Linac Relics: Before OBI, There Was Haynes

Haynes Simulator Head (pictured above) affixed to a 1976 Varian Clinac 4 that was originally installed at a hospital in Los Angeles, California.

At first glance, the device pictured above looks almost improvised—a boxy X-ray tube housing bolted to the side of a linear accelerator with cables and analog controls. Yet this unusual attachment represents an important step in the history of image guidance in radiation therapy. Known as the Haynes Simulator Head, the system allowed clinicians to obtain diagnostic-energy radiographs at the treatment machine long before integrated kilovoltage imaging became standard.

Innovation in radiation therapy technology has often followed a familiar path: new capabilities first appear as add-on devices to existing linear accelerators, developed by smaller or highly specialized companies responding quickly to emerging clinical needs. Over time, as these innovations prove their value in the clinic, the major linac manufacturers adopt and integrate them as standard features of their treatment platforms. And the original companies fade off into the sunset.

This pattern has played out repeatedly in the history of radiation oncology. Multileaf collimators, for example, were initially introduced by now-defunct companies such as NOMOS and 3D Line Medical Systems before becoming ubiquitous on modern treatment machines. Electronic portal imaging devices (EPID) followed a similar trajectory, first appearing in products like Theraview. Kilovoltage imaging also had its early beginnings as a bolt-on solution to existing accelerators—illustrated by the Haynes system shown above.

The Haynes Simulator Head, a bolt-on X-ray tube assembly, first appeared in the 90s and early 2000s. Before the OBI or the XVi, the Haynes Simulator was used to provide KV imaging capability directly on the linac. Early linac models, including Varian Clinac 4, Clinac 6/100, and 1800 series, and even newer C-Series models like the Varian 21EX, benefited from this technology. Today, very few linacs are manufactured without kV Imaging already standard.

The novel Haynes Simulator Head was an important and practical solution to a growing clinical need: better verification of treatment fields directly at the treatment unit.

The Clinical Challenge of the Era

In the early days of linear accelerators, patient setup verification was primarily film-based. Portal films were acquired using megavoltage (MV) beams, which provided adequate geometric verification but limited soft-tissue contrast. Dedicated radiographic simulators existed, but once the patient moved to the treatment vault, verification options were limited.

Clinics needed a way to:

• Produce higher-quality radiographic images
• Verify field placement at the treatment machine
• Improve confidence in patient setup
• Reduce reliance on separate simulator sessions

This was the environment in which the Haynes Simulator Head emerged.

What Was the Haynes Simulator Head?

The Haynes system consisted of a kV X-ray tube assembly mounted directly onto the linac gantry. Unlike megavoltage portal imaging, which uses the treatment beam itself, this device generated diagnostic-energy X-rays, allowing for improved image contrast and clearer visualization of bony anatomy.

Physically, the system included:

• A rectangular housing containing the X-ray tube
• A support arm assembly bolted to the linac gantry
• A collimation structure
• External cabling and control electronics
• A mechanical control panel with analog dials

It was, quite literally, imaging that was “bolted on.”

How It Was Used Clinically

With the Haynes Simulator Head installed, clinicians could obtain radiographic-quality images of the patient positioned on the treatment couch. This allowed for:

• Verification of field borders relative to anatomy
• Confirmation of block placement
• Improved geometric alignment
• Enhanced documentation of setup

In many ways, the system functioned as a hybrid between a traditional simulator and an early onboard imaging system.

Are They Still Around?

In 2005, Varian Medical Systems (now a division of Siemens Healthineers) started shipping out OBI® (On Board Imaging) systems. It was initially integrated into the 21EX model, and later the iX, Trilogy, and TrueBeam models. Many linear accelerator models were upgraded in the field, and eventually, newer machines were being shipped with OBI as a standard option. The same was happening with Elekta. Eventually, that put an end to the Haynes Simulator.

The Haynes system might have lasted longer had it included cone beam CT software, which it never developed. By 2007, the company shut down.

When was the last time you came across a Haynes Simulator? Drop us a line—we would love to hear from you.