SEARCH · PubMed Health

Results for “Comparison”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 433 records · Page 24Linked to original sources

PubMed2004

Evaluation of the genotoxicity of cis-bis(3-aminoflavone)dichloroplatinum(II) in comparison with cis-DDP.

Short-term tests that detect genetic damage have provided information needed for evaluating carcinogenic risks of chemicals to man. The mutagenicity of cis-bis(3-aminoflavone)dichloroplatinum(II) (cis-[Pt(AF)2Cl2]) in comparison with cis-diamminedichloroplatinum(II) (cis-DDP) was evaluated in the standard plate-incorporation assay in four strains of Salmonella typhimurium: TA97a, TA98, TA100 and TA102, in experiments with and without metabolic activation. It was shown that cis-[Pt(AF)2Cl2] acts directly and is mutagenic for three strains of S. typhimurium: TA97a, TA98 and TA100. In comparison with cis-DDP this compound showed a weaker genotoxicity. Contrary to cis-DDP it has not shown toxic properties in the tester bacteria. The genotoxicity of both tested compounds was evaluated using chromosomal aberration, sister chromatid exchange and micronucleus assays, without and with metabolic activation, in human lymphocytes in vitro. The inhibitory effects of both compounds on mitotic activity, cell proliferation kinetics and nuclear division index were also compared. In all test systems applied, cis-[Pt(AF)2Cl2] was a less effective clastogen and a weaker inducer of both sister chromatid exchanges and micronuclei in comparison with cis-DDP, with and without metabolic activation. cis-[Pt(AF)2Cl2] has a direct mechanism of action and is less cytostatic and cytotoxic than the other compound. These results provide important data on the genotoxicity of cis-[Pt(AF)2Cl2] and indicate its beneficial properties as a potential anticancer drug, especially in comparison with cis-DDP.

Chromosome Aberrations↗

PubMed2006

Evaluation of P53 and BAX gene expression and induction of apoptosis and necrosis by the cis-Pt(II) complex of 3-aminoflavone in comparison with cis-diamminedichloroplatinum(II) (cis-DDP) in human lymphocytes.

Currently cis-diamminedichloroplatinum(II) (cis-DDP) is one of the most commonly applied compounds in chemotherapy of many types of cancer. However, a drawback is that its effectiveness presents with many side effects. Therefore, human normal lymphocytes were chosen as a model system to study cis-bis(3-aminoflavone)dichloroplatinum(II) (the cis-Pt(II) complex of 3-aminoflavone) in comparison with cis-DDP. We examined the effect of both tested compounds on cell viability and induction of apoptosis and necrosis. Trypan blue and acridine orange/ethidium bromide staining were carried out, as well as quantitative analysis of the apoptotic signal of P53 and BAX induction caused by the cis-Pt(II) complex of 3-aminoflavone in comparison with cis-DDP. cis-DDP induced a decrease of cell viability and led to a higher increase in necrosis and apoptosis than did the cis-Pt(II) complex of 3-aminoflavone. Moreover, at the molecular level cis-DDP increased P53 and BAX expression in comparison with the other tested compound. The cis-Pt(II) complex of 3-aminoflavone showed a weaker genotoxic effect in normal lymphocytes in comparison with cis-DDP, which was a stronger inducer of apoptosis and necrosis.

Apoptosis↗

PubMed2005

Empirical comparison of maximal voxel and non-isotropic adjusted cluster extent results in a voxel-based morphometry study of comorbid learning disability with schizophrenia.

