Radiation: facts, fallacies and phobias.

There is frequent debate in the media and the scientific published reports about the use of radiation for diagnosis and treatment, the benefits and risks of the nuclear industry, uranium mining and the storage of radioactive wastes. Driving this debate is increasing concern about reliance on fossil fuels for power generation for which alternatives are required. Unfortunately, there is generally a poor understanding of the relevant basic sciences compounded by widespread irrational fear of irradiation (radiation phobia). Radioactivity, with special reference to uranium and plutonium is simply described. How radiation affect tissues and the potential hazards to individuals and populations are explained. The origins of radiation phobia and its harmful consequences are examined. Whether we like it or not, Australia is heavily involved in the uranium industry by virtue of having one-third of the world's known reserves, exports of which are worth approximately $470m annually. As this paper has been written as simply as possible, it may also be of interest to readers who may have had little scientific training. It may be downloaded from the web using references provided in this article. It is concluded that ignorance and fear are major impediments to rational debate on radiation issues.

Radiation oncology in Australia: workforce, workloads and equipment 1986-1999.

Regular national surveys of all public and private radiation oncology facilities in Australia have been carried out between 1986 and 1999. Workforce data recorded were numbers of radiation oncologists and trainees, radiation therapists, medical physicists and physics technicians, nursing staff, data managers, social workers and clerical staff. Workloads included treatments with megavoltage beams (linear accelerators, cobalt-60), orthovoltage/superficial X-rays, brachytherapy, total body irradiation and stereotactic radiosurgery. Major equipment recorded included numbers of megavoltage and orthovoltage/superficial X-ray machines, planning simulators, computerized dosimetry systems and brachytherapy equipment. The use of radiotherapy beds and the public-private mix of treatments were also documented. Data were assembled for Australia based on each individual state. Within Australia the number of public and private treatment facilities has increased by 44% from 18 in 1986 to 26 in 1999. The population has increased by 16.4%, cancer incidence by 51.8% and megavoltage workloads (fields) by 102%. The number of radiation therapists and physicists and the number of linear accelerators have, in general, increased with the growth in workloads. The number of radiation oncologists has increased by 60% from 4.5 full-time equivalent (FTE) radiation oncologists per million population in 1986 to 7.2 per million in 1999. There is currently a deficit of at least 40 radiation oncologists to be able to treat the 50% of newly diagnosed cancer patients requiring radiotherapy. In addition, a significant deficiency exists in numbers of radiation therapists, nursing staff, data managers, social workers and clerical staff. Clearly the demands for medical physicists has increased but the data are insufficient to comment on deficiencies. Despite the increases in workloads the proportion of patients with cancer receiving radiotherapy remains below 40%. A positive correlation has been shown between the proportion of newly diagnosed cancer patients treated and the number of FTE radiation oncologists, the number of megavoltage machines and number of radiation therapists. This was shown for Australia as a whole, for each state and for the years 1986 to 1999. This was also the case when total megavoltage fields was used as the dependent variable. Multiple regression analysis using the same independent variables confirmed these positive correlations. It is concluded that the low treatment rate with radiation oncology for cancer patients in Australia is due mainly to the lack of resource allocation. The stated commitment of governments and health departments to a 50% treatment rate can only become a reality if there is a concerted effort to increase the numbers of radiation oncologists, radiation therapists, megavoltage machines and support staff. Otherwise at least one in every 10 newly diagnosed cancer patients will continue to be denied adequate and equitable access to radiotherapy - in 1999 that total figure was 9400 persons.

Is there a role for fractionated radiotherapy in the treatment of arteriovenous malformations?

Single fraction radiotherapy for the treatment of arteriovenous malformations (AVMs) is appropriate when brain tolerance is not a limiting factor, but when tolerance is a concern, there is a potential for therapeutic gain with fractionated treatment. alpha/beta values for AVM obliteration have been derived and found to be higher than previously assumed and are likely to be approximately 10.0 Gy or more compared with approximately 1.5 Gy for the tolerance of small volumes of brain. Models are derived to describe, qualitatively, the potential gain that can be achieved with fractionation. Past experience has identified an important volume effect that has limited the use of stereotactic treatments to small volumes. Volume-dependent, dose-volume relationships are described, including a tissue-specific volume exponent (phi) which was found to apply across a relatively wide range of target volumes, thereby permitting the derivation of tolerance guidelines to volumes larger than previously available. More data to define parameter values more precisely are desirable.

Chronic radiation injury to the intestine: a clinico-pathological study.

This paper draws attention to the continuing problem of chronic radiation injury to bowel. Fifty-seven symptomatic patients with this disorder were studied, 31 with predominantly small bowel injury and 26 with colonic disease. The mean latent interval following irradiation was 4.7 years. Small bowel disease presented initially as intestinal obstruction (19 cases) or malabsorption (11 cases) and the radiation related mortality in small bowel disease was 32%, while that for colonic disease was 4%. There was a high incidence of prior pelvic surgery and of adjunctive chemotherapy in patients developing small bowel disease. Analysis of the radiotherapy techniques used highlighted that an unsatisfactory distribution of radiation dosage occurred when parallel opposed fields were used particularly where one field only was treated daily. Difficulty in matching external beams with intracavity sources may also have contributed to radiation injury.

Tolerance of the central nervous system to photon irradiation: endocrine complications.

Dose-response isoeffect equations have been determined for hypothalamic pituitary insufficiency following cranial irradiation. Of particular importance is the occurrence of complications at doses substantially less than those commonly used for the treatment of central nervous system tumors. Such complications may be severe and potentially life threatening. These complications occur when a small midline 'target' volume containing the pituitary gland, infundibulum and adjacent inferior hypothalamic structures is irradiated. Direct pituitary irradiation is unlikely to be a factor, at least in some cases. The possible role of incidental hypothalamic irradiation in the control of acromegaly and pituitary dependent Cushing's syndrome is discussed.

Tolerance of the mature human central nervous system to photon irradiation.

Tolerance of mature human brain to photon irradiation is described. Isoeffect curves have been derived for tolerance of large and small volumes of brain, by examination of doses determined empirically and in clinical use. These have been compared with isoeffect curves of thoracic myelitis, optic nerve and chiasm damage, and brain necrosis. The results show that the best-fitting Ellis-type equations, when five fractions per week are used, have low exponents for overall treatment time and high exponents for the number of increments (N), and are similar to published data on rat myelitis. Of the equations used to test the relationship between total dose and number of increments, the power curve was the best fit. Mean values of exponents for N derived for brain and spinal cord tolerance were 0.4 or more. These were similar to values obtained for optic nerve and chiasm damage, though the data are more limited for this complication. Brain necrosis is observed at slightly higher doses probably because of a difference in the end-point observed rather than because of any fundamental difference in tissue response. Evidence is presented to suggest that some repopulation may occur in widely spaced schedules. The use of the Ellis equation derived from connective-tissue data is inappropriate for central nervous system tissue, and its use may lead to a substantial risk of overdosage. A plea is made for adequate documentation of treatment details when human data are reported. The importance of dose per fraction is emphasized.