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Biomedical subjects

E E Klein

Publications and source records attributed to E E Klein.

42 records · Page 3Linked to original sources
PubMed1993

Entrance and exit dose regions for a Clinac-2100C.

PURPOSE: While significant advances have taken place in confirming dose in homogeneous media and accounting for changes due to distant heterogeneities, interface dosimetry is still a dose assessment problem. The entrance and exit surfaces of the patient are a prime example where dose assessment is questionable, but important, in many clinical situations. METHODS AND MATERIALS: Data were taken to examine the effect of such parameters as field size, source-to-skin distance, blocking tray, compensation materials (lead, aluminum and brass) and various patient support materials (Mylar, graphite, thermal plastic, and foam) on the surface doses from a dual energy (6 MV, 18 MV) linear accelerator. Measurements were conducted with a thin window parallel-plate chamber. RESULTS: Relative surface dose was found to have a proportional dependence on field size for both energies with surface doses ranging from 6% to 53%. A surface depth dose of 22.6% for a 15 cm field was measured for the low energy beam while a surface dose of 22.3% was observed for the 18 MV beam. The surface dose increased significantly for short source to skin distances and with the presence of a blocking tray. Compensating filter materials had little influence on surface dose. However, patient support devices such as Alpha Cradle and the graphite of the table can increase the surface dose to as much as 92%. CONCLUSION: We found there was a loss in dose at the exit surface (in comparison with percent depth dose tables, which assume infinite depth) on the order of 15% and 11% for the 6 MV and 18 MV beams, respectively. However, this loss is quickly compensated for with the introduction of most inherent backscattering media, [which in fact can increase the dose] for example, graphite in the patient support assembly tabletop.

Humans↗
PubMed1993

Changes in photon dose distributions due to breast prostheses.

PURPOSE: Subcutaneous prosthetic implants had been routinely used for cosmetic augmentation and for tissue replacement following mastectomy over the last 15 years. The implants come in many forms as the gel filler material and surrounding shell material(s) vary significantly. METHODS AND MATERIALS: This study uses a thin window parallel-plate chamber and thermoluminescent dosimeters to quantify and dosimetric changes to surrounding breast tissue due to the presence of the prosthesis. A mammographic phantom was compared to four commercial prostheses, namely two silicon gel fillers within two different shells (silicon or silicon/polyurethane), a tri-glyceride within silicon and a bio-oncotic gel within silicon/polyurethane. The latter two implants were designed with a low-Z fill for diagnostic imaging benefits. RESULTS: Ion chamber results indicate no significant alteration of depth doses away from the implant with only minor canceling (parallel opposed) interface perturbations for all implants. In addition the physical changes to the irradiated prostheses were quantified by tonometry testing and qualified by color change. Each implant exhibited color change following 50 Gy, and the bio-oncotic gel became significantly less formable following irradiation, and even less formable 6 weeks postirradiation. CONCLUSION: The data indicates that prostheses do not affect the photon beam distribution, but radiation does affect the prostheses.

Breast↗
PubMedDate not supplied

Dosimetry and techniques for simultaneous hyperthermia and external beam radiation therapy.

An increased biological effect is realized when hyperthermia and radiation therapy are combined simultaneously. To take advantage of this effect, techniques have been developed that combine existing hyperthermia devices with a linear accelerator. This allows concomitant delivery of either ultrasound or microwave hyperthermia with photon radiation therapy. Two techniques have been used clinically: the orthogonal technique, in which the microwave or ultrasound beam and the radiation beam are orthogonal to one another, and the en face technique, in which the ultrasound or microwave beam and the radiation beam travel into the tumour through the same treatment window. The en face technique has necessitated the development of special attachments so that the hyperthermia device can be mounted to the linear accelerator and so that non-uniform portions of the hyperthermia device can be removed from the radiation beam. For microwave therapy, applicators are mounted onto the linear accelerator using the compensating filter tray holder. For ultrasound, special reflector devices are mounted to a frame that is mounted onto the compensating filter tray holder of the linear accelerator. Because the linear accelerator is an isocentric device, the height of the radiation source is fixed, and this has necessitated specially designed devices so that the ultrasound support system is compatible with the linear accelerator. The treatment setups for both the en face technique and the orthogonal technique require the interaction of both hyperthermia and radiation therapy personnel and equipment. The dosimetry and day-to-day operations for each technique are unique. The simulation for the en face technique is much different from the simulation of a normal radiation treatment and requires the presence of a hyperthermia physicist. Also, for the en face technique, the attenuation of the microwave applicator and the thickness and attenuation of the ultrasound reflector system are taken into account for radiation dosimetry. This paper presents details of the dosimetry and logistics of the techniques for simultaneous thermoradiotherapy based on 7 years of experience treating more than 50 patients.

Cobalt Radioisotopes↗
PubMedDate not supplied

Clinical system for simultaneous external superficial microwave hyperthermia and cobalt-60 radiation.

A system for simultaneous thermoradiotherapy was devised to investigate the possible benefits and/or complications of thermal radiosensitization in human superficial tumours. The system combines the well-known treatment modalities of external 915 MHz microwave hyperthermia and cobalt-60 teletherapy. Single waveguide applicators are utilized either attached to blocking trays, so that the gamma beam travels through a waveguide and into the patient (en face setup), or in a conventional way with the microwave propagation vector orthogonal to the gamma beam (orthogonal setup). With these setups a radiation fraction can be delivered in the middle of a 60-min, non-interrupted hyperthermia treatment. Temperatures and power level are remotely monitored and recorded outside the Cobalt room. Extensive measurements and testing showed that the operation of the hyperthermia system (generator, applicators, thermometry unit and temperature sensors) was not disrupted by irradiation and that the microwaves were confined to the treatment room and did not interfere with the operation of the Cobalt unit, of an adjacent linear accelerator or of an adjacent radiotherapy simulator. For the en face setup the dose distributions induced in solid water phantoms were uniform with the exception of a narrow (< 0.5 cm) region under the applicators' internal probes where 10-18% reduction exists. This dose defect is clinically smoothed using feathering techniques. The system has been successfully used without technical problems in 51 treatments in 15 patients (18 lesions) in a phase I/II clinical trial. An analysis of the thermal data showed that the temperature distributions achieved during simultaneous delivery have the same general characteristics of those achieved in conventional sequential hyperthermia with microwaves, and that the steady state distributions are maintained during the time of simultaneous irradiation. The tests performed in addition to the preliminary clinical experience clearly indicate that this type of combined therapy is technically feasible and safe. Here the system for simultaneous, external, superficial thermoradiotherapy and the implementation tests performed are described in detail. Preliminary clinical experience and results are also reported.

Cobalt Radioisotopes↗