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PubMed2001

Dose-image optimisation in digital radiology with a direct digital detector: an example applied to pelvic examinations.

In diagnostic radiology increasing attention has been focused on dose reduction while maintaining a clinically good image quality. With the use of digital detectors balancing dose vs image quality is done differently than in film-screen radiography, since dose and image brightness are uncoupled in digital imaging. In this study a new direct digital detector (flat-panel detector) was used in a dose-image optimisation of a simulated pelvic examination. X-ray images were taken with a direct digital detector (DDD), of the pelvic of a phantom using varying tube current (varying stochastic noise). The entrance surface dose was measured for each image. These images were scored by two radiologists according to EU guidelines. A dose comparison was made with an older PCR system (storage phosphor plates). With decreasing tube current the noise in the images increased and the image with the lowest dose and still acceptable image quality was identified. The results showed that the entrance surface dose using the DDD decreased from 1.4 mGy (PCR value) to 0.48 mGy (DDD standard settings). Through the optimisation the dose could be further decreased to 0.24 mGy while still maintaining an acceptable image quality. A substantial dose reduction was obtained with this new direct digital detector. This simple but efficient optimisation approach is easily applicable to other examinations and both DDD and storage phosphor plate detectors.

Humans↗
PubMed2001

Dynamic wedge versus physical wedge: a Monte Carlo study.

The purpose of this study is to analyze the characteristics of dynamic wedges (DW) and to compare DW to physical wedges (PW) in terms of their differences in affecting beam spectra, energy fluence, angular distribution, contaminated electrons, and dose distributions. The EGS4/BEAM Monte Carlo codes were used to simulate the exact geometry of a 6 MV beam and to calculate 3-D dose distributions in phantom. The DW was simulated in accordance with the segmented treatment tables (STT). The percentage depth dose curves and beam profiles for PW, DW, and open fields were measured and used to verify the Monte Carlo simulations. The Monte Carlo results were found to agree within 2% with the measurements performed using film and ionizing chambers in a water phantom. The present EGS4 calculation reveals that the effects of a DW on beam spectral and angular distributions, as well as electron contamination, are much less significant than those for a PW. For the 6 MV photon beam, a 45 degrees PW can result in a 30% increase in mean photon energy due to the effect of beam hardening. It can also introduce a 5% dose reduction in the build-up region due to the reduction of contaminated electrons by the PW. Neither this mean-energy increase nor such dose reduction is found for a DW. Compared to a DW, a PW alters the photon-beam spectrum significantly. The dosimetric differences between a DW and a PW are significant and clearly affect the clinical use of these beams. The data presented may be useful for DW commissioning.

Electrons↗
PubMed1991

An open, parallel, comparative evaluation of amlodipine and nitrendipine in the monotherapeutic treatment of mild and moderate essential hypertension.

The efficacy and safety of the dihydropyridine calcium antagonists amlodipine and nitrendipine as single-agent therapy of mild to moderate hypertension were compared in an open, parallel-group study. Interim analysis of data from 74 patients (43 male, 31 female) from an expected final total of 96 patients is reported. Amlodipine normalized blood pressure (< or = 90 mm Hg) in 94.7% of patients with a mean final dose of 8.3 mg/day, compared with normalization of blood pressure in 83.3% of patients treated with nitrendipine with a mean final dose of 28.3 mg/day. Only nitrendipine produced a statistically significant increase in heart rate after 2 and 4 weeks of therapy. Nitrendipine-treated patients reported more adverse events (47.2%) than the amlodipine-treated group (26.3%). Two patients from the nitrendipine group discontinued treatment due to treatment-related adverse events and one patient required a dose reduction. In the amlodipine-treated group, all adverse events were mild to moderate and dose reduction was required in one patient. In conclusion, although amlodipine and nitrendipine have comparable antihypertensive efficacy, in this study amlodipine was associated with fewer adverse effects.

Amlodipine↗
PubMed1994

[Clinico-pharmacologic studies on pefloxacin].

