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Publications (6)12.36 Total impact

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    ABSTRACT: Stereotactic body radiotherapy (SBRT) is a treatment option for patients with early stage lung cancer. Treatment duration can be >30 minutes per fraction with non-coplanar 3D-conformal radiotherapy (3D-CRT). Whilst this is generally well tolerated, faster delivery techniques are desirable. Volumetric modulated arc therapy (VMAT) allows for fast delivery of radiation treatment. The purpose of this planning study was to compare SBRT with 3D-CRT and VMAT, with VMAT plans generated using both single arc and 3 non-coplanar partial arcs. Ten patients who previously underwent SBRT (48 Gy in 4 fractions) with 3D-CRT were selected. VMAT plans were generated to treat the PTV while limiting doses to organs at risk. Cumulative dose volume histogram (DVH) parameters were compared between the 3 techniques using the Wilcoxon matched pairs test. Treatment delivery time was also assessed. Both VMAT techniques covered target volumes more conformally than 3D-CRT with a mean V48/VPTV of 1.21 for 3D-CRT, 1.03 for 3 arc plans and 1.01 for single arc plans (p = 0.005). Dose constraints to organs at risk were met using all three techniques. Mean lung doses were 2.93 Gy for 3D-CRT, 2.87 Gy for single arc and 2.73 Gy for the 3 arc technique (3-arc vs. 3D-CRT: p = 0.009). Lung V20 for 3D-CRT, 1 arc and 3 arcs were 3.24%, 2.89% and 2.73%, respectively (3 arc vs. 3D-CRT: p 5 0.028). Mean time to deliver a single fraction was 13 minutes for 3D-CRT, 9.2 minutes for 3 arcs and 5.5 minutes for 1 arc. VMAT resulted in improved conformality compared to 3D-CRT. The 3 arc technique appears to have the lowest dose to lung although the magnitude is unlikely to be clinically significant. The main advantage of VMAT over 3D-CRT is faster treatment delivery time. Shortened treatment times are anticipated to improve tolerability of this treatment and reduce the chance of error due to intra-fraction motion.
    Technology in cancer research & treatment 04/2013; · 1.94 Impact Factor
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    ABSTRACT: The purpose of this work is threefold: (1) to explore biological consequences of the multileaf collimator (MLC) calibration errors in intensity modulated radiotherapy (IMRT) of prostate and head and neck cancers, (2) to determine levels of planning target volume (PTV) and normal tissue under- or overdose flagged with clinically used QA action limits, and (3) to provide biologically based input for MLC QA and IMRT QA action limits. Ten consecutive prostate IMRT cases and ten consecutive head and neck IMRT cases were used. Systematic MLC offsets (i.e., calibration error) were introduced for each control point of the plan separately for X1 and X2 leaf banks. Offsets were from - 2 to 2 mm with a 0.5 mm increment. The modified files were imported into the planning system for forward dose recalculation. The original plan served as the reference. The generalized equivalent uniform dose (gEUD) was used as the biological index for the targets, rectum, parotid glands, brainstem, and spinal cord. Each plan was recalculated on a CT scan of a 27 cm diameter cylindrical phantom with a contoured 0.6 cc ion chamber. Dose to ion chamber and 3D gamma analysis were compared to the reference plan. QA pass criteria: (1) at least 95% of voxels with a dose cutoff of 50% of maximum dose have to pass at 3 mm/3% and (2) dose to chamber within 2% of the reference dose. For prostate cases, differences in PTV and rectum gEUD greater than 2% were identified. However, a larger proportion of plans leading to greater than 2% difference in prostate PTV gEUD passed the ion chamber QA but not 3D gamma QA. A similar trend was found for the rectum gEUD. For head and neck IMRT, the QA pass criteria flagged plans leading to greater than 4% differences in PTV gEUD and greater than 5% differences in the maximum dose to brainstem. If pass criteria were relaxed to 90% for gamma and 3% for ion chamber QA, plans leading to a 5% difference in PTV gEUD and a 5%-8% difference in brainstem maximum dose would likely pass IMRT QA. A larger proportion of head and neck plans with greater than 2% PTV gEUD difference passed 3D gamma QA compared to ion chamber QA. For low modulation plans, there is a better chance to catch MLC calibration errors with 3D gamma QA rather than ion chamber QA. Conversely, for high modulation plans, there is a better chance to catch MLC calibration errors with ion chamber QA rather than with 3D gamma QA. Ion chamber and 3D gamma analysis IMRT QA can detect greater than 2% change in gEUD for PTVs and critical structures for low modulation treatment plans. For high modulation treatment plans, ion chamber and 3D gamma analysis can detect greater than 2% change in gEUD for PTVs and a 5% change in critical structure gEUD since either QA methods passes the QA criteria. For gEUD changes less than those listed above, either QA method has the same proportion of passing rate.
    Medical Physics 04/2012; 39(4):1917-24. · 2.91 Impact Factor
  • Medical Physics 01/2011; 38(6):3583-. · 2.91 Impact Factor
  • Fuel and Energy Abstracts 01/2011; 81(2).
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    ABSTRACT: Volumetric modulated arc therapy (VMAT) is a novel form of intensity-modulated radiotherapy (IMRT) optimization that allows the radiation dose to be delivered in a single gantry rotation of up to 360 degrees , using either a constant dose rate (cdr-VMAT) or variable dose rate (vdr-VMAT) during rotation. The goal of this study was to compare VMAT prostate RT plans with three-dimensional conformal RT (3D-CRT) and IMRT plans. The 3D-CRT, five-field IMRT, cdr-VMAT, and vdr-VMAT RT plans were created for 10 computed tomography data sets from patients undergoing RT for prostate cancer. The parameters evaluated included the doses to organs at risk, equivalent uniform doses, dose homogeneity and conformality, and monitor units required for delivery of a 2-Gy fraction. The IMRT and both VMAT techniques resulted in lower doses to normal critical structures than 3D-CRT plans for nearly all dosimetric endpoints analyzed. The lowest doses to organs at risk and most favorable equivalent uniform doses were achieved with vdr-VMAT, which was significantly better than IMRT for the rectal and femoral head dosimetric endpoints (p < 0.05) and significantly better than cdr-VMAT for most bladder and rectal endpoints (p < 0.05). The vdr-VMAT and cdr-VMAT plans required fewer monitor units than did the IMRT plans (relative reduction of 42% and 38%, respectively; p = 0.005) but more than for the 3D-CRT plans (p = 0.005). The IMRT and VMAT techniques achieved highly conformal treatment plans. The vdr-VMAT technique resulted in more favorable dose distributions than the IMRT or cdr-VMAT techniques, and reduced the monitor units required compared with IMRT.
    International journal of radiation oncology, biology, physics 05/2008; 72(4):996-1001. · 4.59 Impact Factor
  • International Journal of Radiation Oncology Biology Physics - INT J RADIAT ONCOL BIOL PHYS. 01/2008; 72(1).