Biomedical subjects

G P Glasgow

Publications and source records attributed to G P Glasgow.

At least 19 recordsLinked to original sources

PubMed2000

Elimination of field size dependence of enhanced dynamic wedge factors.

Enhanced dynamic wedge factors (EDWF) are characterized by a strong field size dependence. In contrast to physical wedge factors, the EDWF decrease as the field size is increased: for 6 MV 60 degrees wedge, the EDWF decreases by 50% when the field size is increased from 4 x 4 cm2 to 20 x 20 cm2. A method that eliminates the field size dependence of EDWF was developed and investigated in this work. In this method, the wedged field shape is determined by a multileaf collimator. The initial position of the moving Y jaw is determined by the field size and the stationary Y jaw is kept fixed at 10 cm for field sizes < or = 20 cm in the wedged direction. For all other fields, the stationary Y jaw setting is determined by the field size. The modified method results in EDWF that are independent of field size, with no change in the wedge dose distribution when compared with the conventional use of EDW.

Models, Statistical↗

PubMed1999

Effect of metal reconstruction plates on cobalt-60 dose distribution: a predictive formula and clinical implications.

PURPOSE: We sought to create a predictive formula for the dose perturbations caused by head and neck reconstruction plates in the delivery of postoperative radiotherapy with 60Co beams. MATERIALS AND METHODS: The dose perturbation effects of Vitallium and Titanium reconstruction plates and flat metal plates of aluminum (13Al), stainless steel (26Fe), tin (50Sn) and lead (82Pb) irradiated with a 60Co beam were measured in polystyrene phantoms using a film dosimetry system. We then used these results to create formulas to predict the effect of a metal reconstruction plate dependent upon its effective atomic number. RESULTS: Percentage dose increases secondary to back scattering were 10% at 1 mm in front of the Vitallium plate and 40% at the plate while the percentage dose decrease was 29% at the plate and 10% 1 mm behind the plate. For the Titanium plate, the percentage dose increase was 5% at 1 mm in front the plate and 25% at the plate while the percentage dose decrease was 20% at the plate and 5% 1 mm behind the plate. For flat plates the percentage dose increases and decreases, respectively, at the plate surfaces were: 13Al (8%, 6%), 26Fe (35%, 16%), 50Sn (60%, 24%), and 82Pb (85%, 13%). A second order polynomial predicting the back scatter and shadowing effects was created, Y = a + bZ + cZ2, where Z is the effective atomic number of the plate while a, b, and c are the following constants: for back scatter a = 0.854 +/- 0.082, b = 0.0212 +/- 0.0044, c = -0.00011 +/- 0.00004 and for shadowing a = 1.108 +/- 0.021, b = -0.0141 +/- 0.0011, c = 0.00014 +/- 0.00001. CONCLUSIONS: It is possible to predict the effect of a metal reconstruction plate upon the delivered postoperative radiotherapy dose. The dose perturbations around the plate only exist for a few millimeters, but this is substantially greater than the thickness of a normal tissue or tumor cell. Perhaps a coating of a low effective atomic number, biologically inert, substance might allow for greater dose homogeneity and decrease the risks of plate failure or tumor recurrence.

Bone Plates↗

PubMed1998

Technique charts for Kodak's new film-screen systems for portal localization.