The impact of liver impairment, renal insufficiency and age-related changes on the pharmacokinetics of pefloxacin was studied in 55 patients. The elderly patients were stratified into three age groups (61-70, 71-80 and above 81 years). The patients suffering from various infections were treated with oral or intravenous pefloxacin in a dose of 400 mg bid. Blood samples were withdrawn on the first and seventh day of therapy. The pharmacokinetics of pefloxacin was characterized by marked interindividual differences that became even more pronounced during multiple dosing. The elimination rate of pefloxacin during therapy slowed down, presumably due to its decreased metabolism. In elderly patients, the rate of cumulation is greater than in the young ones, but no significant differences could be detected among the elderly age-groups. Pefloxacin elimination also decreased in renal and hepatic impairment. There was no correlation between serum concentrations of pefloxacin and the development of adverse effects. In elderly subjects and in patients with renal or hepatic impairment, dose reduction might be considered. In mild or moderate infections or in urinary tract infections smaller doses of pefloxacin also could assure good therapeutic results. However, in severe infections especially caused by less susceptible pathogens, routine dose reduction is not recommended because of the significant interindividual differences in serum concentrations of pefloxacin.

Administration, Oral↗
PubMed1992

[A comparative study of the possibility of reducing the dosage in lateral teleradiographs].

Thanks to their capability for post-processing of image data, the digital radiological techniques introduced from 1970 onwards permit dose reduction with no loss of clinical information. The aim of this study was to establish the extent of possible dose reduction in orthodontic lateral cephalography. For this purpose, lateral cephalograms of a head phantom taken with varying radiation doses (5 to 150 mAs, constant 70 kV) were evaluated. The evaluations of ten judges were compared statistically. Conventional lateral cephalograms showed a statistically proven superiority of a number of exposure parameters for the sagittal and vertical localisation of reference points. This correlated with the radiological density of the structures. In contrast to the conventional technique, the reference points in all images obtained by digital luminescence radiography showed no such tendency. Digital luminescence thus meets the clinical need to reduce radiation dose (to about 20% of the usual dose) while providing no less diagnostic information.

Cephalometry↗
PubMed2005

[Organ doses from CT examinations in children].

PURPOSE: To estimate radiation doses from routine pediatric CT scans (body) and to propose dose reduction protocols. MATERIAL AND METHODS: [corrected] Study performed with a phantom equivalent to the body of 5 year old child with evaluation of doses delivered to breast, gonads, bone marrow (sternum, T12) and thyroid for CT examinations of the chest, abdomen, pelvis and spine. Extrapolation is made to estimate the doses for 1 year old and 10 year old children. Finally, dose reduction protocols are evaluated. RESULTS: CT of the chest delivers significant doses to breast tissue and bone marrow, CT of the abdomen and pelvis delivers significant doses to the ovaries and CT pf the spine delivers significant doses to thyroid and bone marrow. Optimization can be achieved without degradation of the image quality, by reducing Kv and mAs within reasonable limits. This study may be used in order to evaluate the doses delivered by multi-detector CT units.

Bone Marrow↗
PubMed1992

Accelerated fast neutron therapy: a pilot study.

The clinical role of fast neutron therapy has been limited by excessive late normal tissue damage. A pilot study of accelerated fractionation of fast neutron therapy was performed, based on the rationale that this should result in an increase in the response in acute reacting tissues (normal and malignant), with no change in late damage and a consequent increase in the therapeutic ratio. Further accelerated fractionation should improve the local control of rapidly proliferating tumour, without the potential problem of inadequate reoxygenation inherent in accelerated photon schedules. 6 or 12 fractions of 62 MeV (p-Be) neutrons were given over 12 days to 27 sites in 23 patients with locally advanced tumours. With a dose reduction of 12% (18 Gy), acceptable skin and oral mucosa early reactions were obtained. A larger dose reduction (15%) was required at pelvic sites. The incidence of late EORTC/RTOG grade 4 toxicity was 46%. The overall response rate was 76% with a complete response rate of 16%. For locally advanced breast cancer, the complete response rate was 9%, which compares unfavourably with previous results with conventional neutron fractionation schedules. The combination of a low overall complete response rate and excessive late normal tissue toxicity suggests that accelerated fractionation of fast neutrons does not lead to an improvement in the therapeutic ratio, and that late normal tissue damage will continue to be dose limiting.

Adult↗
PubMed2002

Tolerance of mycophenolate mofetil in end-stage renal disease patients with ANCA-associated vasculitis.

