Microanatomy of the skin

Radio-induced malignancies of the scalp about 98 patients with 150 lesions and literature review

INTRODUCTION

- The induction of malignant diseases is one of the most concerning late effects of ionizing radiation. The topic of this study deals with skin tumors developed in the irradiated areas in children given X-ray therapy for tinea capitis.

MATERIAL AND METHODS

- All patients with malignant tumors of the scalp referred to Salah Azaiz Institute between 1970 and 2001 have been questioned in order to determine if there had been a prior X-ray irradiation for tinea capitis, its modality, and its consequences. The first scalp irradiation goes back to 1922 and the last was performed in 1963.

RESULTS

- Ninety-eight patients with 150 radio-induced cancers of the scalp following irradiation for tinea capitis are reported (1.5 lesion per patient). The patients were irradiated in various hospitals and dispensaries throughout the country. Eighty-one patients (82%) had only one session of radiation. The average age at irradiation was 12 (+/-6) years, the latent period for radiation-induced skin cancers was 36 (+/-14) years. In 61 patients (62%), the scalp appeared normal and in 38% radiodermatitis was noted. Patient age at diagnosis of malignancy varied from 20 to 83 years with an average of 47 years. Basal cell carcinomas (125 cases) and spinocellular carcinomas (16 cases) were the most common, three other cases of annexial tumors, two malignant non-Hodgkin's lymphomas and four melanoma lesions are also present. Radiotherapy was used for the treatment of 74 patients (alone in 42 and associated with surgery in 32 patients); 14 patients had exclusive surgical excision.

CONCLUSIONS

- Basal cell carcinomas are the most frequent tumors arising on chronic radiodermatitis. In spite of the long latency period, patients' young age at irradiation explained the occurrence of these cancers at a relatively young age. Literature review is suggesting recessive mutation of tumor-suppressor genes as the characteristic abnormality in radio-induced cancer.

Basal cell carcinoma of the eyelid and periocular skin

Basal cell carcinoma is the most common human malignancy. This locally invasive tumor rarely metastasizes, but can cause considerable morbidity when on the eyelids and periocular skin. The successful management of BCC requires an awareness of its broad clinical spectrum and knowledge of the risk factors associated with therapeutic failure. The optimal therapy for basal cell carcinoma is controversial. Treatment strategy is formulated on an individual basis, taking into account tumor size, anatomic location, and growth pattern. The immune status and life expectancy of the patient also must be considered. While complete eradication of the tumor is desirable, this can be challenging since basal cell carcinomas often extend beyond their apparent clinical margins. Since prevention is preferable to treatment, the public needs to be informed that the incidence of periocular skin cancers can be reduced with the longterm use of sunscreens, sunglasses, and hats with brims.

Radiation protection guidelines for the skin

The past recommendations of the ICRP about dose limits to the skin are reviewed. Recently, an ICRP Task Group has been revisiting the old arguments and setting them against new data. With the exception of the function of cells in the skin associated with immunocompetence, non-stochastic effects have been well characterized and threshold doses are known with a precision appropriate for setting radiation protection standards. The current dose limitations of 0.5 Sv per year and a working lifetime dose limit of 20 Sv should protect the worker population against deterministic effects. When the ICRP made its recommendations in 1977 for dose limits there was no appreciation of the importance of the interaction of ultraviolet radiation (UVR) and X-rays. Both clinical and experimental data show that the risk of ionizing-radiation-induced cancer is significantly increased by subsequent exposures to UVR. Therefore, risks for sun-exposed areas of skin differ from those that are shielded. The risk estimate for skin cancer is very dependent on the selection of the projection model and on the mortality rate assumed. Based on the relative risk model a mortality rate of 0.2 per cent and summing risks for both UVR exposed and shielded skin the risk is about twice (1.94 x 10(-4) Sv-1) that which ICRP derived in 1977. With the absolute model the risk is considerably less, about 0.5 x 10(-4) Sv-1. There is still insufficient understanding of the effects of multiple or protracted exposures on the risk of skin cancer induction. Experimental results suggest that exposures, at least to relatively high total doses, that are protracted over a long period are more carcinogenic than a small number of exposures over a short period.

