Biomedical subjects

F M Khan

Publications and source records attributed to F M Khan.

At least 73 records · Page 4Linked to original sources

PubMed1978

Spinal cord protection during cross-fire irradiation of the intrathoracic esophagus: tube-tilt vs. Shielding.

The protection of the upper thoracic spine achieved by a tube-tilt technique was found to be comparable to that obtained from direct shielding during cross-fire therapy of the intrathoracic esophagus. An isocentric technique was utilized which included one anterior and two posterior-oblique fields. Significant underdosages to the esophagus at levels superior to the isocenter are caused by tube-tilt, whereas direct shielding resulted in a uniformity of esophageal doses to within 5%. The need for a tissue compensator for the anterior field must be assessed on an individual basis from off-axis treatment planning.

Esophageal Neoplasms↗

PubMed1978

Effect of air space and depth dose in electron beam therapy.

In electron beam therapy, alterations in dosimetry occur as a result of air space between the end-of-treatment cone and the skin surface. A large air gap may be introduced in order to obtain a field size larger than that available at the cone end. Needed dosimetry corrections related to these air space problems are discussed, along with a proposed method of measuring effective source-to-cone end distance. Data presented show the modifications of a dosimetric field which occur with an increase in the air space below the treatment cone.

Electrons↗

PubMed1978

An efficient patient data entry system for a busy computer.

The authors describe an independent minicomputer consisting of a CRT and a cassette unit which was designed to store patient data and interact with the main computer at a convenient time. This system permits the computer to handle data entry and treatment planning functions simultaneously. The layout of the overall system, the function of the program and a time analysis of the system are discussed.

Beta Particles↗

PubMed1978

Variations in depth-dose data between open and wedge fields for 4-MV X-rays.

Central-axis depth-dose data for 4-MV x rays, including tissue-maximum ratios, were measured for wedge fields. Comparison with corresponding open-field data revealed differences in magnitude which increased with depth, field size, and wedge thickness. However, phantom scatter correction factors for the wedge fields differed less than 1% from corresponding open-field factors. The differences in central-axis per cent depth doses between the two types of fields indicate beam hardening by the wedge filter. This study also implies that the derivation of tissue-maximum ratios from central-axis per cent depth is as valid for wedge as for open fields.

Humans↗

PubMed1977

Physical aspects of electron-beam arc therapy.

The effect of different parameters on dose distribution in electron-beam arc therapy was studied in order to develop a technique for routine clinical use. A special diaphragm was designed to facilitate telecentric rotation. Dosimetry was performed with an ion chamber, film, and LiF powder in cylindrical polystyrene phantoms and an Alderson Rando phantom. Dose distributions were evaluated with regard to dose homogeneity, and a method of sharpening the dose fall-off near the ends of the arc was proposed. Criteria for selection of isocenter depth and field size were developed. Methods of dose calculation, calibration, and treatment planning are discussed.

Electrons↗

PubMed1976

Field shaping in electron beam therapy.

In the treatment of superficial lesions with 8-13 MeV electrons, lead shields are often used to protect the underlying tissue. Measurements were made with film and ion chamber to analyse various aspects of external and internal shielding in electron beam therapy. Data were obtained on the thickness of lead required for shielding, the effect of blocking on dose-rate, electron-backscattering from lead and X-ray contamination. Practical applications of a lead clay for shielding are discussed.

Electrons↗

PubMed1975

Nominal standard dose and tumor standard dose. Tables for radiation therapy planning and analysis.

The method of treatment planning for a predetermined NSD value is described in detail using various example-problems. The Fret tables allow the finding of the total number of fractions needed (NT) for the NSD. This is done through the NSD/d ratio, d standing for the fractional dose in rad. The Fret tables are for 1 to 7 fractions-per-week treatment schedules. The corresponding value of T (elapsed days) are shown for different week days of the therapy initiation with their respective Fret and NSD/d values. The handling of the rest and multi-rest periods is described. A method of finding the NSD value for a treatment which has reached the maximum connective tissue tolerance is described, covering even the most complex treatment plans. Fret-tumor tables for NSD-tumor and their use are described by appropriate example-problems. Ret equivalent therapy planning through direct NSD methods (Fret tables) and through an approximation method (tables provided) is described and the usage demonstrated by example-problems. The usage of parallel opposing and multiple portals is evaluated in ret-dose values (peripheral radiobiologic effect) and certain conclusions drawn to guide the therapist. These show in which situations all portals per session should be used and when alternate portals are more beneficial. The effect of portal weighting is included in this analysis. The application of ELLIS' NSD method for radium therapy is described. If, in the future, any changes in the power factors of the present NSD formula become necessary, the basic handling of the NSD problems described in this manuscript will remain unchanged. The values obtained from these tables can then be adjusted by the appropriate factors.

Cobalt Radioisotopes↗

PubMed1974