We present an empirical comparison of cluster extent and maximal voxel results in a voxel-based morphometry (VBM) study of brain structure. The cluster extents are adjusted for underlying deviation from uniform smoothness. We implement this comparison on a four-group cohort that has previously shown evidence of a neuro-developmental component in schizophrenia (Moorhead, T.W.J., Job, D.E., Whalley, H.C., Sanderson, T.L., Johnstone, E.C. and Lawrie, S.M. 2004. Voxel-based morphometry of comorbid schizophrenia and learning disability: analyses in normalized and native spaces using parametric and nonparametric statistical methods. NeuroImage 22: 188-202.). We find that adjusted cluster extent results provide information on the nature of deficits that occur in the schizophrenia affected groups, and these important structural differences are not all shown in maximal voxel results. The maximal voxel and cluster extent results are corrected for multiple comparisons using Random Fields (RF) methods. In order to apply the cluster extent measures, we propose a post-hoc method for determining the primary threshold in the analysis. Unadjusted cluster extent results are reported, for these, no allowance is made for non-isotropic smoothness, and comparison with the adjusted extent results shows that the unadjusted results can be either conservative or anti-conservative depending upon the underlying tissue distributions.

Cluster Analysis↗

PubMed2004

Valid across-group comparisons with labeled scales: the gLMS versus magnitude matching.

Labeled scales are commonly used for across-group comparisons. The labels consist of adjective/adverb intensity descriptors (e.g., "very strong"). The relative distances among descriptors are essentially constant but the absolute perceived intensities they denote vary with the domain to which they are applied (e.g., a "very strong" rose odor is weaker than a "very strong" headache), as if descriptors were printed on an elastic ruler that compresses or expands to fit the domain of interest. Variation in individual experience also causes the elastic ruler to compress or expand. Taste varies genetically: supertasters perceive the most intense tastes; nontasters, the weakest; and medium tasters, intermediate tastes. Taste intensity descriptors on conventional-labeled scales denote different absolute perceived intensities to the three groups making comparisons across the groups invalid. Magnitude matching provides valid comparisons by asking subjects to express tastes relative to a standard not related to taste (e.g., supertasters match tastes to louder sounds than do nontasters). Borrowing the logic of magnitude matching, we constructed a labeled scale using descriptors unrelated to taste. We reasoned that expressing tastes on a scale labeled in terms of all sensory experience might work. We generalized an existing scale, the Labeled Magnitude Scale (LMS), by placing the label "strongest imaginable sensation of any kind" at the top. One hundred subjects rated tastes and tones using the generalized LMS (gLMS) and magnitude matching. The two methods produced similar results suggesting that the gLMS is valid for taste comparisons across nontasters, medium tasters, and supertasters.

Adult↗

PubMed2005

Comparison times are longer for hedonic than for intensity judgements of taste stimuli.

Response times of intensity and hedonic comparisons were determined in a within-subjects experimental design. Forced-choice paired comparisons of orange lemonades with various concentrations of added quinine sulfate were made by 48 subjects. Depending on experimental condition, the subjects had to focus either on intensity or on pleasantness and give their responses as fast as possible. The data showed shorter response times for intensity comparisons than for pleasantness comparisons. Although taste processing may be partially serial and partially parallel, the larger part of the response times and the differences between them may be due to cognitive processing.

Adolescent↗

PubMed1983

Behavioral and emotional factors: comparisons of anovulatory infertile women with fertile and other infertile women.

This controlled study compared behavioral and emotional factors in a group of anovulatory infertile women requesting treatment to achieve pregnancy. The sample comprised 49 women with secondary amenorrhea or oligomenorrhea in the treatment group, 141 women in the fertile comparison group, and 104 women with diagnoses other than anovulation in an infertile comparison group. Scores on the Hopkins Symptom Checklist (HSCL-90), the Eysenck Personality Inventory, the Langner Screening Scale, a Mood Analog Scale, and the Minnesota Multiphasic Personality Inventory (MMPI) were in the normal range and did not differ significantly between the groups. On other measures, the treatment group rated itself significantly less potent than to partner, mother, or father and reported more inhibited sexual attitudes than the comparison groups. Conclusions were that neurotic personality structure or psychopathology were not significantly greater in the treatment group than in the comparison groups. Whether the lower self-esteem and inhibited sexual attitudes of the treatment group resulted from or preceded infertility could not be determined.

