Long-term effects of radiotherapy for acromegaly on circulating prolactin

Dose to neuroanatomical structures surrounding pituitary adenomas and the effect of stereotactic radiosurgery on neuroendocrine function: an international multicenter study

OBJECTIVE

Stereotactic radiosurgery (SRS) provides a safe and effective therapeutic modality for patients with pituitary adenomas. The mechanism of delayed endocrine deficits based on targeted radiation to the hypothalamic-pituitary axis remains unclear. Radiation to normal neuroendocrine structures likely plays a role in delayed hypopituitarism after SRS. In this multicenter study by the International Radiosurgery Research Foundation (IRRF), the authors aimed to evaluate radiation tolerance of structures surrounding pituitary adenomas and identify predictors of delayed hypopituitarism after SRS for these tumors.

METHODS

This is a retrospective review of patients with pituitary adenomas who underwent single-fraction SRS from 1997 to 2019 at 16 institutions within the IRRF. Dosimetric point measurements of 14 predefined neuroanatomical structures along the hypothalamus, pituitary stalk, and normal pituitary gland were made. Statistical analyses were performed to determine the impact of doses to critical structures on clinical, radiographic, and endocrine outcomes.

RESULTS

The study cohort comprised 521 pituitary adenomas treated with SRS. Tumor control was achieved in 93.9% of patients over a median follow-up period of 60.1 months, and 22.5% of patients developed new loss of pituitary function with a median treatment volume of 3.2 cm3. Median maximal radiosurgical doses to the hypothalamus, pituitary stalk, and normal pituitary gland were 1.4, 7.2, and 11.3 Gy, respectively. Nonfunctioning adenoma status, younger age, higher margin dose, and higher doses to the pituitary stalk and normal pituitary gland were independent predictors of new or worsening hypopituitarism. Neither the dose to the hypothalamus nor the ratio between doses to the pituitary stalk and gland were significant predictors. The threshold of the median dose to the pituitary stalk for new endocrinopathy was 10.7 Gy in a single fraction (OR 1.77, 95% CI 1.17-2.68, p = 0.006).

CONCLUSIONS

SRS for the treatment of pituitary adenomas affords a high tumor control rate with an acceptable risk of new or worsening endocrinopathy. This evaluation of point dosimetry to adjacent neuroanatomical structures revealed that doses to the pituitary stalk, with a threshold of 10.7 Gy, and doses to the normal gland significantly increased the risk of post-SRS hypopituitarism. In patients with preserved pre-SRS neuroendocrine function, limiting the dose to the pituitary stalk and gland while still delivering an optimal dose to the tumor appears prudent.

Postradiation therapy hypopituitarism

The increasing use of radiation treatment for head and neck cancers and other tumors, including pituitary adenomas, from the mid-20th Century onwards led to the recognition that pituitary function may be affected - often leading to some degree of pituitary insufficiency. Our knowledge is mostly based on observational or retrospective rather than randomized prospective studies. The various axes may be impacted at the hypothalamic or pituitary levels, or both. Some axes - the somatotropic and gonadotropic - appear to be especially vulnerable to radiation damage and may be affected quite early, whereas posterior pituitary function is rarely affected. Increased use of stereotactic radiosurgery, which focuses the radiation dose on the abnormal tissue, may be expected to reduce the impact on normal pituitary function, but such studies that are available are, as yet, relatively short term. Prospective studies of the effect of stereotactic radiosurgery on pituitary function would be valuable.

Applications of radiotherapy and radiosurgery in the management of pediatric Cushing's disease: a review of the literature and our experience

Surgical extirpation of pituitary adenomas is considered the mainstay of therapy in pediatric patients with Cushing's disease. However, a small subset of patients will require adjuvant therapy either due to tumor invasiveness, or disease recurrence. Conventional radiation therapy (or radiotherapy) delivers ionizing radiation to control hormonally active cells in fractionated doses (spread out over time) in order to give normal cells time to recover, while radiosurgery involves focusing a high dose of radiation structures in a single treatment session to the adenoma while generally sparing the normal gland and surrounding of any substantial amount of radiation. This paper reviews the effectiveness of radiation in the treatment of pediatric Cushing's disease.

Effects of gamma knife radiosurgery of pituitary adenomas on pituitary function

Object. The authors undertook a retrospective analysis of the incidence and time course of pituitary insufficiency following gamma knife radiosurgery (GKS) for pituitary adenomas.

