LINAC Bunker Design for Radiotherapy Centres

Cancer cases are increasing across Pakistan, and radiotherapy is needed by a large proportion of cancer patients at some point in their treatment. Yet the country still has far fewer radiotherapy machines than international benchmarks suggest, and many patients travel long distances or wait weeks for treatment. Every new radiotherapy centre therefore matters. At the heart of each centre is the LINAC bunker, a massive shielded room that houses the linear accelerator.

A LINAC bunker is unlike any other hospital room. Its walls may be well over a metre thick, its design is governed by radiation physics, and mistakes are extremely expensive to correct once concrete is poured. This guide explains LINAC bunker design for radiotherapy centres in Pakistan: how shielding works, typical dimensions, the maze and door, services, structure, construction quality control and the approval process.

🏢 About Hospital Design Hub

Hospital Design Hub is a specialist hospital design and construction company, established in 2000 and focused on healthcare infrastructure: design, construction, consultancy and project management, and the renovation and maintenance of hospital facilities. With more than 50 successfully completed projects, our team has worked on healthcare facilities across Pakistan, including projects such as LDMC, MCH Islamkot, King Edward Medical University / Mayo Hospital, and UOL Hospital Lahore.

Radiotherapy projects demand exceptional construction discipline. We coordinate with medical physicists and equipment vendors and control concrete quality so bunkers perform exactly as designed.

☢️ What Is a LINAC and Why Does It Need a Bunker?

A medical linear accelerator (LINAC) produces high-energy X-ray (photon) and electron beams to destroy cancer cells. The beam energy is typically in the megavoltage range, far higher than diagnostic X-ray machines. The machine’s gantry rotates around the patient, so the primary beam can point at the floor, ceiling and two opposite walls. Radiation also scatters from the patient and leaks from the machine head in all directions.

At these energies, ordinary walls provide almost no protection. Massive barriers are needed to reduce radiation outside the room to safe levels for staff, other patients and the public. Machines operating above about 10 MV also produce neutrons, which require additional design attention, particularly at the maze and door.

📐 Bunker Layout and Typical Dimensions

Depending on energy, workload and neighbouring spaces, primary barriers in normal-density concrete are often in the order of 2 metres or more thick, and secondary barriers often around 1–1.5 metres. These are general indications only. Every bunker must be calculated individually.

🧮 How Bunker Shielding Is Calculated

A qualified medical physicist calculates barrier thickness using recognised methods, most commonly NCRP Report No. 151 and guidance from the International Atomic Energy Agency (IAEA). Inputs include:

• Beam energy (for example 6 MV only, or 6/10/15 MV).
• Workload: number of patients and dose delivered per week, including special techniques such as IMRT, VMAT and SBRT, which change leakage workload.
• Use factor for each barrier.
• Occupancy of each adjacent space: control room, corridor, waiting area, offices, parking, roof.
• Distance from the machine isocentre to each point of interest.
• Design dose limits for controlled and uncontrolled areas.

The physicist then specifies the thickness and material for every wall, the ceiling, the maze, the door, and any additional shielding around penetrations. This shielding report is central to the regulatory submission.

🧱 Shielding Materials Compared

In Pakistan, cast-in-place normal-density concrete is the most common choice because it is economical and familiar to local contractors, but it demands excellent quality control.

🏗️ Construction Quality: Where Bunkers Fail

A bunker is only as good as its concrete. The design assumes a specific density and continuous, void-free walls. Common construction risks include:

1. Low concrete density from poor mix design or aggregates, reducing shielding.
2. Honeycombing and voids from poor compaction in thick sections congested with reinforcement.
3. Cold joints between pours that are not properly treated.
4. Thermal cracking in massive pours, especially in Pakistani summer heat, if temperature is not controlled.
5. Unplanned penetrations drilled after construction, creating radiation leakage paths.
6. Dimension errors that reduce wall thickness below design.

Good practice includes trial mixes and density testing, a pour plan with joint details approved by the physicist, temperature control for mass concrete (early morning or night pours, cooled water or ice), careful vibration, continuous supervision, and density verification of samples. After the machine is installed, a radiation survey confirms that shielding meets design.

