J Woollard

Development and Application of Neutron Field Optimization Parameters for an Accelerator-Based Neutron Source for Boron Neutron Capture Therapy

Design parameters for an epithermal neutron field for an accelerator-based source of neutrons for boron neutron capture therapy are developed. The parameters that are developed incorporate predicted biological effects in patients` heads. They are based on an energy-spectrum-dependent neutron normal-tissue relative biological effectiveness and the treatment planning methodology of Gahbauer and his coworkers, which includes the effects of dose fractionation. The neutron field optimization parameters are evaluated for two epithermal neutron fields resulting from an accelerator-based neutron source with two different moderator assemblies. For the two moderator assemblies and moderator thicknesses evaluated, the D{sub 2}O-Li{sub 2}CO{sub 3} moderator assembly is superior to the BeO-MgO moderator assembly. The absorbed-dose delivered to the tumor for the D{sub 2}O-Li{sub 2}CO{sub 3} moderator assembly is larger than that for the BeO-MgO moderator assembly for almost all tumor depths. The treatment times for the D{sub 2}O-Li{sub 2}CO{sub 3} moderator assembly are slightly longer than for the BeO-MgO moderator assembly. However, for a 10-mA proton current, the treatment times for both are reasonable.

A comparison of neutron beams for BNCT based on in‐phantom neutron field assessment parameters

In this paper our in-phantom neutron field assessment parameters, T and DTumor, were used to evaluate several neutron sources for use in BNCT. Specifically, neutron fields from The Ohio State University (OSU) Accelerator-Based Neutron Source (ABNS) design, two alternative ABNS designs from the literature (the Al/AIF3-Al2O3 ABNS and the 7LiF-AI2O3 ABNS), a fission-convertor plate concept based on the 500-kW OSU Research Reactor (OSURR), and the Brookhaven Medical Research Reactor (BMRR) facility were evaluated. In order to facilitate a comparison of the various neutron fields, values of T and DTumor were calculated in a 14 cm x 14 cm x 14 cm lucite cube phantom located in the treatment port of each neutron source. All of the other relevant factors, such as phantom materials, kerma factors, and treatment parameters, were kept the same. The treatment times for the OSURR, the 7LiF-Al2O3 ABNS operating at a beam current of 10 mA, and the BMRR were calculated to be comparable and acceptable, with a treatment time per fraction of approximately 25 min for a four fraction treatment scheme. The treatment time per fraction for the OSU ABNS and the Al/AlF3-Al2O3 ABNS can be reduced to below 30 min per fraction for four fractions, if the proton beam current is made greater than approximately 20 mA. DTumor was calculated along the bean centerline for tumor depths in the phantom ranging from 0 to 14 cm. For tumor depths ranging from 0 to approximately 1.5 cm, the value of DTumor for the OSURR is largest, while for tumor depths ranging from 1.5 to approximately 14 cm, the value of DTumor for the OSU-ABNS is the largest.

An expression for the RBE of neutrons as a function of neutron energy

The goal of this paper is to develop a relationship between a neutron RBE and neutron energy, En, which can be used to design neutron sources for BNCT. In an earlier calculation of a neutron RBE as a function of En, we approximated the contribution to a total neutron RBE, RBEt (En), arising from 14N(n,p)14C reactions. In this paper, we recalculate RBEt (En), accounting more exactly for the contribution to RBEt (En) from 14N(n,p)14C reactions.

Evaluation of moderator assemblies for use in an accelerator-based neutron source for boron neutron capture therapy

The neutron fields produced by several moderator assemblies were evaluated using both in-phantom and in-air neutron field assessment parameters. The parameters were used to determine the best moderator assembly, from among those evaluated, for use in the accelerator-based neutron source for boron neutron capture therapy. For a 10-mA proton beam current and the specified treatment parameters, a moderator assembly consisting of a BeO moderator and a Li{sub 2}CO{sub 3} reflector was found to be the best moderator assembly whether the comparison was based on in-phantom or in-air neutron field assessment parameters. However, the parameters were discordant regarding the moderator thickness. The in-phantom neutron field assessment parameters predict 20 cm of BeO as the best moderator thickness, whereas the in-air neutron field assessment parameters predict 25 cm of BeO as the best moderator thickness.

