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PubMed2003

Advances in cardiac imaging with 16-section CT systems.

RATIONALE AND OBJECTIVES: The authors present advances in electrocardiographically (ECG) gated cardiac spiral scanning with recently introduced 16-section computed tomographic (CT) equipment. MATERIALS AND METHODS: The authors discuss the technical principles of ECG-gated cardiac scanning. They give an overview on system properties and on the detector design. They describe ECG-gated scan- and image-reconstruction techniques and ECG-controlled dose modulation ("ECG pulsing") for a reduction of the patient dose. They discuss key parameters for image quality and present simulation and phantom studies and they give preliminary values for the patient dose. RESULTS: An extension of the adaptive cardiac volume reconstruction for ECG-gated spiral CT provides adequate image quality for up to 16 sections. With the smallest reconstructed section width (about 0.83 mm) and overlapping image reconstruction, cylindrical holes 0.6-0.7 mm in diameter can be resolved in a transverse resolution phantom independent of the heart rate. For coronary CT angiography, the influence of transverse resolution is most pronounced for coronary segments that are only slightly tilted relative to the scan plane. In this case, visualization of stents and plaques is considerably improved with 1.0-mm or smaller section width. For 0.42-second gantry rotation time, temporal resolution reaches its optimum (105 msec) at a heart rate of 81 beats per minute. Effective patient dose for the standard protocols recommended by the manufacturer ranges from 0.45 mSv (male) for ECG-triggered calcium scoring to 7.1 mSv (male) for high-resolution ECG-gated coronary CT angiography. With ECG pulsing, the dose is reduced by 30%-50% depending on the patient's heart rate. CONCLUSION: Clinical experience will be needed to evaluate fully the potential of 16-section technology for cardiac imaging.

Artifacts↗
PubMed2006

A comparison of liquid nitrogen and liquid helium as cryogens for electron cryotomography.

The principal resolution limitation in electron cryomicroscopy of frozen-hydrated biological samples is radiation damage. It has long been hoped that cooling such samples to just a few kelvins with liquid helium would slow this damage and allow statistically better-defined images to be recorded. A new "G2 Polara" microscope from FEI Company was used to image various biological samples cooled by either liquid nitrogen or liquid helium to approximately 82 or approximately 12 K, respectively, and the results were compared with particular interest in the doses (10-200 e-/A2) and resolutions (3-8 nm) typical for electron cryotomography. Simple dose series revealed a gradual loss of contrast at approximately 12K through the first several tens of e-/A2, after which small bubbles appeared. Single particle reconstructions from each image in a dose series showed no difference in the preservation of medium-resolution (3-5 nm) structural detail at the two temperatures. Tomographic reconstructions produced with total doses between 10 and 350 e-/A2 showed better results at approximately 82 K than approximately 12 K for every dose tested. Thus disappointingly, cooling with liquid helium is actually disadvantageous for cryotomography.

Cryoelectron Microscopy↗
PubMed1995

Radiolabeled antibody combined with external radiotherapy for the treatment of head and neck cancer: reconstruction of a theoretical phantom of the larynx for radiation dose calculation to local tissues.

