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ABSTRACT: Radiation in space generally produces higher dose rates than that on the Earth's surface, and contributions from primary galactic and solar events increase with altitude within the magnetosphere. Presently, no personnel monitor is available to astronauts for real-time monitoring of dose, radiation quality and regulatory risk. This group is developing a prototypic instrument for use in an unknown, time-varying radiation field. This microdosemeter-dosemeter nucleon instrument is for use in a spacesuit, spacecraft, remote rover and other applications. It provides absorbed dose, dose rate and dose equivalent in real time so that action can be taken to reduce exposure. Such a system has applications in health physics, anti-terrorism and radiation-hardening of electronics as well. The space system is described and results of ground-based studies are presented and compared with predictions of transport codes. An early prototype in 2007 was successfully launched, the only solid-state microdosemeter to have flown in space.
Radiation Protection Dosimetry 01/2011; 143(2-4):398-401. · 0.82 Impact Factor
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ABSTRACT: A model of irradiated cell survival based on rigorous accounting of microdosimetric effects is developed. The model does not assume that the distribution of lesions is Poisson and is applicable to low, intermediate and high acute doses of low or high LET radiation. For small doses, the model produces the linear-quadratic (LQ) model. However, for high doses the best-fitting LQ model grossly underestimates cell survival. The same is also true for the conventional LQ model, only more so. It is shown that for high doses, the microdosimetric distribution can be approximated by a Gaussian distribution, and the corresponding cell survival probabilities are compared.
Physics in Medicine and Biology 08/2010; 55(16):4687-702. · 2.83 Impact Factor
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ABSTRACT: Purpose: Eye plaques provide a good alternative to enucleation for ophthalmic tumors. The majority of eye plaques in the U.S. use 125I brachytherapy seeds in a Collaborative Ocular Melanoma Study (COMS) standardized design. The plaques are 3 mm thick and uncomfortable to the patients, dosimetrically having localized hot spots. Implant Sciences developed 1 mm thick 125I eye plaques using ion‐implantation techniques. Dosimetric characterization of prototype plaques using radiochromic film and a silicon diode is reported. Method and Materials: Prototype 16 mm 125I eye plaques consisted of titanium‐encapsulated hemispheric quartz substrates with an 125I layer at the inner surface, and a gold backing. Dosimetry was performed using GAFCHROMIC XR‐T and EBT film in a specially designed Solid Water “eye” phantom inserted into a 30 cm × 30 cm × 23 cm full scatter Solid Water phantom, as well as using a Scanditronix stereotactic diode in a water tank. Films were sandwiched between 1 mm thick phantom inserts perpendicular to the plaque's central axis. The diode was used for point measurements along the central axis and scans across the plaques. The films and diode were calibrated using a calibrated I‐Plant 3500 125I seed in Solid Water and water respectively, applying the TG‐43 formalism. Results: Dose distributions in planes perpendicular to the central axis of the plaques were radially isotropic and uniform. Film results, reproducible within 4%, agree well with silicon‐diode measurements. At 5 mm depth, measured dose rates are between 50 and 200 cGy/hour. Conclusion: Implant Sciences' ion‐implantation technique enables manufacturing of thin 125I eye plaques with optimal dose distributions and clinically‐useful dose rates. GAFCHROMIC film in a Solid Water phantom and the stereotactic diode in water are convenient and reproducible dosimeters for 125I eye plaque dosimetry. Conflict of Interest: Supported in part by SBIR NIH Grant 2R44CA092913‐02.
Medical Physics 05/2008; 35(6):2632-2632. · 2.83 Impact Factor
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ABSTRACT: This work provides information pertaining to the performance of Silicon-On-Insulator (SOI) microdosimeters in heavy ion radiation fields. SOI microdosimeters have been previously tested in light ion radiation fields for both space and therapeutic applications, however their response has not been established in high energy, heavy ion radiation fields which are experienced in space. Irradiations were completed at the NASA Space Radiation Laboratory at BNL using 0.6 GeV/u Fe and 1.0 GeV/u Ti ions. Energy deposition and lineal energy spectra were obtained with this device at various depths within a Lucite phantom along the central axis of the beam. The response of which was compared with existing proportional counter data to assess the applicability of SOI microdosimeters to future deployments in space missions.
