Radiation oncology has evolved remarkably over the past 50 years. Following the discovery of X-rays by W. C. Roentgen, their ionising property - especially their ability to damage DNA - became central to cancer treatment. Rapidly dividing cancer cells are particularly susceptible, making radiation therapy a powerful curative tool.

X-rays also revolutionised medical imaging. Initially, physicians managed both diagnostic imaging and therapy, but growing complexity led to the bifurcation of the branch into diagnostic and therapeutic radiology in the 1950s. Since therapeutic radiologists primarily treated cancer, they became known as radiation oncologists.

In the 1940s-50s, chemotherapeutic drugs like mustine hydrochloride, cyclophosphamide, and methotrexate emerged. Radiation oncologists first administered these drugs due to their role in cancer care being already established. However, managing the toxicity and other medical aspects led to the emergence of a new field - medical oncology. This speciality expanded with monoclonal antibodies and immunotherapies, offering targeted treatment options.

Simultaneously, diagnostic radiology advanced with the development of ultrasound, CT, MRI, PET scans, and interventional techniques, significantly increasing the workload and specialisation within the field.

In the early 20th century, X-ray machines produced low-energy beams (<500 kV), limiting their ability to penetrate deep tissues, often causing severe skin reactions. Deep-seated tumours in areas like the thorax or pelvis could not receive adequate doses. A breakthrough came in the 1940s with Cobalt-60 (Co-60), emitting gamma rays akin to 1.4 MV X-rays. Co-60 teletherapy gained global traction in the 1950s-60s, though it’s now being phased out in developed countries. Caesium-137 (Cs-137) also saw brief use due to limited penetration.

Technological advancements led to high-energy machines like the Betatron and Linear Accelerators (Linacs), capable of generating X-rays up to 30 MV. Linacs became the standard due to their technological superiority. Although early models used higher energies, 6 MV X-rays are now optimal for human treatment, minimising skin toxicity while delivering effective doses to deeper tissues. Electron beams from Linacs are used for superficial cancers such as Mycosis Fungoides, as they deposit most of the energy near the surface.

The rise of complex machines necessitated computer-based treatment planning. Radiotherapy evolved from 2D fixed-field treatments to 3D conformal therapy (3DCRT), Intensity-Modulated Radiotherapy (IMRT), Image-Guided Radiotherapy (IGRT), using dynamic beam shaping and in-treatment imaging to enhance precision. Sophisticated systems like Tomotherapy now deliver rotation-based treatments with precision.

Traditionally, curative radiotherapy spans 25–35 daily sessions over 5–7 weeks. In contrast, Stereotactic Radiotherapy (SRT) delivers very high doses over 1–6 sessions. Stereotactic Radiosurgery (SRS), although non-surgical, uses ablative doses in a single session for benign brain tumours. The Gamma Knife, using Co-60, pioneered this approach with a fixed head frame. Later, Linac-based SRT systems with special collimators and the CyberKnife – delivering SRT via robotic arms enabled precise treatment of tumours in various parts of the body.

A major recent advancement is Proton Beam Therapy (PBT). Protons, derived from hydrogen atoms and accelerated via a cyclotron, have a unique feature - the Bragg Peak - where radiation is deposited precisely at a target depth with minimal exposure beyond the tumour. This property makes PBT ideal for treating tumours near critical organs, especially in the brain and spinal cord. However, the complex design and requirement of large infrastructure for PBT make treatment very expensive. In India, two centres – Apollo Hospitals, Chennai, and Tata Memorial Hospital, Mumbai – offer PBT, with treatment costs up to ₹30 lakhs. Without insurance, it remains inaccessible to the middle class.

Brachytherapy is another key modality, delivering radiation directly within or adjacent to the tumour, minimising exposure to surrounding tissues. The earliest source was Radium, used successfully from 1902 for cervical cancer via intra-cavitary application. Its long half-life and logistical challenges such as long treatment duration and radiation safety, eventually made it obsolete.

In Kerala, Prof. Keshavan Nair brought radium from the UK in the 1950s. Initially stored at General Hospital, Thiruvananthapuram, and later moved to the Medical College, it was used until safety concerns and practical challenges, including lost radium sources, led to its replacement. Caesium and Cobalt isotopes followed, employed in afterloading techniques where empty applicators are first inserted and then loaded with radioactive sources based on computerised treatment planning.

A landmark innovation was the high-activity Iridium-192 (Ir-192) source. With much shorter treatment times (30–60 minutes), compact applicators, and CT-guided planning, Ir-192 revolutionised brachytherapy. Treatment can now be conducted on an outpatient basis with enhanced safety and patient comfort. For multiple sessions, the same applicators could be reused daily.

Permanent implants are another development, such as Iodine-125 (I-125) seeds for prostate cancer. Implanted via catheters into the prostate, they deliver a slow radiation dose over a year and remain inert in the body afterwards.

Radiation Oncology in India

India’s first radiotherapy department was established at Calcutta Medical College in 1910, offering deep X-ray therapy and Radium. Subsequent Radium Institutes emerged in Madras, Agra, Patna, and Lahore. In the 1940s, Tata Memorial Hospital (TMH), Mumbai, began with Radium and later acquired a Telecobalt unit. In the 1950s, the Adyar Cancer Institute in Chennai started similar services.

Kerala joined the movement in the late 1950s with Radium, followed by deep X-ray and Telecobalt machines. When I joined the Thiruvananthapuram Radiology Department in 1967, it had Radium, deep X-ray, and a basic Eldorado Telecobalt machine with a stationary head, requiring patients to be manually repositioned for multi-angle treatment. At that time, there was no MD Radiology course in South India, so I pursued my degree in Lucknow, where the curriculum still included both diagnostic and therapeutic radiology.

In the late 1970s, Thiruvananthapuram Medical College acquired the dual-head Janus Telecobalt machine, enabling alternate room usage to improve efficiency. Later, newer Telecobalt units and a Linear Accelerator were procured. The Radium stock was replaced by a Selectron afterloading machine for gynaecological brachytherapy using medium-dose-rate sources.

In 1980, the Radiology Department formally split into Radiodiagnosis and Radiotherapy. Two years later, the Cancer Department at Thiruvananthapuram Medical College was designated as a Regional Cancer Centre (RCC). Historically, the cancer care infrastructure was limited due to high costs. That changed in 1993 when Apollo Hospitals, Chennai, established a state-of-the-art cancer facility with Linear Accelerators, HDR brachytherapy, SRS, CyberKnife, and, later, Proton Beam Therapy. This set a trend, and many leading private hospitals in India now offer advanced radiotherapy, drawing patients from across India and neighbouring countries.

Conclusion

Radiation Oncology, though a century old, has undergone tremendous transformation. Initially named Radiology, it evolved through therapeutic radiology, radiotherapy, and is now known as radiation oncology. The speciality’s progress mirrors advancements in imaging, precision therapy, computational planning, and equipment design. These innovations, driven by research and technology, have revolutionised the cancer treatment landscape, significantly improving patient outcomes.