Biomedical subjects

Sasa Mutic

Publications and source records attributed to Sasa Mutic.

24 records · Page 2Linked to original sources

PubMed2002

Applicator-guided intensity-modulated radiation therapy.

PURPOSE: We are introducing a novel method for delivering highly conformal dose distributions to cervical cancer tumors using external beam intensity-modulated radiation therapy. The method, termed applicator-guided intensity-modulated radiation therapy (AGIMRT), will use an applicator substitute placed in the vagina and uterus to provide spatial registration and immobilization of the gynecologic organs. The main reason for the applicator substitute will be to localize the fornices, cervix, and uterus with the expectation that the other nearby organs will also be reproducibly positioned with respect to the applicator substitute. Intensity-modulated radiation therapy (IMRT) dose distributions will be used as a substitute for high-dose-rate intracavitary brachytherapy procedures. The flexibility of IMRT will enable customized dose distributions that have the potential to reduce complications and improve local control, especially for locally advanced disease. METHODS AND MATERIALS: To test the advantages of IMRT over intracavitary brachytherapy, volumetric scans of three cervical cancer patients were obtained with implanted CT-compatible applicators. IMRT dose distribution simulations using tomotherapy, were compared against intracavitary brachytherapy using cesium tubes to investigate the dosimetric differences of the two modalities. Because these tumor volumes do not image well on CT, the target volumes were defined as the isodose surface containing the traditional point A, defined as 2 cm superior to the vaginal fornices and 2 cm lateral to the intrauterine canal. One patient had a uterus that wrapped superior and anterior to the bladder. For this case, the cervix and uterus were selected as the target volume. To determine the potential for using an applicator substitute to localize internal organs, the posterior bladder and anterior rectal surfaces were localized relative to the colpostats. Comparisons of the colpostat-localized surfaces were conducted for two scan studies for 3 patients. RESULTS: The IMRT distributions covered the point-A isodose surfaces while reducing doses to the bladder and rectum. Brachytherapy showed extensive underdose regions in the target volume for the wrapped-around target. Spatial positioning was better than 0.7 and 1.3 cm in the rectum and bladder, respectively, indicating the potential that an applicator substitute may be able to localize these structures. CONCLUSIONS: AGIMRT has the potential for improving critical structure avoidance while maintaining highly reproducible and accurate internal organ registration found with brachytherapy.

Female↗

PubMed2002

Performance evaluation of an 85-cm-bore X-ray computed tomography scanner designed for radiation oncology and comparison with current diagnostic CT scanners.

INTRODUCTION: The demand for computed tomography (CT) virtual simulation is constantly increasing with the wider adoption of three-dimensional conformal and intensity-modulated radiation therapy. Virtual simulation CT studies are typically acquired on conventional diagnostic scanners equipped with an external patient positioning laser system and specialized planning and visualization software. Virtual simulation technology has matured to a point where conventional simulators may be replaced with CT scanners. However, diagnostic CT scanner gantry bores (typically 65-70 cm) can present an obstacle to the CT simulation process by limiting patient positions, compared to those that can be attained in a conventional simulator. For example, breast cancer patients cannot always be scanned in the treatment position without compromising reproducibility and appropriateness of setup. Extremely large patients or patients requiring special immobilization or large setup devices are often unable to enter the limited-bore gantry. A dedicated 85-cm-bore radiation oncology CT scanner has the potential to eliminate these problems. The scanner should provide diagnostic-quality images at diagnostic-comparable dose levels. The purpose of this study was to independently evaluate the performance of a novel 85-cm-bore CT X-ray scanner designed specifically for radiation oncology and compare it against diagnostic-type, 70-cm-bore scanners that may be used in the same setting. MATERIALS AND METHODS: We performed image quality and dosimetric measurements on an 85-cm-bore CT scanner (AcQSim CT, Marconi Medical Systems, Inc., Cleveland, OH) and a 70-cm-bore, diagnostic-type scanner (UltraZ CT, Marconi Medical Systems, Inc.). Image quality measurements were performed using a manufacturer-supplied phantom (Performance Phantom, Marconi Medical Systems, Inc.), following the manufacturer's suggested testing procedures, and an independent image quality phantom (CATPHAN 500, The Phantom Laboratory, New York, NY). The standard image quality parameters evaluated for the purpose of comparison were as follows: slice thickness accuracy, high-contrast resolution (limiting spatial resolution), low-contrast resolution, uniformity and noise, and CT number accuracy and linearity. Standard head and body protocols were employed throughout most of our measurements and were kept equal between the two scanners. The computed tomography dose index was measured for standard head and body imaging protocols using accepted methods and procedures. For comparison purposes, data for a diagnostic-type, 70-cm-bore scanner (GE HighSpeed CT/i) were extracted from the literature. The results obtained for the 85-cm-bore scanner are compared with the following: (1) manufacturer-provided autoperformance phantom test results (validating its use for routine quality assurance), (2) a similar set of measurements performed on a conventional 70-cm-bore, diagnostic-type CT scanner (UltraZ CT, Marconi Medical Systems, Inc.), and (3) current available data on other diagnostic-type CT scanners (GE HighSpeed CT/i). RESULTS: Head and body doses seem on average to be slightly (1-2 cGy) higher for the 85-cm-bore unit than for conventional 70-cm units. Measured slice thickness was within acceptable criteria, +/-0.5 mm. There does not seem to be any significant difference in high-contrast resolution. Both units render a limiting value of approximately 7-8 lp/cm for slice thickness 8-10 mm. Both units exhibit comparable CT number uniformity, accuracy, and linearity. Noise levels seem to be slightly increased (by approximately 0.05-0.2%) for the large-bore geometry. Low-contrast resolution for both units was comparable (4.5-5.5 mm @ 0.35%). All image quality parameters are well within diagnostic acceptable levels. CONCLUSION: The overall imaging performance and mechanical integrity of the 85-cm-bore scanner are comparable to those of conventional diagnostic scanners that may be employed in a radiation oncology setting.

