Endocrine Abstracts (2002) 3 P194

Influence of age on the vulnerability of the hypothalamic-pituitary axis to radiation damage

HK Gleeson, CF Baylis & SM Shalet

Department of Endocrinology, Christie Hospital, Manchester, UK.

Survival figures following the treatment of brain tumours continue to improve. Patients receiving cranial radiotherapy (XRT) frequently suffer a progressive loss of anterior pituitary function secondary to radiation damage to the hypothalamic pituitary axis (HPA), therefore long-term follow up is required. The time frame of radiation damage to the HPA is not known. There is also a suggestion from animal data that the HPA is more sensitive to damage by radiation when treated at a younger age, there is little information in humans.

We have performed a retrospective audit on case notes of patients who have received cranial XRT for the treatment of brain tumours which did not anatomically involve the HPA. Information was gathered on age, histology and surgery. Details of XRT (dose, fractions, duration) were collated and the biological effective dose (BED) calculated. Anterior pituitary function was reviewed at five, ten and greater than ten years.

36 (20 male) had received XRT in childhood, median age 7.5 years (range 0.5-15) and 17 (6 male) had received XRT as adults, age 25 years (17-59). The median BED for the children was 52 Gy (22-99.65) and for the adults 73.3 Gy (36-131).

There was a decline in all aspects of anterior pituitary function following XRT with GH as the most commonly affected hormone which increased with time from radiation. GH and ACTH deficiency developed in 5 children, and GH deficiency in 3 adults more than 10 years after XRT. Despite a lower median BED in children than in adults they are more likely to be GHD than adults at 10 years (p=0.006).

In conclusion loss of pituitary function continues for greater than 10 years following XRT. Our GH studies also suggest that the HPA of children is more radiosensitive than adults. This emphasises the need for long-term follow up with pituitary function testing beyond 10 years particularly in those receiving XRT in childhood.

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