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Mitchell Carroll, PhD

Assistant Professor (CHS)

Department of Human Oncology

Education

PhD, University of Texas MD Anderson Cancer Center, Medical Physics (2018)

MS, Texas A&M University, Nuclear Engineering (2010)

BS, Furman University, Physics (2007)

Academic Appointments

Assistant Professor, Department of Human Oncology (2019)

Selected Honors and Awards

Radiation Research Society Scholars in Training (SIT) Award (2017)

Council on Ionizing Radiation Measurements and Standards Student Grant Award (2017)

Student Research Retreat Senior Speaker Award (2016)

CIRMS Student Grant Award (2015)

CIRMS Student Grant Award (2014)

Graduate School Biomedical Sciences Student Travel Award (2011-2017)

Boards, Advisory Committees and Professional Organizations

The Council of Ionizing Radiation Measurements and Standards (CIRMS)

Radiation Research Society (RSS-Junior SIT Member)

The American Association of Physicists in Medicine (AAPM)

Young Adult Advisory Council (YAAC-Senior Member)

  • Investigation of magnetic field effects on the dose-response of 3D dosimeters for magnetic resonance - image guided radiation therapy applications. Radiother Oncol
    Lee HJ, Roed Y, Venkataraman S, Carroll M, Ibbott GS
    2017 12; 125 (3): 426-432
    • More

      BACKGROUND AND PURPOSE: The strong magnetic field of integrated magnetic resonance imaging (MRI) and radiation treatment systems influences secondary electrons resulting in changes in dose deposition in three dimensions. To fill the need for volumetric dose quality assurance, we investigated the effects of strong magnetic fields on 3D dosimeters for MR-image-guided radiation therapy (MR-IGRT) applications.

      MATERIAL AND METHODS: There are currently three main categories of 3D dosimeters, and the following were used in this study: radiochromic plastic (PRESAGE®), radiochromic gel (FOX), and polymer gel (BANG™). For the purposes of batch consistency, an electromagnet was used for same-day irradiations with and without a strong magnetic field (B0, 1.5T for PRESAGE® and FOX and 1.0T for BANG™).

      RESULTS: For PRESAGE®, the percent difference in optical signal with and without B0 was 1.5% at the spectral peak of 632nm. For FOX, the optical signal percent difference was 1.6% at 440nm and 0.5% at 585nm. For BANG™, the percent difference in R2 MR signal was 0.7%.

      CONCLUSIONS: The percent differences in responses with and without strong magnetic fields were minimal for all three 3D dosimeter systems. These 3D dosimeters therefore can be applied to MR-IGRT without requiring a correction factor.

      View details for PubMedID 28964533
  • SU-E-T-132: Investigation of Photon and Proton Overlapping Fields in PRESAGE- Dosimeters. Med Phys
    Carroll M, Ibbott G, Grant R, Adamovics J, Gillin M
    2012 Jun; 39 (6Part11): 3733
    • More

      PURPOSE: To evaluate the effects of overlapping dose volumes for varying field arrangements in two formulations of PRESAGE®: one intended for, and irradiated with, proton beams and the other photon beams.

      METHODS: For each treatment modality (photon, proton), three overlapping field setups were performed. These included a stationary dosimeter irradiated over six fractions, a dosimeter shifted laterally to the field to deliver a dose plateau in two fractions, and a dosimeter rotated on its axis to deliver a two-field (for protons) and four-field (for photons) box treatment overlapping in the center of the dosimeter. All subsequent fractions were given within ten minutes and never less than one minute apart. Two cylindrical PRESAGE® dosimeters approximately 7.5 cm in length by 7.5 cm in diameter were irradiated for each setup. The dosimeters were paired, with one dosimeter given total dose by a single fraction while the other followed one of the overlapping field setups. The dosimeters were analyzed using an optical CT scanner and exported to the CERR environment where the doses were compared between paired dosimeters.

      RESULTS: Dose profile comparisons showed relative dose agreement between paired dosimeters within 5% along the SOBP region of the proton formulation. In the case of the fractionated proton irradiation, there was an over-response while other setups resulted in under-responses. Dose agreement between the photon dosimeter treated with six fractions showed a dose under-response within 11% and never less than 5%. Future measurements will include the remaining field setups.

      CONCLUSIONS: The proton formulation of PRESAGE® showed good dose agreement between single and multiple field irradiations. While the photon formulation had slightly less agreement, additional field setup comparisons may show improved results. These results will aid future measurements of overlapping field treatment plans delivered to PRESAGE® for treatment verification for proton and photon 3D dosimetry.

