In external beam radiation therapy, a radiation beam is directed through the skin to the cancerous area in order to destroy the main tumor and surrounding cancer cells. To minimize side effects, treatments are typically given over several weeks, five days a week, from Monday to Friday. This ensures that the tumor receives an adequate dose of radiation to kill the cancer while giving healthy cells time to recover.
The radiation beam is typically generated by a machine called a linear accelerator. The linear accelerator (LINAC) is a highly advanced treatment device capable of producing high-energy X-rays and electrons. Prior to treatment, careful planning is required to determine the radiation dose and direction, using high-tech treatment planning software to calculate the size, shape, and direction of the radiation beam to effectively target the tumor while sparing surrounding healthy tissue.
Tumors move due to factors such as respiration and organ filling. Four-dimensional tomography, which includes respiratory motion imaging, is used to identify the tumor area while considering this movement. This treatment planning and radiation therapy technique is especially preferred for tumors in the lungs, upper abdomen, and liver.
Image-guided radiation therapy uses imaging technology to more accurately and safely target cancerous tissue and avoid damage to healthy tissue. Tumors may move between treatments due to daily changes in organ filling (urine, stool, gas, etc.) or movement during breathing. IGRT helps monitor and adjust for changes in tumor size, growth, or shape during treatment. Radiation oncology devices, such as linear accelerators, are equipped with imaging systems to verify the precise location of the tumor before and during treatment. CT scans, X-rays, ultrasound, and MRI are used just before radiation to ensure more accurate delivery of radiation. Pre-treatment imaging is compared with the planning CT images to allow necessary adjustments, ensuring better targeting of the cancer while avoiding normal surrounding tissue. Small markers may sometimes be placed inside or near the tumor to pinpoint its exact location.
Respiratory-controlled radiation therapy takes into account breathing movements during radiation. This helps minimize exposure to the heart and lungs, reducing the risk of damage. Special respiratory tracking systems are used during the treatment.
? Stereotactic radiation therapy, also known as stereotactic radiosurgery (SRS) or stereotactic body radiotherapy (SBRT), is a technique where radiation beams are precisely focused on a specific point to deliver a very high dose of radiation to tumors. This focused radiation therapy uses advanced imaging techniques to minimize damage to surrounding normal tissue while effectively treating cancer. Stereotactic treatments are typically effective for tumors smaller than 3 cm. Traditional radiation therapy is often given in small daily doses over several weeks, while stereotactic radiation therapy is typically delivered in one or a few sessions after careful planning. When performed on brain tumors in multiple sessions, it is called "stereotactic radiation therapy," and when delivered in a single session, it is called "stereotactic radiosurgery." When applied outside the brain to other organs, it is referred to as "stereotactic body radiation therapy." This method is known to provide better results with fewer side effects compared to traditional radiation therapy, especially for small tumors.
3D conformal radiation therapy uses special imaging techniques to determine the size, shape, and location of the tumor. Detailed, three-dimensional models of the tumor and surrounding organs are created using CT, MRI, and/or PET-CT imaging. Radiation beams are then shaped using field-shaping blocks (multi-leaf collimators or MLC) to match the tumor's size and shape. This precise targeting of radiation reduces the dose to healthy tissues and improves side effect management.
IMRT and VMAT represent some of the most significant and up-to-date developments in oncology. IMRT allows radiation to be shaped according to the tumor's form, and different angles are used to deliver radiation. With IMRT/VMAT, the radiation beam can be divided into thousands of smaller "beamlets," with each beamlet's intensity adjusted individually. These beamlets are directed at the tumor using highly precise planning systems, ensuring that the radiation dose matches the three-dimensional volume of the tumor. During treatment, the machine continuously adjusts the shape of the radiation to match the tumor. IMRT/VMAT allows cancerous tissue to receive higher and more effective doses of radiation while minimizing exposure to healthy tissues and organs. This increases the chances of successful treatment while reducing the likelihood of side effects.
