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At least 235 records · Page 13Linked to original sources
PubMed2003

Low-dose reduction in transformation frequency compared to unirradiated controls: the role of hyper-radiosensitivity to cell death.

Calculations based on plausible parameters taken from the existing experimental database, and new measurements on the cell cycle dependence of low-dose hyper-radiosensitivity (HRS) of non-tumorigenic HeLa x skin fibroblast human hybrid cells, provide the first experimental evidence that the selective killing of a transformation-sensitive G(2)/M-phase subpopulation as a consequence of low-dose HRS could account in part for the observed reduction of induced transformation frequencies at low doses to values below that observed spontaneously. However, it is clear that other mechanisms associated with classical adaptive response, such as induced DNA repair, are also likely to be involved.

Cell Death↗
PubMed2005

MRI-based volumetric assessment of cardiac anatomy and dose reduction via active breathing control during irradiation for left-sided breast cancer.

PURPOSE: Heart dose-volume analysis using computed tomography (CT) is limited because of motion artifact and poor delineation between myocardium and ventricular space. We used dedicated cardiac magnetic resonance imaging (MRI) to quantify exclusion of left ventricular (LV) myocardium via active breathing control (ABC) during left breast irradiation and to determine the correlation between irradiated whole heart and LV volumes. METHODS AND MATERIALS: Fifteen patients who completed adjuvant irradiation for early-stage left breast cancer participated. Treatment consisted of 45 Gy to the entire breast using ABC followed by a 16-Gy electron boost to the lumpectomy cavity. Patients underwent planning CT scans in free breathing (FB) and moderate deep inspiration breath hold (mDIBH). Electrocardiogram-gated cardiac MRI was performed in the treatment position using alpha-cradle immobilization. MRI scans were acquired in late diastole (LD), mid-diastole (MD), and systole (S) for both FB and mDIBH. After image fusion with the patients' radiation therapy planning CT scan, MRI LV volumes were defined for the three examined phases of the cardiac cycle, and comparative dose-volume analysis was performed. RESULTS: Cardiac volume definition was found to differ significantly because of combinations of respiratory and intrinsic heart motion. The fraction of LV myocardium receiving 50% (22.5 Gy) of the prescribed whole breast dose (V(22.5)) was reduced by 85.3%, 91.8%, and 94.6% via ABC for LD, MD, and S, respectively. Linear regression revealed strong correlation between MRI-defined whole heart and LV V(22.5) reduction via ABC, suggesting that LV myocardium accounts for up to approximately 50% of the excluded heart volume through this technique. Significant but weaker correlations were noted between CT-defined whole heart and LV V(22.5) reductions with marked variability in the measurements of patients with larger amounts of heart in the treatment field. CONCLUSIONS: Cardiac MRI demonstrated a significant reduction in LV myocardium irradiated with the use of ABC. The correlation between reduction in V(22.5) values for LV wall and CT-defined whole heart suggests that CT is adequate for determining which patients are likely to benefit from ABC treatment, but inaccuracies inherent to standard CT dictate that more detailed imaging studies such as MRI are required for accurate cardiotoxicity assessment.

Breast Neoplasms↗
PubMed2001

Dose reduction in evacuation proctography.

The goal of this study was to reduce the patient radiation dose from evacuation proctography. Ninety-eight consecutive adult patients referred for proctography to investigate difficult rectal evacuation were studied using a digital imaging system with either a standard digital program for barium examinations, a reduced dose digital program (both with and without additional copper filtration), or Video fluoroscopy. Dose-area products were recorded for each examination and the groups were compared. All four protocols produced technically acceptable examinations. The low-dose program with copper filtration (median dose 382 cGy cm2) and Video fluoroscopy (median dose 705 cGy cm2) were associated with significantly less dose than other groups (p < 0.0001). Patient dose during evacuation proctography can be reduced significantly without compromising the diagnostic quality of the examination. A digital program with added copper filtration conveyed the lowest dose.

Adult↗
PubMed1983

Fluoroscopic dose reduction using a digital television noise-reduction device.

A digital video image processor, connected to a video system in a conventional pediatric fluoroscopy room, was used to determine whether the device could provide satisfactory fluoroscopic images during routine examinations when the x-ray tube was operated at substantially lower than normal radiation-dose levels. A 50% reduction resulted in image quality which was indistinguishable from conventional fluoroscopic views.