We propose to use radiolabeled antibodies in combination with external beam radiotherapy to improve locoregional control of head and neck cancer. In this case radiation toxicity to mucosa may become a dose-limiting factor and a calculation of the possible compensatory decrease to the external beam radiotherapy would be needed. For this purpose, the following theoretical phantom of a representative organ of this anatomic region, the larynx, was reconstructed and local dosimetric data were derived for a selection of beta-emitting isotopes. The phantom was reconstructed as cylindrical concentric tubes using the established values of an outer diameter of 38 mm and a height of 44 mm. Published mean adult larynx weight (28 g) and cartilage weight (14.7 g) were used. Mean mucosa weight from 5 mucosa samples of our patients was calculated to be 2.0 +/- 0.4 (SD) g. The remaining weight was apportioned to a fat/muscle compartment (11.3 g). The specific gravity of cartilage (1.10 g/cm3), mucosa (1.04 g/cm3), and fat/muscle (1.04 g/cm3) were used to cross-check the volume/mass disparity of the theoretical tubular tissue shells. The established maximum glottic diameter of 24 mm was used to calculate the central air column volume. Mean laryngeal tumor volume from 8 representative laryngeal tumors was 4.4 +/- 3.1 cm3. Tissue compartment thickness was 660 microns for mucosa, 3100 microns for muscle/fat, and 3320 microns for cartilage. These values allowed the calculation of dose absorbed fractions for a number of theoretical radioimmunoconjugates by extending the established calculation of absorbed fractions for spheres of known diameter to absorbed fractions of tissue planes (annuli) of known thickness. We calculated a Deq for the respective tissues in the larynx for 131I-, 186Re-, 188Re-, 67Cu-, 90Y-, and 153Sm-labeled HMFG1. Compensatory decrease to the external radiotherapy dose is 1.1 Gy for each injection of the radioimmunoconjugate we propose to use (131I-HMFG1). This would be best implemented through the modification of the external radiotherapy fractions falling within 2 effective half-lives of this radioconjugate in the mucosa.

Aged↗
PubMed1999

Multimodality nuclear medicine imaging in three-dimensional radiation treatment planning for lung cancer: challenges and prospects.

The purpose of this study was to determine the utility of quantitative single photon emission computed tomography (SPECT) lung perfusion scans and F-18 fluorodeoxyglucose positron emission computed tomography (PET) during X-ray computed tomography (CT)-based treatment planning for patients with lung cancer. Pre-radiotherapy SPECT (n = 104) and PET (n = 35) images were available to the clinician to assist in radiation field design for patients with bronchogenic cancer. The SPECT and PET scans were registered with anatomic information derived from CT. The information from SPECT and PET provides the treatment planner with functional data not seen with CT. SPECT yields three-dimensional (3D) lung perfusion maps. PET provides 3D metabolic images that assist in tumor localization. The impact of the nuclear medicine images on the treatment planning process was assessed by determining the frequency, type, and extent of changes to plans. Pre-radiotherapy SPECT scans were used to modify 11 (11%) treatment plans; primarily altering beam angles to avoid highly functioning tissue. Fifty (48%) SPECT datasets were judged to be 'potentially useful' due to the detection of hypoperfused regions of the lungs, but were not used during treatment planning. PET data influenced 34% (12 of 35) of the treatment plans examined, and resulted in enlarging portions of the beam aperture (margins) up to 15 mm. Challenges associated with image quality and registration arise when utilizing nuclear medicine data in the treatment planning process. Initial implementation of advanced SPECT image reconstruction techniques that are not typically used in the clinic suggests that the reconstruction method may influence dose response data derived from the SPECT images and improve image registration with CT. The use of nuclear medicine transmission computed tomography (TCT) for both SPECT and PET is presented as a possible tool to reconstruct more accurate emission images and to aid in the registration of emission data with the planning CT. Nuclear medicine imaging techniques appear to be a potentially valuable tool during radiotherapy treatment planning for patients with lung cancer. The utilization of accurate nuclear medicine image reconstruction techniques and TCT may improve the treatment planning process.

Humans↗
PubMed2002

Spectral reconstruction of high energy photon beams for kernel based dose calculations.

A kernel-based dose computation method with finite-size pencil beams (FSPBs) requires knowledge of the photon spectrum. Published methods of indirect spectral measurements using transmission measurements through beam attenuators use mathematical fits with a large number of parameters and constraints. In this study, we examine a simple strategy for fitting transmission data that models important physical characteristics of photon beams produced in clinical linear accelerators. The shape of an unattenuated bremsstrahlung spectrum is known, varying linearly from a maximum at zero energy to a value of zero at a maximum energy. This unattenuated spectrum is altered primarily by absorption of low energy photons by the flattening filter, causing the true spectrum to roll off to zero at low photon energies. A fitting equation models this behavior and has these advantages over previous methods: (1) the equation describes the shape of a bremsstrahlung spectrum based on physical expectations; and (2) only three fit parameters are required with a single constraint. Results for 4 MV and 6 MV accelerators for central axis and off-axis beams show good agreement with the maximum, average and modal energies for known spectra. Previously published models, representations of beam fluence (energy fluence, dN/dE), experimental methods, and the fitting process are discussed.