BACKGROUND: Mycophenolate mofetil (MMF) has been used successfully in patients with ANCA-associated vasculitis as maintenance therapy. Only transient and moderate side effects have been reported with a daily dose of 2 g. Since all the treated patients who have been reported so far had no or only moderate renal insufficiency when MMF was initiated, no data are available regarding side effects in patients with end-stage renal disease (ESRD). METHODS: Five ESRD patients with ANCA-associated vasculitis and a relapsing course of their disease were treated. All patients had pretreatment with cyclophosphamide for at least 17 months. MMF was initiated as a remission maintenance therapy, and started with a dose of 1 g/d. The aim was to increase the MMF dose to 2 g/d. Blood counts, liver enzymes and gastrointestinal side effects were monitored. RESULTS: Four patients developed severe anemia, 2 requiring blood transfusion with permanent or temporary cessation of MMF treatment. One patient developed leukopenia. Gastrointestinal symptoms led to a dose reduction to 1 g/d (n = 2) or cessation of treatment (n = 1). Three patients remained on longer MMF treatment; however, their daily dose did not exceed 1 g. CONCLUSION: MMF, a promising drug regarding maintenance therapy in ANCA-associated vasculitis, seems to have more side effects in ESRD patients, leading to dose reduction or even cessation of treatment. Therefore, in this patient group a lower dose and closer monitoring for side effects seems to be required compared to patients with no or moderate renal insufficiency.

Adult↗
PubMed1990

Dose-dependent reduction of myocardial infarct size with the perfluorochemical Fluosol-DA.

The perfluorochemical Fluosol-DA has been shown to reduce infarct size. However, the dose-response relationship of the agent is unknown. Because perfluorochemicals (PFC) can potentially saturate the reticuloendothelial system and decrease carbon clearance as well as cause a transient elevation in liver enzymes, the present study was conducted to determine the lowest effective dose. New Zealand White rabbits (n = 73) were randomly selected prior to infarction to receive 10, 15, 20, 25, or 30 ml/kg PFC or an equivalent volume of 5% dextran (control) intravenously. Animals underwent 30 minutes of coronary artery occlusion with PFC or dextran infused over a 30-minute period starting at 20 minutes into the occlusion. Animals were put to death at 24 hours and infarct size was determined histologically and quantitated by computerized planimetry. Neutrophil infiltration into the ischemic myocardium was evaluated semiquantitatively. No hemodynamic differences were noted within groups. Infarct size was similar to that of controls in animals treated with 10 or 15 ml/kg PFC. Significant infarct size reduction, however, was noted in animals treated with 20, 25, and 30 ml/kg PFC versus controls; (p = 0.05, 0.04, and 0.02, respectively). Maximal infarct size reduction was seen with 30 ml/kg PFC (35%). Neutrophil infiltration was significantly decreased in all groups treated with PFC. These results show that intravenous Fluosol-DA significantly reduces infarct size at a minimal dose of 20 ml/kg.

Animals↗
PubMed2005

A phase I trial of liposomal doxorubicin, paclitaxel and valspodar (PSC-833), an inhibitor of multidrug resistance.

PURPOSE: The aim of this study was to determine (i) the maximum tolerated dose (MTD) of liposomal doxorubicin (L-DOX) and paclitaxel (DP), (ii) the MTD of DP plus valspodar (DPV) and (iii) pharmacokinetic (PK) interactions of valspodar with L-DOX and paclitaxel. METHODS: Twenty-three patients with metastatic cancers received DP, followed 4 weeks later by DPV. Dose levels of DP were (mg/m2 for L-DOX/paclitaxel): 30/135 (n = 7), 30/150 (n = 4), 35/150 (n = 8) and 40/150 (n = 4). Dose levels of DPV were 15/70 (n = 10) and 15/60 (n = 10). Serial, paired PK studies were performed. RESULTS: The MTD of DP was 40/150. For DPV at 15/70, five of 10 patients experienced grade 4 neutropenia. In the next cohort, a reduced dose of 15/60 was well tolerated. Valspodar produced reversible grade 3 ataxia in seven patients, requiring dose reduction from 5 to 4 mg/kg. Paired PK studies indicated no interaction between L-DOX and valspodar, and a 49% increase in the median half-life of paclitaxel. Two partial and one minor remissions were noted. CONCLUSIONS: The use of valspodar necessitated dose reductions of DP, with neutropenia being dose limiting. Valspodar PK interactions were observed with paclitaxel but not L-DOX.

Adult↗
PubMed2001

Evaluating the effectiveness of a longitudinal magnetic field in reducing underdosing of the regions around upper respiratory cavities irradiated with photon beams--a Monte Carlo study.