Anovulation↗

PubMed1997

Quantitative and qualitative comparisons of spontaneous and radiation-induced specific-locus mutation in the ad-3 region of heterokaryon 12 of Neurospora crassa.

The data from forward-mutation experiments to obtain specific-locus mutations at two closely linked loci in the adenine-3 (ad-3) region of heterokaryon 12 (H-12) of Neurospora crassa have been used to determine the relative frequencies and mutational spectra of ad-3 mutants occurring spontaneously and those induced by 7 different radiation treatments. Previous studies have demonstrated that specific-locus mutants at these two loci result from 5 major genotypic classes, namely two classes of gene/point mutations (ad-3AR and ad-3BR), and 3 classes of multilocus deletion mutations ([ad-3A]IR, [ad-3B]IR and [ad-3A ad-3B]IR). Two different approaches were used to compare spontaneous mutation in the ad-3 region with that induced by 7 different radiation treatments (UV, 32P, 447 MeV protons, 85Sr, 250 kVp X-rays, 39 MeV helium ions, and 101 MeV carbon ions). These comparisons included X2-tests on the numbers of ad-3 mutants resulting in the following two sets of ratios: (1) gene/point mutations and multilocus deletion mutations; and (2) complementing and non-complementing ad-3BR mutants. Combination of the data from these two methods of comparison has demonstrated that each of the 7 radiation treatments induced a spectrum of ad-3 mutants that is statistically different from the spontaneous spectrum. In addition, these same two methods of comparison have been used to compare the mutagenic effects of each of the 7 radiation treatments with each other. Combination of the data from these two methods of comparison demonstrated that the majority of radiation-induced specific-locus mutations: (90.5% (19/21 of the pairwise combinations)) are qualitatively different from each other. We conclude that the mechanisms by which various radiations modify DNA tend to exhibit fundamental differences from each other and from the processes involved in spontaneous mutation.

Alleles↗

PubMed1998

On the interaction of numerical and size information in digit comparison: a behavioral and event-related potential study.

To investigate effects of dimensional congruity in digit comparison processes we recorded response latencies, error rates and event-related potentials (ERPs) in a situation when the relevant and the irrelevant dimension of judgement, the digit's physical size or its numerical value, varied unpredictably from trial to trial. Congruity effects may arise at early processing stages, where both numerical and size information are mapped onto a common, integrated representation. Alternatively, numerical and size information may be processed in functionally independent channels and interact only at a later stage of response activation. For both, numerical and size comparisons, reliable distance effects on ERPs (starting 224 ms post-stimulus at frontal electrode sites) and on behavioral data were observed. Congruity effects follow a timecourse that mirror-images the temporal pattern found for the distance effects: while distance effects on difference potentials start about 64 ms earlier for numerical comparisons, congruity effects due to the irrelevant attribute are seen about 88 ms earlier for size comparisons. While Lateralized Readiness Potentials (LRPs) for incongruent trials are shifted in time, there was no indication of an activation for the incorrect response in incongruent trials, as an account of congruity effects in terms of response competition would predict. The most parsimonious explanation of our results is that numerical and size information are extracted in parallel, are both converted into an integrated representation and potentially interact during these early parallel stages.

Adult↗

PubMed1996

Effective protein sequence comparison.

