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At least 811 records · Page 45Linked to original sources
PubMed1997

Pharmacokinetics and pharmacodynamics of ranitidine in renal impairment.

OBJECTIVE: The pharmacodynamics and pharmacokinetics of ranitidine were examined in subjects with varying degrees of renal function to determine the effect of this condition on acid-antisecretory activity. METHODS: Subjects with creatinine clearances (Ccr) ranging from 0 to 213 m1.min-1 received single 50-mg and 25-mg i.v. doses of ranitidine. This was followed by determination of serum and urine ranitidine concentrations, and continuous gastric pH monitoring for 24 h. RESULTS: Serum ranitidine concentrations were described by a two-compartment model linked to a sigmoidal Emax model describing gastric pH. Ranitidine renal clearance, ranging from 0 to 1003 m1.min-1, correlated with CPAH (r2 = 0.707), while non-renal clearance was unaltered. Steady-state volume of distribution decreased by half in severe renal impairment. No changes in the effective concentration at half-maximal response (EC50), maximal response (Emax), or basal response (E0) were observed. Thus, renal elimination of ranitidine declined in parallel with renal function, while sensitivity to the pharmacologic effect (gastric pH elevation) was unaltered. Ranitidine was cell tolerated in these renally impaired subjects. CONCLUSION: These data indicate that the current recommendation for renal impairment dose reduction (by two-thirds when Ccr < 50 m1-min-1) might result in under-treating moderately impaired patients, and suggests a less conservative dose reduction (by half when Ccr < 10 m1.min-1) to avoid therapeutic failure while remaining within the wide margin of safety for this drug.

Adult↗
PubMed2002

'Reasonable' regulation of low doses in The Netherlands?

As long as it is not clear exactly what the risks of low doses are, exposures should be regulated to be 'as low as reasonably achievable' (ALARA). In radiation protection, for normal situations, this means that a projected dose reduction can only be obligatory when the efforts needed to achieve the reduction are 'reasonable' in comparison with it, economical and social aspects being taken into account. In the recent Dutch regulations, 'reasonable' values have been established for the relevant parameters used in the ALARA concept and the paper discusses the values required to calculate the doses for the critical group due to a source. In some cases, the effort expended in making the ALARA dose assessments might not be reasonable in comparison with the dose reduction to be expected. The system which has been developed in the Netherlands to avoid these 'unreasonable' dose calculations, measurements and assessments is explained.

Humans↗
PubMed2006

Cytotoxicity of docetaxel (Taxotere) used as a single agent and in combination with radiation in human gastric, cervical and pancreatic cancer cells.

BACKGROUND: Docetaxel (Taxotere) has gained increasing attention in clinical applications. We investigated the cytotoxic and radiosensitizing potential of docetaxel at nanomolar concentrations in six cell lines derived from tumors that rarely respond to radiation or chemotherapy, with special consideration of mechanisms of resistance, including the p53 mutational status. METHODS: Cells derived from carcinomas of the human stomach (p53 mutant Hs746T, p53 wild type AGS), cervix (p53 wild type CaSki, p53 mutant HeLa) or pancreas (p53 mutant BxPC3 and Capan-1) were treated for 24 h with docetaxel at various concentrations (0.1-5 nM) to obtain drug doses for inhibiting clonogenicity by approximately 50% (IC(50)). Cells were X-irradiated without docetaxel or after 24 h of docetaxel treatment at IC(50). Radiation doses ranged from 0 up to 10 Gy. Mitotic index, multinucleation, apoptosis and necrosis after 24 h of drug exposure at 1 nM were quantified in representative gastric and cervical cell lines by fluorescence microscopy. RESULTS: Docetaxel treatment for 24 h resulted in a dose-dependent loss of clonogenicity, with 1.0 or 0.3 nM producing approximately 50% survival of gastric or cervix and pancreatic cells, respectively. After correction for the drug toxicity, the combination of isoeffective concentrations of docetaxel with graded X-ray doses resulted either in a moderate synergy or additivity. The dose reduction factors at the 50 and 20% survival levels were statistically greater than those for Hs746T or AGS cells. For CaSki, HeLa, BxPC3 or Capan-1 cells, the dose reduction factors were statistically not different from unity. CONCLUSION: Docetaxel was active against tumor cells of different origins. Combined effects of docetaxel and radiation were at least additive and depended on the intrinsic sensitivity to drug alone. There was no significant evidence of drug-induced mitotic arrest. Compared to drug-resistant gastric cells, exposure to the drug alone of drug-sensitive cervical cells resulted in more severe multinucleation. The p53 status did not contribute directly to the effect of drug alone or in combination with radiation.