🔌 Planning Penetrations and Services

Every cable, duct and pipe that enters the bunker is a potential radiation leak. The machine needs power, data and cooling water; the room needs HVAC, lighting, fire detection, CCTV, intercom and sometimes medical gases. Principles include:

• Route services through the maze or ceiling at the lowest-dose locations wherever possible.
• Use angled or stepped sleeves and ducts through walls so there is no straight line from inside to outside.
• Add compensating shielding around larger ducts.
• Cast all sleeves in place: nothing should be drilled after the pour.
• Provide spare sleeves for future cables.
• Coordinate vendor cable trenches in the floor from the start.

❄️ HVAC, Power and Structure

• HVAC: the LINAC and its electronics produce heat; the room needs reliable cooling, controlled humidity and ventilation. Many machines also need a dedicated water chiller.
• Power: dedicated supply with power conditioning, protection against voltage fluctuation, and backup for control systems. Unexpected shutdowns interrupt treatment schedules.
• Structure: massive walls and roofs impose very large loads on foundations. Bunkers are often placed on the ground floor or in basements, and soil investigation is essential.
• Future-proofing: design for the highest energy you might use later, because upgrading a bunker afterwards is very difficult and expensive.

🏥 The Complete Radiotherapy Department

The bunker is one part of a larger department that typically includes:

For department planning, see our guides on cancer treatment centre design and radiation shielding and PNRA approval.

⚖️ Single-Energy vs Multi-Energy LINAC Bunkers

✅ Pros and Cons of Cast-In-Place Concrete Bunkers

📋 From Concept to First Patient

1. Define services: machine type, energies, techniques, number of bunkers now and in future.
2. Select equipment and obtain vendor site planning requirements.
3. Appoint a qualified medical physicist for shielding design.
4. Complete architectural, structural and MEP design with all penetrations fixed.
5. Prepare and submit regulatory documentation to PNRA.
6. Construct with strict concrete quality control and inspections.
7. Install and commission the LINAC; carry out radiation survey and acceptance testing.
8. Obtain authorisation and begin treatment.

🛠️ How Hospital Design Hub Supports Radiotherapy Projects

We plan radiotherapy departments and build LINAC bunkers in coordination with medical physicists and equipment vendors, focusing on the construction discipline that bunkers demand: mix design, pour planning, temperature control, penetration coordination and inspection. We also plan future bunkers into the master plan so expansion is straightforward. Explore our imaging and diagnostic facility setup and oncology hospital design. The World Health Organization also publishes guidance on radiotherapy services planning.

❓ Frequently Asked Questions

What is a LINAC bunker?

A LINAC bunker is a heavily shielded treatment room, usually built of thick reinforced concrete, that houses a medical linear accelerator used for radiotherapy and protects people outside from radiation.

How thick are LINAC bunker walls?

Thickness depends on beam energy, workload and surroundings. In normal concrete, primary barriers are often in the order of two metres or more and secondary barriers often around one to one and a half metres, but each bunker must be calculated individually.

Why do LINAC bunkers have a maze?

The maze forces scattered radiation to bounce several times before reaching the entrance, greatly reducing dose at the door and allowing a lighter door than a direct entrance would need.

Who designs LINAC bunker shielding?

A qualified medical physicist calculates the shielding using recognised methods, and the design team integrates it into architectural, structural and MEP drawings.

Do LINAC bunkers need PNRA approval in Pakistan?

Yes. Radiotherapy facilities are regulated by the Pakistan Nuclear Regulatory Authority, and shielding design, construction verification and radiation surveys are part of the authorisation process.

Can high-density concrete reduce wall thickness?

Yes. High-density concrete provides more shielding per unit thickness, useful where space is limited, but it costs more and requires strict quality control.

Can services be drilled into a bunker after construction?

This should be avoided. All sleeves and penetrations should be planned and cast in place, using angled or stepped routes, to avoid creating radiation leakage paths.

Where should a LINAC bunker be located?

Usually on the ground floor or in a basement, away from high-occupancy areas where possible, with good access for machine delivery and future replacement.