PubMed Health⌕ Search

Biomedical subjects

B H Curran

Publications and source records attributed to B H Curran.

9 recordsLinked to original sources
PubMed1997

A technique for accurate planning of stereotactic brain implants prior to head ring fixation.

PURPOSE: A two-step procedure is described for accurate planning of stereotactic brain implants prior to head-ring fixation. METHODS AND MATERIALS: Approximately 2 weeks prior to implant a CT scan without the head ring is performed for treatment-planning purposes. An entry point and a reference point, both marked with barium and later tattooed, facilitate planning and permit correlation of the images with a later CT scan. A plan is generated using a conventional treatment-planning system to determine the number and activity of I-125 seeds required and the position of each catheter. I-125 seed anisotropy is taken into account by means of a modification to the treatment planning program. On the day of the implant a second CT scan is performed with the head ring affixed to the skull and with the same points marked as in the previous scan. The planned catheter coordinates are then mapped into the coordinate system of the second CT scan by means of a manual translational correction and a computer-calculated rotational correction derived from the reference point coordinates in the two scans. RESULTS: The rotational correction algorithm was verified experimentally in a Rando phantom before it was used clinically. For analysis of the results with individual patients a third CT scan is performed 1 day following the implant and is used for calculating the final dosimetry. CONCLUSION: The technique that is described has two important advantages: 1) the number and activity of seeds required can be accurately determined in advance; and 2) sufficient time is allowed to derive the best possible plan.

Brachytherapy↗
PubMed1996

Use of a 1 mm collimator to test the accuracy of stereotactic radiotherapy.

PURPOSE: To develop a method of measuring locations of the center of dose in stereotactic radiotherapy relative to the center of the target, and thereby obtain a test of the accuracy of stereotactic radiotherapy (SRT). METHODS AND MATERIALS: An insert was mounted in an SRT collimator on a 6 MV linear accelerator to provide a photon beam approximately 1 mm in diameter at isocenter, and a method of measuring radiation center coordinates of arced SRT beams. To simulate a small intracranial target, two halves of a Barium paste column were embedded in two adjacent slabs of a humanoid phantom. A film was placed between the slabs to image the radiation relative to the target center. A surgical head ring and computerized tomography (CT) localizer were attached to the phantom and CT scans were obtained. The scans were entered in a three-dimensional computerized treatment-planning system and radiation isocenter coordinates determined by iteratively moving the 90% isodose surface center of arced beam dose distributions to coincide with the target center. The phantom was bolted to an SRT floorstand with isocenter coordinates obtained from the treatment plan, and then irradiated in two sets of experiments. The first set applied five 1 mm noncoplanar arced beams with and without offsets of the planned coordinates in the transverse plane. The second set applied one large transverse arc coplanar to the film with and without offsets in the craniocaudal direction. Irradiations with coordinate offsets tested the sensitivity of the method. Films were developed and digitized with a high resolution film scanner to measure the location of the radiation relative to the target center. RESULTS AND CONCLUSION: The radiation center was found from 0.0 to 0.3 mm of the target center, within requirements of our clinical quality assurance program. The measurement and evaluation of coincidence of radiation and target centers are, thus, proposed as elements of radiosurgery facility acceptance and annual quality assurance.

Models, Anatomic↗
PubMed1996

The measurement of linear accelerator isocenter motion using a three-micrometer device and an adjustable pointer.

PURPOSE: The small motions of the major axes of a linear accelerator observed during gantry and treatment table rotation were measured to improve beam-target alignment during stereotactic radiosurgery (SRS). METHODS AND MATERIALS: Measurements of gantry isocenter motion and table rotational axis wobble were performed with an adjustable front pointer and a three-micrometer device. Nominal gantry and table isocenters were specified. The gantry motion path and table isocenter coordinates were then applied to offset simulated treatment target coordinates so as to compensate for gantry sag. Target simulation films were examined to document improvement of beam-target alignment. RESULTS: The overall precision of the measurement of gantry and table isocenter coordinates was 0.2 mm. Over gantry rotation of 0 to 360 degrees, the gantry isocenter was found to follow a pinched loop with a maximum point to point distance of 1 mm. Table axis motion was found to be negligible relative to the reproducibility of gantry isocenter motion. Thus, a table isocenter was defined that was invariant to table rotation. CONCLUSION: Results indicate that the three-micrometer device and adjustable front pointer are useful tools for three-dimensional (3D) mapping of gantry, collimator and table isocenters and their motions. It is suggested that such measurements may be useful in the quality assurance of linear accelerators, particularly to improve beam-target alignment during SRS and other high dose external beam therapy.