Cell Nucleus↗
PubMed1994

Interferon antibodies in patients with chronic hepatitic C virus infection treated with recombinant interferon alpha-2 alpha.

Patients treated with alpha-2a interferon for chronic hepatitis C may produce anti-interferon antibodies whose effect, if any, on the individual response to therapy has not been fully clarified. The prevalence and kinetics of anti-interferon, including those of neutralizing type, have been studied in 60 patients with chronic hepatitis C enrolled in a randomized controlled trial of recombinant alpha-2a interferon. Thirty patients received interferon while 30 were untreated controls. Two different methods, an enzyme immunoassay and an antiviral neutralization bioassay, were used and serial serum samples from each patient were analyzed. Enzyme immunoassay-positive anti-interferon appeared in 60.7% of treated patients within 6 months of therapy; antiviral neutralization bioassay-positive anti-interferon appeared in 52.9% of these enzyme immunoassay-positive patients, and was associated with high enzyme immunoassay reactivity and long-term persistence. Anti-interferon was detected in 75% of patients showing no response to interferon. Antibodies were also detected in three out of six patients who showed alanine aminotransferase normalization persisting up to the end of treatment and in 8 out of 14 patients who showed an initial marked reduction or even normalization of alanine aminotransferase, followed by reactivation of liver damage during treatment. Interestingly, patients who became anti-interferon positive before complete alanine aminotransferase normalization later showed reactivation of liver damage independently of interferon dose reduction, while patients who became positive for anti-interferon after complete alanine aminotransferase normalization either did not reactivate or did so only after interferon dose reduction.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1998

Dose perturbation caused by high-density inhomogeneities in small beams in stereotactic radiosurgery.

The influence of high-density tissue heterogeneities in small-diameter beams used in stereotactic radiosurgery has been investigated. Dose perturbation immediately behind aluminium sheets, used to simulate a high-density tissue inhomogeneity such as bone, was studied in a solid water phantom. Dose reduction factors (DRFs), which are the ratios of the dose in the presence of the inhomogeneity to dose in a uniform density solid water phantom, were measured with a diamond detector for three thicknesses of aluminium. DRFs exhibit dependence on both the inhomogeneity thickness and the beam diameter. The DRF decreases with inhomogeneity thickness. The DRF initially decreases with increase in the beam diameter from 12.5 to 25 mm. For fields greater than 25 mm, the DRFs are nearly constant. The commonly used algorithms such as the TAR ratio method underestimate the magnitude of the measured effect. A good agreement between these measurements and Monte Carlo calculations is obtained. The influence of the high-density inhomogeneity on the tissue maximum ratio (TMR) was also measured with the inhomogeneity at a fixed depth dmax from the entrance surface. The TMR is reduced for all detector-inhomogeneity distances investigated. The dose build-up phenomenon observed in the presence of low-density air inhomogeneity is absent in the presence of a high-density inhomogeneity. The beam width (defined by 50% dose points) immediately beyond the inhomogeneity is unaffected by the high-density inhomogeneity. However, the 90%-10% and 80%-20% dose penumbra widths and the dose outside the beam edge (beyond the 50% dose point) are reduced. This reduction in dose outside the beam edge is caused by the reduced range of the secondary radiation (photons and electrons) in the high-density medium.

