radiation therapy
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radiation therapy is a core treatment modality in oncology that uses high-energy radiation to damage the DNA of cancer cells, inhibiting their ability to proliferate. It is delivered via sophisticated equipment like linear accelerators and is prescribed by a radiation oncologist as part of a comprehensive care plan. The field has evolved significantly from its origins with X-rays and radium to incorporate advanced techniques such as intensity-modulated radiation therapy and proton therapy.
Overview
The fundamental principle involves directing ionizing radiation, such as X-rays, gamma rays, or charged particles, at a defined tumor volume. This radiation induces irreparable double-strand breaks in the DNA of malignant cells, leading to cell death. Treatment planning is a meticulous process conducted by a multidisciplinary team including a radiation oncologist, medical physicist, and dosimetrist, often utilizing imaging from computed tomography (CT) or magnetic resonance imaging (MRI) scans. The goal is to maximize dose to the cancer while sparing surrounding healthy tissues, a concept known as the therapeutic ratio.
Types of radiation therapy
The two primary categories are external beam radiation therapy (EBRT) and brachytherapy. EBRT, delivered from outside the body by machines like linear accelerators or cobalt machines, includes specialized forms such as stereotactic body radiotherapy (SBRT) for precise lung cancer treatments and whole-brain radiation therapy for brain metastasis. Brachytherapy involves placing radioactive sources, like iodine-125 or cesium-131, directly inside or next to the tumor, commonly used for prostate cancer and cervical cancer. Systemic radiation therapy uses radiopharmaceuticals, such as radioiodine therapy for thyroid cancer or radium-223 for metastatic castration-resistant prostate cancer.
Medical uses
It serves as a definitive, curative treatment for localized cancers, including early-stage Hodgkin lymphoma, laryngeal cancer, and prostate cancer. As an adjuvant therapy, it is administered after surgeries, such as a lumpectomy for breast cancer, to eradicate microscopic residual disease. Neoadjuvantly, it can shrink tumors before operations for cancers like rectal cancer. For palliative care, it effectively relieves symptoms from bone metastasis, brain metastasis, and superior vena cava obstruction. It is also a key component of combined modality therapy with chemotherapy, as in the treatment of lung cancer and esophageal cancer.
Side effects and risks
Side effects are typically localized to the treatment area and can include acute reactions like dermatitis, mucositis, and fatigue. Late effects may manifest months or years later, such as fibrosis, xerostomia after treatment for head and neck cancer, or radiation proctitis following pelvic radiation. There is a small but increased lifetime risk of developing a second primary cancer, such as sarcoma within a previously irradiated field. Advances like intensity-modulated radiation therapy have significantly reduced the incidence of severe complications like radiation pneumonitis and damage to organs like the spinal cord.
Treatment process
The journey begins with a consultation and simulation, where immobilization devices are crafted and imaging with computed tomography is performed. During the complex planning phase, the radiation oncologist delineates target volumes and organs at risk on software, and the medical physicist and dosimetrist calculate optimal beam arrangements. Treatment delivery involves daily sessions on a linear accelerator, with image guidance via cone-beam CT or kilovoltage imaging ensuring accuracy. Patients are monitored weekly by the radiation oncologist and oncology nurse for side effect management, with follow-up continuing for years at institutions like the MD Anderson Cancer Center.
Technological developments
Major advances include the widespread adoption of intensity-modulated radiation therapy (IMRT) and its extension, volumetric modulated arc therapy (VMAT), which conform dose more precisely to irregular tumor shapes. Image-guided radiation therapy (IGRT) utilizes technologies like CyberKnife and cone-beam CT for real-time targeting. Particle therapy, particularly proton therapy, offers a superior dose distribution due to the Bragg peak effect, making it valuable for pediatric cancers and skull base tumors. The integration of artificial intelligence and machine learning is now optimizing treatment planning and radiosensitivity prediction.
History
The therapeutic use of radiation began shortly after Wilhelm Röntgen's 1895 discovery of X-rays, with early treatments for skin cancer. The discovery of radium by Marie Curie and Pierre Curie led to the development of brachytherapy. The mid-20th century saw the introduction of the cobalt machine, which provided more penetrating gamma rays. The invention of the linear accelerator in the 1950s, pioneered by scientists at Stanford University and in the United Kingdom, revolutionized external beam delivery. The latter decades brought the integration of computed tomography for 3D planning and the subsequent development of conformal techniques, establishing modern oncology practice.