Algorithms↗
PubMed1995

Performance evaluation of a prototype high resolution digital radiographic/near real-time fluoroscopic computerized tomographic system for radiotherapy simulation.

PURPOSE: A new prototype digital radiographic/near real-time fluoroscopic and computerized tomographic (CT) imaging system has been developed and its performance is evaluated for future implementation in a radiotherapy simulator. METHODS AND MATERIALS: The new imaging modality uses a slow scan cooled charge-coupled device (CCD) camera with 2 k x 2 k x 12 bit image resolution. X-ray images formed by a Gd2O2S:Tb flat screen are directly viewed by the CCD camera via a 45 degrees angled mirror and a high speed objective lens. For CT image reconstruction, digital data from a slit image on the CCD array obtained from time-controlled x-ray scans around the object are transferred to a second tomographic computer for processing and display. RESULTS: In the digital radiographic mode, and for a 43.2 x 43.2 cm field size at the phosphor plane, the spatial resolution of the system is 2.3 +/- 0.1 lp/mm (1 sigma) as measured at the 4% level of the modulation transfer function (MTF), whereas the contrast resolution has a value of 0.5%. In the fluoroscopic mode, the system may be operated at a maximum rate of eight frames/s at a relatively lower spatial and contrast resolution. For CT scans, although the potential intrinsic spatial resolution at the isocenter is 0.35 mm, display-limited spatial resolutions of 1.2 and 1.6 mm were obtained for 30 and 40 cm reconstruction circle diameters, respectively. A contrast resolution of 1% at 0.015 Gy entrance dose was achieved, and CT reconstruction circles of up to 51 cm were attainable. CONCLUSION: The new CCD-based imaging system is capable of delivering high-quality digital radiographic and CT images for radiotherapy simulation, whereas the near real-time fluoroscopic mode yields acceptable flicker-free lower quality images at object speeds typical of simulation motions.

Fluoroscopy↗
PubMed1995

Estimation of pneumonitis risk in three-dimensional treatment planning using dose-volume histogram analysis.

PURPOSE: Investigations to study correlations between the estimations of biophysical models in three dimensional (3D) treatment planning and clinical observations are scarce. The development of clinically symptomatic pneumonitis in the radiotherapy of thoracic malignomas was chosen to test the predictive power of Lyman's normal tissue complication probability (NTCP) model for the assessment of side effects for nonuniform irradiation. METHODS AND MATERIALS: In a retrospective analysis individual computed-tomography-based 3D dose distributions of a random sample of 46/20 patients with lung/esophageal cancer were reconstructed. All patients received tumor doses between 50 and 60 Gy in a conventional treatment schedule. Biological isoeffective dose-volume histograms (DVHs) were used for the calculation of complication probabilities after applying Lyman's and Kutcher's DVH-reduction algorithm. Lung dose statistics were performed for single lung (involved ipsilateral and contralateral) and for the lung as a paired organ. RESULTS: In the lung cancer group, about 20% of the patients (9 out of 46) developed pneumonitis 3-12 (median 7.5) weeks after completion of radiotherapy. For the majority of these lung cancer patients, the involved ipsilateral lung received a much higher dose than the contralateral lung, and the pneumonitis patients had on average a higher lung exposure with a doubling of the predicted complication risk (38% vs. 20%). The lower lung exposure for the esophagus patients resulted in a mean lung dose of 13.2 Gy (lung cancer: 20.5 Gy) averaged over all patients in correlation with an almost zero complication risk and only one observed case of pneumonitis (1 out of 20). To compare the pneumonitis risk estimations with observed complication rates, the patients were ranked into bins of mean ipsilateral lung dose. Particularly, in the bins with the highest patient numbers, a good correlation was achieved. Agreement was not reached for the lung functioning as a paired organ. CONCLUSIONS: Realistic assessments for the prediction of radiation-induced pneumonitis seem to be possible. In this respect, the implementation of DVH-analysis in 3D planning could be a helpful tool for the evaluation of treatment plans.