Methods. Pituitary adenomas in 92 patients were analyzed. There were 61 hormonally inactive tumors, 18 prolactinomas, and nine somatotropic and four adrenocorticotropic adenomas. The mean tumor volume was 3.8 cm3 (range 0.2–14.6 cm3). The mean prescription dose was 15 Gy. The mean prescription isodose was 50.7%.

The mean follow-up time was 4.6 years (range 1.2–10 years). The following new or deteriorating insufficiencies that did not require treatment were recorded for the different pituitary axes: follicle-stimulating hormone (FSH)/luteinizing hormone (LH) 19 (20.6%), thyroid-stimulating hormone (TSH) 32 (34.8%), adenocorticotropic hormone (ACTH) 10 (10.9%), and growth hormone (GH) 26 (28.3%). For new insufficiencies or deterioration requiring replacement therapy, the figures were as follows: FSH/LH 20 (21.7%), TSH 22 (23.9%), ACTH eight (8.7%), and GH 12 (13%). Spot dosimetry was performed in 59 patients in the hypothalamic region, the pituitary gland, and pituitary stalk. The pituitary stalks in patients with deterioration of pituitary function received a statistically higher dosage of radiation, 7.7 ± 3.7 Gy compared with 5.5 ± 3 Gy (p = 0.03).

Conclusions. The function of the residual normal pituitary gland is less affected following GKS of pituitary adenomas than after fractionated radiotherapy. Nonetheless, increased attention needs to be exercised to reduce the dose to the stalk and pituitary gland to minimize the incidence of these complications.

Long-term follow-up results of postoperative radiotherapy in 36 patients with acromegaly

In acromegaly, pituitary irradiation is a slow, but effective, intervention in decreasing GH concentration. Few studies addressing the outcome of radiotherapy have used the currently accepted strict criteria for remission in the analysis of data. These studies report a low percentage of remission after radiotherapy. Doubt has especially been raised as to whether radiotherapy is effective in normalizing serum insulin-like growth factor (IGF)-I concentration. We analyzed the long-term follow-up data of postoperatively administered radiotherapy in 36 patients with postoperative persistent acromegaly, using both the normalization of GH suppression during oral glucose loading (GTT) and the normalization of IGF-I concentration as criteria for remission. Before radiotherapy, mean suppressed GH was 9.8 +/- 1.9 mU/L (n = 31), and mean IGF-I concentration was 44.3 +/- 3.9 nmol/L, equivalent to + 4.76 +/- 0.78 age-related IGF-I SD score (n = 13). The median radiation dose was 40 Gray (range, 25-50 Gray). At 5, 10, and 15 yr follow-up, 18 out of 30 patients (60%), 23 out of 31 patients (74%), and 16 out of 19 patients (84%), respectively, achieved normal serum IGF-I concentration. At the last assessment of all patients, after a mean follow-up period of 139 +/- 12 months, 27 out of 36 (75%) patients had a normal IGF-I concentration without additional medication, whereas 5 patients still required treatment with octreotide. Remission, as judged by normalization of GH suppression during GTT, was documented in 65% of patients from 2-5 yr after radiotherapy (n = 34); in 69% of patients, up to 10 yr after radiotherapy (n = 29); and in 71% of patients, up to 15 yr post irradiation (n = 17). At the latest assessment, a mean of 125 +/- 11 months after radiotherapy, 71% of patients (n = 35) were in remission, as defined by normal suppression of serum GH during GTT. Remission, as judged by normalization of both GTT and IGF-I, was found in 40% of patients 3-5 yr after radiotherapy (n = 30); in 61% of patients, 6-10 yr after radiotherapy (n = 28); in 65%, after 11-15 yr after radiotherapy (n = 17); and in 63% of patients, at the end of the follow-up period (n = 35). Substitution of one or more pituitary hormone deficiencies was required in 11% of patients postoperatively; in 29%, 5 yr after radiotherapy; in 54%, 10 yr after radiotherapy; and in 58%, more than 15 yr after radiotherapy. Our findings support the use of radiotherapy as an effective intervention in the treatment of residual clinical activity of disease after surgery for acromegaly.