Data Interpretation, Statistical↗
PubMed2006

Low dose CT: practices and strategies of radiologists in university hospitals.

PURPOSE: We surveyed the practices and policies of the radiology departments of academic institutions in Turkey regarding the use of low dose CT in daily practice. MATERIALS AND METHODS: Surveys were mailed electronically to radiology departments of 40 university hospitals. Information gathered included modifications of standard protocols for dose reduction according to body parts being examined or depending on specific patient groups such as children, pregnant, or slim patients. RESULTS: Thirty-three radiology departments (82%) responded. Twenty-eight (85%) reported that they modify CT scanning parameters in order to reduce the patient dose. Of these, 5 (18%) reported that they always modulate the scan parameters, 10 (36%) often, 11 (39%) sometimes, and 2 (7%) seldom. Reduced dose CT is applied mostly in pediatric and pregnant patients, reported by 93% and 57% of respondents, respectively. The most common body part for the application of low dose CT was chest examination followed by imaging of paranasal sinuses, abdomen, and CT-guided interventions. The most common modification for dose reduction is using low mA, followed by increasing the pitch value. CONCLUSION: Most respondents are aware of low dose CT, but the frequency of application varies considerably in routine practice. Reduced mA and increased pitch are the most commonly used modifications.

Dose-Response Relationship, Radiation↗
PubMed1993

5-fluorouracil and interferon-alpha-2a in advanced colorectal cancer. Results of two treatment schedules.

BACKGROUND: Potential synergy between 5-fluorouracil (5-FU) and interferon alpha-2a (IFN-alpha-2a) has been demonstrated in the treatment of colorectal carcinoma. Continuous low-dose infusion of 5-FU may have superior response rates to bolus 5-FU in these malignancies. This report presents results of two Phase II trials using these principles in colorectal cancer. METHODS: Forty-eight patients were entered onto two protocols; 18 were treated with 5-FU by a bolus infusion schedule with concurrent IFN-alpha-2a (Group 1). Thirty patients were treated with continuous low-dose 5-FU and IFN-alpha-2a thrice weekly (Group 2). RESULTS: The overall response rates were 33% (95% confidence interval [CI], 16-68%) and 33% (95% CI, 17-53%), respectively, for Groups 1 and 2. In Group 2, in 16 previously untreated patients, there was a response rate of 56% (95% CI, 30-80%). The median survival was 11 months and 6 months for Groups 1 and 2, respectively. Toxicity in Group 1 was as expected, except the incidence of central nervous system toxicity was low, with only one patient requiring dose reduction because of cerebellar ataxia. The toxicity in Group 2 was substantial, with four patients being removed from study because of toxicity and all patients treated for more than 2 months requiring dose reductions. The most common (67%) toxicity was mucositis, with 33% of those patients classified as Grade III or IV (Southwest Oncology Group criteria). Other major toxicities were fatigue and hand/foot syndrome. CONCLUSIONS: The first trial confirms previous response rate data for bolus injection 5-FU and IFN-alpha-2a. The second trial of low-dose continuous infusion 5-FU with IFN-alpha-2a demonstrates similar efficacy with substantially greater toxicity.

Adenocarcinoma↗
PubMed1991

Treatment of cutaneous T cell lymphoma with a combination of low-dose interferon alfa-2b and retinoids.

In a pilot study the therapeutic effect and side effect profile of low-dose interferon alfa-2b in combination with a retinoid for the treatment of cutaneous T cell lymphoma were evaluated. Seven patients (four women, three men) with histologically confirmed cutaneous T cell lymphoma were included. Four patients had received therapy previously. The treatment schedule consisted of 2 million U of interferon alfa-2b administered subcutaneously three times per week and oral 13-cis-retinoic acid, 1 mg/kg/day, with subsequent dose reduction in case of response. The combination therapy produced two complete and two partial remissions. Responses were maintained by continuous therapy for up to 15 months even after dose reduction of both agents by 50%. Side effects were negligible and did not result in discontinuation of treatment in any patient.

