I am an assistant professor in the Department of Human Oncology with primary roles in the clinic and research. In the clinic, I focus primarily on the clinical applications of the Siemens Somatom Definition Edge Dual Energy CT scanner. This includes preparation of the CT simulator for clinical use, ongoing quality assurance, implementation of motion management techniques, such as respiratory gating and 4DCT acquisitions, and the use of dual-energy scans to produce images with higher contrast.
My research has been primarily focused on expanding the clinical use of our dual-energy CT (DECT) simulation techniques to provide better options for our physicians to visualize certain tissues. In particular, I am investigating the use of DECT scans to better visualize and delineate bone marrow and bone lesions to provide more information to the physicians during contouring.
PhD, University of Wisconsin–Madison, Medical Physics (2016)
MS, University of Wisconsin–Madison, Medical Physics (2012)
BS, Boston College, Physics (2010)
Assistant Professor, Human Oncology (2016)
Selected Honors and Awards
Scholar Athlete Award, Boston College (2010)
Phi Beta Kappa Honor Society (2010)
Thomas McElroy Memorial Scholarship Recipient (2009)
Dean's Scholar Award, Boston College (2009)
Boards, Advisory Committees and Professional Organizations
UW Accredited Dosimetry Calibration Laboratory Advisory Board Member (2017-pres.)
American Association of Physicists in Medicine (2010-pres.)
UW Medical Radiation Research Center Research Oversight Committee Member (2013-2016)
Imaging, Radiation Measurements, Motion Management, Clinical Use of Dual Energy CT (DECT) Simulation Techniques
Dr. Michael Lawless focuses primarily on the clinical applications of the Siemens Somatom Definition Edge Dual Energy CT scanner. This includes preparation of the CT simulator for clinical use, ongoing quality assurance, implementation of motion management techniques and the use of dual-energy scans to produce images with higher contrast.
High-quality imaging lays an important foundation for a radiation oncology clinic and can aid in other aspects of the treatment delivery process.
The imaging systems in a radiation oncology department can be used for much more than a simple treatment planning aid. In my research, I hope to leverage the tools available in our clinic to produce higher quality treatments for our patients.
Dual Energy Computed Tomography for Bone Delineation
Using the tools available to us as a part of the Siemens Somatom Definition Edge Dual Energy CT (DECT) scanner, we have the ability to better visualize tissues that are historically difficult to differentiate. With this technology, we are working toward being able to delineate the red and yellow bone marrow present near a patient’s treatment site. Additionally, we are investigating the radiation response of bone marrow to doses in the therapeutic range, so as to be able to predict any effect on a patient’s hematopoetic system. Through the creation of virtual non-calcium images, we can better visualize abnormalities within bony structures, which will increase the visibility of bone lesions. The research project is founded in optimizing the algorithm parameters for our purposes and leveraging the system to perform optimally for these purposes.
Cone Beam Computed Tomography Dose Investigation
The dose from pre-treatment cone beam computed tomography scans has been investigated extensively, but most assessments focus on the in-field dose. In certain instances, such as the treatment of pregnant patients, the out-of-field dose from imaging procedures could contribute a significant dose to areas of concern (such as the fetus). Measuring this dose can prove difficult, and this research will investigate which radiation detectors can and should be used for these purposes and how to calibrate them. The dose information gathered from this investigation will be used to inform decisions on imaging protocols for clinical patients.
Targeting the GTV in medically inoperable endometrial cancer using brachytherapy Brachytherapy
Merfeld EC, Kuczmarska-Haas A, Burr AR, Witt JS, Francis DM, Ntambi J, Desai VK, Huang JY, Miller JR, Lawless MJ, Wallace CR, Anderson BM, Bradley KA
2022 Nov-Dec;21(6):792-798. doi: 10.1016/j.brachy.2022.07.006. Epub 2022 Aug 24.
PURPOSE: We aimed to determine the relationship between gross tumor volume (GTV) dose and tumor control in women with medically inoperable endometrial cancer, and to demonstrate the feasibility of targeting a GTV-focused volume using imaged-guided brachytherapy.
METHODS AND MATERIALS: An endometrial cancer database was used to identify patients. Treatment plans were reviewed to determine doses to GTV, clinical target volume (CTV), and OARs. Uterine recurrence-free survival was evaluated as a function of CTV and GTV doses. Brachytherapy was replanned with a goal of GTV D98 EQD2 ≥ 80 Gy, without regard for coverage of the uninvolved uterus and while respecting OAR dose constraints.
