Cuidados del cáncer

IMRT is an advanced, precise form of radiation therapy that delivers higher doses of radiation to the tumor and lower doses to nearby healthy tissue. IMRT allows patients to receive more concentrated radiation each day, potentially shortening the overall treatment time and improving treatment success. Some patients also experience fewer side effects during IMRT than more conventional treatment.

The radiation is delivered by a linear accelerator equipped with a multileaf collimator which helps to shape or sculpt the beams of radiation. The machine producing radiation can be rotated around the patient so that beams can be delivered from the best angles. Carefully planned and precisely manipulated beams conform as closely as possible to the shape of the tumor.

IMRT planning is done using sophisticated computer software that shapes the radiation dose to what the radiation oncologist specifies. Treatment is planned using 3D computed tomography (CT) images of the patient in conjunction with computerized dose calculations to determine the dose intensity pattern that will best conform to the tumor shape. Instead of radiation coming out of the machine via a single beam, IMRT uses as many as 80-120 sliding metal leaves to shape the beam to fit the specific shape of the tumor or treatment site. The beam is actually composed of thousands of tiny beamlets. The metal leaves and manipulability of the beam prevent radiation from getting to nearby healthy tissue.

Although IMRT is primarily used to treat tumors in the brain, head and neck, nasopharynx, breast, liver, lung, prostate and uterus, this new technology is not always appropriate or necessary for every patient and/or type of cancer.

IGRT, or image guided radiation therapy, is a form of radiotherapy using X-ray imaging during treatments to locate and focus dosing beams more precisely on tumors. IGRT brings scanning and radiation equipment together to permit the doctor to see the area of the body almost simultaneously while treating.

Prior to IGRT, physicians were unable to know the daily position of the tumor or tissues. With IGRT, more frequent imaging just prior to daily treatment enables physicians to pinpoint the position of the tumor and the surrounding normal tissues just as they are at time of treatment. With these more defined targets, patients can receive higher, more precise doses of radiation for better control of cancer and minimal effect to surrounding, normal tissues.

IGRT also enables doctors to make real-time adaptations to the treatment plan. The high-quality images of the tumor or treatment area obtained at the time of treatment allow clinicians to quickly reposition the patient as needed on the table. 3D cone beam CT images give clinicians a clear view of the tumor site and surrounding bones, organs and soft tissue. With IGRT, radiation oncologists no longer need to treat a relatively large margin of healthy tissue around the tumor, but can minimize the amount of healthy tissue exposed to the treatment beam.

Stereotactic radiosurgery (SRS) is a highly precise form of radiation therapy initially developed to treat small brain tumors and functional abnormalities of the brain. Despite its name, SRS is a non-surgical procedure that delivers precisely-targeted radiation at much higher doses, in only a single or few treatments, as compared to traditional radiation therapy. This treatment is only possible due to the development of highly advanced radiation technologies that permit maximum dose delivery within the target while minimizing dose to the surrounding healthy tissue. The goal is to deliver doses that will destroy the tumor and achieve permanent local control.

Although SRS commonly refers to a one-day treatment, physicians sometimes recommend multiple stereotactic delivered treatments. This is important for tumors larger than one inch in diameter as the surrounding normal tissue exposed to the single high dose of radiation must be respected and limited, and the volume of normal tissue treated increases proportionally to the tumor size. Delivering the radiation in a few sessions as opposed to one, can improve safety and allow the normal tissue to heal in between treatments. Therefore, fractionating the treatment allows for high doses to still be delivered within the target, while maintaining an acceptable safety profile. This procedure is usually referred to as fractionated stereotactic radiotherapy (SRT), and typically refers to the delivery of two to five treatments of focused radiation.

Stereotactic body radiation therapy (SBRT) is a similar procedure to brain stereotactic radiosurgery and radiotherapy, except it is used on tumors outside the brain (extracranial), generally in the lungs, liver and spine. SBRT is an emerging treatment for lung cancer in patients who are not candidates for surgery.

SBRT uses highly accurate imaging to deliver precise, high dose radiation (either in a single dose or in a small number of high-dose fractions) to areas located close to vital organs/anatomic regions or areas with substantial normal organ motion inside the body. SBRT involves patient immobilization and image-guided radiation therapy (IGRT). The technologically advanced imaging techniques used in this treatment can predict tumor motion and guide the dose to the tumor site, ensuring safe and effective cancer treatment.

Respiratory gating is used in some instances when treating with SBRT. In certain locations of the body, such as the lungs and abdomen, tumors can move as the patient breathes, making it difficult to accurately deliver radiation therapy to these tumors. Respiratory gating solves this problem by timing the radiation treatment to an individual's breathing pattern, targeting the tumor only when it is in the best breathing phase. This approach decreases amount of normal tissue receiving radiation, thus reducing complications and side effects, while using higher doses and achieving better outcomes.