Co‐60 tomotherapy is the treatment modality of choice for developing countries in transition toward IMRT

Radiation oncologists in developing countries want to do the best for their patients, so they are attracted to the use of the latest high-tech developments such as IMRT and tomotherapy. They do face significant fiscal constraints, however, so provision of these new technologies as inexpensively as possible is essential. It has been suggested that Co-60 tomotherapy might be the most appropriate way to provide IMRT in developing countries, and this is the premise debated in this month's Point/Counterpoint. Since the early 1950s the dissemination of robust, low-cost Co-60 teletherapy units has enabled many of the world's cancer patients to receive treatment. In the late 1990s, Van Dyk and Battista1 revisited Co-60 with a fresh perspective and concluded that with improved technology, patients in both developed and developing countries might benefit from Co-60 teletherapy. More recently, Co-60 has been considered as a source for IMRT2 and tomotherapy delivery,3,4 with studies showing that the plan quality may rival IMRT treatments delivered with a linac. The Renaissance® System 1000, ViewRay Inc., Gainesville, FL is currently under development and will use Co-60 as a compatible source for MRI-based, image-guided IMRT. Perhaps Co-60 will not go the way of the dinosaur after all. Rudimentary Co-60 teletherapy units are still making an impact in many parts of the world today (see IAEA, DIRAC database at www-naweb.iaea.org/nahu/dirac); the number of units worldwide is currently estimated at 2386 compared to 8460 clinical accelerators. Many developing countries are now in a position to consider newer technologies and more advanced treatment techniques such as IMRT. Limited capital, technical and physical resources, however, make decisions difficult. The advantages of a Co-60 source over a linac-produced treatment beam can be easily argued from the maintenance and quality assurance standpoint. Another consideration for advanced radiation therapy is the choice of multileaf collimator (MLC); a conventional MLC is an electromechanical device that must operate under strict positional tolerances during delivery and requires highly trained staff for maintenance and repair. A binary MLC, with ON or OFF states and pneumatic actuators, could be engineered to be inexpensive and robust and may continue to operate (along with the source transfer mechanism) from a small backup power source during outages. Even in the “developed world,” good quality IMRT treatment plans are difficult to achieve without the expertise of highly trained and skilled individuals. Treatment planning methodologies need to be simpler to use and more consistent in terms of plan quality before they become more widely accepted. The tomotherapy inverse planning method is straightforward. Dose from each beamlet, created by the binary MLC openings, is precalculated, making the process of adjusting planning parameters and reoptimization very efficient. There are no machine parameters to optimize at each planning iteration as there are with a conventional MLC, which adds additional layers of complexity to the inverse planning algorithms and methods. Developing countries have a strong desire for those things that are perceived to be necessary in the “high-tech” world even though they may be totally inappropriate for the local environment. There is no doubt that advanced radiation therapy techniques such as IMRT are being considered by developing countries with limited resources. To ensure success, the technology chosen must be accessible, simple to use, easy to maintain, and reliable. I believe that Co-60 tomotherapy offers the best choice to fulfill these requirements. Is cobalt-IMRT really cost-effective radiation therapy? For countries with limited fiscal resources, considerable attention needs to be given to cost/benefit.1,5–9 A maxim in today's culture of reducing costs is that we need to provide the most effective therapy at the lowest possible cost. The challenge inherent in this thinking is our ability to put a price on the risk of harm a subpar modality contributes for the patient, and the effect it has on security and safety for the public.10,11 First, one of the basic principles of medical practice is “First do no harm.” I believe that the radiation oncology profession transitioned to the use of higher energy photon beams because Co-60 therapy was not only less effective in controlling cancer, but it also did harm to a significant fraction of patients in terms of increased normal organ and skin toxicity, resulting in poor quality of life. Percent depth dose, dose rate, skin dose, and beam penumbra are some of the well-documented limitations of a cobalt unit.6 The impact of these factors is not necessarily eliminated by an IMRT plan. Compared to linac-based IMRT, cobalt-60 IMRT will result in a higher radiation dose “bath” to the peripheral regions of the body and therefore result in increased risk of induction of secondary cancers. Dose rate is also an important factor in determining suitability of Co-60 IMRT treatment. A modern linac can produce about 10 Gy/min at the isocenter, whereas the best a cobalt source can provide is about 2.5 Gy/min, a factor of 4 lower. It would mean a factor of 4 longer treatment delivery times. Patient positioning and internal motion are important factors in the efficacy of an IMRT optimized treatment, and these would be compromised. Moreover, compared to