RESULTS: Fifty-four patients were identified. In the delivered plans, GTV D90 EQD2 ≥ 80 Gy was achieved in 36 (81.8%) patients. Uterine recurrence-free survival was 100% in patients with GTV D90 EQD2 ≥ 80 Gy and 66.7% in patients with EQD2 < 80 Gy (p = 0.001). On GTV-only replans, GTV D98 EQD2 ≥ 80 Gy was achieved in 39 (88.6%) patients. Mean D2cc was lower for bladder (47.1 Gy vs. 73.0 Gy, p < 0.001), and sigmoid (47.0 Gy vs. 58.0 Gy, p = 0.007) on GTV-only replans compared to delivered plans. Bladder D2cc was ≥ 80 Gy in 11 (25.0%) delivered plans and four (9.1%) GTV-only replans (p = 0.043). Sigmoid D2cc was ≥ 65 Gy in 20 (45.4%) delivered plans and 10 (22.7%) GTV-only replans (p = 0.021).
CONCLUSIONS: OAR dose constraints should be prioritized over CTV coverage if GTV coverage is sufficient. Prospective evaluation of image-guided brachytherapy to a reduced, GTV-focused volume is warranted.
PMID:36030167 | DOI:10.1016/j.brachy.2022.07.006
View details for PubMedID 36030167
Characterization of size-specific effects during dual-energy CT material decomposition of non-iodine materials Journal of applied clinical medical physics
Miller J, DiMaso L, Huang-Vredevoogd J, Shah J, Lawless M
2021 Dec;22(12):168-176. doi: 10.1002/acm2.13471. Epub 2021 Nov 16.
PURPOSE: The dual-energy CT (DECT) LiverVNC application class in the Siemens Syngo.via software has been used to perform non-iodine material decompositions. However, the LiverVNC application is designed with an optional size-specific calibration based on iodine measurements. This work investigates the effects of this iodine-based size-specific calibration on non-iodine material decomposition and benchmarks alternative methods for size-specific calibrations.
METHODS: Calcium quantification was performed with split-filter and sequential-scanning DECT techniques on the Siemens SOMATOM Definition Edge CT scanner. Images were acquired of the Gammex MECT abdomen and head phantom containing calcium inserts with concentrations ranging from 50-300 mgCa/ml. Several workflows were explored investigating the effects of size-specific dual-energy ratios (DERs) and the beam hardening correction (BHC) function in the LiverVNC application. Effects of image noise were also investigated by varying CTDIvol and using iterative reconstruction (ADMIRE).
RESULTS: With the default BHC activated, Syngo.via underestimated the calcium concentrations in the abdomen for sequential-scanning acquisitions, leaving residual calcium in the virtual non-contrast images and underestimating calcium in the enhancement images for all DERs. Activation of the BHC with split-filter images resulted in a calcium over- or underestimation depending on the DER. With the BHC inactivated, the use of a single DER led to an under- or overestimate of calcium concentration depending on phantom size and DECT modality. Optimal results were found with BHC inactivated using size-specific DERs. CTDIvol levels and ADMIRE had no significant effect on results.
CONCLUSION: When performing non-iodine material decomposition in the LiverVNC application class, it is important to understand the implications of the BHC function and to account for patient size appropriately. The BHC in the LiverVNC application is specific to iodine and leads to inaccurate quantification of other materials. The inaccuracies can be overcome by deactivating the BHC function and using size-specific DERs, which provided the most accurate calcium quantification.
PMID:34783427 | PMC:PMC8664138 | DOI:10.1002/acm2.13471
View details for PubMedID 34783427
Radiation-induced Hounsfield unit change correlates with dynamic CT perfusion better than 4DCT-based ventilation measures in a novel-swine model Scientific reports
Wuschner AE, Wallat EM, Flakus MJ, Shanmuganayagam D, Meudt J, Christensen GE, Reinhardt JM, Miller JR, Lawless MJ, Baschnagel AM, Bayouth JE