Dose-Response Relationship, Radiation↗
PubMed2005

Photon dose conversion coefficients for human teeth in standard irradiation geometries.

Photon dose conversion coefficients for human tooth materials are computed in energy range from 0.01 to 10 MeV by the Monte Carlo method. The voxel phantom "Golem" of the human body with newly defined tooth region and a modified version of the EGS4 code have been used to compute the coefficients for 30 tooth cells with different locations and materials. The dose responses are calculated for cells representing buccal and lingual enamel layers. The computed coefficients demonstrate a strong dependence on energy and geometry of the radiation source and a weaker dependence on location of the enamel voxels. For isotropic and rotational radiation fields, the enamel dose does not show a significant dependence on tooth sample locations. The computed coefficients are used to convert from absorbed dose in teeth to organ dose or to integral air kerma. Examples of integral conversion factors from enamel dose to air kerma are given for several photon fluences specific for the Mayak reprocessing plant in Russia. The integral conversion factors are strongly affected by the energy and angular distributions of photon fluence, which are important characteristics of an exposure scenario for reconstruction of individual occupational doses.

Humans↗
PubMed1999

Postradiation sarcomas: 20 cases and a literature review.

PURPOSE: To analyze 20 cases of postradiation sarcoma (PRS) to determine dose levels at which this condition developed, the pathology of the initial and postradiation tumors, latency period, and outcome; and to review the literature and propose modified criteria for diagnosis. METHODS AND MATERIALS: Patient records were reviewed. Previous radiation fields and isodose charts were reconstructed to determine the dose received in the tissue in which the PRS subsequently developed. RESULTS: There were 16 female patients and 4 male patients. Mean age at the time of initial radiotherapy was 28 years. Mean latency was 14 years, with no difference in latency between the adult and pediatric group (t = 0.45, p = 0.37), but shorter latency in the retinoblastoma than in the nonretinoblastoma patients (t = 3.18, p = 0.003). The outcome was poor; 2 patients were alive and disease-free at 2 and 5 years. The 18 patients who died as a result of PRS had a median survival of 1 year. CONCLUSION: PRSs are rare. Unnecessary radiation must be avoided. Cases should be reported with full details so that risk factors can be ascertained. PRSs usually arise in moderate to higher dose areas. Diagnostic criteria should allow soft tissue tumors and short latency.

Adult↗
PubMed1988

Radiation dose and second cancer risk in patients treated for cancer of the cervix.

The risk of cancer associated with a broad range of organ doses was estimated in an international study of women with cervical cancer. Among 150,000 patients reported to one of 19 population-based cancer registries or treated in any of 20 oncology clinics, 4188 women with second cancers and 6880 matched controls were selected for detailed study. Radiation doses for selected organs were reconstructed for each patient on the basis of her original radiotherapy records. Very high doses, on the order of several hundred gray, were found to increase the risk of cancers of the bladder [relative risk (RR) = 4.0], rectum (RR = 1.8), vagina (RR = 2.7), and possibly bone (RR = 1.3), uterine corpus (RR = 1.3), cecum (RR = 1.5), and non-Hodgkin's lymphoma (RR = 2.5). For all female genital cancers taken together, a sharp dose-response gradient was observed, reaching fivefold for doses more than 150 Gy. Several gray increased the risk of stomach cancer (RR = 2.1) and leukemia (RR = 2.0). Although cancer of the pancreas was elevated, there was no evidence of a dose-dependent risk. Cancer of the kidney was significantly increased among 15-year survivors. A nonsignificant twofold risk of radiogenic thyroid cancer was observed following an average dose of only 0.11 Gy. Breast cancer was not increased overall, despite an average dose of 0.31 Gy and 953 cases available for evaluation (RR = 0.9); there was, however, a weak suggestion of a dose response among women whose ovaries had been surgically removed. Doses greater than 6 Gy to the ovaries reduced breast cancer risk by 44%. A significant deficit of ovarian cancer was observed within 5 years of radiotherapy; in contrast, a dose response was suggested among 10-year survivors. Radiation was not found to increase the overall risk of cancers of the small intestine, colon, ovary, vulva, connective tissue, breast, Hodgkin's disease, multiple myeloma, or chronic lymphocytic leukemia. For most cancers associated with radiation, risks were highest among long-term survivors and appeared concentrated among women irradiated at relatively younger ages.

