Toxicity and Risks of Current Therapy
Late side effects rather than acute side effects are of crucial importance, given the excellent treatment results achieved by complex cancer therapy. The expected side effects of radiotherapy depend on the irradiated area and the dose administered.
The risk of late effects steadily increases with the time interval from completed radiotherapy and does not reach a plateau. Once emerged, most of the severe adverse effects are not causally influenced by any treatment, and their prevention is of the utmost importance.
An Overview of the Most Serious Late Side Effects of Conventional Radiotherapy:
Cardiotoxicity rarely occurs during radiotherapy. It is usually manifested as pericardial effusion or constrictive pericarditis. Coronary artery endothelial damage with an increased risk of ischemic heart disease is a more common adverse effect of radiotherapy. Typically, we see this adverse effect in patients treated for mediastinal lymphoma or chest sarcoma.
These adverse effects are encountered if a significant radiation dose is delivered to irradiate the hypothalamus, pituitary gland, thyroid gland or gonads, and the hypothalamus is more sensitive to radiation than the pituitary gland.
Growth hormone deficiency (GHD) already occurs with low doses of radiation – its incidence increases with doses higher than 27 Gy delivered to the cranium. Despite the growth hormone treatment, which is now standard treatment in the case of diagnosed deficiency, achieved body height may be lower.
Very common adverse effects are TSH deficiency, increased prolactin levels, deficiency in testosterone production and others.
Hypoplasia or growth disorders of bones and soft tissues may occur in the irradiated field following radiotherapy, depending on the dose. The consequences are asymmetric growth of the irradiated area, scoliosis and lower body height in adulthood. In addition to growth disorders, the endocrinological abnormalities mentioned above may also contribute to the lower body height.
Fertility is maintained after irradiation of ovaries with doses up to 2.5 Gy in 52% of pediatric patients, and decreases rapidly with the increasing dose – with doses of 10 Gy, fertility is maintained in only about 3% of patients. Doses above 10 Gy delivered to the uterus area significantly increase the risk of a stillborn fetus or premature birth. However, the incidence of birth defects in fetuses of mothers receiving anticancer treatment is not different compared to that in the healthy population.
Cataracts occur after irradiation of the eye lens with very small doses (from 0.8 Gy), and the absence of a threshold dose cannot be ruled out. The risk of retinopathy increases from a dose of 45 Gy and has not been reported at doses below 25 Gy using standard fractionation. In contrast, doses tolerated by the optic nerve and chiasm are higher – the risk of damage at doses lower than 55 Gy is less than 3%.
Hearing impairment occurs as a consequence of ototoxic chemotherapy or radiotherapy, but has also been reported in connection with shunt insertion. Its risk increases with decreasing age at the time of radiotherapy (higher in children below the age of three) and with increasing radiation dose (from doses of 35 to 40 Gy). Following radiotherapy it may emerge with a delay of several years and tends to progress over time in some patients.
Changes or loss of the sense of taste or smell are reported fairly often, but there are no clearly defined threshold doses for the individual sensory functions.
The impact on specific aspects of the quality of life varies according to the irradiated region of the brain (e.g. irradiation of the temporal lobe affects the emotional aspect more than irradiation of the frontal lobe) and has been found to be dose-dependent. Deterioration of overall physical health has been described in 12-27% of patients, while a decreased social quality of life was observed in 23-37% of patients who underwent CNS irradiation during childhood
These are a significant aspect of late mortality in pediatric cancer patients. The most common secondary malignant tumors (SMN) are tumors of the central nervous system, breast, thyroid, bone and secondary leukemia. The appearance of secondary solid tumors after radiation therapy is dose dependent and also dependent upon the age of the child when radiotherapy was carried out. The risk of secondary solid tumors after radiotherapy, in contrast to secondary leukemia, has increased steadily, SMN can appear ten years, twenty years or more after primary diagnosis.
The prognosis of SMN has now greatly improved and in many cases approaches the prognosis of newly diagnosed tumors. Due to this improvement we now encounter more frequently a new phenomenon – the development of subsequent (tertiary) malignancies.
Purchase the book via the link below.
Purchase the book via the link below.