IEEE Transactions on Nuclear Science 01/2008; · 1.45 Impact Factor
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ABSTRACT: Two major factors preventing the routine clinical use of finite-element analysis for image registration are: 1) the substantial labor required to construct a finite-element model for an individual patient's anatomy and 2) the difficulty of determining an appropriate set of finite-element boundary conditions. This paper addresses these issues by presenting algorithms that automatically generate a high quality hexahedral finite-element mesh and automatically calculate boundary conditions for an imaged patient. Medial shape models called m-reps are used to facilitate these tasks and reduce the effort required to apply finite-element analysis to image registration. Encouraging results are presented for the registration of CT image pairs which exhibit deformation caused by pressure from an endorectal imaging probe and deformation due to swelling.
IEEE Transactions on Medical Imaging 11/2007; · 3.64 Impact Factor
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D.L. Cutajar,
G.J. Takacs,
M.L.F. Lerch,
T. Braddock,
J.A. Bucci,
J. Brady,
L.J. Duggan,
K.E. Enari, M. Zaider,
M. Zelefsky,
A.B. Rosenfeld
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ABSTRACT: This paper presents in phantom testing of a recently developed intraoperative minidosimetry system, designed to measure the dose along the urethra during low dose rate prostate brachytherapy. This system is based on a silicon minidetector and uses spectroscopy to calculate the localized dose from the treatment radiation. The minidosimetry system was demonstrated to be operational at body temperature, with a near isotropic response to radiation at all angles. Phantom measurements have shown the minidosimetry system to measure the dose from multiple seeds to within 5% of planning system calculated doses. This system is an ideal complement to ultrasound guided seed placement in providing online direct dosimetry during seed implantation, as well as providing dose planning system verification through post implant dosimetry.
IEEE Transactions on Nuclear Science 07/2006; · 1.45 Impact Factor
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ABSTRACT: Silicon mini-semiconductor detectors are found in wide applications for in vivo personal dosimetry and dosimetry and microdosimetry of different radiation oncology modalities. These applications are based on integral and spectroscopy modes of metal oxide semiconductor field effect transistor and silicon p-n junction detectors. The advantages and limitations of each are discussed.
Radiation Protection Dosimetry 02/2006; 120(1-4):48-55. · 0.82 Impact Factor
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V L Pisacane,
J F Ziegler,
M E Nelson,
M Caylor,
D Flake,
L Heyen,
E Youngborg,
A B Rosenfeld,
F Cucinotta, M Zaider,
J F Dicello
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ABSTRACT: MIDN (MIcroDosimetry iNstrument) is a payload on the MidSTAR-I spacecraft (Midshipman Space Technology Applications Research) under development at the United States Naval Academy. MIDN is a solid-state system being designed and constructed to measure microdosimetric spectra to determine radiation quality factors for space environments. Radiation is a critical threat to the health of astronauts and to the success of missions in low-Earth orbit and space exploration. The system will consist of three separate sensors, one external to the spacecraft, one internal and one embedded in polyethylene. Design goals are mass <3 kg and power <2 W. The MidSTAR-I mission in 2006 will provide an opportunity to evaluate a preliminary version of this system. Its low power and mass makes it useful for the International Space Station and manned and unmanned interplanetary missions as a real-time system to assess and alert astronauts to enhanced radiation environments.
Radiation Protection Dosimetry 01/2006; 120(1-4):421-6. · 0.82 Impact Factor
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ABSTRACT: The microdosimetric spectra derived by silicon microdosimeter in a proton radiation field traversing heterogeneous structures were simulated using the GEANT4 toolkit.
