Radiation Therapy for Acromegaly

Acromegaly is an uncommon hormonal condition that occurs when the pituitary gland produces too much growth hormone after normal growth has ended. The most frequent cause of acromegaly is a noncancerous tumor (known as an adenoma) in the pituitary gland that releases growth hormone.

Radiation therapy is one potential treatment option that may be administered after surgery, or as the primary treatment if surgery is deemed too risky. In this article, we discuss what radiation therapy is and what it will entail for the treatment of acromegaly

The first-line treatment for acromegaly is removal of the pituitary tumor via transsphenoidal surgery. This minimally invasive procedure entails using long instruments inserted through the nasal passages to reach the pituitary gland and remove the tumor. Reported success rates for this surgery range between 70% and 80%.

When a tumor cannot be removed completely, there is a recurrence of the tumor, or surgery is considered too risky, medications and/or radiation therapy might be suggested as an alternative course of action.

These medications include somatostatin analogs such as octreotide and lanreotide, which suppress growth hormone secretion. Dopamine agonists such as cabergoline and bromocriptine can also be used to reduce growth hormone production.

In addition, growth hormone antagonists such as pegvisomant can be used to block the effects of growth hormone on the body. These medications play a role in managing acromegaly by controlling growth hormone levels and alleviating symptoms associated with the condition.

However, while medications may provide some relief of symptoms, they do not address the cause of the condition. In some cases, radiation therapy may be used after surgery to target and inhibit growth of any remaining tumor cells.

Stereotactic radiosurgery can be used to deliver precise radiation to an adenoma (pituitary tumor), where the excess growth hormone is produced. The term “stereotactic” refers to image-guided techniques that ensure precise placement of radiation beams at a specific location in the body. Although it is not a surgical procedure, the term “radiosurgery” reflects its high level of precision.

Radiation can help to shrink the tumor and reduce the production of growth hormone, thereby alleviating the symptoms of acromegaly. Because radiosurgery is often used in combination with other treatment options such as surgery, there is limited evidence of its effectiveness as a stand-alone therapy.

However, studies have found that radiation therapy causes the tumor size to decrease or stabilize in most patients, with most also experiencing a decrease in excessive growth hormone secretion over time. This typically happens gradually, over the course of months to years. 

There are 2 ways to deliver radiation therapy.

• Fractionated radiotherapy—multiple short sessions using small doses of radiation
• Stereotactic radiosurgery—a single, longer session with a large dose of radiation
  • Gamma Knife: Gamma Knife is a form of stereotactic radiosurgery that uses beams of gamma rays (photons) to target tumors with high precision. The beams converge at the target location, providing a concentrated dose of radiation while minimizing exposure to surrounding healthy tissues. It is a noninvasive treatment option that can typically be completed in just one session, although sometimes multiple sessions are required.
  • Linear accelerator–based systems: These systems (for example, CyberKnife and Novalis) focus x-ray beams (photons) on the target area while allowing for different angles of approach to minimize radiation exposure to healthy surrounding tissues. CyberKnife uses a robotic arm to deliver radiation therapy precisely, and Novalis combines a linear accelerator with advanced imaging technology to provide highly targeted treatment.
  • Heavy charged particles: Heavy charged–particle therapy (for example, proton beam) focuses particles (protons) at a specific target to deliver a high dose of radiation to the tumor while minimizing exposure to surrounding healthy tissues.

Heavy charged–particle therapy is a newer form of radiation therapy that is available only at specialized centers. It has shown promising results in treating certain types of cancers, particularly those in the brain, spine, and head and neck regions.

However, it is generally more expensive and less widely available than other forms of radiation therapy. Nonetheless, radiation therapy may not be suitable for every patient.

It is crucial to engage in a comprehensive discussion with your physician to determine the most suitable treatment plan.

A stereotactic radiosurgery session to treat acromegaly will likely entail the following steps. Note that the entire process can take up an entire morning or afternoon.

The treatment duration, however, may be only 1 or 2 hours. Most patients go home the same day.

• Preparation—a head frame or mask will be attached to the patient's head to immobilize it and ensure precise positioning.
• Imaging—imaging, such as computed tomography (CT) or magnetic resonance imaging (MRI) is performed to locate the tumor or target area within the body and create a 3-dimensional image for treatment planning
• Treatment planning—medical professionals use specialized software to plan the radiation treatment by determining the optimal angle, intensity, and duration of the radiation beams
• Radiation delivery—during the procedure, the patient lies on a table, and a machine moves around the head to deliver the precise radiation dose to the targeted area
• Recovery—after the procedure, the head frame or mask is removed; there could be some minor bleeding and tenderness at the pin sites

Although additional radiosurgery sessions might be recommended in certain cases, typically only one session is necessary.

Because radiosurgery is so precise, the chance of side effects and complications is typically low, but it is not zero. Radiation exposure can harm healthy pituitary tissue, which can lead to a deficit in other hormones produced by the pituitary gland.

This can lead to symptoms such as fatigue, weight fluctuations, changes in menstruation in females, sexual dysfunction, cold intolerance, among other signs. Severe hormone deficiency may require hormone supplementation.

Depending on the position and dimensions of the tumor and the type and dosage of radiation administered, there is a potential risk of surrounding structures within the brain and nervous system being harmed.

This can lead to vision changes, headaches, difficulty concentrating, and memory issues. However, these complications are rare. If you experience new symptoms after radiation therapy, communicate with your medical team promptly for an evaluation.

• Stereotactic radiosurgery is a precise method for administering targeted radiation to the pituitary tumor (adenoma) responsible for the excessive production of growth hormone.
• Transsphenoidal surgery is still the first-line treatment for acromegaly.
• Radiation is generally used when the pituitary tumor responsible for symptoms cannot be removed completely by surgery or when surgery is not a viable option.

• Pituitary Network Association: Acromegaly
• The Pituitary Foundation [UK]: Acromegaly
• National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK): Acromegaly
• National Health Service (NHS) [UK]: Acromegaly