Time filter

Source Type

BLOOMINGTON, IN, United States

Hartford A.C.,Dartmouth Hitchcock Medical Center | Paravati A.J.,Dartmouth Hitchcock Medical Center | Spire W.J.,Dartmouth Hitchcock Medical Center | Li Z.,Norris Cotton Cancer Center | And 9 more authors.
International Journal of Radiation Oncology Biology Physics | Year: 2013

Purpose: Radiation therapy following resection of a brain metastasis increases the probability of disease control at the surgical site. We analyzed our experience with postoperative stereotactic radiosurgery (SRS) as an alternative to whole-brain radiotherapy (WBRT), with an emphasis on identifying factors that might predict intracranial disease control and overall survival (OS). Methods and Materials: We retrospectively reviewed all patients through December 2008, who, after surgical resection, underwent SRS to the tumor bed, deferring WBRT. Multiple factors were analyzed for time to intracranial recurrence (ICR), whether local recurrence (LR) at the surgical bed or "distant" recurrence (DR) in the brain, for time to WBRT, and for OS. Results: A total of 49 lesions in 47 patients were treated with postoperative SRS. With median follow-up of 9.3 months (range, 1.1-61.4 months), local control rates at the resection cavity were 85.5% at 1 year and 66.9% at 2 years. OS rates at 1 and 2 years were 52.5% and 31.7%, respectively. On univariate analysis (preoperative) tumors larger than 3.0 cm exhibited a significantly shorter time to LR. At a cutoff of 2.0 cm, larger tumors resulted in significantly shorter times not only for LR but also for DR, ICR, and salvage WBRT. While multivariate Cox regressions showed preoperative size to be significant for times to DR, ICR, and WBRT, in similar multivariate analysis for OS, only the graded prognostic assessment proved to be significant. However, the number of intracranial metastases at presentation was not significantly associated with OS nor with other outcome variables. Conclusions: Larger tumor size was associated with shorter time to recurrence and with shorter time to salvage WBRT; however, larger tumors were not associated with decrements in OS, suggesting successful salvage. SRS to the tumor bed without WBRT is an effective treatment for resected brain metastases, achieving local control particularly for tumors up to 3.0 cm diameter. © 2013 Elsevier Inc. All rights reserved. Source

Nichiporov D.,Indiana University | Hsi W.,Procure Treatment Centers, Inc. | Farr J.,Westdeutsches Protonentherapiezentrum
Medical Physics | Year: 2012

Purpose: To compare clinically relevant dosimetric characteristics of proton therapy fields produced by two uniform scanning systems that have a number of similar hardware components but employ different techniques of beam spreading. Methods: This work compares two technologically distinct systems implementing a method of uniform scanning and layer stacking that has been developed independently at Indiana University (IU) and by Ion Beam Applications, S. A. (IBA). Clinically relevant dosimetric characteristics of fields produced by these systems are studied, such as beam range control, peak-to-entrance ratio (PER), lateral penumbra, field flatness, effective source position, precision of dose delivery at different gantry angles, etc. Results: Under comparable conditions, both systems controlled beam range with an accuracy of 0.5 mm and a precision of 0.1 mm. Compared to IBA, the IU system produced pristine peaks with a slightly higher PER (3.23 and 3.45, respectively) and smaller, symmetrical, lateral in-air penumbra of 1 mm compared to about 1.9/2.4 mm in the inplane/crossplane (IP/CP) directions for IBA. Large field flatness results in the IP/CP directions were similar: 3.0/2.4 for IU and 2.9/2.4 for IBA. The IU system featured a longer virtual source-to-isocenter position, which was the same for the IP and CP directions (237 cm), as opposed to 212/192 cm (IP/CP) for IBA. Dose delivery precision at different gantry angles was higher in the IBA system (0.5) than in the IU system (1). Conclusions: Each of the two uniform scanning systems considered in this work shows some attractive performance characteristics while having other features that can be further improved. Overall, radiation field characteristics of both systems meet their clinical specifications and show comparable results. Most of the differences observed between the two systems are clinically insignificant. © 2012 American Association of Physicists in Medicine. Source

Zheng Y.,Proton Therapy | Liu Y.,INTEGRIS Cancer Institute | Zeidan O.,Proton Therapy | Schreuder A.N.,Procure Treatment Centers, Inc. | Keole S.,Proton Therapy
Medical Physics | Year: 2012

Purpose: Neutron exposure is of concern in proton therapy, and varies with beam delivery technique, nozzle design, and treatment conditions. Uniform scanning is an emerging treatment technique in proton therapy, but neutron exposure for this technique has not been fully studied. The purpose of this study is to investigate the neutron dose equivalent per therapeutic dose, HD, under various treatment conditions for uniform scanning beams employed at our proton therapy center. Methods: Using a wide energy neutron dose equivalent detector (SWENDI-II, ThermoScientific, MA), the authors measured HD at 50 cm lateral to the isocenter as a function of proton range, modulation width, beam scanning area, collimated field size, and snout position. They also studied the influence of other factors on neutron dose equivalent, such as aperture material, the presence of a compensator, and measurement locations. They measured HD for various treatment sites using patient-specific treatment parameters. Finally, they compared HD values for various beam delivery techniques at various facilities under similar conditions. Results: HD increased rapidly with proton range and modulation width, varying from about 0.2 mSvGy for a 5 cm range and 2 cm modulation width beam to 2.7 mSvGy for a 30 cm range and 30 cm modulation width beam when 18 × 18 cm2 uniform scanning beams were used. HD increased linearly with the beam scanning area, and decreased slowly with aperture size and snout retraction. The presence of a compensator reduced the HD slightly compared with that without a compensator present. Aperture material and compensator material also have an influence on neutron dose equivalent, but the influence is relatively small. HD varied from about 0.5 mSvGy for a brain tumor treatment to about 3.5 mSvGy for a pelvic case. Conclusions: This study presents HD as a function of various treatment parameters for uniform scanning proton beams. For similar treatment conditions, the HD value per uncollimated beam size for uniform scanning beams was slightly lower than that from a passive scattering beam and higher than that from a pencil beam scanning beam, within a factor of 2. Minimizing beam scanning area could effectively reduce neutron dose equivalent for uniform scanning beams, down to the level close to pencil beam scanning. © 2012 American Association of Physicists in Medicine. Source