IEEE Transactions on Nuclear Science 01/2006; · 1.45 Impact Factor
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M.I. Reinhard,
I. Cornelius,
D.A. Prokopovich,
A. Wroe,
A.B. Rosenfeld,
V. Pisacane,
J.F. Ziegler,
M.E. Nelson,
F. Cucinotta, M. Zaider,
J.F. Dicello
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ABSTRACT: The response of a solid state microdosimeter based on semiconductor on insulator (SOI) technology to a <sup>238</sup>PuBe neutron source was investigated. Simulations of the device response using the GEANT4 Monte Carlo toolkit are also presented. The microdosimetric spectra was measured for lineal energies above 1 keV/mum. The possible application of the SOI microdosimeter for radiation protection applications in the form of a personnel microdosimeter is suggested
Nuclear Science Symposium Conference Record, 2005 IEEE; 11/2005
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ABSTRACT: The need for fast, accurate and high resolution dosimetric quality assurance in radiation therapy has been outpacing the development of new and improved 2D and 3D dosimetry techniques. This paper summarizes the efforts to create a novel and potentially very fast, 3D dosimetry method based on the observation of scintillation light from an irradiated liquid scintillator volume serving simultaneously as a phantom material and as a dose detector medium. The method, named three-dimensional scintillation dosimetry (3DSD), uses visible light images of the liquid scintillator volume at multiple angles and applies a tomographic algorithm to a series of these images to reconstruct the scintillation light emission density in each voxel of the volume. It is based on the hypothesis that with careful design and data processing, one can achieve acceptable proportionality between the local light emission density and the locally absorbed dose. The method is applied to a Ru-106 eye plaque immersed in a 16.4 cm3 liquid scintillator volume and the reconstructed 3D dose map is compared along selected profiles and planes with radiochromic film and diode measurements. The comparison indicates that the 3DSD method agrees, within 25% for most points or within approximately 2 mm distance to agreement, with the relative radiochromic film and diode dose distributions in a small (approximately 4.5 mm high and approximately 12 mm diameter) volume in the unobstructed, high gradient dose region outside the edge of the plaque. For a comparison, the reproducibility of the radiochromic film results for our measurements ranges from 10 to 15% within this volume. At present, the 3DSD method is not accurate close to the edge of the plaque, and further than approximately 10 mm (<10% central axis depth dose) from the plaque surface. Improvement strategies, considered important to provide a more accurate quick check of the dose profiles in 3D for brachytherapy applicators, are discussed.
Physics in Medicine and Biology 08/2005; 50(13):3063-81. · 2.83 Impact Factor
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ABSTRACT: We report calculations of the excitonic spectra for trans-polyacetylene obtained in the Hartree–Fock, Tamm–Dancoff, and random-phase approximations. In the first case, in terms of two-particle propagator theory, the interaction between the excited electron and the hole is neglected. In the latter two cases, this interaction is considered in the first order. In this framework, the interaction between excitations of different bands and k-vectors has been included. We discuss the bandwidths and density of states for π–π*, σ–π*, π–σ*, and σ–σ* excitons. © 1993 John Wiley & Sons, Inc.
International Journal of Quantum Chemistry 10/2004; 47(2):119 - 127. · 1.36 Impact Factor
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A.B. Rosenfeld,
D. L. Cutajar,
M.L.F. Lerch,
G. J. Takacs,
J. Brady,
T. Braddock,
V. Pervertailo,
J. Bucci,
J. Kersley, M Zaider,
M. Zelefsky
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ABSTRACT: This paper reports on the development of an interactive, intraoperative dose planning system for seed implant brachytherapy in cancer treatment. This system involves in-vivo dosimetry and the ability to determine implanted seed positions. The first stage of this project is the development of a urethral alarm probe to measure the dose along the urethra during a prostate brachytherapy treatment procedure. Ultimately the system will be used to advise the physicians upon reaching a preset dose rate or dose after total seed decay in urethra during the seed placement. The second stage is the development of a method and instrumentation for in-vivo measurements of the location of implanted seeds in the same frame as for dose planning, and using these in intraoperative treatment planning. We have developed a silicon mini-detector and preamplifier/amplifier system to satisfy the spectroscopic requirements of the urethral probe. This technique will avoid complications related to overdosing the urethra and the rectum.