In July 1996, Kodak released new film-screen systems with enhanced contrast (EC) for portal localization with megavoltage therapeutic beams. This study presents the generation of general-purpose technique charts for Kodak's new film-screen combinations: the Enhanced-Contrast localization (EC-L) film in EC-L cassette and the EC-L film in fast ECL (fECL) cassette for use with cobalt-60, 6 MV, 10 MV, and 18 MV beams. These technique charts were based on the assumption that a film with an optical density (OD) of 1.8 provides the best viewing density. The doses to produce such as OD, Dexp, were obtained from the H & D curves and were 1.5, 1.6, 1.7, and 1.8 cGy for cobalt-60, 6 MV, 10 MV, and 18 MV beams, respectively, with the EC-L-film + EC-L-cassette combination. The corresponding values were 1.3, 1.3, 1.3, and 1.4 cGy, respectively, for the above four beams with the EC-L-film + fEC-L-cassette combination. The dose to the film is assumed to be proportional to the calibrated dose rate (D0), field size factor (FSF), inverse square factor relative to 100.0 cm (INV), and the transmission factor through the patient, which is equal to e-uT, where u is the broad beam attenuation coefficient and T is the patient thickness. With the above assumptions, the exposure time or monitor unit, t, is then calculated from the following equation: t = Dexp/(D0*FSF*INV*e-uT). For an average port size of 15 x 15 cm, the attenuation coefficients were obtained from the fitting of TAR (cobalt-60) or TMR (6 MV, 10 MV, and 18 MV) as a function of depth from 10 to 30 cm and were 0.0564 cm-1, 0.03714 cm-1, and 0.02271 cm-1 for cobalt-60, 6 MV, 10 MV, and 18 MV beams, respectively. The FSF were explicitly obtained from the clinical physics data books and were 1.028, 1.032, 1.036, and 1.053 for cobalt-60, 6 MV, 10 MV, and 18 MV, respectively. For cobalt-60 beam, the D0 was assumed to be 100.0 cGy/min. For the 6 MV, 10 MV, and 18 MV beams, the D0 in cGy per monitor unit is 1.030, 1.051, and 1.061, respectively. Technique charts were then generated as a function of patient thickness from 10 to 45 cm for filming distance from 110 to 140 cm for all four beams. These technique charts can be easily customized to portal localization practices in a radiation therapy department.

Film Dosimetry↗

PubMed1998

High dose-rate brachytherapy treatment delivery: report of the AAPM Radiation Therapy Committee Task Group No. 59.

The goals of this task group are to examine the current high dose-rate (HDR) treatment delivery practices and to prepare a document to assure safe delivery of HDR treatments. The document consists of detailed HDR procedures for design of an HDR brachytherapy program, staffing and training, treatment specific quality assurance, and emergency procedures. The document provides an extensive quality assurance (QA) check list. It reviews all aspects of HDR treatment delivery safety, including prescription, treatment plan, treatment delivery, and radiation safety.

Brachytherapy↗

PubMed1995

Output factors for irregularly shaped electron fields.

It is necessary to know the output factors (dose per monitor unit at depth of maximum) for irregularly shaped electron beam fields to accurately deliver the prescribed dose to the target. Measuring the output factors for individually shaped electron beam fields for each patient is inconvenient. Using the measured output factors for two square fields, one can obtain the output factor for an irregular shaped electron portal with area intermediate between the areas of the two square fields, by obtaining the equivalent square area (as with photons) of the irregularly shaped field, and then interpolating between the output factors of the two square field areas to obtain the output factor for the irregularly shaped field. This empirical method offers a simple, practical solution. The accuracy of the method is about 1% to 2%, depending on the shape and size of the irregularly shaped electron field.

Humans↗

PubMed1995

Installation of 60Co 100 cm source-to-axis distance teletherapy units in vaults designed for 80-cm units.

60Co teletherapy units featuring 100 cm source-to-axis distances and with nominal source activities of 481 TBq (13,000 Ci) are available as replacements for older model 80 cm source-to-axis teletherapy units that generally have source activities of less than 370 TBq (10,000 Ci). We have redesigned and renovated two vaults--one of which required supplemental shielding--designed for older 80 cm source-to-axis units with 333 TBq (9,000 Ci) sources and installed modern 100 cm source-to-axis units with 481 TBq (13,000 Ci) sources. Renovation costs (in 1991 U.S. dollars) were about $40,000 and $160,000; the latter, including shielding costs, was about two-thirds of projected costs for installation of a 6 MV electron beam linear accelerator (linac). We have designed the treatment heads of these 100 cm 60Co units to accept the secondary field shaping blocks used on 100 cm source-to-axis linacs, allowing the 60Co units to be used as emergency back-up units for linacs when they are inoperable.

Cobalt Radioisotopes↗

PubMed1995

Radiation design and control features of a hospital room for a low dose rate remote afterloading unit.