Child↗
PubMed1986

Radiation dose reduction during hysterosalpingography: an application of scanning-beam digital radiography.

Hysterosalpingography was performed in 31 patients by means of a low-dose scanning-beam digital radiographic system. The technique permits adequate evaluation of gynecologic abnormalities while allowing significant reduction in radiation: 2.4-mR (6.1 X 10(-7) C/kg) exposure to the skin and 0.7-mrad (7 X 10(-6) Gy) mean dose to the ovaries per image obtained. Sixteen patients demonstrated readily recognizable and documented abnormalities, corroborated by laparoscopy, laparotomy, or other supportive evidence.

Adolescent↗
PubMed1979

Autoradiographic enhancement of mammograms. Investigation of a new dose reduction technique.

Autoradiographic image enhancement using thiourea labeled with 35S was investigated as a means of reducing dose in mammography. It was found that mammograms underexposed as much as tenfold can be autoradiographically intensified so that the enhanced image is comparable with a normal exposure. Limitations to routine use include cost, processing time, and disposal of radioactive solutions.

Breast Neoplasms↗
PubMed2002

[Clinical application of a spot filter for exposure dose reduction].

An added filter on the collimator of the X-ray tube is useful for reducing exposure dose in interventional radiology (IVR). During IVR, high-quality fluoroscopic images are needed around the target region, but the portion of the fluoroscopic image that shows catheter/guide wires need not to be of high quality. Thus, we constructed an additional filter (spot filter) consisting of a copper sheet with an open hole in the center. The spot filter is moved by a remote control technique and can be used in cases of neurological, cardiac, abdominal, and pelvic IVR. Using this filter, image quality was improved at the target region of the image intensifier, because scatter radiation was attenuated in the periphery. Although image quality was deteriorated in the periphery, there was no significant disadvantage for IVR. The spot filter would be effective in reducing exposure dose in cases where the image quality of the target region needs to be maintained and in prolonged fluoroscopy.

Filtration↗
PubMed1981

Dose reduction in the low-energy X-ray diagnostics of extremities.

The authors determined the surface absorbed dose (Ds = 67-68 mGy) and the average absorbed dose (Dav = 13-15 mGy) by means of non-screen film radiography of the extremities. The authors recommend the use of xeroradiography (with a tungsten anode tube) or, first of all, a rare-earth screen - film combination (e.g. Kodak min-R + Nuklearmedizin NMB film). The two methods permit the dose values to be decreased by a factor of about 4 and 15, respectively. The dose values are smaller, at least for the 8 cm thick tissue equivalent phantom, when a tungsten anode is used instead of a Mo anode.

Extremities↗
PubMed2005

[Current practice of pediatric MDCT in Japan: survey results of demographics and age-based dose reduction].

PURPOSE: To assess the current practice of pediatric MDCT in Japan, with particular reference to age-related dose adjustment. MATERIALS AND METHODS: During the first three months of 2004, a questionnaire was mailed to 996 institutions, among which listed MDCT users ranged from private hospitals to large university-based hospitals. RESULTS: We received responses from 348 (34.9%) institutions. Fifty-three percent of the respondents had four-detector MDCT units. Approximately 70% of examinations were head and 22% were body. Scanning parameters were determined by full-time radiologists in 40%, and by CT technologists in 28% of respondents. Eighty-nine percent (head CT) and 85% (abdominal CT) of respondents indicated that they changed parameters for children. More than 90% changed tube current for optimization. Change was based on the technologist's experience (56%, head CT; 43%, abdominal CT), and automatic exposure control has been used as a basis of mAs control in 17% of respondents for head CT and in 34% for abdominal CT. Age-related mAs settings for abdominal CT were almost the same as those published in a United States survey. CONCLUSION: Although Japan has approximately 40% of the world's CT units, optimized pediatric MDCT settings might be moved away from a fixed mA protocol as recommended by the FDA and in conformity with the ALARA (as low as reasonably achievable) concept.

Adolescent↗
PubMed1995

The potential for normal tissue dose reduction with neoadjuvant hormonal therapy in conformal treatment planning for stage C prostate cancer.

