Experimental validation of a kilovoltage x‐ray source model for computing imaging dose

Poirier, Yannick; Kouznetsov, A.; Koger, Brandon; Tambasco, Mauro

doi:10.1118/1.4869159

Cited by 17 publications

(31 citation statements)

References 36 publications

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“…It is therefore easier to implement than modeling the beam using conventional MC simulation. While adapted MV TPS are interesting due to their clinical feasibility, they still require the measurement of many percent depth‐dose and profile curves (2) which represent more measurements than required using our beam characterization method (12) …”

Section: Discussionmentioning

confidence: 99%

“…This virtual point source is used to create the photons which are transported in the biased MC calculations of the scattered component of the differential angular flux density. In this model, photons are generated with a given energy and trajectory from the source location (the focal spot on the X‐ray tube anode) to the isocenter plane (12) . To model rotating CBCT sources, the software was modified to incorporate a starting gantry angle and arc size.…”

Section: Methodsmentioning

confidence: 99%

“…1) using a previously validated kV source characterization method and virtual point source model (12) . Briefly, this method involves measuring the half‐value layer (HVL) along the transverse axis and the in‐air kerma profiles along the radial and transverse axes.…”

Section: Methodsmentioning

confidence: 99%

“…This method was validated computationally using the MCNP (6) and EGSnrc (7) MC simulation techniques (5) . It was also validated experimentally for therapeutic kV x‐ray beams, 8 , 9 radiographic imaging procedures using open beams, (10) diagnostic CT scanners, (11) and radiographic beams produced with added bowtie filters (12) . A machine‐specific virtual point source model was developed by Poirier et al 10 , 12 to simulate the X‐ray beam input.…”

Section: Introductionmentioning

confidence: 99%

“…It was also validated experimentally for therapeutic kV x‐ray beams, 8 , 9 radiographic imaging procedures using open beams, (10) diagnostic CT scanners, (11) and radiographic beams produced with added bowtie filters (12) . A machine‐specific virtual point source model was developed by Poirier et al 10 , 12 to simulate the X‐ray beam input. This source model is characterized from simple in‐air ionization chamber measurements without the need for specialized equipment or knowledge of MC modeling techniques.…”

Section: Introductionmentioning

confidence: 99%

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Experimental validation of a kV source model and dose computation method for CBCT imaging in an anthropomorphic phantom

Poirier¹,

Tambasco

2016

J Applied Clin Med Phys

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We present an experimental validation of a kilovoltage (kV) X‐ray source characterization model in an anthropomorphic phantom to estimate patient‐specific absorbed dose from kV cone‐beam computed tomography (CBCT) imaging procedures and compare these doses to nominal weighted CT‐dose index (CTDIw) dose estimates. We simulated the default Varian on‐board imager 1.4 (OBI) default CBCT imaging protocols (i.e., standard‐dose head, low‐dose thorax, pelvis, and pelvis spotlight) using our previously developed and easy to implement X‐ray point‐source model and source characterization approach. We used this characterized source model to compute absorbed dose in homogeneous and anthropomorphic phantoms using our previously validated in‐house kV dose computation software (kVDoseCalc). We compared these computed absorbed doses to doses derived from ionization chamber measurements acquired at several points in a homogeneous cylindrical phantom and from thermoluminescent detectors (TLDs) placed in the anthropomorphic phantom. In the homogeneous cylindrical phantom, computed values of absorbed dose relative to the center of the phantom agreed with measured values within ≤2% of local dose, except in regions of high‐dose gradient where the distance to agreement (DTA) was 2 mm. The computed absorbed dose in the anthropomorphic phantom generally agreed with TLD measurements, with an average percent dose difference ranging from 2.4%±6.0% to 5.7%±10.3%, depending on the characterized CBCT imaging protocol. The low‐dose thorax and the standard dose scans showed the best and worst agreement, respectively. Our results also broadly agree with published values, which are approximately twice as high as the nominal CTDIw would suggest. The results demonstrate that our previously developed method for modeling and characterizing a kV X‐ray source could be used to accurately assess patient‐specific absorbed dose from kV CBCT procedures within reasonable accuracy, and serve as further evidence that existing CTDIw assessments underestimate absorbed dose delivered to patients.PACS number(s): 87.57.Q‐, 87.57.uq, 87.10.Rt

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Section: Discussionmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

Experimental validation of a kV source model and dose computation method for CBCT imaging in an anthropomorphic phantom

Poirier¹,

Tambasco

2016

J Applied Clin Med Phys

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Direct and fast measurement of CT beam filter profiles with simultaneous geometrical calibration