We have renovated, and used for four years, a small 3.4 m x 4.3 m conventional patient second floor hospital room to accommodate a low dose rate remote afterloading unit containing 13 GBq (0.35 Ci) of 137Cs. Supplemental room shielding consists of a power assisted door (536 kg, 1.7 cm thickness of lead), 1.3 cm lead wall shielding at selected wall locations and on a projector shield beneath the bed, and 0.6 cm of lead over the floor above. Radiation control features consisted of a room interior radiation detector independent of the remote afterloading unit, a redundant patient/nurse communication system, a remote control system, a door interlock system to insert and retract the radioactive pellets, and a visible and audible status indicator system located at a nearby nurses' work station. Renovation costs (in 1990 dollars) were $383 per square foot; total project costs were $187,000. Nursing personnel radiation exposure was reduced from about 6 microSv (mg Ra eq)-1 (0.6 mrem (mg Ra eq)-1) to about 0.7 microSv (mg Ra eq)-1 (0.07 mrem (mg Ra eq)-1, almost a tenfold reduction.

Costs and Cost Analysis↗

PubMed1994

Patient dosimetry quality assurance program with a commercial diode system.

PURPOSE: To evaluate a commercial silicone diode dosimeter for a patient dosimetry quality assurance program. METHODS AND MATERIALS: The diode dosimeter was calibrated against an ion chamber and percentage depth dose, linearity, anisotropy, virtual source position, and field size factor studies were performed. Correction factors for lack of full scatter medium in the diode entrance and exit dose measurements were acquired. Dosimetry equations were proposed for calculation of dose delivered at isocenter. Diode dose accuracy and reproducibility were tested on phantom and on four patients. A patient dosimetry quality assurance program based on diode measured dose was instituted and patient dose data were collected. RESULTS: Diode measured percentage depth dose and field factors agreed to within 3% with those measured with an ion chamber. The diode exhibited less than 1.7% angular dose anisotropy and less than 0.5% nonlinearity up to 4 Gy. Diode dose measurements in phantom showed that the calculated doses differed from the prescribed dose by less than 1.5%; the diode exhibited a daily dose reproducibility of better than 0.2%. On four selected patients, the measured dose reproducibility was 1.5%; the average calculated doses were all within +/- 7% of the prescribed doses. For 33 of 40 patients treated with a 6 MV beam, measured doses were within +/- 7% of the prescribed doses. For 58 of 63 patients treated with an 18 MV beam, measured doses were within +/- 7% of the prescribed doses. For 11 out of 12 patients, a second repeat measurements yielded doses within +/- 7% of the prescribed doses. CONCLUSIONS: The proposed diode-based patient dosimetry quality assurance program with dose tolerance at +/- 7% is simple and feasible. It is capable of detecting certain serious treatment errors such as incorrect daily dose greater than 7%, incorrect wedge use, incorrect photon energy and patient setup errors involving some incorrect source-to-surface-distance vs. source-to-axis-distance treatments.

Anisotropy↗

PubMed1994

Beam-hardening effects of wedges on a spoiled 6 MV beam.

The beam-hardening effects of the wedges on a 6-MV spoiled beam has been studied. The beam quality of all the wedged beams was found to be the same as the open beam. The dmax also stayed unchanged for all the wedges at all field sizes. The relative wedge factors were found to reflect the beam-hardening effect, which is a function of the wedge angles, depths, and field sizes. For the 15 degrees and 30 degrees wedges, the relative wedge factor at depths less than 15 cm were found to deviate less than +2% for all fields, while those for the 45 degrees and 60 degrees wedges for the same depth range from +3% to +4%. The surface doses were found to decrease with the wedged fields. For 15 degrees, 30 degrees, and 45 degrees wedges, the decreases were found to be from 0 to -2.0%. For 60 degrees wedges, the largest deviation was found to be -2.5% for a field size of 10 cm x 10 cm at a depth of 2 mm. The wedge factors at dmax were found to depend slightly on the field sizes. The use of an averaged wedge factor for each individual wedge was found to produce less than +/- 1.2% of error for all field sizes.

Humans↗

PubMed1993

Dosimetry of a kilovoltage radiotherapy x-ray machine.

We present the percent depth doses, half-value thicknesses, exposure rates in air, dose uniformity, backscatter factors, isodose curves, and penumbra widths for 75-kVp, 100-kVp, 150-kVp, 200-kVp, and 250-kVp beams for rectangular cones (4 cm x 6 cm, 6 cm x 8 cm, and 8 cm x 10 cm) and exposure rates in air and backscatter factors for cylindrical cones (diameters 2 cm, 3 cm, and 3.5 cm) with flat and bevelled ends for the Philips RT-250 x-ray machine. Published dosimetry data specific to this machine are limited to percent depth doses and beam qualities. Rectangular cone percentage depth dose curves and beam quality agreed with published values. While measured backscatter factors for large rectangular fields generally agree with calculated and published values, smaller field backscatter factors were less than those reported by others. Monte Carlo calculations for small field backscatter factors appear more accurate than those measured.