Female↗
PubMed1999

Precision of estimates of an ADI (or TDI or PTWI).

Factors influencing the precision of an acceptable daily intake (ADI) are discussed in this paper. As the same principles apply to tolerable daily intake (TDI) or provisional tolerable weekly intake (PTWI), although not specifically mentioned, this paper also refers to TDI and PTWI. The allocation of an ADI is in principle based on the most critical (many times the lowest) no-observed (adverse)-effect level [NO(A)EL] established in toxicological studies in experimental animals or in humans by applying a uncertainty factor for extrapolation from animals or humans to the general human population (and for the extrapolation from high to low intake levels). As the ADI predicts a virtual safe intake level for a life span exposure, to establish a NO(A)EL in general the toxicological database should include long-term studies, otherwise only a provisional ADI will be allocated for which a higher uncertainty factor is applied. The validity of an ADI greatly depends on the precision of the toxicological studies considered for the safety of a food additive or contaminant. The precision of the ADI is also inversely related to the uncertainty factors applied, although these uncertainty factors are not totally independent of the completeness and precision of the toxicological data from which a NO(A)EL is derived. This paper focuses on the precision of the toxicological data and the established NO(A)EL. Human data on the toxicity of a chemical which are preferred for the safety evaluation or hazard assessment are frequently not available or incomplete with respect to a quantitative dose-response assessment. Epidemiological studies will have inherent difficulties for hazard assessment such as possible confounders, restricted number of toxicological end points which can be studied, and limited quantitative data on oral exposure levels. Case report studies include the same limitations but in addition the exposure data are usually very imprecise due to reconstruction of the possible dose level(s). Case reports of intoxication are mainly restricted to acute and at best subacute effects. Controlled human exposure studies (human volunteer studies) are restricted in their experimental design such as the level of the dose and the toxicological end points due to medical ethical reasons. Therefore, quite rarely a safety evaluation of a food chemical will be solely based on human data. In the practice of hazard assessment of chemicals in foods the experimental animal studies will be totally or partly the basis for establishing an ADI. In these toxicological studies in animals there are many experimental variables which can affect the precision of an ADI, such as (1) duration of the experiment, dose ranges, identity, and purity of the substance; (2) the parameters and toxicological end points studied; (3) the species and strain used; (4) the gut microflora of the test animals; (5) dietary composition; (6) statistics performed; and (7) knowledge about the kinetic behavior and metabolism (e.g., elimination half-life and bioavailability of the chemical and its main metabolites) of the chemical considered. How these factors can influence the precision of a NO(A)EL, respectively the ADI, is illustrated by several examples. In relation to the question of incidental excursions of an ADI, it can be concluded that due to the variation in precision of experiments slight incidental excursions would not lead to an increased risk. However, to answer in general the question of how often and/or how much the total intake of a chemical in food may exceed the ADI is not possible. This should be considered case by case. To answer such a question, the precision for those studies representative for incidental excursions should be considered. Other factors which should be considered are (1) type of effect on which the ADI was based, (2) mechanism of toxicity, (3) toxicokinetics and metabolism, and (4) difference in NO(A)ELs from short-term toxicity studies with the NO(A)EL on

Animals↗
PubMed2004

[Image quality of thin- and thick-slice MSCT reconstructions in low-contrast objects (liver lesions) with equal doses].

