Radiotherapy, which is also commonly referred to as radiation therapy, involves the use of ionizing radiation to induce damage to tumor cells in an effort to prevent their growth and division. Since the first description of X-rays in 1895, radiotherapy has become a standard treatment option for a wide range of cancers around the world.
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Early history
A few months after Wilhelm Conrad Roentgen discovered X-rays in 1895, the fields of radiology and radiation oncology were born. Between 1895 and 1900, X-ray treatments were used for a wide range of malignancies including gastric and skin carcinomas, as well as several benign conditions like eczema and lupus.
The earliest radiation treatments were generally delivered as single large exposures. More specifically, these treatments involved the placement of low-energy cathode-ray tubes or radium-filled glass tubes close to tumors. Unfortunately, these high doses were insufficient in their ability to effectively treat malignancies and were often associated with extensive damage to normal surrounding tissues.
By 1911, the principle of fractionation for external beam radiotherapy (XRT) and slow, continuous low-dose-rate (LDR) radium treatments were established. These approaches differed considerably from the conventional approach that instead opted for shorter and more tense treatments. By fractionating the total radiation dose, physicians were able to gain better control over cancer growth while simultaneously reducing adverse effects associated with radiotherapy.
The orthovoltage era
Between 1930 and 1950, a period that became known as the Orthovoltage era, significant progress was made in the treatment of deep cancers by radiation. The Orthovoltage era is often characterized by advances in brachytherapy and supervoltage X-ray treatment.
Brachytherapy, which involves the use of radium-based interstitial radiation, allowed physicians to specifically target tumors while minimizing any unwanted exposure to surrounding normal tissues. Comparatively, supervoltage X-ray tubes, which can deliver energy in the range of 50 kilovolts (kV) to 200 kV), acted as the introduction to electron beam therapy, which enabled the delivery of higher and variable energies to deep tumors.
The megavoltage era
Between 1950 and 1980, a three-decade period otherwise known as the Megavoltage era, several studies were focused on the development of more innovative radiotherapeutic devices that were capable of treating cancers residing in the deep tissues. Some of the most notable discoveries of this period include the Cobalt teletherapy, which is a technique that produces high-energy gamma rays, as well as potent linear accelerators that could deliver megavoltage X-rays.
The 1970s and 1980s of this era are often characterized by the discovery of proton beam therapy. Although this radiotherapy approach was first developed in 1954, it was not until the late 1970s that a computer-assisted accelerator was developed to successfully apply protons to various types of tumors.
Taken together, the devices developed during this period allowed for the delivery of much higher energy doses as compared to those utilized in previous years. Again, a common theme in new radiotherapy technologies was to minimize damage to surrounding tissues and instead deliver radiation doses deep into the tumor.
Recent advances in radiation therapy
Over the past several decades, several advances in radiation physics and computer technology have increased the precision of radiation for the treatment of various malignancies. Conformal radiation therapy (CRT), for example, combines computer tomography (CT) images with specialized tumors to allow physicians to identify tumors in three dimensions. Physicians are then able to carefully deliver radiation beams that are matched to the exact shape of the tumor in several directions.
Similar to CRT, intensity-modulated radiation therapy (IMRT) also allows for photon beams to be delivered in several directions. One distinct characteristic of IMRT is that the intensity of the beams can be adjusted, thus allowing physicians to gain even more control in how much radiation is delivered to both the tumor and normal tissues.
Conformal proton beam radiation therapy utilizes a similar approach to both CRT and IMRT; however, instead of X-rays, this approach instead delivers protons to cancer.
Radiation surgery
Radiation surgery is defined as an external radiation treatment that involves the use of specialized equipment for the precise delivery of a high dose of radiation to a tumor. Some examples of radiation surgeries include stereotactic radiosurgery, stereotactic radiation therapy, and stereotaxic radiosurgery. Although the term surgery is used in the names of these procedures, it should be noted that no cutting is required for these treatments.
The brain is the most common site that is treated with radiation surgery. Some of the different systems that are used to deliver this treatment include a linear accelerator, Gamma Knife, or a CyberKnife.
In addition to radiation surgery, radiation can also be administered at the same time as when a surgical resection of a tumor is performed. This type of treatment is known as intraoperative radiation therapy (IORT) and involves the delivery of radiation directly to cancer or nearby tissues after the malignant tissues have been removed. Some of the common indications for IORT include abdominal and pelvic cancers.
References:
- Gianfaldoni, S., Gianfaldoni, R., Wollina, U., et al. (2017). An Overview on Radiotherapy: From Its History to Its Current Applications in Dermatology. Open Access Macedonian Journal of Medical Sciences 5(4); 521-525. doi:10.3889/oamjms.2017.122.
- Connell, P. P., & Hellman, S. (2009). Advances in Radiotherapy and Implications for the Next Century: A historical Perspective. Cancer Research. doi:10.1158/0008-5472.CAN-07-6871.
- Huh, H. D., & Kim, S. (2020). History of Radiation Therapy Technology. Progres sin Medical Physics 31(3); 124-134. doi:10.14316/pmp.2020.31.3.124.
- History of Cancer Treatments: Radiation Therapy [Online]. Available from: https://www.cancer.org/cancer/cancer-basics/history-of-cancer/cancer-treatment-radiation.html.
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