Balancing the risk and Benefits of RT in adolescent and young adult Patients

In pediatric neurooncology, the vulnerability of the growing brain (<7-10 years of age) to the consequences of RT has led to a range of trials attempting to minimize radiation doses and fields by using complementary chemotherapy in order to limit neurocognitive consequences. The endocrine consequences of cranio-

spinal RT (CrSp) in this group are considerable, and include secondary hypothyroidism, growth hormone deficiency, and in girls, either precocious puberty or incomplete pubertal development, as well as risking infertility from irradiation of the hypothalamus, pituitary, and ovaries. Irradiation to the vertebrae will result in failure of these bones to grow during the adolescent growth spurt, causing loss of up to 5 cm in height; this is unresponsive to growth hormone therapy.

The same balance of risks concerning efficacy versus toxicity must be considered for the adolescent and young adult population, even though the neurocogni-tive toxicity of conventional RT doses at this age is not clear-cut due to the scarcity of good evidence from long-term follow-up studies. There is concern that, although early estimates of neurocognitive function after cranial radiation may be acceptable, long-term survival may reveal progressive accelerated cognitive decline in a proportion of the population, representing a hidden toxicity [100]. The risk of ovarian radiation from spinal fields is an important consideration, worthy of ovarian ultrasound for assessment and consideration of oophoropexy to a location outside the planned radiation fields. These concerns are greatest for those diagnosed in this young age group, as they have the longest time to live and to experience the tox-icity. The endocrine consequences of cranial RT are considerable. However, the availability of endocrine replacement therapy, coupled with the more advanced state of skeletal growth in the adolescent and young adult patient prior to diagnosis, means that the growth and development consequences may be less severe than in younger patients. Careful endocrine follow-up of these young adult patients is essential, as the endo-crinopathies may develop at a later time. These patients are also at increased risk for malignancies of endocri-nological structures that have been irradiated, especially the thyroid. In addition, the late-effects clinic for young adult survivors of childhood cancer, with its specialist, multidisciplinary, cooperative team, should be of help to these patients.

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