PURPOSE: To evaluate the image quality of thin-section MSCT examinations of low-contrast objects such as liver lesions, and to find out whether a thin slice technique requires an increase in radiation dose. MATERIALS AND METHODS: MSCT examinations of the liver were performed in the portal venous phase on a Volume Zoom Scanner (Siemens, Erlangen) with a collimation of 4 x 2.5 mm, 120 kV, 125 mAs and table speed of 12.5 mm. Forty small hypodense liver lesions with a mean size of 3 mm (1 to 8 mm) were reconstructed using a slice thickness of 3, 5, 7, and 10 mm. All lesions were evaluated for each slice thickness by 3 independent radiologists using a 5-point scale (excellent to poor) for the following 7 criteria: contrast, demarcation and contour of the lesion, image noise and quality, demarcation of liver veins and liver contour. The mean values of the reviewers' scores were calculated. The correlation of the three observers in the evaluation of the criteria was determined using the Kendall's Tau coefficient. RESULTS: The 3-mm thin sections were excellent in the evaluation of lesion detection, lesion contrast and lesion contour with a mean score of 1.4 compared to 4.1 for 10-mm sections. Concerning the criteria image quality and liver contour, thin sections achieved the best results in our series. Image noise was pronounced in thin sections but did not affect negatively the image analysis. Interrater agreement was 0.53 for the criterium image noise. CONCLUSION: Thin sections in MSCT examinations of low contrast objects such as liver lesions do not require an increase in radiation dose because the increase in image noise is compensated by improved lesion contrast.

Contrast Media↗
PubMedDate not supplied

Dental prosthetic reconstruction of osseointegrated implants placed in irradiated bone.

Nineteen patients who were treated for oncologic pathology by surgery and radiotherapy (average dose = 57 Gy) received prosthetic reconstruction with 53 implants placed in the residual mandible or maxilla and/or replacement bone graft. Implants were placed within a minimum period of 5 months after radiotherapy. The healing period before placement of the prosthesis also was at least 5 months. Two to six implants were placed as a function of tooth loss and required prosthetic design. Prostheses included both removable and fixed restorations. Two implants were lost as a result of osseointegration failure. Fifteen implants in six patients could not be followed throughout the study because of patient expiration. Patients were followed up to 68 months and for an average of 38 months. No osteoradionecrosis phenomenon was seen in this study. However, caution is urged in placing implants in irradiated bone because of the potential for osteoradionecrosis. Patients should be carefully selected and a strict therapeutic protocol should be followed.

Adult↗
PubMed1994

The tetrad and hexad: maximum beam separation as a starting point for noncoplanar 3D treatment planning: prostate cancer as a test case.

PURPOSE: In contrast to computer optimized three-dimensional (3D) treatment planning, we have used maximally separated, noncoplanar beams as the starting point for 3D treatment planning of prostate cancer to maximize the rate of dose fall off from the target volume and minimize dose to surrounding tissues. MATERIALS AND METHODS: A planar four-field plan, a planar six-field plan, a tetrad plan, and a hexad plan are analyzed using a 3D treatment planning system which is capable of displaying real-time 3D dose distributions within volume reconstructed data sets (VISTAnet--an extension of the virtual simulator). The tetrad plan is based on the methane molecule and the hexad plan has a minimum separation of 58 degrees on beam entrance. All fields are conformal. The irradiated volume equals the clinical target volume plus a 1 cm margin. Competing plans are compared using cumulative dose-volume histograms and normal tissue complication probabilities. RESULTS: The crossover point, the isodose surface that conforms more to the beams than the target, is introduced and described. The hexad and tetrad plans result in tighter dose distributions when compared to the planar plans with the same number of beams. The tetrad plan treats a volume less than or equal to the planar six-field plan at isodose surfaces above 18% except between 37% and 44% where the tetrad volume is slightly larger. As expected from integral dose considerations, the amount of normal tissue receiving some radiation increases, but the amount receiving clinically significant amounts of radiation decreases as the number of beams increase. The plan involving the largest number of noncoplanar beams results in the tightest isodose distribution. Analysis of rectal and bladder cumulative dose volume histograms does not reveal a clearly superior plan based on normal tissue complication probabilities. CONCLUSIONS: Using basic principles of solid geometry, maximally separated beams without significant overlap on exit or entrance can be designed which minimize clinically significant dose to surrounding tissues and tighten the isodose distribution around the target volume. The emphasis of this treatment plan optimization is geometric in contrast to methods using computer optimization or artificial intelligence.