Although there are several different comparison programs available (e.g., BLASTP, FASTA, SSEARCH, and BLITZ) that can be used with different scoring systems (e.g., PAM120, PAM250, BLOSUM50, BLOSUM62) and different databases (e.g., PIR, SWISS-PROT, GenPept), the following search protocol should identify homologous sequences whenever they can be found. 1. Always compare protein sequences if the genes encode proteins. Protein sequence comparison will typically double the evolutionary lookback time over DNA sequence comparison. 2. Search several sequence databases using a rapid sequence comparison program (e.g., BLASTP or FASTA, ktup = 2). Well-curated databases like PIR or SWISS-PROT tend to have fewer redundant sequences, which improves the statistical significance of a match, but they are less comprehensive and up-to-date than GenPept. 3. If there is good agreement between the distribution of scores and the theoretical distribution, and the alignments do not include "simple sequence" domains, accept sequences with FASTA E() values or BLASTP P() values below 0.02 as homologous. 4. If no library sequences are found with E values below 0.02, perform additional searches with FASTA, ktup = 1, or SSEARCH. If library sequences with E values less than 0.02 are found, the sequences are probably homologous, unless a low-complexity domain is aligned. However, sequences with similarity scores from 0.02 to 10.0 may be homologous as well. To characterize these more distantly related sequences, select "marginal" library sequences and use them to search the databases. Additional family members should have E values less than 0.05. 5. Homologous sequences share a common ancestor, and thus a common protein fold. Depending on the evolutionary distance and divergence path, two or more homologous sequences may have very few absolutely conserved residues. However, if homology has been inferred between A and B, between B and C, and between C and D, A and D must be homologous, even if they share no significant similarity. 6. Sequences with marginal E values should also be tested using the PRSS program. Compare the query and library sequences using at least 200 (and preferably 1000) shuffles. Shuffles using a window (-w) of 10-20 are more stringent than a uniform shuffle. Use the E value after 1000 shuffles to confirm an inference of homology. 7. Homologous sequences are usually similar over an entire sequence or domain, typically sharing 20-25% or greater identity for more than 200 residues. Matches that are more than 50% identical in a 20- to 40-amino acid region occur frequently by chance and do not indicate homology. By following these steps, one will very rarely assert that two sequences are homologous when in fact they are not. However, these criteria are stringent; distantly related homologous sequences may fail to be detected because their similarity is not statistically significant. These tests are biased toward missing some distantly related sequences to avoid the possibility of misidentifying unrelated ones. In most database searches, the ratio of related to unrelated sequences is more than 4000:1 (e.g., 10 related and 40,000 unrelated sequences). Thus, one is more likely to mistakenly identify two sequences as related than to overlook a genuine relationship, and our conservative evaluation criteria reflect that bias.

Amino Acid Sequence↗

PubMed2000

Evaluations of child transgressions, disciplinary choices, and expected child compliance in a no-cry and a crying infant condition in physically abusive and comparison mothers.

OBJECTIVE: Several components of a social information processing model of child physical abuse were tested. Abusive and comparison mothers' evaluations of children's transgressions, choices of disciplinary techniques, expectations for children's compliance following discipline, and appraisals of the appropriateness of disciplinary choice were examined in a no-cry and a crying-infant condition. METHOD: Thirty physically abusive and 30 matched comparison mothers were individually matched on ethnic background, age, education, marital status, number of children, and cognitive ability. Mothers were asked to respond to questions related to vignettes describing children engaging in moral, conventional, and personal transgressions. RESULTS: As predicted, abusive, relative to comparison, mothers evaluated conventional and personal, but not moral, transgressions as more wrong, used more power assertion (physical and verbal force), expected less compliance from their own children, and appraised their own disciplinary responses as less appropriate. In contrast to expectations, there were no group by cry condition interaction effects on any of the study measures. CONCLUSIONS: The findings provide additional support for the view that abusive, relative to comparison, mothers are different in their evaluations and expectations of their own children's behaviors and that they more frequently select aversive disciplinary techniques. However, given the lack of an expected differential impact of a stressful condition on the cognitions and disciplinary choices in abusive mothers, additional research is needed.

Adult↗

PubMed1996

A comparison of the ventilatory responses to exercise in pregnant, postpartum, and nonpregnant women.

