History of X-rays
Learn how X-ray therapy has evolved and how superficial and orthovoltage treatments are an integral component of modern radiation programs.
Early Therapeutic X-ray Application
The 1890’s represented an important period in the development of radiation therapy and applying its use to treat cancer. These significant discoveries led to the understanding not only of the diagnostic properties of X-rays but also their therapeutic applications.
In 1895, Röntgen first discovered X-rays while working in his laboratory, experimenting with a Crookes tube; a glass bulb with positive and negative electrodes, evacuated of air, which displayed a fluorescent glow when a high voltage current was passed through it. On shielding the tube with heavy black cardboard, he found that a greenish fluorescent light could be seen from a platinobaium screen nine feet away. He concluded that a new type of ray emitted from the tube which passed through most substances, including the soft tissues of the body, but left the bones and most metals visible.
In 1896, Becquerel first noted the concept of radioactivity while investigating phosphorescence in uranium salts.
In 1898, the radioactive properties of radium were noted by Marie and Pierre Curie.
Radiation & Cancer Treatment
The first reported “cure” of cancer was documented in literature in 1899 when a basal cell epithelioma (now referred to as a basal cell carcinoma or BCC) was treated by the application of radiation via a radium source to the skin. This instigated the evolution of radiation therapy as a treatment modality for cancer.
In the early days, treatment was delivered with little understanding or knowledge of the physical nature and biological effects of radiation; there were no methods of calculating the dosage and equipment was cumbersome and unwieldy. Additionally, as the equipment could only deliver low energy therapeutic X-rays only tumors arising in superficial tissue layers could be treated, usually in one single session and over a large area of the body, in the hope that the tumor would be destroyed. As a consequence, there were many reported complications arising from the treatment; literature from this period documents numerous examples of effects resulting in destruction of normal tissue such as necrosis, infection, and even death. Unsurprisingly, the rate of recurrence following these early treatments was high.
Cancer Treatment Evolution
By the late 1920’s, this treatment modality had somewhat evolved, enabling a better understanding of the nature of radiation and its biological effects which, in turn, led to the introduction of fractionated treatment schedules and the concept of the use of dosage units, although even during this stage radiation dose was often monitored according to the patients skin reaction. As the correlation between dose and biological effects were realized treatment schedules were developed and refined, however treatment was still only used to treat malignant and benign skin lesions and only with palliative intent.
Treating Superficial Skin Tumors
Developments in the type and nature of the equipment provided significant technological advances. The introduction of the vacuum X-ray tube allowed the production of X-ray energies up to 200 kV, which highlighted a major breakthrough in the application of radiation for therapeutic purposes. For the first time in its history, radiation therapy had the capacity to cure superficial skin tumors, without the associated complications previously observed.
Complementary Technologies
In the 1940’s, the development of teletherapy equipment and the subsequent linear accelerator enabled the production of much higher energy therapeutic X-rays, which allowed deep seated tumors to be treated and with the reduction of severe skin reactions, as the maximum dose now occurred below the skin surface.
However, the use of low energy therapeutic X-rays remained the treatment of choice when treating lesions at shallow depths, due to the physics of low energy X-rays and the relatively low cost, simplicity, and low maintenance requirements of the equipment.
Modernizing Therapy
Following a period of development throughout the 1990’s, superficial and orthovoltage machines have undergone several advances including the addition of integrated dosimetry, a record and verify system, and the ability to network the machines with other departmental patient information systems and electronic medical records. Such advances have ensured that kilovoltage X-ray equipment maintains an integral role in the modern radiation therapy department for the treatment of both malignant and benign conditions.
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