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Biomedical subjects

F E Holly

Publications and source records attributed to F E Holly.

10 recordsLinked to original sources
PubMed1995

Implications of tissue heterogeneity for radiosurgery in head and neck tumors.

PURPOSE: This study was undertaken to investigate the perturbation of small radiation beams by low density heterogeneities and to evaluate the ability of a Monte Carlo code to account for such perturbation. Performance of an inexpensive film scanning system was also evaluated. METHODS AND MATERIALS: Film and diode measurements were made in an acrylic phantom in which the size and position of an air gap were varied. Monte Carlo analysis was used to obtain additional verification of the measurements, to provide insight into photon and electron transport phenomena not directly measurable, and as a benchmark for the code. RESULTS: With 10 MV photons and a 1 cm circular field, a small 3-mm air cavity placed 2.6 cm deep in acrylic (full buildup) results in a reduction in central axis dose of 21% immediately following the cavity. Equilibrium is then reestablished over the next centimeter, after which the dose exceeds that of the homogeneous case by 3-4%. The loss in central axis equilibrium is highly field-size dependent, with some loss occurring even for the largest (32 mm) collimator. In addition, the presence of the air cavity produces a significant increase in dose up to 2 cm lateral and outside the primary field. CONCLUSIONS: Tissue heterogeneities are not presently accounted for in radiosurgery calculations, yet have the ability to perturb dose significantly. Targets may potentially be underdosed, and adjacent critical structures overdosed. Inability to account for tissue heterogeneities may limit the use of the radiosurgery approach in some areas. A Monte Carlo approach may be the method of choice for small field dose calculation when tissue heterogeneities are encountered.

Air↗
PubMed1994

A universal, multi-modality localization system for animal radiosurgery.

We have developed a stereotactic localization system allowing a radiosurgical approach in a number of animal models. The system utilizes fixation adapters specially designed for a particular animal, which in turn are attached to a common Brown-Roberts-Wells (BRW) compatible Delrin head ring. Each fixation adapter is constructed using materials compatible with CT, MRI, PET, and angiographic imaging studies. With such a system, radiographic localization, computerized treatment planning, and stereotactic radiation delivery can subsequently be performed in a manner identical to the procedures used for humans.

Animals↗
PubMed1993

Radiosurgery of cavernous sinus tumors.

Stereotactic radiosurgery was applied to concentrate high dose of photon irradiation to tumors enclosed in the cavernous sinus. We have treated 10 meningiomas, five pituitary tumors, and three metastatic lesions in the past two years. Follow-up time ranges from 3 to 18 months with an average of 10 months. Tumor volume ranged from 0.92 to 53.31 cc with an average 10.79 cc. CT scans and MRIs were used to demonstrate the tumor relationship to cranial nerves and structures of the brain. One to 6 isocenters were used. Collimator size varied from 7 to 28 mm, and the dose to the margin of the tumor ranged from 1400 to 2500 cGy with an average of 1650 cGy. Maximal dose range of 1575 to 5000 cGy. The margin of the tumor was encompassed within the 50 to 95% isodose volume with an average treatment prescribed to the 57% isodose volume. Symptomatic response was seen in 12 patients, and stabilization of symptoms in three patients with progression of symptoms observed in three patients. Radiographic imaging revealed response in eight patients, unchanged in three patients and progression in three patients. This report shows the feasibility of applying linear accelerator radiosurgery to the treatment of cavernous sinus tumors. This form of therapy promises to play an important role in complementing tumor resection.

Adult↗
PubMed1993

Comparison between radiosurgery and stereotactic fractionated radiation for the treatment of brain metastases.

