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ProBeam Superconducting Cyclotron

A superconducting cyclotron has several advantages compared to a cyclotron:

  • Compact design, reduced weight
  • High beam extraction efficiency, which translates into large dose rates
  • Highly linear, reproducible machine function
  • Less power consumption


ProBeam Superconducting Cyclotron

ProBeam Superconducting Cyclotron

The Varian ProBeam® system features an isochronous cyclotron (ISC) with superconducting coils (also termed a superconducting cyclotron). Its energy capabilities allow for dose delivery to deep-seated tumors, offering the broadest energy treatment range available without the use of range shifters (tumors at depths of 4-30 cm). Additional features of the ProBeam cyclotron include:

  • No warm-up phase, since it operates continuously for maximum efficiency
  • A continuous beam
  • A scalable beam intensity
  • A pillbox design for easy access with an automatic lifting system of the upper iron yoke
  • A compact internal ion source for reduced size and cost
  • A compact footprint for reduced structural cost and improved serviceability
  • No need for high power consumption and heat dissipation associated with room temperature electromagnets
  • Proven performance
Superconducting Cyclotron

Superconducting Cyclotron Functionality

The superconducting magnet coils of the ISC provide high extraction efficiency, low energy consumption, excellent reliability, and reduced overall operating costs. Unlike some other accelerators, the Varian ISC functions in a very linear, predictable manner. This enhances automation for the facility; cyclotron tuning by an operator is not necessary. The minimal need for intervention by an operator can lead to maximized clinical efficiency.

Proton Accelerator ISC Cyclotron

ISC Cyclotron Delivers IMPT

Varian's ISC accelerator is compact in size, with a high thermal stability. It was the industry's first commercially available ISC with superconducting coils for medical use, and it has been used since 2007. Its continuous and stable proton beam is able to deliver intensity-modulated proton therapy (IMPT) in a shorter time, and with a more conformal dose, than passive scattering delivery—though passive scattering is what most proton therapy centers use today.

ProBeam Proton Delivery Pencil Beam Scanning or Passive Scattering

Type of Proton Delivery: Pencil Beam Scanning or Passive Scattering

The type of proton therapy delivery is a critical consideration: pencil beam scanning versus passive scattering. Passive scattering is an earlier generation of proton therapy, which is what most established proton centers use. Today pencil beam scanning is a more precise form of proton therapy, and it is the choice of the majority of new proton centers. Though some centers with passive scattering technology are able to upgrade individual treatment rooms, this can be a slow process with significant technology changes that may even interrupt a center’s availability to treat patients.

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ProBeam Passive Scatter Delivery

Passive Scatter

Using passive scattering, the proton beam is widened and shaped to fit the tumor by placing scattering material in its path. Some characteristics to consider about passive scattering:

  • It uses patient-specific beam-modifying devices to conform the dose. Such tumor-specific devices must be manufactured in-house or sourced from suppliers.
  • Patients must wait to begin treatment until the devices are made.
  • The beam-modifying devices become radioactive and must be stored for months after use (requiring a dedicated storage area). 
  • When the scattered proton beam contacts the scattering material or the beam-modifying devices, it produces neutrons—secondary radiation.
  • It deposits unnecessary dose from proton radiation in healthy tissues proximal to the target.
  • When protons encounter scattering material and beam-modifying devices, they lose energy—or the range available to treat the patient.
  • Less optimal dose conformance.
  • Though passive scattering may be preferred over traditional radiation therapy for some treatment protocols, it cannot provide true intensity-modulated proton therapy (IMPT)—only pencil beam scanning can.


Pencil Beam Scanning vs Passive Scattering

Technology Considerations Pencil Beam Scanning Passive Scattering
Can provide true intensity-modulated proton therapy (IMPT) Yes No
Patient-specific compensators and collimators required for every treatment
  • Such devices can delay start of treatment since they must be custom made for each patient
  • These devices may result in longer setup times per treatment
  • The devices can add to overall cost of treatment
  • Centers may need special procedures to lift and store these radioactive components
No Yes
Secondary radiation produced as protons encounter beam-modifying devices Only if range shifters are needed Much greater secondary radiation, since devices are used for all treatments
Control of energy loss Controlled loss of energy when range shifters are used Uncontrolled energy loss due to use of beam modifying devices in all treatments
Patient treatment time Treatment with radiation beam "on" may be as short as a couple of minutes Depending on the treatment plan, radiation beam "on" time only a couple of minutes, more setup time required for overall treatment per day due to compensators and collimators
Treatment Field Size Larger field size than scattering Smaller field size than PBS
Precision in dose delivery Dose delivered directly to the tumor, with lower dose to surrounding tissue. This is particularly important in pediatric cases or when the tumor is close to a critical structure. Dose delivered to tumor, with higher dose delivered to the surrounding tissue
Scanning penetration Yes, in a more precise manner, which aids in treating deep-seated and/or complex tumors Yes, less precise manner
Year technology introduced to treat patients 2007 1980's*
Equipment selected by majority of centers in the last 3 years Yes No


* Source: Particle Therapy Cooperative Group