Computer Simulation↗

PubMed2002

PET-guided three-dimensional treatment planning of intracavitary gynecologic implants.

PURPOSE: Positron emission tomography (PET) provides physiologic information that is not available from computed tomography (CT) or magnetic resonance studies. PET images may allow more accurate delineation of three-dimensional treatment planning target volumes of brachytherapy gynecologic (GYN) implants. This study evaluates the feasibility of using PET as the sole source of target, normal structure, and applicator delineation for intracavitary GYN implant treatment planning. MATERIALS AND METHODS: Standard Fletcher-Suit brachytherapy tandem and colpostat applicators were used for radiation delivery. After insertion of the applicator in the operating room, the patient was taken to a PET scanner, where 555 MBq (15 mCi) 18F-fluorodeoxyglucose (18F-FDG) was administered intravenously. Forty-five minutes later, three localization tubes containing 18F-FDG were inserted into the source afterloading compartments of the tandem and colpostat. A whole-pelvis scan was performed, and the images were transferred to a commercial brachytherapy three-dimensional treatment planning system. A Foley catheter was inserted into the urinary bladder while the patient was in the operating room. The regions of radioactivity in the three applicator tube image were contoured for reconstruction of the applicator, along with the bladder, rectum, and 18F-FDG-defined target volumes. A treatment plan was generated that included dose-volume histograms and three-dimensional dose distribution displays, allowing the physician an opportunity to determine if adequate target coverage and normal-tissue sparing had been obtained. For a more conservative approach, three-dimensional dose distributions and dose-volume histograms delivered with conventional source arrangements and loading could be observed. The accuracy of applicator localization from the PET images was verified using a water phantom containing two aluminum CT-compatible tandems. The PET-defined and CT scan applicator reconstructions were compared. RESULTS: Feasibility of using PET images for treatment planning of brachytherapy intracavitary GYN implants has been demonstrated. A phantom study demonstrated applicator reconstruction accuracy in the axial direction to be better than 2 mm. Reconstruction accuracy in the longitudinal direction (principally craniocaudal) was similar to the PET scanner's voxel size of 4.3 mm. CONCLUSIONS: Brachytherapy intracavitary GYN implant design has traditionally been based on patient tumor staging, palpation, and clinical experience. PET images have the potential to provide better spatial information about the relationship of tumor and normal structures to the applicator. This information can be used to optimize the delivery of radiation therapy treatments. Thus far, six patients have been scanned using this process.

Brachytherapy↗

PubMed2002

Dosimetry of therapeutic photon beams using an extended dose range film.

