Evolution of radioactive therapy in cancer treatment

Dr Manish Chandra

X-ray and radioactivity were discovered in last decade of 19th century in Europe. Not only do they resemble in many physical characteristics, they were also discovered very close to each other in 1895 and 1898 respectively. Medical use of both X-ray and radioactivity soon after. X-ray was used for preliminary diagnostic imaging and radioactivity was used to treat superficial skin cancer. With further technological advancement, higher energies of X-ray could be generated. This led to the use of X-ray in treating deep-seated tumours. However, early 20th century proved that these techniques can cure cancer but may cause cancer as well.

This led to further refinement in the techniques and equipment delivering radiation for treatment. It has steadily improved since then and today, radiation is delivered precisely to destroy cancer cells while saving the normal tissues around them.

A 2-year-old boy – the f irst patient to receive radiation from the original medical linear accelerator at Stanford	Radiation unit at Jupiter Hospital

Radium discovered in 1898 was the main radiation-delivering isotope used in the treatment of cancer till mid-1900s. But with radium kept getting costlier, difficult to procure and people become aware of the health hazards to the health workers. So, cobalt was then developed as an alternative and the first Cobalt 60 unit was installed in 1951 at the University Hospital in Saskatoon, Canada. This machine treated 6728 patients before it was decommissioned in 1972. Parallel to this, there was a major revolution in the field of linear accelerators which had grown from low voltage to very high voltage beams. The first mega voltage linear accelerator was installed at the Stanford University in 1956. The iconic photograph of a two-year-old child suffering from Retinoblastoma (tumour of the eye) receiving treatment is still kept by the Radiation Oncologist (Fig 1). During the same time there was a renewed interest in internal radiation therapy known as brachytherapy (radiation therapy started with brachytherapy but later shifted its focus to external beam radiation therapy). In 1940s there was considerable development in the field of brachytherapy, mainly for gynaecological cancers, prostate cancers and superficial skin cancers.

The primary advantage of Linear Accelerator over Cobalt unit was short treatment time as well as uniform and higher dose rate. The limitation of the accelerators in the early years was its fixed gantry, but by 1960s, this problem was also resolved. Linear accelerators became the preferred mode of treatment along with electron beams. Its use was limited because of higher cost and frequent breakdown. Till 1980s linear accelerators and Cobalt units were fighting for their superiority in terms of treatment delivery, stability and cost effectiveness.

Hand with Rings: print of Wilhelm Röntgen’s first “medical” X-ray, of his wife’s hand, taken on December 22, 1895 and presented to Ludwig Zehnder of the Physik Institut,University of Freiburg, on January 1, 1896

In late 1970s, computer started infiltrating medical equipment and linear accelerator took the full advantage of it. In early 1980s, cobalt unit were replaced by linear accelerator in Western countries. After a decade, cobalt units were limited to only third world countries.

There is no denying that computers changed our life and it had an impact on radiation therapy as well. After adopting the computer with open arms, it changed completely in over a decade (mid 1980s to mid-1990s). With better linear accelerators it was possible to deliver a uniform dose to the designated site and could shape the beam with lead blocks. However, the preparation of these blocks was a very labour-intensive and difficult task. Then, Multi-leaf collimator came into picture in mid-1980s, though it was conceived way back in 1965. It changed the complete dynamics of linear accelerators. 3-D conformal treatment became the basic treatment and then graduated to intensity modulated radiation therapy (IMRT).

Imaging in radiation therapy was not far behind and it too was simultaneously improving over the years. It evolved from film- based imaging to digital imaging and then to cone-beam computed tomography. Then, when some thought there is nothing else in radiation therapy to be explored, cone beam computed tomography with low voltage radiation emerged, offering diagnostic quality of images.

It is a pleasure to work in this golden era of radiation oncology where an oncologist can offer treatment that can be delivered to the patient with minimal adverse reactions. Popular to the contrary belief, radiation therapy in this era is completely safe to the health worker and the dosimetry analysis has shown that radiation oncologist health workers receive the least amount of occupational radiation as compared to other health workers (cardiology, operation theatre, orthopaedics and radiology)

Techniques that can be used with current medical linacs:

With the current trend using linear accelerator a variety of treatment techniques are possible.

Some of the techniques as follows

1. 3D Conformal Radiotherapy: Through the advancement of imaging technology, enhanced images of the body allow for programming of treatment beams to conform better to the shape of a tumour. Hence treatment is more effective and side effects are reduced. By treating with large numbers of beams, each shaped with a multileaf collimator (MLC) or cerrobend block, radiation dose is delivered uniformly and conformally to the tumour.
2. Intensity Modulated Radio therapy (IMRT): IMRT is one of the latest advancements in radiation therapy. This new approach to treatment allows for dose sculpting and even distribution of delivery to avoid critical structures while delivering precise uniform treatment. In this technique, the multileaf collimator (MLC) moves and modulates the radiation as the linac treats the patient
3. Stereotactic Radiotherapy & Radiosurgery (SRT): SRT is a three-dimensional navigational technique to target the tumour volume with very low to minimal dose to the surrounding normal tissues.
4. Dynamic Adoptive Radiotherapy (DART): Imaging, in the field of radiation therapy, has improved a lot and this led to evaluation of the tumour dynamically during the treatment and adapt as per the regression and change in the tumour size.
5. Image Guided Radiotherapy (IGRT): As the name suggests, it is the technique where we use image guidance to deliver radiation therapy.

I am really privileged to have my wish list of the latest and complete radiation therapy unit at Jupiter Hospital in Thane, to treat the patient in the best way possible.

The field of radiation oncology is going to see many more new changes in the years to come and future of radiation therapy appears to be image-guided and adaptive.

In the next decade, the only mode of treatment delivery in radiation therapy would be image-guided.