PURPOSE: Preirradiation hormonal cytoreduction of prostate cancer has been proven to reduce exposure of normal structures by decreasing the size of the target volume. Dose-volume histogram (DVH) analysis, however, does not always appear to demonstrate a strong positive benefit with the use of neoadjuvant hormone therapy. This study analyzes various other factors influencing dose to normal organs, which may determine the success or failure of neoadjuvant hormonal therapy in achieving its goals. METHODS AND MATERIALS: Patients with bulky clinical Stage C adenocarcinoma of the prostate were given 3 months of hormone treatment consisting of oral Flutamide and monthly Zoladex injections prior to irradiation. Computerized tomography (CT) scans of the pelvis were obtained both prior to and following hormonal treatment. Treatment plans were generated by three-dimensional (3D) conformal treatment planning. The change in the volume of the prostate was assessed along with the percentage of prescribed dose delivered to the rectum and bladder. Various factors such as prostate size, bladder/rectum size, and organ shape were studied. Both dose-volume histograms (DVH) and dose-surface area histograms (DSH) were used for analysis. RESULTS: Six of seven patients had reduction in the size of their prostates. The mean volumes of the prostate before and after hormonal manipulation were 129.1 +/- 32.9 standard deviation (SD) cm3 and 73.0 +/- 29.5 SD cm3, respectively (p = 0.0059). The volume of rectum receiving 80% of the prescribed dose was reduced in five of seven patients from a mean of 83.2 to 59.9 cm3 (p = 0.045). The volume of bladder receiving 80% of the prescribed dose was also reduced in five out of seven patients from a mean of 74.5 to 40.2 cm3 (p = 0.098). Correlation between the size of the prostate and volume of rectum and bladder treated was not always consistent: greater reduction in prostate size did not necessarily result in large decreases in dose to bladder or rectum. The total size of the bladder and rectum were found to be important factors in normal tissue radiation exposure; the benefits of hormone therapy may be lost if the bladder and rectum are allowed to decrease in size. Also, the bladder may be prone to sagging into the pelvis of some patients following hormone therapy, resulting in a less optimal therapeutic ratio. CONCLUSION: Reduction in prostate size by neoadjuvant hormonal manipulation does decrease the amount of normal tissue irradiated in most patients. However, the correlation between the reduction in prostate size and amount of rectum or bladder treated is not linear if other variables are not controlled. Factors such as the shape of the organs, as well as the distensible nature of the bladder and rectum, play major roles in dose to normal tissues. These facts may mask the benefits of cytoreduction and could be obstacles in realizing consistent benefits from preirradiation hormonal treatment in the clinical setting if they are ignored.

Adenocarcinoma↗
PubMed2003

Radiation dose reduction in invasive cardiology by restriction to adequate instead of optimized picture quality.

In this study, the cinegraphic image intensifier entrance dose level for coronary angiography was changed in four steps from dose level A (0.041 microGy frame(-1)), allowing high contrast, but coarse mottled background, to level D (0.164 microGy frame(-1)), affording high transparency and sharpness. Using this new approach throughout the course of 404 consecutive cardiac catheterizations, we reduced patient radiation exposures down to 11 to 16% of currently typical values: i.e., mean dose area products of 5.97 Gy cm2 (n = 91), 6.73 (n = 113), 8.11 (n = 91), and 8.90 (n = 109); cinegraphic dose area products of 2.34, 3.64, 4.56, and 5.49; and cinegraphic dose area products frame(-1) of 13.3, 19.8, 27.0, and 30.2 mGy cm2, for levels A, B, C, and D, respectively. The number of cinegraphic frames ranged within 168 to 182 per case. Our results show that during catheterization interventionalists should vary image intensifier entrance dose levels in accordance with documented structure, angulation, and body mass index. With the exception of cases with special requirements, lower dose levels typically guarantee an adequate image quality.

Aged↗
PubMed2004

High-dose, frequently administered interferon beta therapy for relapsing-remitting multiple sclerosis must be maintained over the long term: the interferon beta dose-reduction study.