Administration, Oral↗
PubMed1990

[NIOBI-X filter: reduction of patient exposure and effect on image quality].

Patient protection against ionizing radiation has become more and more important and the subject has been included in all the latest ICRP publications. Recently a 50 microns Niobium filter (NIOBI-X) has come out, which, installed on tungsten anode X-ray apparatuses, allows patient dose reduction by absorbing the radiation which does not contribute to the image. In order to verify the NIOBI-X actual effect on image quality and on patient dose reduction, image resolution, image contrast and patient exposure (air-Kerma) were measured using a bone-equivalent stepped wedge. The NIOBI-X, added to the total filtration of the X-ray apparatus, allows an air-Kerma reduction of about 50% from 60 to 130 kV. In the case of bone-equivalent material exposure the filter causes a slight contrast loss and does not affect, or even improves, image resolution. Before choosing the NIOBI-X filter for all the X-ray apparatuses a cost-benefit analysis should of course be made by evaluating results and cost related to other kinds of filter. With particular regard to Aluminium filters, whose prices are far lower than Niobium ones, it has to be pointed out that: 1) in order to have the same air-Kerma reduction the Aluminium filter thickness must be quite heavy (2.8 mm) which causes practical problems of use; 2) the Aluminium filter causes image quality loss especially at lower kVs.

Filtration↗
PubMed1997

Clinical efficacy and safety of tolterodine in the treatment of overactive bladder: a pooled analysis.

OBJECTIVES: To examine the safety, efficacy, and tolerability of tolterodine in four randomized, double-blind, parallel, multicenter, 12-week studies of patients with overactive bladder. METHODS: Two of the four studies compared tolterodine (2 mg twice daily) to oxybutynin (5 mg three times daily) and placebo, one study compared tolterodine (2 mg twice daily) to oxybutynin (5 mg three times daily), and one study compared two dosages of tolterodine (1 and 2 mg twice daily) to placebo. Efficacy was determined from micturition diaries and patient perception of their bladder condition. Safety and tolerability were assessed from adverse events and laboratory measures. RESULTS: A total of 1,120 patients were randomized and treated at 134 centers. For the primary efficacy variable, the number of micturitions/24 hours, pooled results showed a significant decrease from baseline for the 1 mg tolterodine (P < 0.001), 2 mg tolterodine (P < 0.001), and 5 mg oxybutynin (P < 0.01) groups, compared to placebo. Both tolterodine doses and oxybutynin significantly decreased incontinence episodes/24 hours and significantly increased volume voided/micturition, compared to placebo. Tolterodine at a dose of 2 mg twice daily and 5 mg oxybutynin twice daily were significantly more effective in improving patient perception of bladder condition than placebo. Tolterodine at a dose of 2 mg and 5 mg oxybutynin were equivalent in their effectiveness. Tolterodine at doses of 1 mg and 2 mg were tolerated significantly better than oxybutynin when adverse events, dry mouth (both frequency and intensity), dose reductions, and patient withdrawals were considered. CONCLUSIONS: Although oxybutynin is highly effective, its clinical utility is limited by systemic side effects that lead to frequent discontinuation of treatment or dose reductions. Patients receiving tolterodine should not experience these limitations and instead will get safe and long-term effective treatment for their condition.

Adult↗
PubMed1987

Pharmacokinetics and dose recommendations of carumonam in renal failure.