Humans↗
PubMed2005

CT computer-optimized high-dose-rate brachytherapy with surface applicator technique for scar boost radiation after breast reconstruction surgery.

PURPOSE: Immediate breast reconstruction has become increasingly prevalent after mastectomy for breast cancer. Postoperative scar boost radiation for the reconstructed breast presents many planning challenges due to the shape, size, and curvature of the scar. High-dose-rate (HDR) surface applicator brachytherapy is a novel and effective method of delivering scar boost radiation. Two cases, one with a saline implant and one with a transverse rectus abdominis musculocutaneous flap reconstruction, illustrate the method and advantages of HDR optimization of surface applicators. METHODS AND MATERIALS: For 2 patients a mold of the breast was made with Aquaplast sheets. A reproducible system was used for arm positioning. Skin fiducials, including tattoos from external beam planning, were matched to fiducials on the mold. HDR catheters were sited on the mold at 1cm intervals, with the central catheter situated along the scar. Topographically, both scars demonstrated extreme curvature in both craniocaudal and mediolateral directions. A CT computer-optimized HDR plan was developed, with the reference dose prescribed at the skin surface. The dosimetry was compared to single-field and matched-field electron plans. RESULTS: This surface applicator technique provided a uniform skin dose of 100% to the entire clinical target volume (CTV) without hot spots in both patients. The patient position and surface applicator setup were consistently reproducible. The patients tolerated the treatment well with minimal skin erythema. In the single-field electron plan, skin dose was decreased to 50% at the periphery of the scar. Matching fields addressed this depth dose decrement, but resulted in large localized hot spots of more than 200% centrally in each field. CONCLUSION: CT computer-optimized HDR surface applicator brachytherapy provided a reproducible homogeneous method of treating highly curved scars on the reconstructed breast. Electron beam treatment would result in longer and more complex treatments yet still provide a less homogeneous dose than this surface applicator technique.

Brachytherapy↗
PubMed2005

Preventing radiation retinopathy with hyperfractionation.

PURPOSE: The purpose of this study was to determine factors associated with the development of radiation retinopathy in a large series of patients with head-and-neck cancer. In particular, we addressed whether the use of hyperfractionated radiation therapy was effective in reducing the risk of retinopathy. METHODS AND MATERIALS: One hundred eighty-six patients received a significant dose to the retina as part of curative radiotherapy. Primary sites included: nasopharynx, 46; paranasal sinus, 64; nasal cavity, 69; and palate, 7. Prescription doses varied depending on primary site and histology. Hyperfractionated (twice-daily) radiation was delivered to 42% of the patients in this study, typically at 1.10 to 1.20 Gy per fraction. The remainder were treated once-daily. Retinal doses were determined from computerized dosimetry plans when available. For all other patients, retinal doses were retrospectively calculated using reconstructed off-axis dosimetry taken from contours through the center of the globes. Retinal dose was defined as the minimum dose received by at least 25% of the globe. The median retinal dose was 56.85 Gy. Patients were followed for a median of 7.6 years. RESULTS: Thirty-one eyes in 30 patients developed radiation retinopathy, resulting in monocular blindness in 25, bilateral blindness in 1, and decreased visual acuity in 4. The median time to the diagnosis of retinopathy was 2.6 years (range, 11 months to 5.3 years). The actuarial incidence of developing radiation retinopathy was 20% at both 5 and 10 years. The incidence of developing ipsilateral blindness due to retinopathy was 16% at 5 years and 17% at 10 years. Site-specific incidences varied considerably, with ethmoid sinus (9 of 25, 36%), nasal cavity (13 of 69, 19%), and maxillary sinus (6 of 35, 17%) being the most common sites associated with radiation retinopathy. Three of 72 patients (4%) receiving retinal doses less than 50 Gy developed retinopathy. Higher retinal doses resulted in a steady increase in the incidence of retinopathy, with 25 of the 30 cases occurring after 60 Gy or more. Of the patients receiving more than 50 Gy to the retina, hyperfractionation was associated with a significantly lower incidence of radiation retinopathy (37% vs. 13%; p = 0.0037). On multivariate analysis, retinal dose (p < 0.0001), fractionation schedule (p = 0.0003), age (p = 0.0365), and prolonged overall treatment time (p = 0.0213) were significant predictors of radiation retinopathy. CONCLUSION: The incidence of ipsilateral radiation retinopathy after treatment of nasal cavity/paranasal tumors is 20% at 5 and 10 years. Retinal dose and fractionation schedule are the strongest predictors of retinopathy. Hyperfractionated radiotherapy is associated with a significant reduction in the incidence of radiation retinopathy, especially when the retina receives more than 50 Gy.