Long-term trials have demonstrated the continued efficacy of interferon (IFN) beta treatment in patients with relapsing-remitting (RR) multiple sclerosis (MS) during prolonged administration. The objective of the work was to evaluate the effects of reducing IFN beta administration frequency and total weekly dose in patients with RR MS who have achieved clinical and MRI disease activity stabilization during long-term IFN beta-1b treatment. Prospective 1-year follow-up of 27 RR MS patients on long-term 250 microg every other day (standard dose) IFN beta-1b treatment were randomized either to gradually reduce dose to 30 microg once-a-week IFN beta-1a (13 patients), or to continue on IFN beta-1b standard dose (14 patients). We found significant differences in the two group of patients. In the group of patients continuously treated with IFN beta-1b standard dose, 79% remained relapse free compared to 23% in the group receiving once-weekly IFN beta-1a (p=0.006). The number of patients without new PD/T2 lesions was higher in the group of patients continuously treated with IFN beta-1b standard dose (77%) compared to the once-weekly IFN beta-1a group (23%) (p=0.04). IFN beta is a long-term treatment for MS. The reduction of IFN beta-1b administration frequency and dose is not advisable even in patients free from clinical and MRI disease activity for many years.

Adult↗
PubMed2005

CT dose reduction in children.

World wide, the number of CT studies in children and the radiation exposure by CT increases. The same energy dose has a greater biological impact in children than in adults, and scan parameters have to be adapted to the smaller diameter of the juvenile body. Based on seven rules, a practical approach to paediatric CT is shown: Justification and patient preparation are important steps before scanning, and they differ from the preparation of adult patients. The subsequent choice of scan parameters aims at obtaining the minimal signal-to-noise ratio and volume coverage needed in a specific medical situation; exposure can be divided in two aspects: the CT dose index determining energy deposition per rotation and the dose-length product (DLP) determining the volume dose. DLP closely parallels the effective dose, the best parameter of the biological impact. Modern scanners offer dose modulation to locally minimise exposure while maintaining image quality. Beyond the selection of the physical parameters, the dose can be kept low by scanning the minimal length of the body and by avoiding any non-qualified repeated scanning of parts of the body. Following these rules, paediatric CT examinations of good quality can be obtained at a reasonable cost of radiation exposure.

Age Factors↗
PubMed1996

Influence of dose reduction recommendations on changes in chest radiography techniques.

A previous dosimetric study on chest radiography identified ways to reduce patient entrance surface dose (ESD). This present study was designed to monitor changes that had occurred in the use of applied potential and film-screen sensitivity, after a series of recommendations were issued. The study falls into two parts: (1) an assessment of the impact of the recommendations and (2) what factors were responsible for change. Where changes had occurred, exposure factors were collected for 30 patients per tube and the mean ESD was calculated for each tube. Intercomparison (r = 0.93, p < 0.001) was made between calculated and measured (TLDs) values of mean ESD for 10 X-ray units, to ensure that the calculated values provided accurate estimates of the new mean ESDs. 89% of units previously monitored for patient ESD now use average applied potentials greater than 90 kVp and 51% are using film-screen sensitivities of 400. The mean ESD has been reduced on average by 47%, from 0.15 mGy to 0.08 mGy. It has been estimated that the annual collective dose from diagnostic radiology procedures in 30 hospitals in the West Midlands has been reduced by a value in excess of 40 man Sv. Reasons for change could be attributed to some of the following factors: (a) a knowledge of dose levels in comparison with other centres; (b) personal contact with departments; (c) feedback in terms of results and dose savings and (d) positive encouragement to make changes.

Humans↗
PubMed1981

[Surface dose reduction achieved by means of a lead glass filter in case of teletherapy with Co 60 radiation (author's transl)].

The surface dose of irradiated patients can be reduced by the insertion of a lead glass filter with a thickness of 4 mm at the ray emergence point of a Co 60 gammatron. The lead glass which is made stable against color alterations by radiation, will absorb the secondary electrons produced by the gamma radiation at the collimator and shutter system of the gammatron. The filter allows to reduce the surface dose in a tissue depth of 0,05 to 0,1 mm by a maximum rate of 16% according to the size of the irradiation field. Measurements were taken with a soft radiation chamber in several tissue depths within and outside the field using three different filtering methods (without any filter, 1 mm plexiglas, 4 mm lead glass). There are essential advantages for teletherapy of deep tumors by the use of a lead glass filter, so that the insertion of such a filter is recommended for all Co 60 units.

Cobalt Radioisotopes↗