The pharmacokinetics of (Z)-[[[(2-aminothiazol-4-yl)[[(2S,3S)-2-(hydroxymethyl)-4-oxo-1- sulfoazetidin-3-yl]carbamoyl]methylene]amino]oxo]acetic acid, disodium salt (carumonam, Ro 17-2301) after a 2 g intravenous infusion (20 min) were evaluated in 10 healthy volunteers and 20 patients with various degrees of renal failure. The main results of the kinetic parameters in healthy volunteers (mean + SD) corrected for zero infusion time and 70 kg body weight were: t1/2 alpha, 29 +/- 12 min; t1/2 beta, 108 +/- 27 min; AUCtot, 327 +/- 40 mg h/l; Vdss, 12.2 +/- 1.5 l/70 kg; urinary recovery, 78.7 +/- 8.2%; total clearance 103 +/- 13 ml/min; renal clearance, 85 +/- 13 ml/min. Because of the large variation in the degree of renal insufficiency, calculations of the mean values for the pharmacokinetic parameters in the patient group were not generally justified with the exception of the volume of distribution (Vdss = 14.4 +/- 3.0 l/70 kg). To derive dose recommendations, a regression analysis was performed using values from both the volunteer and patient group for the total area under curve (AUCtot) and glomerular filtration rate (GFR), divided by the mean AUCtot value for the volunteers. This curve can be interpreted as giving the dose reduction factor (DRF) as a function of GFR, where by definition, DRF = 1 for healthy (and young) subjects. Using this method of equivalent areas, no (or only a slight) dose reduction is necessary for patients with GFR values above 40 ml/min.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed2004

Simultaneous integrated boost intensity-modulated radiotherapy for locally advanced head-and-neck squamous cell carcinomas: II--clinical results.

PURPOSE: To perform a Phase I radiation dose-escalation trial to determine the maximal tolerable dose (MTD) deliverable to the gross tumor volume (GTV) using an accelerated fractionation with simultaneous integrated boost intensity-modulated radiotherapy regimen with parotid gland sparing as the sole therapy in the treatment of locally advanced head-and-neck squamous cell carcinoma. The primary objective was the definition of the MTD using established criteria of quantifying acute dose-limiting toxicity (DLT). Secondary objectives included analysis of failure patterns, tumor control rates, and toxicity. METHODS AND MATERIALS: Between July 1999 and June 2002, eligible patients with bulky Stage II to Stage IVB head-and-neck squamous cell carcinoma, excluding laryngeal primaries, were enrolled. Intensity-modulated radiotherapy was delivered with 6-MV photons using a "sliding-window" technique. Enrollment of 6 patients for each dose level was planned; if DLTs were seen in >2 of 6 patients, the previous dose was to be expanded by an additional 6 patients to confirm that dose level as the MTD. All schedules administered a total of 30 fractions, but with escalating doses per fraction (2.27, 2.36, and 2.46 Gy) to achieve a total dose to the GTV of 68.1, 70.8, and 73.8 Gy, respectively. The remaining target tissues were constrained to receive the same dose in all patients regardless of the GTV dose level. The clinical target volume, defined as tissue within 1 cm around the GTV (at high risk of subclinical disease), received 60 Gy in 30 fractions of 2.0 Gy. The electively irradiated target volume, defined as the clinically uninvolved lymph node-bearing tissues, received 54 Gy in 30 fractions of 1.8 Gy. The parotid glands were spared to the degree possible without compromising target coverage. Acute toxicity was scored weekly using National Cancer Institute Common Toxicity Criteria. DLT was defined as any Grade 4 acute toxicity or any acute toxicity requiring either a dose reduction or a treatment break of >5 treatment days. RESULTS: Of 18 men and 2 women (average age, 57 years; range, 37-80 years), 17 presented with oropharyngeal primary tumors, and 1 each with squamous cell carcinoma of the oral cavity, nasopharynx, and hypopharynx. None of the 6 patients at dose level 1, and 2 of the 6 patients initially enrolled at dose level 2, developed DLT. Both patients treated at dose level 3 required a 3-day treatment break and dose reduction after rapid development of Grade 3 toxicity (by Day 15). Six additional confirmatory patients subsequently enrolled at dose level 2 completed treatment without DLT. At least 50% of the total parotid gland volume received <30 Gy in 14 patients (average, 54% of volume), with an average mean dose of 32 Gy. In contrast, >/=50% of the distal parotid gland volume received <25 Gy in 15 patients (average, 63% of volume), with an average mean dose of 24 Gy. With a median follow-up of 20 months from the date of enrollment and 28 months for surviving patients, the actuarial 2-year local control (primary site), regional control (nodal sites), and distant control rate was 76.3%, 66.7%, and 71.8%, respectively. CONCLUSION: Dose level 2, 70.8 Gy in 30 fractions of 2.36 Gy, was defined as the MTD deliverable to the GTV using this accelerated fractionation with simultaneous integrated boost intensity-modulated radiotherapy regimen with parotid gland sparing as the sole treatment for locally advanced head-and-neck squamous cell carcinoma. Adequate parotid sparing was achievable in most cases. Early toxicity, tumor control, and survival rates compared favorably with the outcomes after other accelerated regimens.