2021 Jun 23;11(1):13156. doi: 10.1038/s41598-021-92609-x.
To analyze radiation induced changes in Hounsfield units and determine their correlation with changes in perfusion and ventilation. Additionally, to compare the post-RT changes in human subjects to those measured in a swine model used to quantify perfusion changes and validate their use as a preclinical model. A cohort of 5 Wisconsin Miniature Swine (WMS) were studied. Additionally, 19 human subjects were recruited as part of an IRB approved clinical trial studying functional avoidance radiation therapy for lung cancer and were treated with SBRT. Imaging (a contrast enhanced dynamic perfusion CT in the swine and 4DCT in the humans) was performed prior to and post-RT. Jacobian elasticity maps were calculated on all 4DCT images. Contours were created from the isodose lines to discretize analysis into 10 Gy dose bins. B-spline deformable image registration allowed for voxel-by-voxel comparative analysis in these contours between timepoints. The WMS underwent a research course of 60 Gy in 5 fractions delivered locally to a target in the lung using an MRI-LINAC system. In the WMS subjects, the dose-bin contours were copied onto the contralateral lung, which received < 5 Gy for comparison. Changes in HU and changes in Jacobian were analyzed in these contours. Statistically significant (p < 0.05) changes in the mean HU value post-RT compared to pre-RT were observed in both the human and WMS groups at all timepoints analyzed. The HU increased linearly with dose for both groups. Strong linear correlation was observed between the changes seen in the swine and humans (Pearson coefficient > 0.97, p < 0.05) at all timepoints. Changes seen in the swine closely modeled the changes seen in the humans at 12 months post RT (slope = 0.95). Jacobian analysis showed between 30 and 60% of voxels were damaged post-RT. Perfusion analysis in the swine showed a statistically significant (p < 0.05) reduction in contrast inside the vasculature 3 months post-RT compared to pre-RT. The increases in contrast outside the vasculature was strongly correlated (Pearson Correlation 0.88) with the reduction in HU inside the vasculature but were not correlated with the changes in Jacobians. Radiation induces changes in pulmonary anatomy at 3 months post-RT, with a strong linear correlation with dose. The change in HU seen in the non-vessel lung parenchyma suggests this metric is a potential biomarker for change in perfusion. Finally, this work suggests that the WMS swine model is a promising pre-clinical model for analyzing radiation-induced changes in humans and poses several benefits over conventional swine models.
PMID:34162987 | PMC:PMC8222280 | DOI:10.1038/s41598-021-92609-x
View details for PubMedID 34162987
Evaluation of a commercial deformable image registration algorithm for dual-energy CT processing Journal of applied clinical medical physics
Huang JY, Lawless MJ, Matrosic CK, Maso DD, Miller JR
2020 Sep;21(9):227-234. doi: 10.1002/acm2.12987. Epub 2020 Jul 25.
PURPOSE: Several dual-energy computed tomography (DECT) techniques require a deformable image registration to correct for motion between the acquisition of low and high energy data. However, current DECT software does not provide tools to assess registration accuracy or allow the user to export deformed images, presenting a unique challenge for image registration quality assurance (QA). This work presents a methodology to evaluate the accuracy of DECT deformable registration and to quantify the impact of registration errors on end-product images.
METHODS: The deformable algorithm implemented in Siemen Healthineers's Syngo was evaluated using a deformable abdomen phantom and a rigid phantom to mimic sliding motion in the thorax. Both phantoms were imaged using sequential 80 and 140 kVp scans with motion applied between the two scans. Since Syngo does not allow the export of the deformed images, this study focused on quantifying the accuracy of various end-product, dual-energy images resulting from processing of deformed images.
RESULTS: The Syngo algorithm performed well for the abdomen phantom with a mean registration error of 0.4 mm for landmark analysis, Dice similarity coefficients (DSCs) > 0.90 for five organs contoured, and mean iodine concentrations within 0.2 mg/mL of values measured on static images. For rigid sliding motion, the algorithm performed poorer and resulted in noticeable registration errors toward the superior and inferior scan extents and DSCs as low as 0.41 for iodine rods imaged in the phantom. Additionally, local iodine concentration errors in areas of misregistration exceeded 3 mg/mL.
CONCLUSIONS: This work represents the first methodology for DECT image registration QA using commercial software. Our data support the clinical use of the Syngo algorithm for abdominal sites with limited motion (i.e., pancreas and liver). However, dual-energy images generated with this algorithm should be used with caution for quantitative measurements in areas with sliding motion.
PMID:32710502 | PMC:PMC7497912 | DOI:10.1002/acm2.12987
View details for PubMedID 32710502
Investigating split-filter dual-energy CT for improving liver tumor visibility for radiation therapy Journal of applied clinical medical physics
DiMaso LD, Miller JR, Lawless MJ, Bassetti MF, DeWerd LA, Huang J
2020 Aug;21(8):249-255. doi: 10.1002/acm2.12904. Epub 2020 May 15.
PURPOSE: Accurate liver tumor delineation is crucial for radiation therapy, but liver tumor volumes are difficult to visualize with conventional single-energy CT. This work investigates the use of split-filter dual-energy CT (DECT) for liver tumor visibility by quantifying contrast and contrast-to-noise ratio (CNR).