Prolactinemia in adolescent males surviving malignancies in childhood: impaired dating activity

A relationship appears to exist between prolactin metabolism and psychosexual development. We studied pubertal stage, testicular size, and serum follicle-stimulating hormone (FSH), luteinizing hormone (LH), testosterone, thyroxine, thyroid-stimulating hormone (TSH), and prolactin concentrations in 94 adolescent males who had survived malignancies in childhood. Of the patients, 22% had elevated serum prolactin, > 300 mU/L. In multivariate analysis, the only therapeutic agents or treatments found to be independently associated with prolactin concentration were cisplatin and cytosine arabinose. Administration of cisplatin was associated with an increase of 55 m U/L (p < 0.01) and that of cytosine arabinoside with an increase of 23 mU/L (p < 0.01) in serum prolactin concentration. Serum prolactin concentration correlated with serum FSH (r = 0.26, p = 0.16) and LH (r = 0.30, p = 0.005). In 45 of the patients 10 criteria of psychosexual development were evaluated using a personal, semi-structured, and psychodynamically-oriented interview. A significant inverse relation existed between serum prolactin concentration and dating with the opposite sex (p = 0.008); none of the patients with elevated serum prolactin were dating. We conclude that even a slight elevation of serum prolactin above normal is associated with or may be reflected in the psychosexual development of adolescent males who have survived malignancies in childhood.

Hormonal and radiological effects of megavoltage radiotherapy in patients with growth hormone-secreting pituitary adenoma

Nineteen acromegalic patients (12 females and 7 males, aged 24-71 yr) were studied for 1-6 yr after radiotherapy (RT), administered by X-rays (18 MeV) by linear accelerator, with parallel opposite beams (doses 45-50.4 Gy, 1.8 Gy daily). Basal GH levels gradually decreased from 6.3-76.2 micrograms/L (mean +/- SE, 27.8 +/- 4.9) to 0.3-43.4 micrograms/L (11.7 +/- 3.6 micrograms/L; p < 0.005) at the last assessment. The earliest significant decrease was observed after one yr (14.9 +/- 3.8 micrograms/L; p < 0.005). Significant changes were observed also in IGF-I values (basal values 1.93-6.85 mU/ml, 3.22 +/- 0.30; last assessment 0.55-4.57 mU/mL, 1.58 +/- 0.31; p < 0.01). The earliest significant decrease of IGF-I values was observed after 2 yr (1.61 +/- 0.16 mU/ml; p < 0.005). GH levels < 5 micrograms/L together with normal IGF-I values were observed in 9 patients, 2-4 yr after RT. No changes were observed in PRL values, either in patients with pretreatment normal or elevated PRL levels. The CT and/or MRI picture of macroadenoma disappeared after 6-12 months in 3/12 patients. Moreover, a reduction (20-55%) in the diameter of the adenoma was shown after 6-36 months in other 4 patients. After RT 5/16 (31%) patients required cortisol and 4/19 (21%) thyroid replacement therapy. In 2/3 men a gonadal impairment was shown, that did not occur in the three female patients with normal gonadal function before RT.(ABSTRACT TRUNCATED AT 250 WORDS)

Inter-relations between growth hormone, insulin, insulin-like growth factor-I (IGF-I), IGF-binding protein-1 (IGFBP-1) and sex hormone-binding globulin in acromegaly

Acromegaly is characterized by a hypersecretion of GH, which in turn results in an excess of IGF-I, an important mediator of its actions. IGF-I itself is intimately related to insulin both in structure and function. IGF-I circulates associated with specific binding proteins which appear to have important effects on its activity. We have examined the inter-relations between GH, prolactin, insulin, IGF-I and one of the binding proteins, IGFBP-1, in 62 patients with acromegaly of varying activity. Serum IGF-I levels were closely related to the logarithm of mean GH levels (r = 0.76; n = 62; P less than 0.001) but multiple regression analysis suggested that, after accounting for the variation due to GH, insulin accounted for some of the additional variation of IGF-I. IGF-I concentrations were independent of prolactin. Fasting insulin levels were high and unrelated to mean GH levels but correlated with those of IGF-I (r = 0.542; n = 57; P less than 0.001). This correlation coefficient was further improved by also accounting for variations in IGFBP-1 (r = 0.684; n = 57; P less than 0.001). Even in subjects whose acromegaly was well controlled or cured, as indicated by GH levels of less than 1 mU/l or IGF-I levels of less than 2 U/ml, fasting insulin levels remained significantly elevated in some individuals. The reason for this persistent abnormality is not clear. Fasting IGFBP-1 levels were low and unrelated to mean GH but were inversely related to fasting insulin levels (r = -0.593; n = 57; P less than 0.001). We propose that a cascade of events occurs in acromegaly.(ABSTRACT TRUNCATED AT 250 WORDS)