Adult↗
PubMed1983

The pharmacokinetics of ceftazidime in normal and impaired renal function.

The concentration of ceftazidime in serum and urine was measured in ten healthy volunteers and 19 patients with renal impairment following a 2 g iv dose of ceftazidime. In impaired renal function the elimination rate of ceftazidime is decreased considerably, whereupon the area under the curve (AUC) rises sharply. Dose reduction factors (DRF) for several degrees of renal function are presented. The urinary recovery decreases with renal function; but therapeutic urine levels can still be detected in patients on dialysis. Patients with renal insufficiency should be given reduced dosage according to a dose reduction factor and according to the table.

Ceftazidime↗
PubMed2003

[Reduction of adverse reactions of anticancer agents with altered dose and schedule].

It is difficult to find out optimal dose and schedule of anticancer agents. To reduce side effects of anticancer agents, there are several methods used: dose reduction, analogue development, utilizations of G-CSF or non-anticancer agent such as mesna for ifosfamide. Taxane agents such as paclitaxel and docetaxel, are widely used for the treatment of cancers of ovary, breast, lung, stomach, and head and neck. Dose-limiting toxicity of taxane is Grade 4 leucopenia with usual 24, 6, and 3-hour infusions. Efforts to reduce this toxicity were made, and one-hour weekly taxane infusion was found as safe and effective treatment, which is now widely used as single agent treatment or in combination. Development of paclitaxel one-hour weekly infusion was reviewed, as one example of reducing adverse reaction of leucopenia in this article.

Antineoplastic Agents↗
PubMed1996

Felbamate-induced headache.

We prospectively investigated drug-induced headaches (HA) among 60 epileptic patients receiving felbamate (FBM). Twenty patients (33%) experienced HA. HA was pounding in 11 (55%), steady in 9 (45%), moderate or severe in 19 (95%), occurred at least once a week in all patients, and was relieved by nonnarcotic analgesics in 14 (70%). Mean duration on FBM before HA onset was 19 days. HA occurred with higher FBM doses and was relieved in 8 of 13 patients (62%) with FBM dose reduction. FBM was discontinued in most cases because of risks of anemia or hepatitis; not because of HA. Other side effects included insomnia (25%), gastrointestinal symptoms (27%), and agitation or restlessness (23%). HA is a common dose-related complication of FBM, occurs early after initiation of FBM treatment, and is relieved by dose reduction.

Adolescent↗
PubMed1993

Organic mood syndrome associated with detoxification from methadone maintenance.

