Deterministic effects of the ionizing radiation

Full text: The deterministic effect is the somatic damage that appears when radiation dose is superior to the minimum value or 'threshold dose'. Over this threshold dose, the frequency and seriousness of the damage increases with the amount given. Sixteen percent of patients younger than 15 years of age with the diagnosis of cancer have the possibility of a cure. The consequences of cancer treatment in children are very serious, as they are physically and emotionally developing. The seriousness of the delayed effects of radiation therapy depends on three factors: a)- The treatment ( dose of radiation, schedule of treatment, time of treatment, beam energy, treatment volume, distribution of the dose, simultaneous chemotherapy, etc.); b)- The patient (state of development, patient predisposition, inherent sensitivity of tissue, the present of other alterations, etc.); c)- The tumor (degree of extension or infiltration, mechanical effects, etc.). The effect of radiation on normal tissue is related to cellular activity and the maturity of the tissue irradiated. Children have a mosaic of tissues in different stages of maturity at different moments in time. On the other hand, each tissue has a different pattern of development, so that sequelae are different in different irradiated tissues of the same patient. We should keep in mind that all the tissues are affected in some degree. Bone tissue evidences damage with growth delay and degree of calcification. Damage is small at 10 Gy; between 10 and 20 Gy growth arrest is partial, whereas at doses larger than 20 Gy growth arrest is complete. The central nervous system is the most affected because the radiation injuries produce demyelination with or without focal or diffuse areas of necrosis in the white matter causing character alterations, lower IQ and functional level, neuro cognitive impairment,etc. The skin is also affected, showing different degrees of erythema such as ulceration and necrosis, different degrees of atrophy, depilation, telangiectasia, hypo- or hyperpigmentation, etc. Damage to the soft tissue evidences in different types of hypo trophy, atrophy, and fibrosis. After irradiation of the orbit, for example, numerous of the above mentioned sequelae are observed: the eyelids become fibrous, diminishing of tears (dry eye), corneal and conjunctival keratinisation, cataracts, retinopathy, neuritis, of growth delay of the orbital bones, among other affections. Other tissues like the mucosa, the lung, the gastrointestinal tract, the liver, the kidneys, the gonads, the breasts, the bone marrow, the endocrine system, the cardiovascular system and the spinal cord are also damaged. They are affected according to the age at irradiation, the dose received and the inherent sensitivity of each tissue. Identification of delayed complications, is necessary to change or modify the therapy without sacrificing the effectiveness. Children surviving cancer should be able to attend school, work according to their capacity, have social insurance, not be discriminated and have relationships and children of their own. (author)