The broad beam project for proton radiation therapy

The scanned broad proton beam

Here follows a description of a project that was running at TSL for several years but today that project has come to halt and has no ongoing activity.

The scanned beam project

To increase the knowledge of compact proton gantry design, a project group implemented a scanning system capable of generating radiation fields of sizes up to 30 x 30 cm2.

The long term goal was to realise a clinical proton radiation facility including gantries in Sweden.

The project was a cooperation between the proton radiation therapy project at the Uppsala University Hospital and the The Svedberg Laboratory.

Why scanned beam?

An advantage when using a scanned beam is that the intensity of the beam can be controlled at each point at the patient surface. Therefore a scanned beam yields dose distributions that in most cases are superior to passively scattered proton beams, and to other external radiation treatment modalities. A possible design for deflecting a proton beam in two orthogonal directions is to use two fixed deflecting magnets, with orthogonal magnetic fields. However, as the polegap of the second magnet can not be too wide, this solution only allows small deflection angles.

Consequently, a large source to surface distance, SSD, resulting in a large diameter of the gantry is required. To minimize the diameter of the gantry, the chosen design of the scanning head, at the TSL in Uppsala, is with a moveable second magnet which is put into a cradle which has its rotational centre in the first magnet. The solution with a small polegap of the magnets and a moveable second magnet results in a very compact scanning head, which therefore can be incorporated in a gantry of relatively limited size. Since the polegaps are small, the proton beam has to be narrow and very well aligned through the scanning head. If not, the scanning head magnets will act as collimators resulting in a degradation of the beam quality and an increased contamination of neutrons.

Test and development has come to halt

Successful tests with the scanning head and control software was made during the years 1999-2005, with a few nightshifts per semester. Today the tests and developments has come to a halt. The equipment and beamline are still there, just in case another group wants to use it.

Published papers

Some papers were published as outcome from this project, here are some of them:

 

 Drawing

N-line

Picture: Beamlines in the proton therapy areas, the broadbeam project is using N-line.

 

 Photo

broadbeam line

Picture: Here we see the scanning head and the movable couch of HERCULES brand.