Users Manual Part 2

IBA | 21-2 |
Clinical User’s Guide
Volume 1 - Treatment Session
|Part III
- The Pencil Beam Scanning (PBS) Suite Introducing PBS Beam Delivery System Equipment
|
PBS Capable Nozzle Types
At your center, PBS can be delivered using the following:
PBS Dedicated Nozzle: for detailed information, refer to section “Nozzle Types
and Components PBS Dedicated Nozzle Structure” on page A-3.
Role of the Scanning Magnets
The two scanning magnets located in the nozzle deflect the beam and continually
paint the treatment field with a small beam area. The upstream magnet scans the
beam in the Y direction. The downstream scanning magnet scans in the X direction.
The beam position is changed using magnetic field(s), to direct the beam to a
particular location on a target. Other properties are modified using other equipment.
When a beam penetrates the target, it delivers dose to that location along the beam
trajectory. The goal of the beam delivery is to deliver the appropriate proton fluence
according to a prescription. This prescription provides a map of the fluence that is
necessary to deliver at each location on the target. Thus the beam is moved to each
location on the target and the appropriate fluence is deposited at each location.
During a PBS irradiation, the lateral position (transverse position), the beam energy
(longitudinal position), and the dose are precisely controlled and adjusted in order for
the pencil beam Bragg peak to cover the patient target volume laterally and in depth
and to deliver at each point of the target the required amount of dose.
Low Ranges
To be able to treat very shallow targets and have full modulation to the skin, the
nozzle includes range shifters and/or a ridge filter. This enables the modulation of
range up to the skin and maintain a pristine peak of sufficient width so that the
number of delivered layers remains reasonable.
The range shifter is installed at the end of the nozzle to minimize its impact on the
beam size. The range shifter reduces the range and the ridge filter reduces the
number of layers required for small ranges by increasing the width of the very thin
low energy Bragg peaks.
Note: Range shifter characteristics must be part of the user commissioning and
Quality Assurance System.
The Scanning Controller
In the PBS beam delivery technique, a narrow particle beam is deflected in two
perpendicular directions, both orthogonal to the beam axis, in order to scan the
beam. These deflections are obtained using both scanning magnets; each of these
magnets is driven by a power amplifier, the so-called Scanning Magnet Power Supply
(SMPS). The SMPS is controlled by the Scanning Controller.