This study evaluates the treatment of intracerebral brain metastases with single dose stereotactic radiosurgery in comparison to stereotactic fractionated radiotherapy (SFR). Twenty six patients with 41 lesions were evaluated. Thirty four lesions in 19 patients were treated with radiosurgery, and 7 lesions in 7 patients were treated with SFR. The radiosurgery group was treated with an average number of isocenters of 1.4, and an average of 9 arcs. The average dose was 2140 cGy delivered to the 70% isodose line. The average volume of the lesions was 5.22 cc. The SFR group lesions received a mean dose to the indicated area delivered by 4 to 6 coplanar fields. The dose was 600 cGy per fraction, 2 to 3 fractions were given. The average volume of the treated lesions was 21.2 cc. Follow-up extended from 2-18 months. Twenty five lesions of the radiosurgery group had image follow-up. The overall local control was seen in 92% of the patients. Six lesions of the SFR group had image follow-up, the local control was 83%. The small number in each group, the non-randomized nature of the study, and the relatively short follow-up preclude a definitive conclusion. SFR may be the method of choice for large lesions surrounded by significant edema. The delivery of the dose in large fractions may obviate the transient acute reactions seen when radiosurgical dose is delivered to large lesions surrounded by edema. However, both forms of therapy have proven to be effective in the control of brain metastases.

Adult↗
PubMed1992

Adriamycin-induced recall of radiation pneumonitis and epilation in lung and hair follicles of mouse.

The influence of Adriamycin and Actinomycin D on the expression of residual damage following irradiation of mouse thorax was evaluated. Drugs were given i.v. at various times starting on the same day, up to 3 months after irradiation, and the mortality from lung damage up to 160 days or epilation up to 98 days after irradiation were noted. Adriamycin (1.2 mg/kg in two equal doses), which on its own did not cause pneumonitic deaths, did so when combined with doses of local thoracic radiation as small as 6 Gy. The dose effect factor was greater if Adriamycin was given at 1 or 2 months (1.68) rather than on the same day (1.49). A reduction in the latent period to death was also observed with a minimum period of 50-60 days after irradiation rather than the normal 80-160 days. Adriamycin enhanced the epilation response to radiation, but only at or above threshold radiation doses. There was no reduction in the latency. Actinomycin D had no dose-modifying effects on the radiation response of both lung and hair follicles. The interaction between irradiation and Adriamycin seen when the interval between the two modalities is long, as it was in this study, may be mechanistically similar to the "radiation recall" phenomenon described in the clinic.

Animals↗
PubMed1984

Verification timer for AECL 780 Cobalt unit.

To obtain verification of the proper time setting of the motorized run down timer for a AECL 780 Cobalt Unit, a digital timer is described, which can be added to the system for under $300.

Cobalt Radioisotopes↗
PubMed1977

Total and individual kidney function assessment with iodine-123 ortho-iodohippurate.

A simple and reliable method of preparing 123l o-iodohippurate (l-123 OIH) is described. The agent was used to evaluate renal function in 329 patients; its use results in significant dose reduction for those with obstruction, hypertension, or transplant. Images from l-123 OIH provide 2.4 times more detectable photons per mCi administered to the patient than images obtained from l-131 OIH. Diagnoses are expected to be more reliable with l-123 OIH due to the decreased random variation of each data point.

Adult↗
PubMedDate not supplied

Anthropomorphic radiation therapy phantoms: a quantitative assessment of tissue substitutes.

Compositional analyses of samples of soft tissue and lung substitutes used in the construction of anthropomorphic radiotherapy phantoms were performed for products from Alderson Research Laboratories Inc., Kyoto Scientific Specimens Company/Capintec Inc., Humanoid Systems Inc., Radiology Support Devices Inc., and The Phantom Laboratory Inc. To assess quality control in the manufacture process, the results of these compositional analyses were compared with individual manufacturer's design specifications and electron densities measured by computed tomography analysis of actual phantom slices. A comparison of the manufacturers design specifications against reference tissue parameters from Tissue Substitutes in Radiation Dosimetry and Measurement (International Commission on Radiation Units and Measurements) indicates marked differences in the basic design of commercially available anthropomorphic phantoms.

Evaluation Studies as Topic↗