The problem of underdosing lesions adjacent to upper respiratory cavities and a proposal to correct it are presented in this work. The EGS4 Monte Carlo code was used to simulate a 6 MV x-ray beam passing through a block of tissues with air cavities 2, 4, and 6 cm wide. The geometry used approximates the tracheal geometry used by previous researchers who investigated the underdosing phenomenon. A uniform longitudinal magnetic field of 0.5 T strength is used to reduce secondary electron outscatter caused by the presence of an air gap, and thus improving the dose at the distal surface of air cavities. We introduce the term "percent dose reduction" (PDR), which is defined as the difference between the dose after the air cavity and the dose at the same depth in soft-tissue phantom normalized to the dose in the tissue phantom, to quantify the reduction in dose after an air gap. We also introduce the term dose improvement ratio (DIR), which is defined as the dose ratio with magnetic field to the dose, at the same point, without magnetic field, to quantify the improvement in dose when the magnetic field is applied. For 2 x 2 x 20 cm3 and 4 x 4 x 20 cm3 air cavities irradiated by 2 x 2 cm2 beams, we found PDRs of 38% and 52%, respectively. This means that for these cavities, there is a 38% and a 52% reduction in dose at the cavity edge compared to the same dose in tissue at the same depth for each cavity. The dose improved by 30% (DIR= 1.3) and 87% (DIR= 1.87), respectively, when applying the magnetic field. The worst effect on dose at the distal side came from larger cavities irradiated with small fields. In these situations, the improvement in dose due to the presence of magnetic field was the largest. This article deals with "ideal" head and neck geometries with a uniform magnetic field. In a paper to follow we will use a CT-based phantom to study the effect in realistic geometries with the presence of a magnetic field from a Helmholtz coil pair.

Electrons↗
PubMed1990

[Continuous infusion of natural interleukin 2 (n IL-2) in treatment of malignant diseases: phase I study].

This is the first report of a phase I study with n-IL 2. N-IL 2 shows a higher biological activity and different immunomodulatory effects compared to recombinant IL 2. 14 patients (9 male, 5 female) entered our phase I study with continuous i.v. n-IL 2 with a median age of 40 years (range 4-65), including 4 children. The study design was a dose rising continuous iv infusion over 5 days with a starting dose of 1 x 10(6) U n-IL 2 up to 6 x 10(6) n-IL 2 over 24 h. In 2 of 16 regimen with n IL-2 there was a dose reduction and in 6 there was an interruption necessary. In 2 patients there was only a dose reduction necessary because of thrombocytopenia and hypotension. In 6 patients n-IL 2 had to break the continuous infusion. Reasons were an increasing BUN, respiratory insufficiency, thrombocytopenia, neurological symptoms and increasing liver enzymes. The 4 children developed an other side effect profile with edema of the face, abdominal cramps and thrombocytopenia. During the study no intensive care was necessary. The most common side effects were erythema, fever, nausea, dyspnea and hypotension. There was no complete remission, 21.5% of the patients had a partial remission, 7% showed no change and 71.5% had a progression. There were no significant differences in toxicity and response was comparable to studies using continuous r IL-2.

Adolescent↗
PubMed2001

Incidence, cost, and outcomes of bleeding and chemotherapy dose modification among solid tumor patients with chemotherapy-induced thrombocytopenia.

PURPOSE: To describe the incidence and outcomes of bleeding and chemotherapy dose modifications associated with chemotherapy-induced thrombocytopenia (platelets < 50,000/microL). PATIENTS AND METHODS: Six hundred nine patients with solid tumors or lymphoma were followed-up during 1,262 chemotherapy cycles complicated by thrombocytopenia for development of bleeding, delay or dose reduction of the subsequent cycle, survival, and resource utilization. The association between survival and bleeding or dose modification was examined using the Cox proportional hazards model. Predisposing factors were identified by logistic regression. RESULTS: Bleeding occurred during 9% of cycles among patients with previous bleeding episodes (P <.0001), baseline platelets less than 75,000/microL (P <.0001), bone marrow metastases (P =.001), poor performance status (P =.03), and cisplatin, carboplatin, carmustine or lomustine administration (P =.0002). Major bleeding episodes resulted in shorter survival and higher resource utilization (P <.0001). Chemotherapy delays occurred during 6% of cycles among patients with more than five previous cycles (P =.003), radiotherapy (P =.03), and disseminated disease (P =.04). They experienced similar clinical outcomes but used significantly more resources. Dose reductions occurred during 15% of cycles but were not associated with poor clinical outcomes or excess resource utilization. Significantly shorter survival and higher resource utilization were observed among the 20% of patients who failed to achieve an adequate response to platelet transfusion. CONCLUSION: The incidence of bleeding is low among solid tumor patients overall but exceeds 20% in some subgroups. These subgroups are easily identifiable using routinely available clinical information. A clinical prediction rule is being developed. Poor response to platelet transfusion is a clinically and financially significant downstream effect of thrombocytopenia and warrants further investigation.

