Proton therapy is an advanced form of radiation treatment that uses a beam of protons instead of traditional X-rays. The distinct physical property of protons, known as the Bragg peak, allows the energy to be deposited precisely at the tumor site before coming to an abrupt stop. This characteristic helps spare healthy tissues and organs located beyond the target area, making it a highly targeted approach. However, because proton therapy is still a form of radiation, it can cause various side effects as it impacts healthy cells within the treatment field. These reactions vary widely depending on the individual, the total radiation dose, and the specific area of the body being treated.
Acute and General Side Effects
The acute side effects of proton therapy are those that typically occur during the course of treatment or within a few weeks after its completion. The most frequently reported systemic reaction is fatigue, which can feel like a profound sense of exhaustion that is not relieved by rest. This fatigue results from the body expending energy to repair healthy cells damaged by the radiation and process the death of cancer cells.
Skin reactions are also common, appearing in the area where the proton beam enters the body, similar to a localized sunburn. The skin may become red, dry, itchy, or sore, and in some cases, it may peel or become moist. Hair loss occurs only in the specific treatment field, unlike the diffuse hair loss often associated with chemotherapy.
While less frequent than with conventional radiation, nausea and loss of appetite can occur, especially when the treatment field includes the chest or upper abdomen. Localized symptoms like headaches may also develop if the proton beam is directed toward the head or brain. These acute symptoms are generally temporary and tend to resolve within a few weeks to months once the treatment regimen has concluded.
Late or Long-Term Side Effects
Late or long-term side effects manifest months or even years after the proton therapy is finished. These effects result from permanent changes to the healthy tissues that received some radiation dose during the treatment. One potential long-term effect is fibrosis, the scarring or hardening of deep tissues within the treatment field.
If the proton beam passes near hormone-producing glands (such as the pituitary or thyroid), endocrine dysfunction can occur, with growth hormone deficiency being one of the more common issues in children. For pediatric patients or those treated for brain tumors, neurocognitive changes, affecting factors like thinking speed and memory, are a recognized risk. Long-term clinical follow-up is necessary for monitoring these delayed effects.
The development of a secondary malignancy is a rare but serious risk associated with any form of radiation, including proton therapy. However, the precision of the Bragg peak helps minimize the radiation dose to surrounding healthy tissues, which is thought to translate into a reduced risk of secondary cancer compared to traditional photon-based radiation. By limiting the exit dose, proton therapy protects a greater volume of healthy tissue, which is particularly advantageous for children.
Side Effects Varying by Treatment Location
The nature and severity of side effects are highly dependent on the specific location of the tumor and the healthy organs that lie near the proton beam path.
Head and Neck
Treatment for tumors in the head and neck area often results in irritation of the mucous membranes. Patients frequently experience dry mouth (xerostomia) due to radiation exposure to the salivary glands. Difficulty swallowing (dysphagia) and a sore throat can also arise if the esophagus is included in the treatment field. The proximity of the beam to the mouth can also cause temporary changes in taste perception. Radiation in this region carries a risk of osteoradionecrosis, the breakdown of jawbone tissue, though modern planning seeks to avoid this complication.
Chest and Lung
When treating tumors in the chest or lung, irritation of the airways and the esophagus can occur. This can lead to radiation pneumonitis (inflammation of the lung tissue) or esophagitis, causing a burning sensation or discomfort when swallowing. Minimizing the dose to the cardiac tissue is important to prevent future cardiac complications.
Pelvis and Abdomen
For cancers treated in the pelvis or abdomen, common side effects involve the gastrointestinal and urinary systems. These can include diarrhea, cramping, and inflammation of the rectum. Bladder irritation (cystitis) may also manifest as urinary urgency or a burning sensation during urination. Sexual dysfunction, such as erectile difficulties in men, is a potential complication when treating tumors in the pelvic region.
Managing and Mitigating Adverse Reactions
Proactive management of adverse reactions is an integral part of proton therapy care and involves a multidisciplinary approach. Acute symptoms like nausea and pain are managed with prescription anti-emetic and analgesic medications to maintain comfort during the treatment course. Patients are advised to use specific non-irritating rinses to manage mouth sores or dryness, particularly for head and neck treatments.
Supportive care for general side effects focuses on maintaining the patient’s strength and overall well-being. This includes working with a dietician to ensure adequate nutrition and hydration, especially if the patient experiences a loss of appetite. Specialized skin care, such as using mild, non-fragranced soaps and protecting the treated area from the sun, helps mitigate the severity of skin reactions.
Clear and continuous communication with the oncology team is important for effective symptom control. Patients are encouraged to report any new or worsening symptoms so that the care team can adjust supportive treatments promptly. In some instances, the care team may recommend a brief, temporary break in treatment to allow healthy tissues to recover before the therapy is resumed.