OBJECTIVE: The authors delineate the clinical characteristics of mood state changes that occur in stable opioid-dependent patients undergoing therapeutic detoxification from methadone maintenance treatment. METHOD: Twenty-four patients participated in a blinded protocol for gradual methadone dose reduction that included weekly assessments of affective state using the Profile of Mood States (POMS) as well as weekly assessments of signs and symptoms of opioid withdrawal. Data obtained before methadone dose reduction and during the 2-week period of maximal dysphoric symptoms were compared. Changes in affective and opioid withdrawal measures were compared in patients who differed in their success in completing the detoxification regimen. RESULTS: Sustained increases in POMS scores of greater than 20 points were observed in 12 of the 24 patients during the course of detoxification. The emergence of symptoms of dysphoria was accompanied by insomnia, loss of appetite, and somatic complaints consistent with symptoms of opioid withdrawal but only minimal levels of objective signs of withdrawal. Greater changes from baseline in mood state and opioid withdrawal measures occurred in patients who were unable to complete the detoxification regimen. CONCLUSIONS: The development of an organic mood syndrome is a common occurrence in patients undergoing slow detoxification from methadone maintenance treatment and is associated with a poor outcome.

Adult↗
PubMed1995

Haloperidol plasma 'threshold' levels for relapse prevention in schizophrenia: a study with haloperidol decanoate.

Forty-eight schizophrenic outpatients treated with flexible doses of haloperidol decanoate were followed up in a naturalistic fashion for 3 years with periodic monitoring of clinical symptoms, side effects and haloperidol plasma concentrations. There was no relationship between plasma level and clinical response, however categorical data analysis showed that patients with plasma levels over 4 ng/ml had a significantly reduced relapse rate compared with patients with plasma levels below this plasma 'threshold' level. This effect could be observed during the first, second as well as third year of treatment. The relapse rate did not change significantly in relation to time (during years 1, 2, 3), when patients with haloperidol plasma levels below and equal to or over 4 ng/ml were considered separately. In patients with haloperidol equal to or over 4 ng/ml, the variability (measured as coefficient of variation %) in the total scores of SAPS and SANS was lower, indicating a better clinical stability. These data are in fairly good agreement with other literature findings showing that an indiscriminate dose reduction strategy during long-term treatment of schizophrenic disorders with haloperidol decanoate should be discouraged, since it leads to an increase in the relapse rate. Before deciding about a dose reduction, clinicians should take into careful consideration some clinically relevant variables (i.e. frequency of previous relapses, severity of symptoms, iatrogenic depression, risk for development of extrapyramidal side effects) for each patient. A better clinical stability during treatment with haloperidol decanoate can be obtained when plasma 'threshold' levels for response are reached.

Adult↗
PubMed1985

Screens in ovoids of a Selectron cervix applicator.

The addition of screens in the vaginal source holders of a cervix applicator for intracavitary brachytherapy reduces the dose to rectum and bladder and therefore diminishes the number of rectal and vesical complications. Shielding properties of tungsten rectal and bladder screens of a Selectron cervix applicator, loaded with spherical cesium sources, were determined for verification of dose calculations. Transmission characteristics of half-disk shaped tungsten screen segments in a single ovoid were measured in a water phantom. The minimum transmission ratios are 60, 70 and 80% for segment thickness of 5.0, 3.5 and 2.0 mm, respectively. The accuracy of the new screen correction algorithm of the Selectron Planning System was assessed by comparing measured and calculated dose rates and was found to be better than +/- 4%. The correction algorithm provides a method to analyse the efficacy of screens in the ovoids for various segment geometries and orientations without extensive phantom measurements. Isotransmission and isodose calculations were made for a typical clinical applicator set-up and source distribution. The dose reduction to rectum and bladder, near the bottom and top of the ovoids was analysed in detail. A 3.5 mm thick rectum and bladder screen in each ovoid reduces the dose approximately by 20% to the rectum and by 15% to the bladder. A distance enlargement of about 5 mm between ovoid and rectum or bladder, e.g. by packing, results in a comparable dose reduction. Shielding properties of a Selectron cervix applicator, provided with screens, were compared with those of some Fletcher-type applicators. Significant differences between the transmission ratios and shielded areas of the screens of both systems near rectum and bladder were observed.

Brachytherapy↗