Biomedical subjects

Timothy Fox

Publications and source records attributed to Timothy Fox.

5 recordsLinked to original sources

PubMed2006

Free breathing gated delivery (FBGD) of lung radiation therapy: analysis of factors affecting clinical patient throughput.

PURPOSE: Accurate radiation targeting and delivery within the chest and abdomen is greatly affected by the respiratory cycle. Prior methods to minimize respiratory effect include breath-hold and abdominal compression techniques; these are subject to error secondary to variable inspiration/expiration volumes, or by the nature of many cancer patients having inherently poor respiratory function. However, advanced technology called free breathing gated delivery (FBGD) allows patients to breath normally during treatment. The photon beam is on only during a particular prescribed percentage of the respiratory cycle where the target tumor volume is minimized. Consequently, by using an intermittent beam, the time required to treat a patient is increased. No previous study has described the patient throughput ramifications of FBGD. PATIENTS AND METHODS: At Emory clinic, a gated treatment delivery system was inaugurated into clinical use beginning in June 2004. As of 12/31/2004, 15 patients have completed treatment with FBGD. The majority of patients had lung cancer (n=12) with single cases of adrenal metastasis, thymoma, and atypical carcinoid. Over 900 gated treatment fields (approximately 375 treatment sessions) were reviewed on an IRB-approved retrospective protocol. Records from the record-and-verify (R&V) system were queried using automated database mining software to obtain the treatment room time, treatment field time, beam-on time (BOT), dose rate, and monitor units (MU) for each treatment. The presence or absence of a dynamic wedge was also noted, as was the prescribed percent of the respiratory cycle treated. For comparison purposes, 13 non-gated lung cancer patients (lesions were not moving with respiration) were selected from the R&V database. RESULTS: Patients receiving FBGD required significantly more time for treatment delivery. The time required for FBGD was, on average, 5.5 times greater (range 1.2-12.2) than calculated BOT without gating. Time was further increased with the use of a dynamic wedge, which occurred in 45% (28/62) of the planned fields. The use of MV imaging also increased the time for FBGD treatment sessions by more than 7.5 min on average. CONCLUSIONS: FBGD uniformly increases the time required for RT delivery, and MV imaging and dynamic wedging even more so. Even though this technology more accurately targets tumor volumes while sparing normal tissue, the patient throughput issue may deter this technology from being implemented into busy clinical practices.

Female↗

PubMed2006

Performance evaluation of an automated image registration algorithm using an integrated kilovoltage imaging and guidance system.

Image-guided radiation therapy delivery may be used to assess the position of the tumor and anatomical structures within the body as opposed to relying on external marks. The purpose of this manuscript is to evaluate the performance of the image registration software for automatically detecting and repositioning a 3D offset of a phantom using a kilovoltage onboard imaging system. Verification tests were performed on both a geometric rigid phantom and an anthropomorphic head phantom containing a humanoid skeleton to assess the precision and accuracy of the automated positioning system. From the translation only studies, the average deviation between the detected and known offset was less than 0.75 mm for each of the three principal directions, and the shifts did not show any directional sensitivity. The results are given as the measurement with standard deviation in parentheses. The combined translations and rotations had the greatest average deviation in the lateral, longitudinal, and vertical directions. For all dimensions, the magnitude of the deviation does not appear to be correlated with the magnitude of the actual translation introduced. The On-Board Imager (OBI) system has been successfully integrated into a feasible online radiotherapy treatment guidance procedure. Evaluation of each patient's resulting automatch should be performed by therapists before each treatment session for adequate clinical oversight.

Algorithms↗

PubMed2006

A quality assurance program for the on-board imagers.

To develop a quality assurance (QA) program for the On-Board Imager (OBI) system and to summarize the results of these QA tests over extended periods from multiple institutions. Both the radiographic and cone-beam computed tomography (CBCT) mode of operation have been evaluated. The QA programs from four institutions have been combined to generate a series of tests for evaluating the performance of the On-Board Imager. The combined QA program consists of three parts: (1) safety and functionality, (2) geometry, and (3) image quality. Safety and functionality tests evaluate the functionality of safety features and the clinical operation of the entire system during the tube warm-up. Geometry QA verifies the geometric accuracy and stability of the OBI/CBCT hardware/software. Image quality QA monitors spatial resolution and contrast sensitivity of the radiographic images. Image quality QA for CBCT includes tests for Hounsfield Unit (HU) linearity, HU uniformity, spatial linearity, and scan slice geometry, in addition. All safety and functionality tests passed on a daily basis. The average accuracy of the OBI isocenter was better than 1.5 mm with a range of variation of less than 1 mm over 8 months. The average accuracy of arm positions in the mechanical geometry QA was better than 1 mm, with a range of variation of less than 1 mm over 8 months. Measurements of other geometry QA tests showed stable results within tolerance throughout the test periods. Radiographic contrast sensitivity ranged between 2.2% and 3.2% and spatial resolution ranged between 1.25 and 1.6 lp/mm. Over four months the CBCT images showed stable spatial linearity, scan slice geometry, contrast resolution (1%; <7 mm disk) and spatial resolution (>6 lp/cm). The HU linearity was within +/-40 HU for all measurements. By combining test methods from multiple institutions, we have developed a comprehensive, yet practical, set of QA tests for the OBI system. Use of the tests over extended periods show that the OBI system has reliable mechanical accuracy and stable image quality. Nevertheless, the tests have been useful in detecting performance deficits in the OBI system that needed recalibration. It is important that all tests are performed on a regular basis.

Equipment Failure Analysis↗

PubMed2005

Measurements of secondary neutron dose from 15 MV and 18 MV IMRT.

Secondary neutron dose-equivalents were determined for conventional and intensity modulated radiation therapy (IMRT) prostate treatments for 15 and 18 MV X-ray beams. Conventional and IMRT treatment plans were generated to deliver 45 Gy to the prostate, seminal vessicles and external and internal iliac lymph nodes. Neutron spectra were determined by unfolding measurements from a TLD-based Bonner sphere system. Treatments using 18 MV IMRT and conventional plans result in neutron ambient dose-equivalents of 687 and 112 mSv, respectively. Delivery of the 15 MV IMRT and conventional plans results in neutron ambient dose-equivalents of 327 and 52 mSv, respectively. The data illustrate that using lower photon energies for IMRT reduces the secondary neutron dose, while still achieving comparable treatment volume coverage and sparing critical normal tissue.

Body Burden↗

PubMed2003

Role of fusion in radiotherapy treatment planning.

The fusion of functional imaging to traditional imaging modalities, such as computed tomography (CT) and magnetic resonance imaging (MRI), is currently being investigated in radiotherapy treatment planning. Most studies that have been reported are in patients with lung, brain, or head and neck neoplasms. There is a potential role for either positron emission tomography (PET) or single photon emission computed tomography (SPECT) to delineate biologically active or tumor-bearing areas that otherwise would not be detected by CT or MRI. Furthermore, target volumes may be modified by using functional imaging, which can have a significant impact in the modern era of three-dimensional radiotherapy. SPECT may also be able to identify "nonfunctional" surrounding tissue and may influence radiotherapy beam arrangement.

Brain Neoplasms↗