Co-60, higher energies are advantageous since the beams are less affected by tissue density and air gap. Second, radioactive sources pose an environmental hazard while being transported, while in service, and finally at the time of disposal. The source is always emitting radiation, whereas a linac x-ray beam can be switched “off.” There is always a risk of a radiation accident such as when a source “gets stuck” in the “on” position. Furthermore, there are numerous accounts of contamination produced by improperly disposed sources. Additionally, a radioactive cobalt source in the hands of poorly trained personnel or an organization determined to cause serious harm to a large population could be devastating. What price are we willing to pay for such risks? As the old edict goes: You get what you pay for. One of the key motivations in proposing Co-60 based IMRT is the promise of making the equipment inexpensive, reliable, and simple. Manufacturers claim: “We are producing machines for $1.5 million without service contracts, while our competitors charge $5–$7 million for complicated machines that need service contracts.” These claims are exaggerated on both ends. There are hidden costs of frequent source changes, service and maintenance, and the much-needed optional items consisting of hardware and software, patient data record and verify systems, imaging options, etc. On the upper end of the linac units, $5–$7 million would buy you a very high-end machine with trips to Las Vegas and Hawaii included! My opponent argues against Co-60 therapy in general and I will attempt to address his points. A 4 MV linac beam is really a “dirty” Co-60 beam (average energy of 1.25 MeV) and this beam energy is very near that used for IMRT with tomotherapy. The studies I have referenced also indicate that the larger beam penumbra associated with a Co-60 source does not significantly impact the quality of IMRT plans. Also, there is no physical reason why there would be a higher “dose bath” or integral dose with arc-type IMRT using Co-60 compared to a linac with approximately the same average energy; any suggestion that secondary cancers will increase is unfounded. A fresh Co-60 source when used in a tomotherapy unit with an 85 cm source-to-axis distance will have an output of . The use of multiple sources, a multislice MLC, and larger and more optimal source designs would reduce treatment times further. The radiation safety issues associated with Co-60 are certainly worthy of serious consideration, but have become a bit of a red herring in the developed world. A database of radiological incidents and related events12 indicates that Co-60 orphaned sources and accidental dispersions account for a small fraction of total fatalities and injuries compared to other radioactive sources. There are many radioisotopes that might be used in a radiological dispersal device. As medical physicists, we should focus on ways to further limit the risks of transporting, use, and disposal of all radioactive sources in general while allowing society to enjoy the benefits. Imported Co-60 sources can be expensive; however, power reactors in many countries may produce indigenous sources of moderate activity at low costs. Where technical support and physical resources are limited, a robust, reliable Co-60 tomotherapy machine that can be depended on to operate for long hours would be very cost-effective, perhaps allowing a trip to Hawaii after all. We have learned valuable lessons from Co-60 radiotherapy. Its adverse effects and the superior characteristics of high-energy photon beams have led us to linac-IMRT. I find it difficult to justify the “big brother” notion that Co-60 was not good enough for us but it is acceptable for developing countries. Mr. Cadman cites the technical and fiscal environment of developing countries to support Co-60 IMRT. He overlooks the fact that today a large fraction of medical physicists, computer programmers, and biomedical engineers in developing countries are educated and support the infrastructure in developed countries. Plentiful manpower in the developing countries is an added asset with multiple shifts per day providing higher throughput with the same upfront investment in superior technology. There is no significant difference in cost between Co-60 IMRT and linac-IMRT. MLC and IGRT systems are equally expensive whether mounted on a linac or a cobalt unit. Mr. Cadman's claim of the Renaissance® System's use of Co-60 as a “compatible” radiation source for MRI-guided-IMRT does not mean a “superior” source. Moreover, in the current sociopolitical environment it is neither trivial nor cheap to provide security and safety for radioactive sources. A high quality product is seldom “cheaper” initially. The US auto industry's customers have suffered from the production of less expensive, but also inefficient, unsafe, and less dependable cars for years, whereas Japan's car industry has produced slightly more expensive, but superior quality cars using better technology to provide a safer, longer, effective lifespan, and cheaper in the long run. We need to learn from our past experiences and not promote outdated concepts. As John Ruskin (1819–1900) once said: “It is unwise to pay too much, but it's worse to pay too little. When you pay too much, you lose a little money—that is all. When you pay too little, you sometimes lose everything because the thing you bought was incapable of doing the thing it was bought to do.”

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