Antineoplastic Agents↗
PubMed1994

Granulocyte colony-stimulating factor and amifostine (Ethyol) synergize to enhance hemopoietic reconstitution and increase survival in irradiated animals.

The reported studies tested whether amifostine could be used to protect hemopoietic stem cells, which, after irradiation, could be stimulated by granulocyte colony-stimulating factor (G-CSF) to proliferate and reconstitute the hemopoietic system. Female C3H/HeN mice were administered amifostine (Ethyol, US Bioscience, Inc, West Conshohocken, PA) (200 mg/kg intraperitoneally 30 minutes before cobalt-60 irradiation and G-CSF (125 micrograms/kg/d subcutaneously from days 1 to 16 after irradiation. Saline, G-CSF, amifostine, and amifostine plus G-CSF treatments resulted in LD50/30 values of 7.85 Gy, 8.30 Gy, 11.30 Gy, and 12.85 Gy, respectively. At these LD50/30 values, the dose reduction factor of 1.64 obtained in combination-treated mice was more than additive between the dose reduction factors of G-CSF-treated mice (1.06) and amifostine-treated mice (1.44). Bone marrow and splenic multipotent hemopoietic stem cell and granulocyte-macrophage progenitor cell recoveries, as well as peripheral white blood cell, platelet, and red blood cell recoveries were also accelerated most in mice treated with amifostine plus G-CSF. These studies demonstrate that therapeutically administered G-CSF accelerates hemopoietic reconstitution from amifostine-protected stem and progenitor cells, increasing the survival-enhancing effects of amifostine, and suggest that classic radioprotectants and recombinant hemopoietic growth factors can be used in combination to reduce the risks associated with myelosuppression induced by radiation or radiomimetic drugs.

Amifostine↗
PubMed1990

Toxicity of combined ganciclovir and zidovudine for cytomegalovirus disease associated with AIDS. An AIDS Clinical Trials Group Study.

OBJECTIVE: To assess the toxicity, efficacy, and pharmacology of combined zidovudine and ganciclovir therapy in patients with the acquired immunodeficiency syndrome (AIDS) and serious cytomegalovirus (CMV) disease. DESIGN: Prospective, phase I multicenter trial (ACTG 004) with patients grouped by previous study drug history. SETTING: Three university-based AIDS Clinical Trials Units sponsored by the National Institute of Allergy and Infectious Diseases (NIAID). PATIENTS: Forty-one patients with AIDS-related CMV disease. Previous therapy with either zidovudine or ganciclovir was allowed. INTERVENTIONS: Patients were treated with zidovudine, 600 to 1200 mg/d; or, if on ganciclovir maintenance, ganciclovir, 5 mg/kg body weight; blood was sampled for pharmacokinetic studies. The other drug was then administered to the patient with blood sampling and, finally, the two drugs in combination were given. Patients were continued on both drug therapies with dose reduction of zidovudine only for grade 3 or 4 toxicity. MEASUREMENTS AND MAIN RESULTS: Forty patients were eligible. Hematologic toxicity was frequent, with 9 of the 10 patients requiring dose reductions for grade 3 or 4 toxicity at zidovudine doses of 1200 mg/d. With zidovudine doses of 600 mg/d, 82% experienced such hematologic toxicity. Median survival was 6 months; 10 patients developed intercurrent infection and 19, progressive CMV disease. Pharmacokinetic variables (alpha and beta half-lives, volume of distribution, clearance) were not affected in combination therapy. CONCLUSION: The combination of zidovudine and ganciclovir is poorly tolerated in patients with AIDS and serious-CMV disease, with 82% developing severe to life-threatening hematologic toxicity. Such toxicity is not a result of pharmacologic interactions, drug metabolism, or excretion.

Acquired Immunodeficiency Syndrome↗
PubMed2006

Coronary calcium scoring with MDCT: the radiation dose to the breast and the effectiveness of bismuth breast shield.