Humans↗

PubMed1992

Field matching of electron beams using plastic wedge penumbra generators.

We describe the use of polystyrene wedges to match adjacent electron beams with improved dose uniformity. These wedges were designed to increase the penumbra width at the field junction from about 1.5 to about 3.5 cm, to achieve dose uniformity. Measurements using thermoluminescent dosimeters (TLD) and therapy localization film showed that the use of polystyrene wedges (penumbra generators) produced only a small increase (less than 3%) in the surface dose and a small increase (less than 1%) in the x-ray contamination. Without wedges at the field junction, lateral mismatching of beam edges by 2 or 3 mm may introduce high dose variations (120% or more or 50% or less). Similar 2-3 mm set-up errors did not cause more than +/- 5% dose variations when plastic wedges were used to match the fields. These wedges are particularly useful when matching fields of different beam energies or matching fields on curved surfaces, such as the chest wall.

Electrons↗

PubMed1991

The safety of low melting point bismuth/lead alloys: a review.

Low melting temperature bismuth alloys that contain about 20% to 25% lead and 10% cadmium are widely used in radiotherapy to construct shielding blocks. Since 1980, five papers have addressed questions concerning potential metal toxicity, safe shop practices, measurement of airborne vapors and metal particulates, and the results of biological testing of personnel fabricating secondary field shaping blocks. In February, 1990, the Occupational Safety and Health Administration (OSHA), proposed new occupational air concentration safety standards for cadmium and cadmium compounds. This review presents the potential toxicity of the components metals in low melting temperature bismuth lead alloys, reviews the proposed OSHA air concentrations standards, and describes proper practices of shop safety required to minimize the hazards of these metals and other potentially hazardous materials used in the block fabrication process. The review reveals that if proper practices are followed, fabrication of those blocks, including those containing cadmium, should not produce a shop environment that would produce metal toxicity in employees, and radiotherapy mold room personnel are unlikely to generate air concentrations of cadmium that exceed new proposed standards.

Alloys↗

PubMed1990

The treatment of progressive non-Hodgkin's lymphoma with intensive chemoradiotherapy and autologous marrow transplantation.

Intensive chemoradiotherapy, with or without additional local radiotherapy, and unpurged autologous marrow transplantation was given to 68 patients with progressive non-Hodgkin's lymphoma. Responses were attained in 44 patients (65%, 95% confidence intervals [CI], 52% to 76%), including 37 who achieved complete responses. Fifteen patients (22%, 95% C.I. 13% to 34%) remain free of disease (including 11 continuously) at a median of 5.3 (range 3.1 to 9.1) years later. Higher Karnofsky scores (P less than .01, Mann-Whitney U test) and the absence of a history of prior radiotherapy (P = .02, chi 2 test) were associated with achievement of complete plus partial responses. Higher Karnofsky scores (P less than .01, Mann-Whitney U test) and less resistant disease status at transplantation (P = .04, chi 2 test) were significant when calculations were limited to complete responses. Karnofsky scores were also associated with the probability of freedom from progression (P = .02, log-rank) for responding patients. Also, Karnofsky scores and the absence of prior radiotherapy (P less than .01 and P = .01, respectively, log-rank) were associated with improved survival. Progressive lymphoma was the chief cause of failure; progression usually occurred less than 6 months after transplantation, most often at the sites of active disease before the transplant. However, five patients (including four with high-grade non-Hodgkin's lymphoma) suffered hematogenous patterns of relapse; four of these five patients had no prior history of marrow involvement. Other causes of mortality included interstitial pneumonitis, sepsis, hemorrhage and renal failure. Intensive chemoradiotherapy and autologous marrow transplantation produces durable remissions in some patients with progressive non-Hodgkin's lymphoma. Since such therapy is more effective when given to patients with signs of less advanced disease, earlier treatment would be the simplest way to produce improved results. However, improved conditioning regimens will also be needed, and measures to reduce occult lymphoma stem cell contamination with the autograft may also be required to increase the likelihood of cure in some patients.