Algorithms↗
PubMed1994

Fine tuning of linear accelerator accessories for stereotactic radiotherapy.

PURPOSE: Experience with the University of Wisconsin's stereotactic radiotherapy (SRT) accessory system was applied to build a new system, facilitate alignment of linac photon beams with a Brown-Roberts-Wells (BRW) stereotaxy, and increase the versatility and stability of the stereotaxy. METHODS AND MATERIALS: High tensile strength stainless steel was used in the floor stand to increase the range of gantry rotation relative to ranges allowed by truss-mounted stands. The collimator assembly and floor stand were each fitted with two-axis gimbal and translation adjustments in addition to the floor stand's three-axis adjustments. The head ring positioning assembly was fitted with two braces to prevent the head ring from deforming with patient motion. Six MV linac photon beam characteristics were measured with a computer-controlled scanning system and a diode in water, at source to surface distances (SSD) of 80 and 100 cm, and for 13 divergent collimators ranging in diameter from 1-4 cm at 100 cm SSD. Quality assurance software was applied to screen data for questionable consistency or symmetry. Integrity of the stereotaxy was evaluated with target simulation films and repeated measurements which were part of the quality assurance of clinical treatments. A method was developed using a glass etched contact reticle to obtain average simulated target to beam center distances (delta av) from target simulation films. RESULTS AND CONCLUSION: New aspects of the current system have improved the ability to fine tune and analyze stereotactic alignment. Beam characteristics met stringent output criteria and penumbral widths were the same or narrower than penumbral widths reported elsewhere. The precision of measuring delta av was 0.1 mm, and delta av averaged over 50 target simulation films was 0.7 +/- 0.1 mm. Results suggest that it may be useful to determine delta av from target simulation films with the method described here.

Humans↗
PubMed1984

Equilibrium (gated) radionuclide ejection fraction measurement in the pressure or volume overloaded right ventricle. Comparison of three methods.

Although equilibrium radionuclide angiographic measurement of right ventricular ejection fraction (RVEF) has been validated in patients with coronary artery disease, the accuracy of this technique has not been demonstrated in patients with other cardiac diseases which may result in RV pressure and/or volume overload. The accuracy of three methods of equilibrium radionuclide analysis for measuring RVEF was compared in several subgroups of patients with a variety of cardiac diseases, including congenital and valvular heart disease, cor pulmonale, and cardiomyopathy. It was concluded that RVEF may be accurately derived by equilibrium radionuclide ventriculography in patients with a wide variety of cardiac diseases, including those resulting in RV volume and/or pressure overload. Accuracy varies depending on analysis method and the nature of the hemodynamic derangement.

Adult↗
PubMed1980

A FORTRAN program for the optimization of radiotherapy treatment planning using the complication probability factor (CPF).

The complication probability factor (CPF) is an objective function, based directly on radiobiological principles and clinical data, for the optimization of radiotherapy treatment planning; it measures the likelihood that a given radiation dose distribution will lead to serious complications in the patient as a result of damage to healthy tissue. A computerized search can be made for that treatment plan which delivers an acceptable tumoricidal dose, yet minimizes the CPF as averaged over the total volume of healthy tissue irradiated. The CPF FORTRAN program, run on a PDP 11/55 in conjunction with a commercially available radiotherapy treatment planning package, is described in detail.

Computers↗
PubMedDate not supplied

Electron contamination due to Lucite in a 45-MV photon beam.

The presence of the Lucite blocking tray in a 45-MV betatron beam leads to a considerable loss in the skin-sparing properties of this unit. Measurements conducted with a parallel-plate chamber show that the surface dose is approximately doubled (up to 58% of the maximum absorbed dose) and the depth of maximum dose is reduced by as much as 1.5 cm by the Lucite. These results suggest that separate dosimetry data should be kept for blocked and unblocked fields. The penetration of the electron contamination to the open field depth of maximum dose can lead to erroneous results if attenuation measurements are made at that depth. Studies of the effect of the lead sheet and leaded acrylic on the surface dose showed that under normal circumstances the presence of high-Z materials increases the surface dose, hence these materials cannot in general be used as electron filters on very high energy x-ray units. A Luciteless blocking tray with universal triangular corner blocks has been designed for use in special cases requiring a reduced surface dose.

Electrons↗