Yang

et al. 2017

Medical Physics

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Purpose To accurately measure the beam filter profiles from a variety of CT scanner models and to provide reference data for Monte Carlo simulations of CT scanners. Methods This study proposed a new method to measure CT beam filter profiles using a linear-array x-ray detector (X-Scan 0.8f3–512, Detection Technology Inc, Finland) under gantry rotation mode. A robust geometrical calibration approach was developed to determine key geometrical parameters, by considering the x-ray focal spot location relative to the linear-array detector and the gantry’s angular increment at each acquisition point. CT beam intensity profiles were synthesized from continuously measured data during a 10° gantry rotation range, with calibrated detector response and system geometry information. Relative transmission profiles of nineteen sets of beam filters were then derived for nine different CT scanner models from three different manufacturers. Equivalent aluminum thickness profiles of these beam filters were determined by analytical calculation using the Spektr Matlab software package to match the measured transmission profiles. Three experiments were performed to validate the accuracy of the geometrical calibration, detector response modeling, and the derived equivalent aluminum thickness profiles. Results The beam intensity profiles measured from gantry rotational mode showed very good agreement with those measured with gantry stationary mode, with a maximal difference of 3%. The equivalent aluminum thickness determined by this proposed method agreed well with what was measured by an ion chamber, with a mean difference of 0.4%. The determined HVL profiles matched well with data from a previous study (max difference of 4.7%). Conclusions An accurate and robust method to directly measure profiles from a broad list of beam filters and CT scanner models was developed, implemented, and validated. Useful reference data was provided for future research on CT system modeling.

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A failure modes and effects analysis quality management framework for image‐guided small animal irradiators: A change in paradigm for radiation biology

et al. 2020

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Purpose: Image-guided small animal irradiators (IGSAI) are increasingly being adopted in radiation biology research. These animal irradiators, designed to deliver radiation with submillimeter accuracy, exhibit complexity similar to that of clinical radiation delivery systems, including image guidance, robotic stage motion, and treatment planning systems. However, physics expertise and resources are scarcer in radiation biology, which makes implementation of conventional prescriptive QA infeasible. In this study, we apply the failure modes and effect analysis (FMEA) popularized by the AAPM task group 100 (TG-100) report to IGSAI and radiation biological research. Methods: Radiation biological research requires a change in paradigm where small errors to large populations of animals are more severe than grievous errors that only affect individuals. To this end, we created a new adverse effects severity table adapted to radiation biology research based on the original AAPM TG-100 severity table. We also produced a process tree which outlines the main components of radiation biology studies performed on an IGSAI, adapted from the original clinical IMRT process tree from TG-100.Using this process tree, we created and distributed a preliminary survey to eight expert IGSAI operators in four institutions. Operators rated proposed failure modes for occurrence, severity, and lack of detectability, and were invited to share their own experienced failure modes. Risk probability numbers (RPN) were calculated and used to identify the failure modes which most urgently require intervention. Results: Surveyed operators indicated a number of high (RPN >125) failure modes specific to small animal irradiators. Errors due to equipment breakdown, such as loss of anesthesia or thermal control, received relatively low RPN (12-48) while errors related to the delivery of radiation dose received relatively high . Errors identified could either be improved by manufacturer intervention (e.g., electronic interlocks for filter/collimator) or physics oversight (errors related to tube calibration or treatment planning system commissioning). Operators identified a number of failure modes including collision between the collimator and the stage, misalignment between imaging and treatment isocenter, inaccurate robotic stage homing/translation, and incorrect SSD applied to hand calculations. These were all relatively highly rated , indicating a possible bias in operators towards reporting high RPN failure modes. Conclusions: The first FMEA specific to radiation biology research was applied to image-guided small animal irradiators following the TG-100 methodology. A new adverse effects severity table and a process tree recognizing the need for a new paradigm were produced, which will be of great use to future investigators wishing to pursue FMEA in radiation biology research. Future work will focus on expanding scope of user surveys to users of all commercial IGSAI and collaborating with manufacturers to increase the breadth of surveyed expert operato...

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Experimental validation of a kilovoltage x‐ray source model for computing imaging dose

Cited by 17 publications

References 36 publications

Experimental validation of a kV source model and dose computation method for CBCT imaging in an anthropomorphic phantom

Experimental validation of a kV source model and dose computation method for CBCT imaging in an anthropomorphic phantom

Direct and fast measurement of CT beam filter profiles with simultaneous geometrical calibration

A failure modes and effects analysis quality management framework for image‐guided small animal irradiators: A change in paradigm for radiation biology

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