METHODS: Split-filter DECT contrast-enhanced scans of 20 liver tumors including cholangiocarcinomas, hepatocellular carcinomas, and liver metastases were acquired. Analysis was performed on the arterial and venous phases of mixed 120 kVp-equivalent images and VMIs at 57 keV and 40 keV gross target volume (GTV) contrast and CNR were calculated.
RESULTS: For the arterial phase, liver GTV contrast was 12.1 ± 10.0 HU and 43.1 ± 32.3 HU (P < 0.001) for the mixed images and 40 keV VMIs. Image noise increased on average by 116% for the 40 keV VMIs compared to the mixed images. The average CNR did not change significantly (1.6 ± 1.5, 1.7 ± 1.4, 2.4 ± 1.7 for the mixed, 57 keV and 40 keV VMIs (P > 0.141)). For individual cases, however, CNR increases of up to 607% were measured for the 40 keV VMIs compared to the mixed image. Venous phase 40 keV VMIs demonstrated an average increase of 35.4 HU in GTV contrast and 121% increase in image noise. Average CNR values were also not statistically different, but for individual cases CNR increases of up to 554% were measured for the 40 keV VMIs compared to the mixed image.
CONCLUSIONS: Liver tumor contrast was significantly improved using split-filter DECT 40 keV VMIs compared to mixed images. On average, there was no statistical difference in CNR between the mixed images and VMIs, but for individual cases, CNR was greatly increased for the 57 keV and 40 keV VMIs. Therefore, although not universally successful for our patient cohort, split-filter DECT VMIs may provide substantial gains in tumor visibility of certain liver cases for radiation therapy treatment planning.
PMID:32410336 | PMC:PMC7484851 | DOI:10.1002/acm2.12904
View details for PubMedID 32410336
Monte Carlo and <sup>60</sup> Co-based kilovoltage x-ray dosimetry methods Medical physics
Lawless MJ, Dimaso L, Palmer B, Micka J, Culberson WS, DeWerd LA
2018 Dec;45(12):5564-5576. doi: 10.1002/mp.13213. Epub 2018 Oct 31.
PURPOSE: This work seeks to investigate new methods to determine the absorbed dose to water from kilovoltage x rays. Current methods are based on measurements in air and rely on correction factors in order to account for differences between the photon spectrum in air and at depth in phantom, between the photon spectra of the calibration beam and the beam of interest, or in the radiation absorption properties of air and water. This work aims to determine the absorbed dose to water in the NIST-matched x-ray beams at the University of Wisconsin Accredited Dosimetry Calibration Laboratory (UWADCL). This will facilitate the use of detectors in terms of dose to water, which will allow for a simpler determination of dose to water in clinical kilovoltage x-ray beams.
MATERIALS AND METHODS: A model of the moderately filtered x-ray beams at the UWADCL was created using the BEAMnrc user code of the EGSnrc Monte Carlo code system. This model was validated against measurements and the dose to water per unit air kerma was calculated in a custom built water tank. Using this value and the highly precise measurement of the air kerma made by the UWADCL, the dose to water was determined in the water tank for the x-ray beams of interest. The dose to water was also determined using the formalism defined in the report of AAPM Task Group 61 and using a method that makes use of a 60 Co absorbed dose-to-water calibration coefficient and a beam quality correction factor to account for differences in beam quality between the 60 Co calibration and kilovoltage x-ray beam of interest. The dose to water values as determined by these different methods was then compared.
RESULTS: The BEAMnrc models used in this work produced simulations of transverse and depth dose profiles that agreed with measurements with a 2%/2 mm criteria gamma test. The dose to water as determined from the different methods used here agreed within 3.5% at the surface of the water tank and agreed within 1.8% at a depth of 2 cm in phantom. The dose-to-water values all agreed within the associated uncertainties of the methods used in this work. Both the Monte Carlo-based method and the 60 Co-based method had a lower uncertainty than the TG-61 methodology for all of the x-ray beams used in this work.
CONCLUSION: Two new dose determination methods were used to determine the dose to water in the NIST-matched x-ray beams at the UWADCL and they showed good agreement with previously established techniques. Due to the improved Monte Carlo calculation techniques used in this work, both of the methods have lower uncertainties compared to TG-61. The methods presented in this work compare favorably with calorimetry-based standards established at other institutions.
