Radiation therapy is a common and effective treatment that uses high-energy rays to destroy cancer cells. The experience often feels shrouded in mystery, leading to anxiety about the physical sensations involved. The actual delivery of the radiation is typically far less uncomfortable than patients initially fear. This article clarifies the physical and sensory experience of external beam radiation therapy, from the preparatory steps to the cumulative effects on the body.
The Setup and Simulation Experience
The first step is the simulation appointment, designed to precisely map out the treatment area. This is often the longest initial visit, lasting between 30 and 45 minutes. During this session, a CT scan or sometimes an MRI is performed while the patient is positioned exactly as they will be for every treatment. This phase allows the radiation oncology team to design a plan that targets the tumor while protecting surrounding healthy tissues.
Custom immobilization devices are created to ensure perfect, repeatable positioning for each session. These devices hold the body still and may include a thermoplastic mask, a vacuum-sealed cushion, or a customized cradle, depending on the treatment site. Being held completely immobilized can be an unfamiliar sensation, especially for treatments involving the head and neck. The patient may feel firm pressure, but this stillness is necessary for high-precision treatment delivery.
During the simulation, therapists use lasers to align the body. They may apply small, temporary ink marks or pin-sized permanent tattoos on the skin. These markings act as external landmarks, allowing the team to align the radiation machine with the internal target before every daily treatment. This preparation requires the patient to remain motionless for an extended period while the treatment plan is finalized.
Sensations During Beam Delivery
The radiation beam itself is invisible, odorless, and painless as it passes through the body. The high-energy photons or particles do not register as a physical sensation on the skin or internally. Patients will not feel any burning, tingling, or other direct sensation from the beam.
The most noticeable sensory experiences during the short daily treatment involve the environment and the machinery. Patients hear the mechanical noises of the linear accelerator, the machine that delivers the radiation, as it rotates around the treatment table. The movement is accompanied by distinct whirring and clicking sounds as it positions itself and turns the beam on and off.
Although the patient is alone in the treatment room during the brief session, they are constantly monitored. Therapists watch the patient via closed-circuit cameras and communicate through an intercom system. A small number of patients, particularly those treated near the head or brain, report transient, unusual sensations. These include perceiving a metallic smell (phantosmia) or seeing flashes of light (phosphenes), which are thought to relate to the radiation interacting with sensory nerves.
Acute Physical Effects During Treatment
The physical effects of radiation therapy are cumulative, developing hours or days after the treatment sessions begin. The most common systemic sensation is radiation-induced fatigue, a persistent exhaustion. This pervasive tiredness often does not improve with rest, as the body expends energy repairing damage to healthy cells caused by the treatment.
Fatigue typically builds up gradually over the course of treatment weeks, becoming most pronounced toward the end of the schedule. The sensation is compounded by the body’s inflammatory response, which releases substances called cytokines that contribute to weariness. This exhaustion can affect physical, emotional, and mental well-being, making daily activities difficult.
Localized effects are felt acutely in the area receiving the radiation. Skin in the treatment field may develop radiation dermatitis, a reaction similar to a sunburn. This begins with redness, warmth, or dryness and can progress to itching, peeling, or moist, sensitive areas. These sensations usually start a few weeks into treatment because skin cells do not fully repair themselves between daily radiation doses.
Depending on the site treated, patients may experience localized inflammation and soreness. For instance, radiation to the head and neck can lead to difficulty swallowing, a sore throat, and a change in taste as the lining of the mouth becomes irritated. Treatment to the pelvis can cause irritation in the bladder, leading to a frequent or urgent need to urinate. These localized discomforts are temporary, managed with supportive care, and gradually resolve weeks or months after the treatment course is completed.