Quality assurance for a six degrees‐of‐freedom table using a 3D printed phantom

Abstract Purpose To establish a streamlined end‐to‐end test of a 6 degrees‐of‐freedom (6DoF) robotic table using a 3D printed phantom for periodic quality assurance. Methods A 3D printed phantom was fabricated with translational and rotational offsets and an imbedded central ball‐bearing (BB). The phantom underwent each step of the radiation therapy process: CT simulation in a straight orientation, plan generation using the treatment planning software, setup to offset marks at the linac, registration and corrected 6DoF table adjustments via hidden target test, delivery of a Winston‐Lutz test to the BB, and verification of table positioning via field and laser lights. The registration values, maximum total displacement of the combined Winston‐Lutz fields, and a pass or fail criterion of the laser and field lights were recorded. The quality assurance process for each of the three linacs were performed for the first 30 days. Results Within a 95% confidence interval, the overall uncertainty values for both translation and rotation were below 1.0 mm and 0.5° for each linac respectively. When combining the registration values and other uncertainties for all three linacs, the average deviations were within 2.0 mm and 1.0° of the designed translation and rotation offsets of the 3D print respectively. For all three linacs, the maximum total deviation for the Winston‐Lutz test did not exceed 1.0 mm. Laser and light field verification was within tolerance every day for all three linacs given the latest guidance documentation for table repositioning. Conclusion The 3D printer is capable of accurately fabricating a quality assurance phantom for 6DoF positioning verification. The end‐to‐end workflow allows for a more efficient test of the 6DoF mechanics while including other important tests needed for routine quality assurance.

An alpha autoradiographic technique for determination of 10B concentrations in blood and tissue

Boron neutron-capture therapy (BNCT) is an experimental radiation therapy which is being developed for the treatment of malignant tumors. One requirement for successful BNCT is that a sufficient amount of 10B concentrates in the tumor while clearing from normal tissues and blood. In order to evaluate the effectiveness of various 10B delivery agents, the concentrations of boron in blood, tumor and normal tissues must be known. Using the solid-state nuclear-track detector (SSNTD) CR-39, we have developed a sequential assay technique for measuring 10B in the blood of rats. We have also developed a CR-39-based assay technique to spatially quantify 10B concentrations across tissue sections. Both techniques rely on alpha-track autoradiography for 10B concentration quantitation. The SSNTD CR-39 is used to record the tracks of the charged reaction products of the 10B(n, α)7Li reaction. Samples are placed on the CR-39 and irradiated. The CR-39 is then etched with sodium hydroxide and the resulting tracks are counted using our SSNTD automatic readout and analysis (SARA) system. This technique has permitted us to determine blood 10B clearance curves on individual animals bled sequentially over 24 hours. The tissue-section assay technique has been used to quantify 10B concentrations in tumor and normal tissues, on lines across tissue sections. This was done by combining 10B concentrations on lines across the CR-39 with color digital images of the tissue section. The minimum detectable concentration for the blood assay technique was 0.2 μg 10B/ml. The methodology that we have developed should be useful in evaluating the potential usefulness of various 10B-containing compounds for BNCT.

Validating kQ=1.0 assumption in TG51 with PTW 30013 farmer chamber for Varian TrueBeam's 2.5 MV imaging beam

Abstract AAPM Report 142 recommends and the State of Ohio requires that the imaging dose be quantified in radiotherapy applications. Using the TG51 dose calibration protocol for MV Imaging dose measurement requires knowledge of the kQ parameter for the beam quality and the ionization chamber type under investigation. The %dd(10)x of the Varian TrueBeam 2.5 MV imaging beam falls outside the range of the available data for the calculation of the kQ value. Due to the similarities of the 2.5 MV imaging beam and the 60Co beam, we and others made the assumption that kQ = 1.0 in TG51 calculations. In this study, we used the TG21 and TG51 calibration protocols in conjunction to validate that kQ = 1.0 for the 2.5 MV imaging beam using a PTW 30013 farmer chamber. Standard measurements for TG51 absolute dosimetry QA were performed at 100 cm SSD, 10 cm depth, 10 × 10 field size, delivering 100 Monitor Units to a waterproof Farmer Chamber (PTW TN30013) for both 2.5 and 6 MV. Both the TG21 and TG51 formalisms were used to calculate the dose to water per MU at dmax (Dw/MU) for the 6 MV beam. The calculated outputs were 1.0005 and 1.0004 cGy/MU respectively. The TG21 formalism was then used to calculate (Dw/MU) for the 2.5 MV imaging beam. This value was then used in the TG51 formalism to find kQ for the 2.5 MV imaging beam. A kQ value of 1.00 ± 0.01 was calculated for 2.5 MV using this method.

