Tangential breast irradiation: simple improvements

A series of studies using phantom and in vivo dosimetry measurements with diodes and thermoluminescent dosimetry were undertaken to establish whether simple methods are available to obtain improvements in homogeneity of dose in the treated breast, and reductions of dose to tissues outside it, when using tangential 6MV photon fields. These studies confirmed that the use of an appropriate lung density correction factor in the planning process is likely to cause a reduction in the amount of wedge compensation predicted to be necessary to produce reasonable dose homogeneity in the central axis of the beam. This was shown to be of value in eliminating potential areas of overdosage in the chest wall medial and lateral to the breast mound, and also in reducing unwanted doses to the contralateral breast and lung. Further reductions in dose to contralateral breast were confirmed to occur when the majority, or all, of the wedge compensation predicted necessary is placed on the lateral field and when the lateral tangential field is angled anteriorly in such a way as to align the posterior beam edges. Skin does above, below, and over the breast mound were observed to depend critically upon angle of incidence of the beam, with its consequent effect upon electron build-up, and the position of the breast contour in the beam. Skin doses above and below the breast mound were shown to exceed over the mound itself. This differential effect was observed to increase with increasing wedge compensation. In some situations skin doses below the breast mound nearly reached prescribed dose within the breast. The design and use of simple lead attenuators to reduce these areas of high dosage is discussed.

CT scanning for definitive radiotherapy planning of prostate cancer: necessity or nicety? Results from survey of radiation oncologists working at different institutions in Australasia

Interactive computerised tomographic (CT) planning techniques offer the prospect of better anatomical localisation, more consistent tumour coverage, and limiting normal tissue dose. However, its value in the management of prostate cancer remains undefined. The present study addresses the impact of planning CT on the designated target volumes for localised carcinoma of the prostate at a multi-institution national level. Nine radiation oncologists from different centres in Australia and New Zealand were asked to designate a target volume on five sample patients with different disease stages (A2-C2) using both conventional cystogram films and planning CT scans. Target volumes estimated by CT means in this study differed by more than 10% from those estimated by conventional means in 75.6% of instances, being smaller in 55.6%. Volumes varied widely between individual radiation oncologists, both using conventional planning and CT information. These variations were found to exceed any differences in the volume caused by the planning technique itself. Results from this survey suggest that volumes appear to change more according to the individual radiation oncologist rather than to any other factor. In most or all of the sample cases six of nine radiation oncologists defined the borders of their CT volumes to be either consistently smaller (5 out of 9) or greater (1 out of 9) than their conventionally defined borders. The results of this survey are potentially important and warrant repetition with larger sample numbers in other countries where interactive CT planning facilities exist, both with and without diagnostic radiological input, to exclude similar variation and to define causes for any variations that do become apparent.

Low dose rate teletherapy using a telecaesium 137 unit radiobiological, physical and clinical considerations

Low dose rate teletherapy aims to combine the supposedly superior results obtained with low dose rate implants with the convenience and staff protection characteristics of external beam therapy. Previous investigators have used telecobalt units to produce dose rates of 1.1 to 1.8 Gy/hr to treat in daily sessions lasting 6-10 hours to total doses of 60-70 Gy. These studies have not discounted the possibility that much of the advantage of interstitial implants results from the low dose rates used per se, and from the fact that the total dose is delivered in a short overall time. The relationship between total dose, dose rate and volume giving normal tissue and anit-tumour effects, however, remains ill-defined. At the Newcastle Mater Misericordiae Hospital a Caesium teletherapy unit has been modified to treat at low dose rates and a study has been designed with a view to establish which permutations of total dose and dose rate are isoeffective for acute mucosal and acute skin reactions in the dose rate range between 0.8 and 9.6 Gy/hr (1.3 and 16 cGy/min).

High-frequency hearing loss in male farmers of Missouri

Farmers are exposed to noise that is potentially hazardous to hearing. We measured the hearing of 161 male farmers and 75 male nonfarmers at the 1979 Missouri Farmers Association Agri-Fair and compared it with the hearing of 129 office workers from central Missouri. Fixed-level screening tests were conducted in both ears at three stimulus frequencies: 1000 and 2000 hertz at 20 decibels hearing level and 4000 hertz at 25 decibels hearing level. Audiometers were calibrated in accordance with the ANSI-1969 standard. The results show that farmers are at risk for hearing loss at 2000 and 4000 hertz when compared with office workers. The prevalence of hearing loss was greater for farmers at both frequencies in every decade age group from 25 to 64 years. Using screening failure at 2000 and 4000 hertz in both ears as a criterion for a loss that would affect communication ability, we found that the failure rate was 16.8 percent for farmers and 6.2 percent for office workers. As other investigators have found, the prevalence of high-frequency hearing loss in male nonfarmers who associate with farmers was nearly as great as for farmers.

Recurrent laryngeal nerve injury following thyroid operations

Preoperative and postoperative laryngoscopy should be performed with thyroid operations. A prospective study of 121 thyroid operations from June 1970 to December 1974 was analyzed. There was a 4.2 per cent recurrent laryngeal nerve injury incidence in 217 nerves at risk, four of nine injuries being permanent. Of 217 superior laryngeal nerves at risk, 1.4% were injured, one of three permanently. Previous thyroid operations may place the laryngeal nerves at a greater risk. Transient edema of the laryngeal nerve in 13.4% of the patients was believed due to endotracheal intubation. There seemed to be no difference in the incidence of injury whether the nerves were seen or palpated. It is recommended that indirect laryngoscopy be performed in the course of evaluating thyroid disorders.

Use of the Doppler ultrasonic flowmeter for pedicle flaps

Summary--The Doppler ultrasonic flowmeter is presented as a method to help in flap outlining, transfer and return. When a directional flowmeter is added, this machine is extremely valuable for returning a flap at the earliest possible time. The Doppler is a safe, inexpensive, atraumatic, reliable instrument that can be learned in a very short time. We have found the Doppler to be very helpful in head and neck flaps.