To evaluate the influence of pregnancy on resting and exercise pulmonary function, we studied 16 nonpregnant and 26 pregnant females in a two-phase study. During phase I, all pregnant subjects (P1) (mean gestational age = 29.5 +/- 7 weeks [X +/- SD]) were compared with 16 control (C) subjects. In phase II, 8 of the pregnant subjects (P2) (mean gestational age = 32.6 +/- 6 weeks) were evaluated again at 12.5 +/- 7 weeks' postpartum (PP). Exercise respiratory function was measured during work on a cycle ergometer during rest and at three submaximal work levels (25, 50, and 75 W), during the last minute of 5 to 7 minutes of steady-level power output. Ventilatory parameters [ventilation (VE), ventilatory frequency (VF), tidal volume (TV), ventilatory equivalent for oxygen (VE/VO2) and ventilatory equivalent for carbon dioxide (VE/VCO2)] and metabolic parameters [oxygen consumption (VO2), oxygen pulse, carbon dioxide production (VCO2), respiratory exchange ratio (RER), and plasma lactate (HLA)] were measured during the submaximal tests and throughout the progressive increase in work after the 75 W work load, until peak VO2 was achieved. The results from the phase I comparison indicated (as expected) higher resting ventilation, tidal volume, oxygen consumption, carbon dioxide production, and respiratory exchange ratio associated with pregnancy, and these findings were similar when the pregnant subjects were compared with their postpartum values. Plasma lactate levels, although similar in the phase I comparison, were significantly higher during pregnancy when compared with postpartum values. No resting differences were observed for VF, O2 pulse, VE/VO, or VE/VCO2 in either phase of the study. The results of the submaximal exercise tests indicated higher submaximal levels of VE, VF, VE/VO2, VE/VCO2 in P1 versus C; however, P2 had significantly higher VE, TV, VO2, VE/VCO2, when compared with PP. The influence of pregnancy on VCO2 and RER differed by workload in both sets of comparisons. Furthermore, no significant differences were observed between P1 and C and P2 and PP for plasma lactate levels. These findings suggest that pregnancy/control versus pregnancy/postpartum studies yield different results in both ventilatory and metabolic comparisons. Consideration must be given to the type of study when discussing and applying the findings.

Adult↗

PubMed2000

The biometrical comparison of cardiac imaging methods.

OBJECTIVES: Biometrical comparison procedures for cardiac imaging methods with continuous outcome are reviewed mainly concentrating on assessment and design adequate comparison of accuracy and precision. Univariate graphical and numerical representation of corresponding deviations is outlined to derive a 'check list' of minimum information necessary to compare the measurement methods. DATA: The methods reviewed here are illustrated by the comparison of standard 2DE bidimensional cardial volumetry versus assessment using TDE colour imaging in 28 normal probands. SOURCES: The paired t-test and the corresponding confidence interval approach are used to assess deviations in location of two imaging methods; the test procedures of Maloney and Rastogi Hahn and Nelson and Grubbs are surveyed as proposals for the comparison of precisions in paired data. The Krippendorff coefficient and the Bradley/Blackwood test are illustrated as surrogate measures for method concordance. CONCLUSIONS: Since these methods can be performed by simple modification of standard options available in most statistics software packages, this review intends to enable cardiologists to choose appropriate methods for statistical data analysis and representation on their own.

Biometry↗

PubMed1994

Familial comparison of bone mineral density at the proximal femur and lumbar spine.