Nuclear Science Symposium Conference Record, 2003 IEEE; 11/2003
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ABSTRACT: This paper describes analytic tools in support of a paradigm shift in brachytherapy treatment planning for prostate cancer--a shift from standard pre-planning to intraoperative planning using dosimetric feedback based on the actual deposited seed positions within the prostate. The method proposed is guided by several desiderata: (a) bringing both planning and evaluation in the operating room (i.e. make post-implant evaluation superfluous) therefore making rectifications--if necessary--still achievable; (b) making planning and implant evaluation consistent by using the same imaging system (ultrasound); and (c) using only equipment commonly found in a hospital operating room. The intraoperative dosimetric evaluation is based on the fusion between ultrasound images and 3D seed coordinates reconstructed from fluoroscopic projections. Automatic seed detection and registration of the fluoroscopic and ultrasound information, two of the three key ingredients needed for the intraoperative dynamic dosimetry optimization (IDDO), are explained in detail. The third one, the reconstruction of 3D coordinates from projections, was reported in a previous article. The algorithms were validated using a custom-designed phantom with non-radioactive (dummy) seeds. Also, fluoroscopic images were taken at the conclusion of an actual permanent prostate implant and compared with data on the same patient obtained from radiographic-based post-implant evaluation. To offset the effect of organ motion the comparison was performed in terms of the proximity function of the two seed distributions. The agreement between the intra- and post-operative seed distributions was excellent.
Physics in Medicine and Biology 06/2003; 48(9):1153-71. · 2.83 Impact Factor
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ABSTRACT: One limitation of intraoperative planning of permanent prostate implants is that needles must already be in the gland before planning images are acquired. Improperly placed needles often restrict the capability of generating optimal seed placement. We developed guiding principles for the proper layout of needles within the treatment volume. The Memorial Sloan-Kettering Cancer Center planning system employs a genetic algorithm to find the optimal seed implantation pattern consistent with pre-assigned constraints (needle geometry, uniformity, conformity and the avoidance of high doses to urethra and rectum). Ultrasound volumes for twelve patients with 1-125 implants were used to generate six plans per patient (total 72 plans) with different needle arrangements. The plans were evaluated in terms of V100 (percentage prostate volume receiving at least the prescription dose), U135 (percentage urethra volume receiving at least 135% of prescription dose), and CI (conformity index, the ratio of treatment volume to prescription dose volume.) The method termed POSTCTR, in which needles were placed on the periphery of the largest ultrasound slice and posterior central needles were placed as needed, consistently gave superior results for all prostate sizes. Another arrangement, labelled POSTLAT, where the needles were placed peripherally with additional needles in the posterior lateral lobes, also gave satisfactory results. We advocate two needle arrangements, POSTCTR and POSTLAT, with the former giving better results.
Physics in Medicine and Biology 09/2002; 47(16):N209-15. · 2.83 Impact Factor
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ABSTRACT: In brachytherapy implants, the accuracy of dose calculation depends on the ability to localize radioactive sources correctly. If performed manually using planar images, this is a time-consuming and often error-prone process-primarily because each seed must be identified on (at least) two films. In principle, three films should allow automatic seed identification and position reconstruction; however, practical implementation of the numerous algorithms proposed so far appears to have only limited reliability. The motivation behind this work is to create a fast and reliable system for real-time implant evaluation using digital planar images obtained from radiotherapy simulators, or mobile x-ray/fluoroscopy systems. We have developed algorithms and code for 3D seed coordinate reconstruction. The input consists of projections of seed positions in each of three isocentric images taken at arbitrary angles. The method proposed here consists of a set of heuristic rules (in a sense, a learning algorithm) that attempts to minimize seed misclassifications. In the clinic, this means that the system must be impervious to errors resulting from patient motion as well as from finite tolerances accepted in equipment settings. The software program was tested with simulated data, a pelvic phantom and patient data. One hundred and twenty permanent prostate implants were examined (105 125I and 15 103Pd) with the number of seeds ranging from 35 to 138 (average 79). The mean distance between actual and reconstructed seed positions is in the range 0.03-0.11 cm. On a Pentium III computer at 600 MHz the reconstruction process takes 10-30 s. The total number of seeds is independently validated. The process is robust and able to account for errors introduced in the clinic.
