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Wang H.,University of Houston | Vassiliev O.N.,Mary Bird Perkins Cancer Center
Physics in Medicine and Biology | Year: 2014

Models based on the amorphous track structure approximation have been successful in predicting the biological effects of heavy charged particles. Development of such models remains an active area of research that includes applications to hadrontherapy. In such models, the radial distribution of the dose deposited by delta electrons and directly by the particle is the main characteristic of track structure. We calculated these distributions with Geant4-DNA Monte Carlo code for protons in the energy range from 10 to 100 MeV. These results were approximated by a simple formula that combines the well-known inverse square distance dependence with two factors that eliminate the divergence of the radial dose integral at both small and large distances. A clear physical interpretation is given to the asymptotic behaviour of the radial dose distribution resulting from these two factors. The proposed formula agrees with the Monte Carlo data within 10% for radial distances of up to 10 μm, which corresponds to a dose range covering over eight orders of magnitude. Differences between our results and those of previously published analytical models are discussed. © 2014 Institute of Physics and Engineering in Medicine. Source

Fontenot J.D.,Mary Bird Perkins Cancer Center | Bloch C.,Washington University in St. Louis | Followill D.,University of Texas M. D. Anderson Cancer Center | Titt U.,University of Texas M. D. Anderson Cancer Center | Newhauser W.D.,University of Texas M. D. Anderson Cancer Center
Physics in Medicine and Biology | Year: 2010

Theoretical calculations have shown that proton therapy can reduce the incidence of radiation-induced secondary malignant neoplasms (SMN) compared with photon therapy for patients with prostate cancer. However, the uncertainties associated with calculations of SMN risk had not been assessed. The objective of this study was to quantify the uncertainties in projected risks of secondary cancer following contemporary proton and photon radiotherapies for prostate cancer. We performed a rigorous propagation of errors and several sensitivity tests to estimate the uncertainty in the ratio of relative risk (RRR) due to the largest contributors to the uncertainty: the radiation weighting factor for neutrons, the dose-response model for radiation carcinogenesis and interpatient variations in absorbed dose. The interval of values for the radiation weighting factor for neutrons and the dose-response model were derived from the literature, while interpatient variations in absorbed dose were taken from actual patient data. The influence of each parameter on a baseline RRR value was quantified. Our analysis revealed that the calculated RRR was insensitive to the largest contributors to the uncertainty. Uncertainties in the radiation weighting factor for neutrons, the shape of the dose-risk model and interpatient variations in therapeutic and stray doses introduced a total uncertainty of 33% to the baseline RRR calculation. © 2010 Institute of Physics and Engineering in Medicine. Source

Fontenot J.D.,Mary Bird Perkins Cancer Center
Journal of applied clinical medical physics / American College of Medical Physics | Year: 2012

Volumetric-modulated arc therapy (VMAT) is an effective but complex technique for delivering radiation therapy. VMAT relies on precise combinations of dose rate, gantry speed, and multileaf collimator (MLC) shapes to deliver intensity-modulated patterns. Such complexity warrants the development of correspondingly robust performance verification systems. In this work, we report on a remote, automated software system for daily delivery verification of VMAT treatments. The performance verification software system consists of three main components: (1) a query module for retrieving daily MLC, gantry, and jaw positions reported by the linear accelerator control system to the record and verify system; (2) an analysis module which reads the daily delivery report generated from the database query module, compares the reported treatment positions against the planned positions, and compiles delivery position error reports; and (3) a graphical reporting module which displays reports initiated by a user anywhere within the institutional network or which can be configured to alert authorized users when predefined tolerance values are exceeded. The utility of the system was investigated through analysis of patient data collected at our clinic. Nearly 2500 VMAT fractions have been analyzed with the delivery verification system at our institution. The average percentage of reported MLC leaf positions within 3 mm, gantry positions within 2°, and jaw positions within 3 mm of their planned positions was 92.9% ± 5.5%, 95.9%± 2.9%, and 99.7% ± 0.6%, respectively. The level of agreement between planned and reported MLC positions decreased for treatment plans requiring larger MLC leaf movements between control points. Differences in the reported MLC position error between the delivery verification system and data extracted manually from the control system were noted; however, the differences are likely systematic and, therefore, may be characterized if appropriately accounted for. Further investigation is needed to confirm the utility and accuracy of the system. Source

Duffin R.A.,Mary Bird Perkins Cancer Center | Feltner F.,University of Kentucky | Funderburk W.,General Surgery | Freeman H.P.,Harold P Freeman Patient Navigation Institute
Cancer | Year: 2012

BACKGROUND: The Ralph Lauren Cancer Center implemented patient navigation programs in sites across the United States building on the model pioneered by Harold P. Freeman, MD. Patient navigation targets medically underserved with the objective of reducing the time interval between an abnormal cancer finding, diagnostic resolution, and treatment initiation. In this study, the authors assessed the incremental cost effectiveness of adding patient navigation to standard cancer care in 3 community hospitals in the United States. METHODS: A decision-analytic model was used to assess the cost effectiveness of a colorectal and breast cancer patient navigation program over the period of 1 year compared with standard care. Data sources included published estimates in the literature and primary costs, aggregate patient demographics, and outcome data from 3 patient navigation programs. RESULTS: After 1 year, compared with standard care alone, it was estimated that offering patient navigation with standard care would allow an additional 78 of 959 individuals with an abnormal breast cancer screening and an additional 21 of 411 individuals with abnormal colonoscopies to reach timely diagnostic resolution. Without including medical treatment costs saved, the cost-effectiveness ratio ranged from $511 to $2080 per breast cancer diagnostic resolution achieved and from $1192 to $9708 per colorectal cancer diagnostic resolution achieved. CONCLUSIONS: The current results indicated that implementing breast or colorectal cancer patient navigation in community hospital settings in which low-income populations are served may be a cost-effective addition to standard cancer care in the United States. © 2012 American Cancer Society. Source

Jagetic L.J.,Louisiana State University | Newhauser W.D.,Louisiana State University | Newhauser W.D.,Mary Bird Perkins Cancer Center
Physics in Medicine and Biology | Year: 2015

State-of-the-art radiotherapy treatment planning systems provide reliable estimates of the therapeutic radiation but are known to underestimate or neglect the stray radiation exposures. Most commonly, stray radiation exposures are reconstructed using empirical formulas or lookup tables. The purpose of this study was to develop the basic physics of a model capable of calculating the total absorbed dose both inside and outside of the therapeutic radiation beam for external beam photon therapy. The model was developed using measurements of total absorbed dose in a water-box phantom from a 6 MV medical linear accelerator to calculate dose profiles in both the in-plane and cross-plane direction for a variety of square field sizes and depths in water. The water-box phantom facilitated development of the basic physical aspects of the model. RMS discrepancies between measured and calculated total absorbed dose values in water were less than 9.3% for all fields studied. Computation times for 10 million dose points within a homogeneous phantom were approximately 4 min. These results suggest that the basic physics of the model are sufficiently simple, fast, and accurate to serve as a foundation for a variety of clinical and research applications, some of which may require that the model be extended or simplified based on the needs of the user. A potentially important advantage of a physics-based approach is that the model is more readily adaptable to a wide variety of treatment units and treatment techniques than with empirical models. © 2015 Institute of Physics and Engineering in Medicine. Source

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