Radiation Treatment Strategies for Acromegaly

Nathan C. Rowland, M.D., Ph.D.; Manish K. Aghi, M.D., Ph.D.

Disclosures

Neurosurg Focus. 2010;29(4):e12 

In This Article

Abstract and Introduction

Abstract

The high morbidity and mortality associated with acromegaly can be addressed with multiple treatment modalities, including surgery, medicines, and radiation therapy. Radiation was initially delivered through conventional fractionated radiotherapy, which targets a wide area over many treatment sessions and has been shown to induce remission in 50%–60% of patients with acromegaly. However, conventional fractionated radiotherapy takes several years to achieve remission in patients with acromegaly and carries a risk of hypopituitarism that may limit its use. Stereotactic radiosurgery, of which there are several forms, including Gamma Knife surgery, CyberKnife therapy, and proton beam therapy, offers slightly attenuated efficacy but achieves remission in less time and provides more precise targeting of the adenoma with better control of the dose of radiation received by adjacent structures such as the pituitary stalk, pituitary gland, optic chiasm, and cranial nerves in the cavernous sinus. Of the forms of stereotactic radiosurgery, Gamma Knife surgery is the most widely used and, because of its long-term follow-up in clinical studies, is the most likely to compete with medical therapy for first-line adjuvant use after resection. In this review, the authors outline the major modes of radiation therapies in clinical use today, and they critically assess the feasibility of these modalities for acromegaly treatment. Acromegaly is a multisystem disorder that demands highly specialized treatment protocols including neurosurgical and endocrinological intervention. As more efficient forms of pituitary radiation develop, acromegaly treatment options may continue to change with radiation therapies playing a more prominent role.

Introduction

Transsphenoidal microsurgery to resect the causative GH-secreting pituitary adenoma remains the initial treatment of choice in the majority of patients with acromegaly.[10,25,48,52,53,74,90] However, the optimal management of the 10%–50% of patients who do not enter remission after transsphenoidal surgery[13,52] and the 20% of patients who experience recurrence of acromegaly after transsphenoidal surgery[13] remains less clear. Radiation represents an evolving treatment modality for acromegaly that warrants consideration as an alternative to medical therapy for tumors refractory to transsphenoidal surgery.

The conceptual groundwork for focused irradiation of GH-secreting pituitary adenomas while avoiding damage to surrounding neural structures was established more than 50 years ago.[2,56,97] Since that time, substantial advances in radiation technology have yielded increasingly precise pituitary adenoma–targeting capability and consequently an expanded set of treatment options for acromegaly to supplement resection and hormonal suppression with medical management. A complex array of factors dictate treatment decisions for acromegaly in the modern era, including adenoma size, degree of secretory hyperactivity, invasion of surrounding structures, and therapeutic side effects and their particular impact in the patient in question. For these reasons, contemporary treatment of patients with acromegaly now routinely involves multiple disciplines, including neurosurgery, endocrinology, and radiation oncology.[1,3,27,34,47,62,64,65,76,78] Indeed, in cases of acromegaly, all 3 approaches (surgery, medication, and radiation) can be beneficial and can play a role in management. Thus, an expert panel, the Acromegaly Consensus Group, formed in 2000, publishes guidelines for acromegaly management, most recently in 2009. The recommendations are that tumors deemed completely resectable undergo surgery, with somatostatin analogs used in cases in which remission after surgery is not achieved. Tumors deemed incompletely resectable are treated with somatostatin analogs. Cases in which remission is not achieved with the use of somatostatin analogs are treated with pegvisomant if there is no mass effect on MR imaging, because the tumor growth that can occur with pegvisomant would be tolerated, or with radiation if there is mass effect on MR imaging.[63] However, because these recommendations are not based on randomized clinical trials, further studies will likely be needed to definitively determine the role of radiation therapy in achieving the best long-term outcome for patients with acromegaly. Here, we review the results to date with radiation as a treatment modality for acromegaly, and we outline future directions that might get us closer to a definitive understanding of the role of radiation in acromegaly management.

Comments

3090D553-9492-4563-8681-AD288FA52ACE
Comments on Medscape are moderated and should be professional in tone and on topic. You must declare any conflicts of interest related to your comments and responses. Please see our Commenting Guide for further information. We reserve the right to remove posts at our sole discretion.
Post as:

processing....