Physics in Medicine and Biology 07/2002; 47(12):2031-48. · 2.83 Impact Factor
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ABSTRACT: A report of recent developments in silicon microdosimetry is presented. SOI based microdosemeters have shown promise as a viable alternative to traditional tissue-equivalent proportional counters. The application of these silicon microdosemeters to such radiation therapy modalities as boron neutron capture therapy (BNCT), boron neutron capture synovectomy (BNCS), proton therapy (PT), and fast neutron therapy (FNT) has been performed. Several shortcomings of the current silicon microdosemeter were identified and will be taken into account in the design of a second-generation device.
Radiation Protection Dosimetry 02/2002; 101(1-4):431-4. · 0.82 Impact Factor
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ABSTRACT: This paper explores the applicability of a mechanistic survival model, based on the distribution of clonogens surviving a course of fractionated radiation therapy, to clinical data on patients with prostate cancer. The study was carried out using data on 1,100 patients with clinically localized prostate cancer who were treated with three-dimensional conformal radiation therapy. The patients were stratified by radiation dose (group 1: <67.5 Gy; group 2: 67.5-72.5 Gy; group 3: 72.5-77.5 Gy; group 4: 77.5-87.5 Gy) and prognosis category (favourable, intermediate and unfavourable as defined by pre-treatment PSA and Gleason score). A relapse was recorded when tumour recurrence was diagnosed or when three successive prostate specific antigen (PSA) elevations were observed from a post-treatment nadir PSA level. PSA relapse-free survival was used as the primary end point. The model, which is based on an iterated Yule process, is specified in terms of three parameters: the mean number of tumour clonogens that survive the treatment, the mean of the progression time of post-treatment tumour development and its standard deviation. The model parameters were estimated by the maximum likelihood method. The fact that the proposed model provides an excellent description both of the survivor function and of the hazard rate is prima facie evidence of the validity of the model because closeness of the two survivor functions (empirical and model-based) does not generally imply closeness of the corresponding hazard rates. The estimated cure probabilities for the favourable group are 0.80, 0.74 and 0.87 (for dose groups 1-3, respectively); for the intermediate group: 0.25, 0.51, 0.58 and 0.78 (for dose groups 1-4, respectively) and for the unfavourable group: 0.0, 0.27, 0.33 and 0.64 (for dose groups 1-4, respectively). The distribution of progression time to tumour relapse was found to be independent of prognosis group but dependent on dose. As the dose increases the mean progression time decreases (41, 28.5, 26.2 and 14.7 months for dose groups 1-4, respectively). This analysis confirms that, in terms of cure rate, dose escalation has a significant positive effect only in the intermediate and unfavourable groups. It was found that progression time is inversely proportional to dose, which means that patients recurring in higher dose groups have shorter recurrence times, yet these groups have better survival, particularly long-term. The explanation for this seemingly illogical observation lies in the fact that less aggressive tumours, potentially recurring after a long period of time, are cured by higher doses and do not contribute to the recurrence pattern. As a result, patients in higher dose groups are less likely to recur; however, if they do, they tend to recur earlier. The estimated hazard rates for prostate cancer pass through a clear-cut maximum, thus revealing a time period with especially high values of instantaneous cancer-specific risk; the estimates appear to be nonproportional across dose strata.
