Radiation Oncology


Radiation Oncology uses radiation to kill cancer cells and shrink tumors. The radiation damages cancer cell DNA so the cell can no longer grow and reproduce. Depending on the type of tumor and the individual case, radiation treatments can be used before surgery to make tumors easier to remove, or afterwards, to make sure no cancer cells are left behind.

Unlike chemotherapy, which is called a “systemic treatment” because it treats the entire body, radiation is considered a local treatment. This means that radiation only works where it is aimed. If any metastases exist outside the radiation field, those cancer cells will not be destroyed by the radiation. However, radiation is usually used in conjunction with other treatments.

Radiation can be administered in one of three ways:

  • External beam radiation therapy, in which the tumor is targeted with high-energy beams
  • Internal radiation therapy, or brachytherapy, in which “seeds” of radioactive material are placed directly inside the body, in and around the tumor
  • Systemic radiation therapy, in which a radioactive substance is introduced into the bloodstream and circulates throughout the body

Our radiation oncologists are pioneers and early adopters of the latest techniques, including the following, which enhance targeting and minimize the dose to healthy tissue.

CT Simulators

CT simulators are used for precision planning of radiation treatments. Our new GE LightSpeed RT CT simulator, which produces thin, clear images for precise tumor delineation, is the first multi-slice CT scanner dedicated to radiotherapy.

Image-Guided Radiation Therapy (IGRT)

Used in conjunction with external radiation, usually IMRT (below), image-guided radiation therapy uses imaging to target the delivery of radiation to a tumor as specifically as possible. IGRT is used to treat tumors that are close to critical organs and tissues, and tumors in areas of the body that are prone to movement, such as the lungs.

Intensity-Modulated Radiation Therapy (IMRT)

This high-precision radiotherapy uses computer-controlled linear accelerators to radiate tumors with exquisitely precise doses of radiation. IMRT modifies the radiation beam so the radiation dose conforms to the tumor’s three-dimensional shape. Treatment is planned by combining 3D computed tomography (CT) or magnetic resonance imaging (MRI) and computerized dose calculations to arrive at a dose intensity pattern that will fit the shape of the tumor.

Linear Accelerators

Linear accelerators interface with computers to create advanced, targeted radiation therapy treatments such as IMRT. The Marin Cancer Institute has recently installed two new state-of-the-art linear accelerators, including the Varian Trilogy system, the world’s first image-guided radiation therapy system optimized for both conventional and stereotactic approaches to treating cancer.

Partial Breast Irradiation

Radiation is often performed after lumpectomy surgery. Partial breast irradiation treats only the site of the lumpectomy and the surrounding tissue, to reduce the amount of radiation to the healthy part of the breast.

Respiratory Gating

Pioneered by radiologists at Marin General Hospital, this technique protects the heart during irradiation by synching radiation treatments with the motion of the patient’s breathing.

Stereotactic Body Radiotherapy (SBRT)

This high-dose precision form of radiotherapy uses the same techniques as SRS (below) to treat tumors elsewhere in the body. It is best suited to the treatment of small tumors.

Stereotactic Radiosurgery (SRS)

Stereotactic radiosurgery is a high-dose, precision form of radiation therapy used to treat brain tumors.