Jarvis L.A.,Dartmouth Hitchcock Medical Center | Simmons N.E.,Dartmouth Hitchcock Medical Center | Bellerive M.,Dartmouth Hitchcock Medical Center | Erkmen K.,Dartmouth Hitchcock Medical Center | And 5 more authors.
International Journal of Radiation Oncology Biology Physics | Year: 2012

Purpose: To analyze 2 factors that influence timing of radiosurgery after surgical resection of brain metastases: target volume dynamics and intracranial tumor progression in the interval between surgery and cavity stereotactic radiosurgery (SRS). Methods and Materials: Three diagnostic magnetic resonance imaging (MRI) scans were retrospectively analyzed for 41 patients with a total of 43 resected brain metastases: preoperative MRI scan (MRI-1), MRI scan within 24 hours after surgery (MRI-2), and MRI scan for radiosurgery planning, which is generally performed <1 week before SRS (MRI-3). Tumors were contoured on MRI-1 scans, and resection cavities were contoured on MRI-2 and MRI-3 scans. Results: The mean tumor volume before surgery was 14.23 cm3, and the mean cavity volume was 8.53 cm immediately after surgery and 8.77 cm before SRS. In the interval between surgery and SRS, 20 cavities (46.5%) were stable in size, defined as a change of <2 cm3; 10 cavities (23.3%) collapsed by >2 cm3; and 13 cavities (30.2%) increased by >2 cm 3. The unexpected increase in cavity size was a result of local progression (2 cavities), accumulation of cystlike fluid or blood (9 cavities), and nonspecific postsurgical changes (2 cavities). Finally, in the interval between surgery and SRS, 5 cavities showed definite local tumor progression, 4 patients had progression elsewhere in the brain, 1 patient had both local progression and progression elsewhere, and 33 patients had stable intracranial disease. Conclusions: In the interval between surgical resection and delivery of SRS, surgical cavities are dynamic in size; however, most cavities do not collapse, and nearly one-third are larger at the time of SRS. These observations support obtaining imaging for radiosurgery planning as close to SRS delivery as possible and suggest that delaying SRS after surgery does not offer the benefit of cavity collapse in most patients. A prospective, multi-institutional trial will provide more guidance to the optimal timing of cavity SRS. © 2012 Elsevier Inc. Source

Agency: Department of Health and Human Services | Branch: | Program: SBIR | Phase: Phase I | Award Amount: 129.02K | Year: 2010

DESCRIPTION (provided by applicant): In comparison to standard x-ray therapy, proton therapy allows an increased dose of radiation to a tumor and by reducing the amount of radiation to healthy tissue. As a result, it provides the best possible option for using radiation to control and eliminate tumors with the least short and long term toxic side effects. Currently less than 1% of all radiation therapy patients receive proton therapy while the number of patients that would benefit substantially from their use with current protocols is estimated to be over 30%. The major barriers to greater utilization of proton therapy are the size and cost of the facilities. The layout of the current proton therapy treatment centers is dominated by the size of the iso-centric gantries that rotate the proton beam dose delivery system around the patient. ProCure's focus for this project is to invent a new gantry concept using modern robotics and high temperature superconducting magnets that will greatly reduce the gantry size and mass, the power needed to operate it and consequently the contribution of these gantries to the facility cost. ProCure proposes to research new technology that would reduce the gantry mass by an order of magnitude and cost by a factor of three. Phase I research will allow ProCure to determine the optimal design and components needed for a compact and low cost gantry based on novel beam scanning concepts and the use of high temperature superconducting magnet technology for use in Intensity Modulated Proton Therapy. In the first 12 months of Phase II, ProCure will work on constructing prototype magnets for the selected gantry concept, build key temporary magnet supports and nozzle components and in the next six months of Phase II, ProCure will carry out experiments using a full scale system in the Proton Dosimetry Test Facility recently commissioned at the Indiana University Cyclotron Facility. In Phase III, ProCure will complete the tests of the magnetic and nozzle operation at IUCF and make initial submission to the FDA. ProCure will construct a first prototype of the full rotating mechanical support system for the gantry and install the full system for mechanical system tests. In parallel, ProCure will start the acquisition process for the first systems that will be installed. Finally, FDA complete system testing for full FDA 510k approval will be performed. PUBLIC HEALTH RELEVANCE: Proton therapy provides the best possible option for using radiation to control and eliminate tumors with the least short and long term toxic side effects; however, only less than 1% of all radiation therapy patients receive proton therapy. The major barriers to greater utilization of proton therapy are the size and cost of the facilities. ProCure's new proton beam delivery concept will greatly reduce the size and mass of the system and the power needed to operate it, and consequently, help to bring this highly effective form of cancer treatment to the mainstream of radiation therapy.

Discover hidden collaborations