What is the Difference Between Cobalt Therapy and Linear Accelerator?

In brief, Cobalt is an older form of radiation. LINAC (Linear Accelerator) is the newer and best form of radiation.

Cancer incidence is increasing alarmingly over the years. It is among the top five causes of death worldwide according to the World Health Organization as of 2010. It is also the second most common cause of mortality in the United States. Here in the Philippines, cancer cases doubled from 1965 to 1985, and had since been increasing in a steady pace as the third leading cause of death for the past three decades as per Department of Health and Philippines Cancer Society registry of 2010.

About 50% of cases are for curative treatment and the other 50% are for palliative care. Unfortunately, most of our local patients lack the resources to undergo treatment and can only avail of some minimal insurance benefits and hospital discounts. Most needed is a multidisciplinary approach which involves surgery, chemotherapy and radiation treatment for long periods of time, not counting the added cost of laboratory and diagnostic work-ups.

In this regard, we as doctors and health care specialists, must do our best to make their efforts for treatment count. Not only should we provide the best medical and nursing care for them, we should also inform them of the best possible treatment options available in our field.

Teletherapy cobalt machines made a mark in the development of currently used treatment protocols. It is preferred by most developing countries for cancer treatment because of its advantages such as low capital outlay, low maintenance cost and power requirement, and less down time. On the clinical side, it provides a long half-life, and a relatively high energy gamma ray emission that is suited for treatment of deep-seated tumors.

However, because of its large penumbra, its minimum fixed square-shaped field size of 5x5cm and a Dmax of 1.5cm, it is very hard to minimize irradiation to organs at risk adjacent the target volume. As a result, early and heightened acute reactions occur that exacerbate the already compromised condition of cancer patients. Likewise, there are more late toxicities noted especially for the head and neck tumors. More treatment sequelae means poor quality of life or ineffective hospice care for terminally ill patients.

Another downside of a Cobalt Unit is its decaying radioactive source that produce a decreasing dose rate that is dependent on source activity. It also has some radiation leakage of the machine head, which pose a health hazard to radiation therapy staff, especially radiation technologists, physicists and radiation oncologists. This is based on the “Linear Hypothesis” employed in the principle of ALARA (As Low As Reasonably Achievable), that any radiation dose of any magnitude can produce some level of detrimental effects like increased risk of genetic mutation and cancer.

With this in mind, dedicated people in the field of radiation oncology coupled the treatment principles with technology, hence the development of linear accelerators (LINAC). With a smaller Dmax, “skin-sparing” was made possible. A guaranteed steady dose rate that is constantly monitored and recorded and a small penumbra, provided accurate delivery of treatment dose. Addition of multi-leaf collimators encouraged conformal treatment with maximum shielding to organs at risk. Computerization provided better three-dimensional planning judgements by visualization of target volume and optimization of dose delivery with hand-in-hand consideration of the tolerance doses of the different organs. This resulted in less acute and late effects within radiation treatment fields. Different fractionation protocols were developed to minimize hospital visits, enhance treatment effectivity, thus minimizing overall treatment cost.

On the treatment center side, modern linear accelerators are compact with built-in beam’s eye view and a maneuverable couch that provides ease and reproducibility of treatment setups. This also minimize daily radiation exposure to staff.  Very good beam matching can be delivered in case the patient needed to be transferred to a second LINAC machine.

Linear accelerators with different energies not only serve the patients but also enable the radiation oncologists to research on better techniques such as 3DCRT, IMRT, IGRT and altered fractionation schedules that we currently employ at some of the cancer centers here in the Philippines.

We cannot discount the fact that daily linear accelerator treatment fee is higher than a regular cobalt treatment cost. But cheaper does not necessarily equate to better. Considering the above advantages of LINAC treatment to the success of patients’ treatment, safety of the personnel and the need of not replacing any radioactive source, as in the case of a cobalt machine, we can clearly say that LINAC treatment is cost-effective and practical. On the government regulatory group, use of LINAC machine will solve the problem of radioactive waste disposal and risk of terrorism.

So as health professionals living in the 21st century, little decisions like what machines or procedures to patronize can really impact the future of our field of specialty. It should be our commitment to give our best effort in the line of service and help win the fight against cancer, while still preserving and developing our environment for the future.

Source: radiationtherapy.ph

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