Radiation-induced skin cancer and radiodermatitis of the head and neck

From a cohort of 2400 patients who had been irradiated 19 to 48 years previously for benign diseases in the head and neck region a randomly selected group of 605 patients was selected and traced back. From the 360 patients alive, 257 were examined clinically and 49 were examined by questionnaire for radiation-induced skin tumors and radiodermatitis. In 21 patients, a total of 30 skin tumors were diagnosed. In 8 of 21 patients, 10 skin carcinomas were detected at recall. A dose-effect relationship of 40 carcinomas/10(4) persons/Gy for a median follow-up period of 41 years for the area exposed was calculated. The severity of radiodermatitis is associated with a higher prevalence of skin cancer. The number of radiation-induced skin cancers rises with the post-treatment time. Because of these late radiation effects, radiotherapy of benign skin lesions is contraindicated, especially now that other therapy modalities are available.

Radiation exposure to personnel in departments of gynaecologic oncology in Sweden

Radium-226 and cesium-137 are used at six departments of gynaecologic oncology in Sweden. A survey of radiation exposure (dose equivalents) to the personnel is reported. The measurements were performed with TL dosemeters. From dose distribution measurements, the dose equivalents in different parts of the body, related to different working procedures, were determined. Effective dose equivalents and collective dose equivalents were also estimated. The estimated collective dose equivalent for this category of personnel in Sweden was 1.3 manSv. The effective dose equivalent was less than the dose equivalent measured with dosemeters worn on the chest, and was less than half the annual limit set by ICRP.

Radiation-induced head and neck tumours: is the skin as sensitive as the thyroid gland?

Six hundred and five persons, randomly selected from a cohort of 2400 patients who had been irradiated 16-46 yr previously for benign diseases in the head and neck region, were traced, recalled and examined for radiation-associated tumours. Three hundred and sixty-seven patients were alive, 179 had died and 66 had emigrated. Two hundred and fifty-seven patients were clinically examined, 87 refused or were not able to participate and 16 could not be contacted. Eighteen of the clinically examined patients had been or were being treated for 20 skin carcinomas with a mean latency of 37 yr. In this group only 7 carcinomas of the thyroid gland were observed, with a mean latency of 38 yr. Eleven carcinomas of the skin and 3 of the thyroid gland were reported in the group which was examined by means of questionnaires. The observed number of carcinomas of the skin is higher than expected according to the dose-effect relationship of UNSCEAR, whereas the number of carcinomas of the thyroid gland is lower. It is concluded that there might be less difference in susceptibility for the induction of tumours by ionizing radiation between the skin and the thyroid gland than is commonly assumed.

The problem of radiation dosage in the measurement of skin blood flow by xenon-133

The skin dose arising from the use of xenon-133 in the measurement of skin blood flow has been calculated for several situations. The results indicate the importance of prior assessment of radiation dose in any technique involving the use of radionuclides. Cases where particular care must be taken have been indicated and practical methods of reducing the dose are suggested.

An approach to the surveying of radiation environments for radiation protection purposes

Many of the inadequacies of the system presently used for surveying environments containing penetrating radiation stem from the impossibility of defining a radiation parameter which is additive, measurable and closely related to peak dose equivalent in the body. Many of the present conceptual difficulties would be eliminated if surveys were made in terms of a quantity 'dose equivalent ceiling' defined as the sum of the peak dose equivalents generated by all the components of the field if each were incident normally to the front face of an anthropomorphic phantom. 'Dose equivalent ceiling' is close to the quantity measured by existing instruments, is both additive and measurable, and can be rigorously related to primary radiation field quantities. It is always greater than peak dose equivalent in the body, and would be used to define an exposure period during which a given dose equivalent could not be exceeded. The dose to specific parts of the person's body would then be estimated by personal dosimetry. Fields of low penetrating radiation could continue to be surveyed in terms of dose to specific superficial organs. Dose equivalent ceiling, which corresponds to the instrumental measurement, exceeds dose equivalent index, an indication of peak dose equivalent in the body, by a factor which can be as large as six.