Familial resemblance of bone mineral density (BMD) was studied in the lumbar spine and three regions of the proximal femur in 41 biological mother-daughter (M-D), 42 mother-son (M-S), 24 mother-grandmother (M-G) pairs and 18 mother-grandmother-daughter (M-G-D) triads. Children were placed into three maturity categories based on an assessment of secondary sex characteristics and growth velocities. Two sets of standardized BMD Z-scores were derived for the children based on either their chronological age or their maturational status. These scores were compared with maternal Z-scores derived from age-specific norms. Similar comparisons were made between the Z-scores of the mothers and grandmothers. For all three regions of the proximal femur and for the total AP lumbar spine the correlations between Z-score values were similar and significant (P < 0.05) between the M-G and M-D pairs ranging from 0.41 to 0.57. In general, the familial correlations improved when maturity-status based Z-scores were used for comparison. The absolute BMD values measured in the grandmothers and the three maturity groups of the children--expressed as a percentage of the BMD of the mothers--showed that at the neck and the trochanteric regions of the proximal femur the late-pubescent girls and boys had a significantly (P < 0.05) greater bone density than their mothers (115-123%), whereas at the AP spine these groups averaged only 88% of their mothers BMD. This site differential was not apparent when comparing the post-menopausal grandmothers with the pre-menopausal mothers (80% at both sites). Three generation comparisons demonstrated a strong familial resemblance in bone mineral density. The value of incorporating maturity-based versus chronological-based parameters for comparison with adult measures in studies that involve growing children at different stages of development was also demonstrated.

Adolescent↗

PubMed2003

The role of social support and self-esteem in the presence and course of depressive symptoms: a comparison of cancer patients and individuals from the general population.

The key focus of this longitudinal study in the Netherlands was to determine the role of social support (i.e. perceived availability of emotional support, lack of received problem-focused emotional support, and negative interactions) and positive and negative self-esteem in depressive symptoms in 475 recently diagnosed cancer patients and 255 individuals without cancer from the general population. Patients and the comparison group were interviewed and filled in a questionnaire at two points in time: 3 months (T1) and 15 months (T2) after diagnosis. The results indicated that social support and self-esteem were weakly to moderately related to each other. Negative self-esteem was more strongly related to all three types of social support, compared to positive self-esteem. Regression analyses showed that social support and self-esteem were independently related to depressive symptoms (concurrently), such that lower levels of social support and self-esteem were strongly associated with higher levels of depressive symptoms. This finding suggests that these two resources supplement each other additively. A longitudinal analysis showed that social support and self-esteem also predicted future levels of depressive symptoms, although the explained variance was much lower than in a cross-sectional analysis. Comparisons between cancer patients and the comparison group generally revealed no significant differences between the two groups in the associations of social support and self-esteem with depressive symptoms. The only exception was a lack of problem-focused emotional support. At three months after diagnosis, a lack of this type of support, characterised by reassuring, comforting, problem-solving, and advice, was more strongly related to depressive symptoms in patients than in the comparison group.

Adult↗

PubMed1999

Social comparison as a mediator of response shift.

Previous research in the domain of social comparison theory has suggested that the same factors that have been hypothesized as antecedents to response shift, primarily significant life events, also prompt an increase in interest in social comparison. Based on this research, it is suggested that social comparison, or more specifically, change in social comparison, is a mediator of the relation between significant life events and the change in self-perspective--or response shift--that they often produce. Evidence supporting this claim is reviewed and new data are presented. Finally, the implications of this mediational relation, including those relevant to the design of interventions, are discussed.

Adaptation, Psychological↗

PubMed2002

A comparison between tandem and ovoids and interstitial gynecologic template brachytherapy dosimetry using a hypothetical computer model.

