proton and heavy particle therapy systems

first idea of using protons for medical treatment came from

R Wilson 1946

proton beam production

ion source, injection, acceleration, extraction, beam transport

ion source

produce protons for acceleration, hydrogen gas

injection

direct protons into accelerator

extraction

direct protons out of accelerator

beam transport

switchyard, direct beam to patient

accelerator types

cyclotron, synchrotron

after acceleration the beam can then be channeled via … to various treatment rooms’

magnets, gantry nozzle(s)

speed of proton determines how

deep they will penetrate in tissue

as protons move through tissue they …, causing increased …

slow down, reaction with the cells

maximum interaction occurs as protons reach their

stopping point, no exit dose

prioritized sites to treat with protons

pediatric, tumors in areas previously treated

protons treated with areas close to

high risk organ (spinal cord, lung, heart)

big factor in deciding who gets proton therapy

cost

most common pediatric sites

CNS, craniospinal radiation

proton impact on naso and oropharynx cancer

decrease esophageal dose, less feeding tubes needed

secondary cancer risk drops … with proton (due to radiating less tissue)

26-39%

conventional xray has more dose to

normal tissue

proton or particle dose more

confined to tumor

medulloblastoma needs

craniospinal radiation

core equipment

accelerator, BTS, beam delivery systems, control systems, treatment nozzles

beam transport system

beam line

fixed beam delivery systems with

beam spreading and shaping capabilities

other proton therapy systems

patient positioning, cone beam, ray station

fixed output energy (250 MeV/u)

cyclotron

energy variation from 70-250 with energy selector

cyclotron

stable beam output

cyclotron

energy variable from pulse to pulse

synchotron

maximum beam intensity (2.4×10^12 pulses per min)

synchotron

larger footprint

synchotron

can accelerate other particles

synchotron.

scattering systems place ___ in the path of the beam

scattering material

scattering systems single beam used for

small tumors

scattering systems large tumors

second scattering material placed in the path

scattering target has varying

lateral thickness

normal tissue in front of the scattering system target receives a

high dose

use for accelerators that have nonuniform output, modulator wheel cannot be used. instead use

degrader and ridge filter

use of ridge filters (degrader slows down, ridge acts like second scatterer)

scatterer, fine degrader, ridge filter, first collimator, tissue compensator, final collimator, body

capable of producing beams to a 30×30 field size

scanning systems

magnets deflect and steer the proton beam, narrow monoenergetic beam paints the treatment volume, voxel by voxel, in each layer of tumor

scanning systems

intensity of beam is controlled at each point after the skin surface

scanning systems

a ___ beam with a ______ peak is scanned over the tumor area as the energy of the beam is ___ (scanning systems)

narrow, narrow bragg, varied

scanning systems produce fewer ___ than double scattering beam, MORE DESIRABLE

neutrons

neutron reduction decreases the risk of

secondary neutron induced cancers in children

less problems with motion of organs

scattering

faster treatment time

scattering

requires gating to overcome organ motion problems

scanning

better conformation to target volume

scanning

pencil beam allows for IMPT

scanning

decreased neutron dose

scanning

able to treat larger, deep tumors

scanning

issues with target motion

precision of stereotactic fixation

fixation mm head

1

fixation mm pelvic region

3

for ions, ____ extremely important

variations in radiological path length

good fixation not feasible for regions with

internal motion

most paticle therapy facilities are now equipped with

robotic patient positioner

robotic patient positioner provides …. dof, can be intgrated into …. to provide remote adjustment, provide more …., especially for fixed beam treatment rooms

6, position verification imaging system, beam entry angles

essential for particle therapy

position verification imaging

robotic imager can provide …… for fixed beam room

nonintrusive volume imaging

patient alignment considerations WSB

weight changes, setup time, beam on after imaging

patient alignment considerations WCA

anything in way effects, critical structures, internal and external alignment

indications proton therapy

previous treatment, target in close proximity to OAR

proton therapy contradictions

metal in path, artifact override

beam transfer line

high powered magnets