Adolescent↗
PubMed1996

Conformal treatment planning for interstitial brachytherapy.

PURPOSE: Quality of a brachytherapy application depends on the choice of the target volume, on the dose distribution homogeneity and radiation injury on critical tissue, which should be postulated by advanced brachytherapy treatment planning systems. MATERIAL AND METHODS: Basic imaging method for conformal treatment planning is the cross-sectional imaging. The clinical applicability of a new type 3D planning system using CT and/or MRT-simulation or US-simulation for planning purposes was studied. The planning system developed at Kiel University differs from usual brachytherapy planning systems because of the obligatory use of cross-sectional imaging as basic imaging method for reconstruction of structures of interest. Dose distribution and normal anatomy can be visualized on each CT/MRT/US slice as well as coronal, sagittal, axial and free chosen reconstruction (3D), as well as dose-volume histogram curves and special colour-coded visualization of dose homogeneity in the target can be analyzed. RESULTS: Because of the experience in the clinical routine, as well as on the base of 30 simultaneous planning procedures on both 2D (semi-3D) and 3D planning systems we observed similar time consumption. Advantages of 3D planning were the better interpretation of target delineation, delineation of critical structures as well as dose distribution, causing more accurate volume optimisation of dose distribution. CONCLUSION: Conformal brachytherapy treatment planning for interstitial brachytherapy means significant advantages for the clinical routine compared to 2D or semi-3D methods.

Algorithms↗
PubMed1998

[Window width as a dosage-relevant factor in high-contrast structures in CT].

PURPOSE: To establish the relationship between window width and dose to be applied in low-dose high-resolution (HR) computed tomography (CT). MATERIAL AND METHODS: Low-dose HR CT-scans of the petrous bone displayed with different window values were analyzed for identification of osseous details. For two homogeneous phantoms, standard deviation of CT-numbers were measured in order to calculate the fraction of pixels not displayed within the correct grey level. RESULTS: The broadest window used (4000 HU) allowed the best distinction of osseous structures. Standard deviation of CT-numbers in the phantoms varied between 28.5 and 43.2 (mean = 33.6) HU. Thus, only 26.6% of all pixels are displayed in the correct grey level for a 1000 HU-window, but 82.3% for a 4000 HU-window. CONCLUSION: When using low doses and HR-reconstruction algorithms, large window widths allow for an optimal assessment of high-contrast structures. Under these conditions, even high standard deviations of the CT-numbers will not compromise image evaluation. Due to the restricted number of grey-levels that can be distinguished by the human eye, image noise is compressed into a smaller number of discernable grey-levels. Because of the inverse square root function between dose to be applied and window width used (derived in the article), an even minor enlargement of window permits considerable reductions of patient exposure while the discernable image noise remains constant.

Artifacts↗