PURPOSE: To evaluate the dose distribution within the clinical target volume between two gynecologic brachytherapy systems---the tandem and ovoids and the Syed-Neblett gynecologic template---using a hypothetical computer model. METHODS AND MATERIALS: Source positions of an intracavitary system (tandem and ovoids) and an interstitial system (GYN template) were digitized into the Nucletron Brachytherapy Planning System. The GYN template is composed of a 13-catheter implant (12 catheters plus a tandem) based on the Syed-Neblett gynecologic template. For the tandem and ovoids, the dwell times of all sources were evenly weighted to produce a pear-shaped isodose distribution. For the GYN template, the dwell times were determined using volume optimization. The prescribed dose was then normalized to point A in the intracavitary system and to a selected isodose line in the interstitial system. The treated volume in the two systems was kept approximately the same, and a cumulative dose-volume histogram of the treated volume was then generated with the Nucletron Brachytherapy Planning System to use for comparison. To evaluate the dose to a hypothetical target, in this case the cervix, a 2-cm-long, 3-cm-diameter cylinder centered along the tandem was digitized as the clinical target volume. The location of this hypothetical cervix was based on the optimal application of the brachytherapy system. A visual comparison of clinical target coverage by the treated volume on three different orthogonal planes through the treated volume was performed. The percentage dose-volume histograms of the target were generated for comparison. Multiple midline points were also placed at 5-mm intervals away from the tandem in the plane of the cervix to simulate the location of potential bladder and rectal dose points. Doses to these normal structures were calculated for comparison. RESULTS: Although both systems covered the hypothetical cervix adequately, the interstitial system had a better coverage of the region lateral to the cervix. Smaller volumes of the vagina and uterine fundus received the full dose from the interstitial implant. The cumulative dose-volume histograms revealed larger high-dose regions within the treatment volume for the intracavitary system. The volumes receiving > or = 180% of the prescription dose were 31 cc and 17 cc for the intracavitary system and interstitial system, respectively. The isodose lines showed that most of this difference results from the high-dose region around the tandem. The percentage dose-volume histograms showed that a larger percentage of cervix received a higher dose in the intracavitary system. Fifty-two percent of the target volume received 200% or higher of the prescription dose with tandem and ovoids, compared with only 20% with the template system. Analysis of dose points outside of the 100% isodose lines showed a slightly more rapid dose drop-off with the interstitial system compared to the intracavitary system. Point doses at 20, 25, and 30 mm from the tandem in the interstitial system were 100%, 69%, and 51% of prescribed dose, and from the intracavitary system were 101%, 76%, and 58%, respectively. CONCLUSIONS: Our dosimetric analysis revealed a better coverage in the parametrial regions, but underdosage of the central cervical region, for the interstitial system. On the other hand, because of the increased distance of source to dose point, there is a more rapid dose drop-off outside the treated volume with the interstitial system, which has the potential to improve tissue sparing. Based on this analysis, we caution against using a radiotherapy system with a homogeneous central dose distribution when treating cervical cancer with an intact uterus. We recommend differential loading of the implant catheters with the majority of dose delivered from the tandem when using an interstitial GYN template with remote afterloader.

Brachytherapy↗

PubMed1997

Comparison of miniature multileaf collimation (MMLC) with circular collimation for stereotactic treatment.

