TSL G-line : Proton Radiotherapy
Proton Radiotherapy
The proton beam extracted from the cyclotron may have exclusive advantages in treatment of certain human malignant tumours and some other disorders where conventional radiotherapy or surgery is not feasible. The depth dose distribution, with "the Bragg-peak", and the relatively sharp penumbra, enables the concentration of radiation to the target volume and minimizes the dose to normal tissue surrounding the target. Proton beam irradiation may lead to cure or shrinkage of tumour burden in cases where other treatment modalities fail.All patients are carefully investigated by computerized tomography and/or magnetic resonance imaging in order to obtain a detailed knowledge of the position and size of the tumour. Angiography and positron emission termography will be used in certain cases. Before the treatments, careful dose planning is performed to ensure an optimal dose distribution.
The medical projects may be divided into the following groups:
- the fixed narrow proton beam (info on this page)
- the scanned broad proton beam (info follows below)
The Broad Beam Project
for Proton Radiation Therapy
Radiotherapy with proton beams is becoming a clinically available modality at several radiation therapy centres around the world, especially in the USA and Japan.
The advantage of proton beams over photon and electron radiation is the well defined range and small lateral scattering of the protons, which makes it possible to spare healthy tissues close to the target. To increase the knowledge of compact proton gantry design, and with the long term goal of realising a clinical proton radiation facility including gantries in Sweden, the proton radiation therapy project at the Uppsala University Hospital and the The Svedberg Laboratory is implementing a scanning system capable of generating radiation fields of sizes up to 30 x 30 cm2. 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 minimise 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.
Successful tests with the scanning head and control software have been made during 1999-2005, with a few nightshifts per semester.
Beam line drawing:
In this drawing the different beamlines can be seen, they host:
- G-line: the fixed narrow proton beam (info on this page)
- N-line: the scanned broad proton beam
- C-line: biological research experiments (info on this page)