For intensity modulated radiation therapy (IMRT) dose distribution verification, multidimensional measurements are required to quantify the steep dose-gradient regions. High resolution, two-dimensional dose distributions can be measured using radiographic film. However, the photon energy response of film is known to be a function of depth, field size, and photon beam energy, potentially reducing the accuracy of dose distribution measurements. The dosimetric properties of the recently developed Kodak EDR2 film were investigated and compared to those of Kodak XV film. The dose responses of both film types to 6 MV and 18 MV photon beams were investigated for depths of 5 cm, 10 cm, and 15 cm and field sizes of 4x4 cm2 and 15x15 cm2. This analysis involved the determination of sensitometric curves for XV and EDR2 films, the determination of dose profiles from exposed XV and EDR2 films, and comparison of the film-generated dose profiles to ionization chamber measurements. For the combinations of photon beam energy, depth, and field size investigated here, our results indicate that the sensitometric curves are nearly independent of field size and depth of calibration. For a field size of 4x4 cm2, a single sensitometric curve for either EDR2 and XV film can be used for the determination of relative dose profiles. For the larger field size, the sensitometric curve for EDR2 film is superior to XV film in regions where the dose falls below 20% of the central axis dose, due to the effects that the increased low energy scattered photon contributions have on film response. The limited field size and depth dependence of sensitometric data measured using EDR2 film, along with the inherently wide linear dose-response range of EDR2 film, makes it better suited to the verification of IMRT dose distributions.

Calibration↗

PubMed2002

Peripheral dose distributions for a linear accelerator equipped with a secondary multileaf collimator and universal wedge.

The American Association of Physicists in Medicine Task Group 36 (AAPM TG-36) data can be used to estimate peripheral dose (PD) distributions outside the primary radiation field. However, the report data does not apply to linear accelerators equipped with a multileaf collimator (MLC) and universal wedge (UW). Tertiary multileaf collimators have been shown to significantly affect PD distributions and TG-36 reported data. Measurements were performed to evaluate PD distributions for a linear accelerator equipped with a secondary MLC, backup diaphragms, and UW. This data can be used to compliment the TG-36 report for estimation of doses to critical structures outside primary radiation fields. For the evaluated linear accelerator, an MLC is incorporated in the upper secondary collimator jaws. Backup shielding diaphragms are located underneath the MLC. At the nominal collimator position, the MLC and the backup diaphragm provide collimation primarily in the transverse direction. Conventional, solid tungsten-alloy jaws, located underneath the backup diaphragms, provide secondary collimation in the longitudinal direction. The universal wedge provides dose modulation in the direction of the conventional jaws. Measurements were made with an ionization chamber inserted into a 20x40x120 cm(3) water-equivalent plastic phantom with the secondary collimator and MLC settings of 5x5, 10x10, 15x15, and 25x25 cm(2) with and without UW. Data was acquired along the machine's longitudinal axis for 6, 10, and 18 MV photons. Peripheral dose distributions were measured with the collimator rotated to 0 degrees and 270 degrees for open field measurements and to 0 degrees, 180 degrees, and 270 degrees for wedged fields (IEC 1217). This allowed evaluation of peripheral dose distributions as a function of collimator rotation. Wedged fields were normalized to deliver the same dose at the depth of maximum dose on the central axis as open fields. The measured PD distributions were generally comparable to data reported by TG-36. At distances close to the field edge (less than 30 or 40 cm), the measured PD distributions were lower when the measurement point was shielded by solid jaws than with MLC and backup diaphragm. At longer distances, this trend reversed for all energies and evaluated field sizes. However, the difference in PD distribution with collimator rotation was not large enough to warrant strategic positioning of the collimator to reduce dose to critical structures outside the primary radiation field. Because internal scatter dominates close to the field edge, wedged PD distributions were comparable to open field doses at distances closer than 30 cm. However, at distances larger than 30 cm from the field edge, wedged PD distributions were significantly grater than those for open fields due to increased contribution of leakage radiation. Increased leakage radiation is due to the increase in wedged field monitor units, which is related to a small wedge factor (0.27 to 0.29).

Humans↗

PubMedDate not supplied

Functional imaging in treatment planning in radiation therapy: a review.

The remarkable technical developments obtained in radiation oncology have resulted in an increasing use of image-based treatment planning in radiation therapy for three-dimensional and intensity modulated radiation therapy, stereotactic irradiation and image-guided brachytherapy. There has been increased use of computer-based record and verify systems as well as electronic portal imaging to enhance treatment delivery. From the data presented it is evident that PET scanning and other functional imaging techniques play a major role in the definition of tumor extent and staging of patients with cancer. The recent introduction of a combined CT and PET scanner will substantially simplify image acquisition and treatment planning.

Brachytherapy↗