Residency training for medical physicists.
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Humans↗
Biomedical subjects
F M Khan
Publications and source records attributed to F M Khan.
Beta irradiation of recurrent ptergia: results and complications.
Although postoperative beta irradiation for prevention of pterygium recurrence is widely used, its complication rate has not been widely appreciated. Thirty-six patients underwent pterygium excision followed by irradiation with 90Sr to between 1600 and 5300 cGy (median 2400) in two to four fractions over 7 to 27 days. A median of three fields were used in each treatment course (range two to 10). Most patients had undergone previous treatment for their pterygia, including surgery alone (25 patients), or both surgery and irradiation (5 patients). Overall, recurrences developed in 10 eyes (28%). Recurrence occurred in one eye after re-irradiation (20%), compared to 9 of 31 (29%) previously non-irradiated eyes (p greater than 0.1). There was no association with number of excisions and recurrences, although all but 6 patients had undergone more than one excision. Thirteen patients (36%) developed complications including: epithelial defect or corneal thinning (3), symblepharon (5), cataract (4) and corneal ulceration (1). Complications developed in 4 of the 5 (80%) re-irradiated eyes compared to 9 of 31 (29%) previously non-irradiated eyes (p less than 0.05). The power of the statistical analysis was limited by sample size, but no significant association was observed between the development of complications or recurrences and total dose, number of abutting fields, number of previous surgical excisions or patient age, even when re-irradiated patients were excluded. Recently described calibration uncertainties with the 90Sr applicator may explain in part these complications. Alternatively, technical factors such as the number of fields or volume treated may play a role. Excessive complications and recurrences with the use of postoperative beta irradiation in this series emphasize the danger of re-treatment and the need for alternative safe and effective therapies.
Adolescent↗
Double-blind comparison of etodolac SR and diclofenac SR in the treatment of patients with degenerative joint disease of the knee.
An on-going multi-centre, double-blind, parallel-group study is being carried out to compare the efficacy and tolerability of sustained-release (SR) formulations of etodolac and diclofenac in patients with degenerative joint disease (osteoarthritis) of the knee. An interim analysis of the findings has been made for 64 patients from two centres which have now completed their part in the study. Thirty-two patients were randomly assigned to receive 600 mg etodolac SR once daily for 4 weeks; the remaining 32 patients received 100 mg diclofenac SR. Primary efficacy assessments rated on a 5-point categorical scale were patient and physician overall assessments of the patient's condition, night pain and pain intensity. Secondary efficacy parameters included weight-bearing pain, stiffness duration, joint tenderness on pressure, degree of swelling and erythema, degree of knee flexion and time to walk 15 metres. The results showed that for both etodolac SR and diclofenac SR treatment groups there was an improvement from baseline in all efficacy parameters at the last visit and no statistically significant difference was observed between treatments. However, although not statistically significant, the improvement rate in the patient's condition at Week 2 was slightly greater in the etodolac SR treatment group, suggesting that improvement may occur more rapidly with etodolac SR than with diclofenac SR. With regard to tolerability, 5 patients in the etodolac SR treatment group and 3 in the diclofenac SR group withdrew from the study because of adverse reactions. Two events (dyspepsia and mouth ulceration) in the etodolac SR group and 4 events (headache, glossitis, depression and insomnia) in the diclofenac SR group were considered to be definitely drug-related. Dyspepsia was reported by 3 patients (1 withdrawal) treated with etodolac SR and by 4 patients (2 withdrawals) treated with diclofenac SR. A statistically significant decrease was observed in haemoglobin and haematocrit values after 4 weeks of treatment in the diclofenac SR group, but this was not considered to be clinically important. In addition, there were no clinically significant changes in blood chemistry and urinalysis for either treatments. In conclusion, the results of the present study indicate that 600 mg etodolac SR once daily for 4 weeks is effective in the treatment of patients with degenerative joint disease of the knee, as is 100 mg diclofenac SR. In addition, both drugs have comparable tolerability profiles.
Aged↗
Single dose total lymphoid irradiation combined with cyclophosphamide as immunosuppression for human marrow transplantation in aplastic anemia.
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Adolescent↗
Total-body superficial electron-beam therapy using a multiple-field pendulum-arc technique.
A technique using pendulum-arc rotation is presented for electron-beam treatment of generalized superficial malignancies. The technique consists of six arcing fields symmetrically dispersed around the body surface for circumferential coverage. The arc angle is selected to scan the height of the body fully. Beam uniformity within 10% over a height of 180 cm is achieved at a treatment distance of 385 cm. Randophantom dosimetry, using an 8 MeV electron beam degraded by 3/8 in. Plexiglas, indicates a surface dose uniformity within +/- 7% over most of the body surface. Underdosages occur at regions obstructed by adjacent body parts.
Abdomen↗
Second neoplasms following megavoltage radiation in a pediatric population.
Previous reports of radiation-related neoplasia have relied primarily upon patients treated by orthovoltage to low doses for benign disease. This survey is believed to be the first to assess the incidence of second neoplasms following megavoltage therapy. The source was the records of all long-term pediatric survivors (88 patients) who were treated with megavoltage radiation (cobalt 60) at the University of Minnesota. There was an average follow-up period of 14 years during which 7 second neoplasms were discovered (8%). Five were not associated with prior radiation. Both radiation-related neoplasms were associated with low doses and one was without significant morbidity. Two of the seven neoplasms were malignant; one was not associated with radiation while the other was associated with prolonged chemotherapy and low dose radiation (1%). The only fatal second neoplasm was not associated with radiation but developed 5 years after prolonged chlorambucil treatment. This review reveals the tendency of childhood cancer victims to develop other neoplasms regardless of radiation. The finding of neoplasia induction only at low radiation doses supports the Gray hypothesis of decreased tumor induction at high doses through increased cell killing.
Adolescent↗
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↗
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↗
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↗
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↗
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↗
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↗
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↗
Computer algorithm for electron beam treatment planning.
A computer algorithm has been developed for electron beam treatment planning. The method uses a limited amount of stored experimental dose distribution data, performs interpolation, and stores generated beam information on an optimized fan line-depth line grid. Experimental verification of the computer program showed agreement within +/-5% for beam generation and air gap correction.
Computers↗
Replacement correction (P(repl)) for ion chamber dosimetry.
The use of replacement correction when depth dose distribution is measured with a cylindrical ion chamber is discussed. A review of relevant data shows that the displacement of the effective point of measurement is an appropriate method to make replacement correction for the entire depth ionization curve.
Calibration↗