      View details for PubMedID 28517122
  • SU-E-T-560: Inter- and Intra-Fraction Variations in Esophageal Dose for Lung Cancer Patients, and the Impact of Setup Technique and Treatment Modality. Med Phys
    Carroll M, Cheung J, Zhang L, Court L
    2012 Jun; 39 (6Part19): 3834
    • More

      PURPOSE: To understand the dose-response of the esophagus in photon and proton therapy, it is important to appreciate the variations in delivered dose caused by inter- and intra-fraction motion.

      METHODS: Four lung cancer patients were identified who had experienced grade 3 esophagitis during their treatment, and for whom their esophagus was close, but not encompassed by, the treatment volume. Each patient had been treated with proton therapy using 35-37 2Gy fractions, and had received weekly 4DCT imaging. IMRT plans were also created using the same treatment planning constraints. In-house image registration software was used to deform the esophagus contour from the treatment plan to each phase of the 4DCT for each weekly image set. Daily setup using both bony and soft tissue (GTV) registration was simulated, and the treatment dose calculated for each CT image. Changes to the esophagus DVH relative to the treatment plan were quantified in terms of the relative volume of the esophagus receiving 45, 55, and 65Gy (V45, V55 and V65).

      RESULTS: For all combinations of treatment modality (photon, proton) and setup method (bony, GTV), intra-fraction motion resulted in a range of V45, V55 and V65 from 3.6 to 5.5%. Inter-fraction motion comparing daily exhale or inhale phases showed the range of V45, V55 and V65 from 8.5 to 18.6% (exhale) and 9.8 to 16.3% (inhale).

      CONCLUSIONS: Inter-fractional motion resulted in larger variations in dose delivered to the esophagus than intra-fractional motion. The inter-fraction range for V45, V55 and V65 varied by around 10% between patients. The treatment modality (photon, proton) and setup technique (bony, GTV) had minimal impact on the results.

      View details for PubMedID 28517074
  • Dynamic contrast enhanced-MRI in head and neck cancer patients: variability of the precontrast longitudinal relaxation time (T10). Med Phys
    Craciunescu O, Brizel D, Cleland E, Yoo D, Muradyan N, Carroll M, Barboriak D, MacFall J
    2010 Jun; 37 (6): 2683-92
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      PURPOSE: Calculation of the precontrast longitudinal relaxation times (T10) is an integral part of the Tofts-based pharmacokinetic (PK) analysis of dynamic contrast enhanced-magnetic resonance images. The purpose of this study was to investigate the interpatient and over time variability of T10 in head and neck primary tumors and involved nodes and to determine the median T10 for primary and nodes (T10(p,n)). The authors also looked at the implication of using voxel-based T10 values versus region of interest (ROI)-based T10 on the calculated values for vascular permeability (K(trans)) and extracellular volume fraction (v(e)).

      METHODS: Twenty head and neck cancer patients receiving concurrent chemoradiation and molecularly targeted agents on a prospective trial comprised the study population. Voxel-based T10's were generated using a gradient echo sequence on a 1.5 T MR scanner using the variable flip angle method with two flip angles [J. A. Brookes et al., "Measurement of spin-lattice relaxation times with FLASH for dynamic MRI of the breast," Br. J. Radiol. 69, 206-214 (1996)]. The voxel-based T10, K(trans), and v(e) were calculated using iCAD's (Nashua, NH) software. The mean T10's in muscle and fat ROIs were calculated (T10(m,f)). To assess reliability of ROI drawing, T10(p,n) values from ROIs delineated by 2 users (A and B) were calculated as the average of the T10's for 14 patients. For a subset of three patients, the T10 variability from baseline to end of treatment was also investigated. The K(trans) and v(e) from primary and node ROIs were calculated using voxel-based T10 values and T10(p,n) and differences reported.

      RESULTS: The calculated T10 values for fat and muscle are within the range of values reported in literature for 1.5 T, i.e., T10(m) = 0.958 s and T10(f) = 0.303 s. The average over 14 patients of the T10's based on drawings by users A and B were T10(pA) = 0.804 s, T10(nA) = 0.760 s, T10(pB) = 0.849 s, and T10(nB) = 0.810 s. The absolute percentage difference between K(trans) and v(e) calculated with voxel-based T10 versus T10(p,n) ranged from 6% to 81% and from 2% to 24%, respectively.

      CONCLUSIONS: There is a certain amount of variability in the median T10 values between patients, but the differences are not significant. There were also no statistically significant differences between the T10 values for primary and nodes at baseline and the subsequent time points (p = 0.94 Friedman test). Voxel-based T10 calculations are essential when quantitative Tofts-based PK analysis in heterogeneous tumors is needed. In the absence of T10 mapping capability, when a relative, qualitative analysis is deemed sufficient, a value of T10(p,n) = 0.800 s can be used as an estimate for T10 for both the primary tumor and the affected nodes in head and neck cancers at all the time points considered.

      View details for PubMedID 20632579

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