Physics in Medicine and Biology 10/2001; 46(10):2745-58. · 2.83 Impact Factor
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ABSTRACT: A review of solid state microdosimetry is presented with an emphasis on silicon-based devices. The historical foundations and basics of microdosimetry are briefly provided. Various methods of experimental regional microdosimetry are discussed to facilitate a comparison with the more recent development of silicon microdosimetry. In particular, the performance characteristics of a proportional gas counter and a silicon microdosimeter are compared. Recent improvements in silicon microdosimetry address the issues of requirement specification, non-spherical shape, tissue equivalence, sensitive volume definition (charge collection complexity) and low noise requirements which have previously impeded the implementation of silicon-based microdosimetry. A prototype based on silicon-on-insulator technology is described along with some example results from clinical high LET radiotherapy facilities. A brief summary of the applications of microdosimetry is included.
Nuclear Instruments and Methods in Physics Research Section B Beam Interactions with Materials and Atoms 10/2001; 184(1-2):135-57. · 1.21 Impact Factor
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ABSTRACT: In current practice, planning for prostate brachytherapy is based on the state of the prostate at a particular instant in time. Because treatment occurs over an extended period, changes in the prostate volume (gland shrinkage) and seed displacement lead to disagreement between planned dosimetry to the prostate and the dose actually received by the prostate. Discrepancies between planned and actual dose to the rectum and urethra also occur. The purpose of this study is to investigate the possibility of defining an "effective planning volume" that compensates for changes in prostate volume and seed displacement.
Waterman's formula is used to estimate prostate shrinkage and seed displacement. The prostate volume and potential seed positions at days 0, 6, 12, 18, 24, and 30 are used in formulating time-dependent dosimetric treatment planning models. Both single-period and multi-period models are proposed and analyzed. A state-of-the-art computational engine generates unbiased, high-quality treatment plans in a matter of minutes. Plans are evaluated using coverage and conformity indices computed at specific times over a period of 30 days. The models allow dose to urethra and rectum to be strictly controlled at specific instants in time, or throughout the 30-day horizon.
For plans generated from the single-period models-based on projected prostate volumes and potential seed positions on days t = 0, 6, 12, 18, 24, 30, respectively-as t increases, the conformity index improves while the coverage worsens. In particular, the best coverage and worst conformity are achieved for the plan generated using t = 0 (day 0) information. This plan provides over 99% coverage over the entire 30-day period, and while it has initial conformity index 1.24, the conformity index climbs to 1.58 by day 30. Conversely, the worst coverage and best conformity are achieved when the plan is generated using projected information from t = 30 (day 30). Plans based on projected data at day 30 yield an initial coverage of only 84%, with conformity scores less than 1.34 over the entire 30-day period. Among the multi-period plans, with the exception of the two-period plan obtained using day 0 and projected day 6 data, the average coverage is 98% while conformity indices below 1.46 are maintained throughout the 30-day horizon. Excessive dose to the urethra and rectum is observed when only day 0 dosimetric and volumetric data are imposed in the planning procedure. In this case, by day 30, 89% of urethra volume receives dose in excess of 120% of the remaining prescription dose. Similarly, 40% of rectum volume receives dose in excess of the prescribed upper dose bound of 78% of the remaining prescription dose. When multi-period dosimetric constraints for urethra and rectum are imposed, dose to these structures is controlled throughout the 30-day period.
A planning method that takes into account prostate shrinkage and seed displacement over time can be used to adjust the balance between coverage and conformity. Incorporating projected future volumetric information is useful in providing more conformal plans, in some cases improving conformity by as much as 21% while sacrificing roughly 7% of initial coverage. Evidence of possible morbidity reduction to urethra and rectum via the use of multi-period dosimetric constraints on these structures is demonstrated. Among all plans considered, the plan obtained via the six-period model provides the best coverage and conformity over the 30-day horizon.
International Journal of Radiation OncologyBiologyPhysics 04/2001; 49(4):1197-206. · 4.11 Impact Factor