PURPOSE: A prototype Miniature Multi-Leaf Collimator (MMLC) designed specifically for radiosurgery and small field radiotherapy has been fabricated and evaluated at the University of Texas M. D. Anderson Cancer Center (UTMDACC). This work demonstrates the advantages of a computer-controlled MMLC vs. conventional circular collimation for the treatment of an irregularly shaped target volume in the brain. METHODS AND MATERIALS: Two patient treatments were selected for this comparison from 38 intracranial tumors treated with radiosurgery at UTMDACC from 8/6/91 to 5/10/94. Target contours and critical structures defined for one of the patients was used to create a simulated target volume and critical structures in a spherical head phantom. Computer simulations were performed using traditional single isocenter treatment with a circular collimator for a set of six arcs. The same arc paths were used to compute the dose distribution for the MMLC and conformed beam geometries were defined using a three-dimensional (3D) treatment planning system with beam's eye view capabilities. Then, the calculated dose distribution for a single isocenter, conformal treatment was delivered to the spherical head phantom under static conditions by shaping the MMLC to conform the target volume shape projected as a function of couch rotation and gantry angle. Planar dose distributions through the target volume were measured using therapy verification film located in the phantom. The measurements were used to verify that the 3D treatment planning system was capable of simulating the MMLC technique. For the second patient with a peanut-shaped tumor, the 3D treatment planning calculations were used to compare dose distributions for the MMLC and for traditional single and multiple isocenter treatments using circular collimators. The resulting integral dose-volume histograms (DVHs) for the target volume, normal brain, and critical structures for the three treatment techniques were compared. RESULTS: (a) Analysis of the film dosimetry data exemplified the degree of conformation of the high-dose region to the target shape that is possible with a computer-controlled MMLC. (b) Comparison of measured and calculated dose distributions indicates that the 3D treatment planning system can simulate the MMLC treatment. (c) Comparison of DVHs from the single isocenter MMLC and circular collimator treatments shows similar coverage of the target volume with increased dose to the brain for circular collimation (4). Comparison of DVHs from the single isocenter MMLC with the multiple isocenter circular collimator treatment approach shows a more inhomogeneous dose distribution through the target volume and increased dose to the brain for the latter. CONCLUSION: Dosimetry data for single isocenter treatments using computer-controlled field shaping with a MMLC demonstrate the ability to conform the dose distribution to an irregularly shaped target volume. DVHs validated that the single isocenter MMLC treatment is preferable to both single and multiple isocenter, circular collimator treatment because it provides a more uniform dose distribution to an irregularly shaped target volume and reduces the dose to surrounding brain tissue for the example cases.

Adenocarcinoma↗

PubMed1999

Comparison of calibration procedures for 192Ir high-dose-rate brachytherapy sources.

PURPOSE: To compare the efficacy of different calibration procedures for 192Ir high-dose-rate (HDR) brachytherapy sources and to determine their suitability in clinical practice. In addition the manufacturer's calibration is compared with our experimental measurements so that the accuracy of the source strength on the manufacturer certificate which is supplied with each new 192Ir source can be accessed. METHODS AND MATERIALS: We compared three types of calibration system: well-type chambers (HDR-1000 and SDS), cylindrical phantom, and plate phantom. The total number of measurements we obtained was 365. The number of sources used for the calibration procedure comparison was 20 and the number used for comparison with the manufacturer's calibration was 46. This study was made during the period 1989-1997. Also, Physikalisch-Technische Bundesanstalt (PTB) calibrated one of our sources using their PTB protocol so that the results could be compared with our own. RESULTS: The sensitivity of each system on scattering from the room walls was studied. It was found that different minimum lateral distances from the walls were required for the different systems tested: 15 cm and 25 cm for the well-type chambers, 75 cm for the cylindrical phantom, and 13 cm for the plate phantom. The minimum thickness required to reach phantom scattering saturation for the plate phantom setup is 24 cm. The influence of the applicator material used in the calibration setup was found to be 1.7% for the stainless steel dosimetry applicator compared to the plastic 5F applicator. The accuracy of source positioning within the applicator can lead to dosimetric errors of +/-1.2% for the radial distance of 8.0 cm used with both solid phantoms. The change in the response for both well-type chambers was only 0.1% for changes in the source position within +/-7.5 mm around the response peak. Good agreement was found between all dosimetry systems included in our study. Taking the HDR-1000 well-type chamber results as a reference, we observed percentage root mean square (RMS) values of 0.11% for the SDS well-type chamber, 0.44% for the cylindrical, and 0.60% for the plate phantom setup. A comparison of our results using the cylindrical phantom with those of the manufacturer showed a percentage RMS value of 3.3% with a percentage fractional error range of -13.0% to +6.0%. The comparison of our calibration results with those of PTB gave deviations less than 0.4% for all systems. CONCLUSIONS: Our results have shown that with careful use of all calibration system protocols an accurate determination of source strength can be obtained. However, the manufacturer's calibration is not accurate enough on its own, and it should be mandatory for clinics to always measure the source strength of newly delivered 192Ir brachytherapy sources. The influence of the applicator material, metal or plastic, should always be taken into account.

Brachytherapy↗