Adolescent↗

PubMed1990

A 100-cm pseudosimulation technique for 80-cm isocentric treatments.

A simulator should mimic the geometry of the treatment machine. If the geometry of the simulator does not match that of the therapy machine, true simulation of treatment could be a problem. Pseudosimulation is a simple, practical solution to this problem. We have successfully implemented this technique for over a year in our clinic for about 70 patients.

Cobalt Radioisotopes↗

PubMed1989

A total body irradiation stand for bone marrow transplant patients.

A stand designed for the immobilization of patients standing during total body irradiation (TBI) with horizontal 10 MV X rays is described. The stand reduces patient movement and facilitates the initial positioning and repositioning of patients during 11 fractions of TBI over a 3 2/3 day period. Details of design and use are presented. The stand is regularly used to treat TBI patients.

Bone Marrow Transplantation↗

PubMed1989

Treatment of progressive Hodgkin's disease with intensive chemoradiotherapy and autologous bone marrow transplantation.

Twenty-six patients with progressive Hodgkin's disease after conventional chemotherapy received intensive chemoradiotherapy and autologous bone marrow transplantation (ABMT); 19 also received additional involved-field radiotherapy. Twenty-one patients [81%, 95% confidence intervals (CI) 61% to 94%] attained complete (n = 18) or partial responses. Ten patients (38%, 95% CI 20% to 59%) are disease-free a median of 4.5 years later (range 3.5 to 7.0 years), including seven patients with continuous complete responses. The likelihood of overall response was not significantly influenced by any clinical or treatment variable examined. However, there was a trend favoring patients with higher Karnofsky scores, and higher scores were associated with attainment of complete responses (P = .06 and P = .02, respectively, Mann-Whitney U test). Both higher Karnofsky scores and shorter durations of disease before transplantation were associated with improved survival in a stepwise Cox multivariate analysis. The chief cause of failure was progression at sites previously involved with Hodgkin's disease. No patient relapsed in the marrow, and two of three patients with a history of marrow involvement with Hodgkin's disease achieved durable complete responses after transplantation. These data suggest that inadequate pretransplant conditioning, and not the reinoculation of occult tumor cells in the autologous marrow, caused most relapses. Fatal treatment-related toxicity occurred in six patients. Three patients died of idiopathic interstitial pneumonitis; each had previously received local mediastinal irradiation before intensive chemoradiotherapy. Intensive chemoradiotherapy and ABMT produces durable responses in some patients with Hodgkin's disease incurable with conventional therapy. Use of such therapies at the first sign of failure with conventional chemotherapy and development of more effective conditioning regimens should further improve results.

Adolescent↗

PubMed1986

Observations on personnel dosimetry for radiotherapy personnel operating high-energy LINACs.

A series of measurements were conducted to determine the cause of a sudden increase in personnel radiation exposures. One objective of the measurements was to determine if the increases were related to changing from film dosimeters exchanged monthly to TLD-100 dosimeters exchanged quarterly. While small increases were observed in the dose equivalents of most employees, the dose equivalents of personnel operating medical electron linear accelerators with energies greater than 20 MV doubled coincidentally with the change in the personnel dosimeter program. The measurements indicated a small thermal neutron radiation component around the accelerators operated by these personnel. This component caused the doses measured with the TLD-100 dosimeters to be overstated. Therefore, the increase in these personnel dose equivalents was not due to changes in work habits or radiation environments. Either film or TLD-700 dosimeters would be suitable for personnel monitoring around high-energy linear accelerators. The final choice would depend on economics and personal preference.

Film Dosimetry↗

PubMed1985

Radiation exposure rates near brachytherapy patients containing 137Cs sources.

For 30 brachytherapy patients, whose lateral pelvic diameters, 2r, ranged from 28 to 47 cm, and who contained activities Ac of 137Cs expressed in equivalent milligrams of 226Ra, the normalized exposure rates, X(r)/Ac, in mR h-1 (mg Ra eq)-1 at 1 m lateral from the midline of the pelvis, can be expressed by X(r)/Ac = (1.3 +/- 0.5)e-(0.07 +/- 0.02)r. Patient and applicator effects that contribute to the large uncertainties in the model coefficients are identified.

Brachytherapy↗