SU-F-R-12: Prediction of TrueBeam Hardware Issues Using Trajectory Log Analysis

PURPOSE To predict potential failures of hardware within the Varian TrueBeam linear accelerator in order to proactively replace parts and decrease machine downtime. METHODS Machine downtime is a problem for all radiation oncology departments and vendors. Most often it is the result of unexpected equipment failure, and increased due to lack of in-house clinical engineering support. Preventative maintenance attempts to assuage downtime, but often is ineffective at preemptively preventing many failure modes such as MLC motor failures, the need to tighten a gantry chain, or the replacement of a jaw motor, among other things. To attempt to alleviate downtime, software was developed in house that determines the maximum value of each axis enumerated in the Truebeam trajectory log files. After patient treatments, this data is stored in a SQL database. Microsoft Power BI is used to plot the average maximum error of each day of each machine as a function of time. The results are then correlated with actual faults that occurred at the machine with the help of Varian service engineers. RESULTS Over the course of six months, 76,312 trajectory logs have been written into the database and plotted in Power BI. Throughout the course of analysis MLC motors have been replaced on three machines due to the early warning of the trajectory log analysis. The service engineers have also been alerted to possible gantry issues on one occasion due to the aforementioned analysis. CONCLUSION Analyzing the trajectory log data is a viable and effective early warning system for potential failures of the TrueBeam linear accelerator. With further analysis and tightening of the tolerance values used to determine a possible imminent failure, it should be possible to pinpoint future issues more thoroughly and for more axes of motion.

SU-F-P-43: Use of Freeware Business Intelligence Software to Trend TG-142 Compliant Linac QA Parameters.

PURPOSE To develop a software platform to track linac QA parameter trends using readily available freeware business intelligence (BI) software METHODS: Spreadsheets were used to collect QA data by many, if not all, institutions; but the trending analysis with data from separate spreadsheets could be a cumbersome task. A freeware version of the Microsoft Power BI software was adapted to trend linac QA parameters to allow us to maintain nine dosimetrically equivalent linacs. A monthly QA spreadsheet (Microsoft Excel) has been used in our institution to collect QA data. We developed a C# computer program to mine QA data from spreadsheets in an automated way and store in a SQL database. The program runs every night automatically, crawls down a predetermined directory in a network hard-drive where all data spreadsheets are saved and searches for new data. If new data are found, they are written into the database. The implemented BI software reads QA data from the database and provides users with dynamic data trending interface as dashboards. The BI dashboard was configured to dynamically filter and drill down to specific parameters and conditions. This enables users to see the existence or missing data for specific tests and trends of linac parameters potentially alerting actions to be taken. RESULTS The developed software platform has been in use since 2015. More than 7680 data points corresponding to TG-142 compliant monthly QAs for nine linacs were automatically retrieved and stored in the database. The developed dashboard has provided access to data for physicists enabling them to dissect the data to observe trends in different parameters in just a few mouse clicks. CONCLUSION The developed BI dashboard has been an invaluable tool providing a common data analysis platform for a quick and easy access to all linac QA parameters and their trends.

SU-G-TeP4-08: Automating the Verification of Patient Treatment Parameters

PURPOSE To automate the daily verification of each patients treatment by utilizing the trajectory log files (TLs) written by the Varian TrueBeam linear accelerator while reducing the number of false positives including jaw and gantry positioning errors, that are displayed in the Treatment History tab of Varians Chart QA module. METHODS Small deviations in treatment parameters are difficult to detect in weekly chart checks, but may be significant in reducing delivery errors, and would be critical if detected daily. Software was developed in house to read TLs. Multiple functions were implemented within the software that allow it to operate via a GUI to analyze TLs, or as a script to run on a regular basis. In order to determine tolerance levels for the scripted analysis, 15,241 TLs from seven TrueBeams were analyzed. The maximum error of each axis for each TL was written to a CSV file and statistically analyzed to determine the tolerance for each axis accessible in the TLs to flag for manual review. The software/scripts developed were tested by varying the tolerance values to ensure veracity. After tolerances were determined, multiple weeks of manual chart checks were performed simultaneously with the automated analysis to ensure validity. RESULTS The tolerance values for the major axis were determined to be, 0.025 degrees for the collimator, 1.0 degree for the gantry, 0.002cm for the y-jaws, 0.01cm for the x-jaws, and 0.5MU for the MU. The automated verification of treatment parameters has been in clinical use for 4 months. During that time, no errors in machine delivery of the patient treatments were found. CONCLUSION The process detailed here is a viable and effective alternative to manually checking treatment parameters during weekly chart checks.