What is SBRT (extracranial radiosurgery)?
Extracranial radiosurgery (SBRT) is a high precision irradiation technique that allows to irradiate with ablative doses, lesions located outside the skull, such as: pancreatic, prostate, head and neck tumors or pulmonary, hepatic, suprarranal and vertebral metastases.
What does SBRT (extracranial radiosurgery) consist of?
Extracranial radiosurgery applies the same principles as intracranial radiosurgery. Both aim to administer a high ablative dose of radiation in a precise manner, over a well-defined volume. The purpose of this is to eliminate the tumor volume outside the skull. This technique combines elements of three-dimensional radiotherapy with those of IMRT and IGRT.
Why is SBRT (extracranial radiosurgery) performed?
It is performed for the treatment of head and neck cancer, lesions or brain tumors outside the skull, as well as for metastasis, pancreatic tumors, etc. Sometimes, due to the respiratory movement, complementary techniques are needed to control breathing which will also be applied to the treatment if necessary. This is quite common in many of the ailments affecting the lung, pancreas or liver.
Preparation for SBRT (extracranial radiosurgery)
SBRT treatments require precision similar to cranial stereotactic treatments, since lesions of the lung, liver or pancreas are influenced by respiratory motion. In this type of pathologies it is necessary to perform the radiotherapeutic treatment with respiratory control techniques and, for this purpose, the following techniques are used:
- Gating: this system allows the irradiation dose to be administered in a selected phase of the patient’s respiratory cycle, interrupting automatically when the patient is breathing in a phase other than the programmed one. Once the patient is immobilized, the positioning of the tumor is verified in all sessions using the image-guided radiation therapy (IGRT) system. The respiratory cycle is monitored in real time by means of infrared monitoring of spheres placed on the patient. Simultaneously, the internal movement of the lesion is correlated with X-ray images that visualize fiducial markers previously implanted in the patient.
- ABC: The ABC (Active Breathing Coordinator) system is a respiratory control technique that allows treatment of thoracic or abdominal lesions during the inspiration phase of the patient’s respiratory cycle. A respiratory device is required to help the patient to maintain breathing during this phase for a period of time. Previously in the simulation CT an individualized training is performed to determine the time for each patient.
- Dampening: this is based on controlled compression of the patient’s abdomen to restrict the displacement of the diaphragm during the respiratory cycle, thus limiting the displacement of lesions located in the lung or upper abdomen. Compression is performed with belt-type or arch-type devices, which are designed so that compression is constant and always the same throughout the treatment. The patient’s positioning must be checked daily with IGRT, but IGRT using 4-D kV CBCT also allows the movement of the treated lesion to be assessed at the time.
What does it feel like during the exam?
Radiosurgery treatments are similar to taking X-rays. Generally, the x-rays are not seen, felt or heard, except for patients receiving treatment to the brain, who may see lights while the machine is on, even with their eyes closed. The treatment itself does not cause any pain or discomfort. If pain is experienced for other reasons, such as back pain or discomfort, the medical or nursing staff should be notified.
When the device is removed from the head, there may be slight bleeding where the screws were placed, but this is a superficial wound that will be covered with a dressing. If you also have a headache, you can ask for a medication to feel more comfortable.
In most cases, patients who have undergone radiosurgery and SBRT can resume normal activities within one to two days.
Side effects of SBRT (extracranial radiosurgery)
Side effects of radiation therapy include problems that occur as a result of the treatment itself, as well as damage done by the treatment to healthy cells in the treatment area.
The number and severity of side effects experienced depends on the type of radiation, the dosage received and the part of the body being treated. Any side effects you experience should be discussed with your doctor so that they can help you manage them.
Radiation therapy may cause early side effects during or immediately after treatment, and they usually disappear within a few weeks. Also, late side effects may appear months or years later.
Common early side effects of radiation therapy include:
- Tiredness or fatigue.
- Sensitive skin.
- Red, irritated or swollen skin.
- Dryness, itching, peeling and blistering.
Depending on the area undergoing treatment, other early side effects may include:
- Hair loss in the treatment area.
- Mouth problems and difficulty swallowing.
- Eating and digestion problems.
- Diarrhea.
- Nausea and vomiting.
- Headaches.
- Tenderness and swelling in the treatment area.
- Urinary and bladder changes.
Rare delayed side effects usually occur months or years after treatment and are often permanent. Some are:
- Brain changes.
- Spinal changes.
- Lung changes.
- Liver changes.
- Colon and rectal changes.
- Infertility.
- Joint changes.
- Lymphedema.
- Changes in the mouth.
- Secondary cancer.
- Bone fractures.
There is a small risk of developing cancer from radiation therapy. Therefore, it is important that patients undergo a regular examination by their radiation oncologist afterwards to detect possible cancers.
When techniques such as SBRT are used, the goal is to maximize the capabilities of radiation therapy to destroy the cancer, while minimizing its effects on healthy tissues and organs, thus avoiding side effects of the treatment itself.