Designing for the safety, security, and high precision of heavy ion therapy

Heavy ion therapy is a type of treatment where a heavy ion beam (carbon ion beam), accelerated to approximately 70% the speed of light using a large device called an accelerator, is targeted at a patient’s cancer cells. This beam is capable of causing far stronger damage to the cancer cells than the radiation used in conventional therapies, with minimal effect to surrounding healthy tissue.

Heavy ion therapy is an advanced medical treatment originating in Japan since it was the first in the world to succeed in actual operation. Although treatment costs are high, insurance coverage was expanded in 2022, enabling this treatment to become available to a larger population. As a form of cancer treatment that is gentle to the human body (no resection, fewer side effects, and no hospitalization), it is attracting attention from around the world.

A heavy ion therapy facility is a place where patients with the serious disease of cancer visit. It is therefore important that the spatial design mitigates their anxieties and physical burden and allows them to feel as safe as possible going in to the treatment. Setting “patient-first” as the design concept of the project, we began our endeavor to explore a facility filled with hospitality as in an airport lounge.

The patient zone (waiting, consultation, examination, and treatment) is concentrated on the first floor to avoid movement between floors. Asian walnut flooring and other solid wood materials are used abundantly to create a warm atmosphere in the double-story atrium entrance lobby. Large windows overlook the green courtyard, offering relaxation. An underfloor radiant cooling and heating system is installed in the lobby space, providing a comfortable thermal environment throughout the building.

While the consultation area is unified with the wooden interior continuing from the entrance lobby, the treatment area has a pure white futuristic interior to elevate the patients’ expectation for cutting-edge medical treatment. However, to avoid a cold and inorganic impression of white space, an indirect lighting system with a toning and dimming function, as well as smooth curving walls are incorporated to provide warmth and tenderness.

Another feature is the exterior which harmonizes with its surroundings. The facade design concept, “layering,” comes from its location at Osaka Castle Otemon Gate, where one can feel the stratum of history. Stone veneer-faced precast concrete panels were used to resonate with the castle’s stone walls. We also aimed to express the “accumulation of life,” by reflecting not only on the history of the area, but on the lives and journeys of the people during the design process.

Radiation exposure control demands special attention in this facility. The accelerator equipment room, the source of radiation, must be covered with a maximum three-meter thick concrete wall. At Nikken Sekkei, we have accumulated expertise that guarantee the same quality of radiation shielding as nuclear power plants.

For example, Nikken Sekkei has assessed the leakage radiation dose using the Monte Carlo simulation, which is a numerical experiment method to simulate the probability of a variety of outcomes using random variables. The usage of a super-computer has elevated the accuracy of this assessment, enabling the calculation of the optimum thickness of the concrete shield wall. They no longer need to be excessively thick. We are able to determine in detail the areas that require thick walls and those that do not, contributing to the reduction of construction cost.

Between the three treatment rooms in the secluded area and each of the entrances facing the main corridor is a zigzagged passageway that cranks multiple times. It was designed so that the radiation beam that leaks from the treatment rooms weakens and scatters as it traverses the zigzag walls. This eliminated the need for the conventional expensive and heavy shield doors at each entrance, which were replaced by general steel doors. Nikken’s original radiation shielding method based on our abundant experience provide both safety and economic efficiency.

Supporting the performance of treatment devices to realize high treatment accuracy is considered the overarching imperative of MEP equipment at heavy ion therapy facilities. The accelerator device circulates heavy ion beams along a round orbit at several million laps per second until it accumulates the required energy necessary for treatment. Since the device is made of metal material, the material tends to stretch when heated.

The distortion caused by the expansion and contraction property of metal may have an influence on treatment accuracy. To prevent any distortion, a cooling water equipment and air conditioning system are installed in the accelerator room to precisely control temperature. Especially for areas around the linear accelerator, an incident device of the heavy ion beam to the accelerator, cooling water with the precision of ±0.5℃ is supplied. For air conditioning, feedback control is set to loop twice, and the cascading system is applied to achieve more stable temperature control. By cascading the required temperature supply gradually (from low, medium, to high temperature), we have established a cooling system that efficiently utilizes different temperature supplies.

The building also implements a variety of energy/cost-saving features. Temperature-controlled outside air, which is supplied to treatment rooms, is reused as supply air and transferred to the accelerator room through the beam transportation area. This reuse helps to minimize the supply of outside air to the entire building. In addition, air-conditioned space inside the accelerator room is restricted to the device area. Energy consumption is further reduced by setting the cooling water at a higher temperature and processing most of the thermal load with the cooling tower.

Currently, there are heavy ion therapy facilities in the following countries outside Japan: USA, Germany, Italy, Austria, China, Taiwan, Korea, etc. More facilities are being planned in other countries and are expected to further spread across the world. At Nikken Sekkei, we have experience in designing heavy ion therapy facilities overseas, including the Taipei Veterans General Hospital Heavy Ion Cancer Therapy Center in Taiwan and the Heavy Ion Cancer Care Center at Severance Hospital of the Yonsei University Health System in Korea.

Heavy ion therapy facilities require advanced safety measures and backup measures for treatment devices. Nikken Sekkei is an architectural design firm that has been involved in much of the world’s heavy ion therapy facility design and has accumulated highly specialized expertise. Based on our experience, we hope to contribute to spreading heavy ion therapy both domestically and abroad.

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