PMID:30273996 | DOI:10.1002/mp.13213
View details for PubMedID 30273996
Design of a modulated orthovoltage stereotactic radiosurgery system Medical physics
Fagerstrom JM, Bender ET, Lawless MJ, Culberson WS
2017 Jul;44(7):3776-3787. doi: 10.1002/mp.12336. Epub 2017 Jun 9.
PURPOSE: To achieve stereotactic radiosurgery (SRS) dose distributions with sharp gradients using orthovoltage energy fluence modulation with inverse planning optimization techniques.
METHODS: A pencil beam model was used to calculate dose distributions from an orthovoltage unit at 250 kVp. Kernels for the model were derived using Monte Carlo methods. A Genetic Algorithm search heuristic was used to optimize the spatial distribution of added tungsten filtration to achieve dose distributions with sharp dose gradients. Optimizations were performed for depths of 2.5, 5.0, and 7.5 cm, with cone sizes of 5, 6, 8, and 10 mm. In addition to the beam profiles, 4π isocentric irradiation geometries were modeled to examine dose at 0.07 mm depth, a representative skin depth, for the low energy beams. Profiles from 4π irradiations of a constant target volume, assuming maximally conformal coverage, were compared. Finally, dose deposition in bone compared to tissue in this energy range was examined.
RESULTS: Based on the results of the optimization, circularly symmetric tungsten filters were designed to modulate the orthovoltage beam across the apertures of SRS cone collimators. For each depth and cone size combination examined, the beam flatness and 80-20% and 90-10% penumbrae were calculated for both standard, open cone-collimated beams as well as for optimized, filtered beams. For all configurations tested, the modulated beam profiles had decreased penumbra widths and flatness statistics at depth. Profiles for the optimized, filtered orthovoltage beams also offered decreases in these metrics compared to measured linear accelerator cone-based SRS profiles. The dose at 0.07 mm depth in the 4π isocentric irradiation geometries was higher for the modulated beams compared to unmodulated beams; however, the modulated dose at 0.07 mm depth remained <0.025% of the central, maximum dose. The 4π profiles irradiating a constant target volume showed improved statistics for the modulated, filtered distribution compared to the standard, open cone-collimated distribution. Simulations of tissue and bone confirmed previously published results that a higher energy beam (≥ 200 keV) would be preferable, but the 250 kVp beam was chosen for this work because it is available for future measurements.
CONCLUSIONS: A methodology has been described that may be used to optimize the spatial distribution of added filtration material in an orthovoltage SRS beam to result in dose distributions with decreased flatness and penumbra statistics compared to standard open cones. This work provides the mathematical foundation for a novel, orthovoltage energy fluence-modulated SRS system.
PMID:28498612 | DOI:10.1002/mp.12336
View details for PubMedID 28498612
Response of TLD-100 in mixed fields of photons and electrons Medical physics
Lawless MJ, Junell S, Hammer C, DeWerd LA
2013 Jan;40(1):012103. doi: 10.1118/1.4773030.
PURPOSE: Thermoluminescent dosimeters (TLDs) are routinely used for dosimetric measurements of high energy photon and electron fields. However, TLD response in combined fields of photon and electron beam qualities has not been characterized. This work investigates the response of TLD-100 (LiF:Mg,Ti) to sequential irradiation by high-energy photon and electron beam qualities.
METHODS: TLDs were irradiated to a known dose by a linear accelerator with a 6 MV photon beam, a 6 MeV electron beam, and a NIST-traceable (60)Co beam. TLDs were also irradiated in a mixed field of the 6 MeV electron beam and the 6 MV photon beam. The average TLD response per unit dose of the TLDs for each linac beam quality was normalized to the average response per unit dose of the TLDs irradiated by the (60)Co beam. Irradiations were performed in water and in a Virtual Water™ phantom. The 6 MV photon beam and 6 MeV electron beam were used to create dose calibration curves relating TLD response to absorbed dose to water, which were applied to the TLDs irradiated in the mixed field.
RESULTS: TLD relative response per unit dose in the mixed field was less sensitive than the relative response in the photon field and more sensitive than the relative response in the electron field. Application of the photon dose calibration curve to the TLDs irradiated in a mixed field resulted in an underestimation of the delivered dose, while application of the electron dose calibration curve resulted in an overestimation of the dose.
CONCLUSIONS: The relative response of TLD-100 in mixed fields fell between the relative response in the photon-only and electron-only fields. TLD-100 dosimetry of mixed fields must account for this intermediate response to minimize the estimation errors associated with calibration factors obtained from a single beam quality.
PMID:23298105 | DOI:10.1118/1.4773030
View details for PubMedID 23298105
Michael Lawless, PhD600 Highland Avenue,
Madison, WI 53792-0001