OBJECTIVE: The purpose of our study was to determine the breast radiation dose during coronary calcium scoring with multidetector computerized tomography (MDCT). We also evaluated the degree of dose reduction by using a bismuth breast shield when performing coronary calcium scoring with MDCT. MATERIALS AND METHODS: The dose reduction achievable by shielding the adult (35 years or older) female breasts was studied in 25 women who underwent coronary calcium scoring with MDCT. All examinations were performed with a 16-MDCT scanner. To compare the shielded versus unshielded breast dose, the examinations were performed with (right breast) and without (left breast) breast shielding in all patients. With this technique the superficial breast doses were calculated. To determine the average glandular breast radiation dose, we imaged an anthropomorphic dosimetric phantom into which calibrated dosimeters were placed to measure the dose to the breast. The phantom was imaged using the same protocol. Radiation doses to the breasts with and without the breast shielding were measured and compared using the Student's t-test. RESULTS: The mean radiation doses with and without the breast shield were 5.71+/-1.1 mGy versus 9.08+/-1.5 mGy, respectively. The breast shield provided a 37.12% decrease in radiation dose to the breast with shielding. The difference between the dose received by the breasts with and without bismuth shielding was significant, with a p-value of less than 0.001. CONCLUSION: The high radiation during MDCT greatly exceeds the recommended doses and should not be underestimated. Bismuth in plane shielding for coronary calcium scoring with MDCT decreased the radiation dose to the breast. We recommend routine use of breast shields in female patients undergoing calcium scoring with MDCT.

Adult↗
PubMed2002

Capecitabine named-patient programme for patients with advanced breast cancer. the UK experience.

Following the encouraging results achieved with the oral fluoropyrimidine capecitabine in clinical trials, a named patient programme was initiated in the UK, through which patients with advanced breast cancer were prescribed capecitabine monotherapy. In this programme, patients were treated with the standard dose of oral capecitabine (1250 mg/m(2) twice daily on days 1-14 of a 21-day treatment cycle). Efficacy and safety data were collected and analysed from 102 patients receiving outpatient treatment with capecitabine. All patients had previously received chemotherapy and for the majority (75%) this was in the metastatic setting. In total, 482 treatment cycles were administered, with a median of 4.5 treatment cycles (range 1-22) per patient. Tumour responses were observed in 20 patients (20%), with an additional 47 patients (46%) achieving disease stabilisation. The median time to disease progression was 4.1 months and median overall survival was 7.7 months. The most common treatment-related adverse events were palmar-plantar erythrodysaesthesia (PPE) (36%) and gastrointestinal toxicities (diarrhoea (33%) and nausea (24%)). Dose reductions due to adverse events were required in 33% of patients, but capecitabine was administered without a dose reduction for 90% of cycles. The results achieved with capecitabine in this named-patient programme confirm that, under 'real practice' conditions, capecitabine is active and well tolerated in patients with advanced breast cancer.

Adult↗
PubMed2005

A three-dimensional computed tomography-assisted Monte Carlo evaluation of ovoid shielding on the dose to the bladder and rectum in intracavitary radiotherapy for cervical cancer.

PURPOSE: To determine the effects of Fletcher Suit Delclos ovoid shielding on dose to the bladder and rectum during intracavitary radiotherapy for cervical cancer. METHODS AND MATERIALS: The Monte Carlo method was used to calculate the dose in 12 patients receiving low-dose-rate intracavitary radiotherapy with both shielded and unshielded ovoids. Cumulative dose-difference surface histograms were computed for the bladder and rectum. Doses to the 2-cm(3) and 5-cm(3) volumes of highest dose were computed for the bladder and rectum with and without shielding. RESULTS: Shielding affected dose to the 2-cm(3) and 5-cm(3) volumes of highest dose for the rectum (10.1% and 11.1% differences, respectively). Shielding did not have a major impact on the dose to the 2-cm(3) and 5-cm(3) volumes of highest dose for the bladder. The average dose reduction to 5% of the surface area of the bladder was 53 cGy. Reductions as large as 150 cGy were observed to 5% of the surface area of the bladder. The average dose reduction to 5% of the surface area of the rectum was 195 cGy. Reductions as large as 405 cGy were observed to 5% of the surface area of the rectum. CONCLUSIONS: Our data suggest that the ovoid shields can greatly reduce the radiation dose delivered to the rectum. We did not find the same degree of effect on the dose to the bladder. To calculate the dose accurately, however, the ovoid shields must be included in the dose model.

Female↗