimizations are running behind the scenes. In this work, an extension to the open-source medical imaging platform 3D Slicer was developed and implemented in our centre for film dosimetry analysis. This extension streamlines importing treatment planning system dose and film imaging data, film calibration, registration, and comparison of 2D dose distributions, enabling greater accessibility to film analysis and higher reliability.