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Radiotherapy Late Effects
Organ/Tissue
Dose Threshold
Late Toxicity
Central Nervous
System
~ 18 Gy
Neuropsychological damage, reduced IQ, learning
and behaviour difficulties
Pituitary
~ 18 Gy for impaired GH secretion,
higher threshold (~ 40 Gy) for other
hormones
Multiple hormone deficiencies, particularly growth
hormone (GH), also adreno-cortico trophic hormone
(ACTH) and thyroid stimulating hormone (TSH)
Thyroid
20 Gy
Reduced thyroid hormone secretion
Gonads
1-2 Gy (testes), 6-10 Gy (ovaries)
Infertility if irradiation of the testes or ovaries
cannot be avoided
Bone
Threshold ~ 10 Gy fractionated RT
Worst in young children treated with >
20 Gy
Impaired bone growth, and associated impairment of
soft tissue development. This is particularly severe in
the facial, head and neck regions
Kidney
12-15 Gy
Hypertension, reduced renal function
Dentition
~ 4-10 Gy
Dental caries, impaired dental development and mal-
development of jaw
Eye
~ 10 Gy (Cataract), ~ 25 Gy Dry eye
Cataract, dry eye
Second (radiation
induced) malignancy
Low threshold for adenocarcinomas,
e.g. breast, thyroid. High threshold for
sarcomas
e.g. breast and thyroid cancers after RT for
Hodgkin
’
s Disease, Sarcomas after RT for many
cancers, including brain tumours