DOS 514 - Week 4 Discussion
Initial Post: Dosimetry Instruments for Proton Therapy
At SCCA Proton Therapy, we use a huge variety of dosimetry devices, some of which are the same as what you’d find in a photon clinic, and some of which are unique to proton therapy.
Landauer Luxel+ OSLD
These badges are distributed to each staff member who might be exposed to radiation. They are worn on the body to measure cumulative long term exposure to x, gamma, and beta radiation. They are collected quarterly to take readings and new ones are distributed.
Landauer Neutrak Fast, Intermediate, and Thermal Neutron Dosimeter
Since we work with high energy particles (up to 230 MeV protons, which might create up to 230 MeV neutron contamination), we also have neutron detectors built into the back of our badges (the yellow square insert). This model can detect a wide range of neutron energies.
Landauer Ring TLD
These are worn by staff who handle equipment that may have low-level radioactivity, such as the apertures and compensators that are used for uniform scanning proton therapy.
Landauer nanoDot OSLD
These can be used for patient-specific QA or other applications where we want to see if dose might be going where it shouldn’t. If a patient has a particularly sensitive area near the area that is being treated, we can tape one of these onto their skin to verify that the beam is not passing through that area, or measure it if it is.
Bonner Sphere (not sure of model)
There is a Bonner sphere connected to a measurement and alarm system inside the imaging control booth in each treatment room to warn staff of possible neutron contamination. The ones we use are only good up to around 10 MeV neutrons. We may have as much as 230 MeV neutrons flying around in a worst case scenario, but since neutron contamination would happen across all energies, these should still catch the problem.
Thermo Scientific FHT 762 Wendi-2 Wide-Energy Neutron Detector
This is a more precise neutron measurement tool than the permanently installed Bonner spheres. It is pretty much only used during commissioning of a treatment room.
Thermo Scientific EPD MK2+
This electronic personal integrating dosimeter operates like a real-time version of our radiation badges. A worker who needs to go into an area that might have high radiation will carry one with them, and audible alarms will go off if the rate or total dose crosses safe thresholds.
Thermo Scientific FH 40 G Multi-Purpose Digital Survey Meter
By itself, this survey meter can detect gamma rays. It can also plug into other devices like our wide energy neutron detector to let it measure other kinds of radiation.
IBA PPC05 Plane Parallel Chamber
This is our workhorse ion chamber for patient-specific QA measurements for uniform-scanning proton plans. We can attach it to positioning rigs on a variety of water tank systems to measure dose at various depths to make sure our spread out Bragg peak is ranged correctly.
PTW PinPoint Ionization Chamber
This can be used with our IBA Blue Phantom2 or other water phantoms to make precise point dose measurements at any point in 3D space.
PTW Bragg Peak Chamber
This is an extra-wide ion chamber that can be used to capture an entire proton beam at once, including protons that may have been scattered slightly off the original path. This can be used in a water phantom to find the Bragg peak.
IBA FC65-G Farmer Chamber
This can be used to help calibrate our other instruments and imaging systems.
They’re not supposed to look like this. This one got broken when the graphite outer chamber got stuck inside a cap and then snapped off. This lets you see the aluminum central electrode quite well.
Sun Nuclear rf-Daily QA 3
For uniform scanning, we can run a daily QA to make sure the beam is behaving appropriately. It has 25 detectors of various types (diodes and ion chambers) scattered around the plate, but since we are using protons, we only read data from 5 of the ion chambers to get a quick and dirty sense of flatness, symmetry, and output of what is supposed to be a uniform beam.
Sun Nuclear IC Profiler
If we want to get a more precise reading of flatness, symmetry, and output, we can measure that with this device, which can produce detailed measurements along four cross sections.
IBA I'mRT MatriXX
This has 1020 individual ion chambers in a 32x32 grid (minus the 4 corners). It can be used for more detailed monthly and annual QA in our uniform scanning rooms. It can also be used for daily QA (instead of the Sun Nuclear rf-Daily QA3) for our pencil-beam scanning (PBS) room.
IBA MatriXX PT
This is pretty much the same device as the IBA MatriXX, but with a slightly different design on the ion chambers to allow for detailed QA of our PBS beam.
This is a multilayer ion chamber (MLIC). By multilayer I mean 180 stacked layers! This thing is crazy expensive. It can characterize the entire length of the beam in 2mm increments from entrance to Bragg peak (or SOBP) all at once. This is used for commissioning of treatment rooms.
This is used for characterization of PBS beams, where you shoot a single spot rather than a whole field. It contains an array of scintillation crystals coupled with CCD photon detectors. We use it to measure spot size.
Gafchromic and EDR2 film
Gafrchromic film is self-developing so it is useful for quick reads, but it is quite expensive. EDR2 film needs to be developed so it can take a while to get results. Either one can be used for QA such as verifying isocenters or beam shapes.
Vidar Dosimetry Pro Advantage
This is a film scanner that automatically scans films and digitizes the intensity information. There is some debate among our physicists about whether readings at the edge give different values than reading near the midline, due to the angle of incidence of the scanning laser inside the unit. They prefer a flatbed scanner.
Epson Expression 11000XL
When the model numbers go into 5 digits, you know they’re serious. ;-) This is a professional grade flatbed scanner (several thousand dollars and not something you’d find at home) that has optimizations for scanning films. Some of our physicists like the fact that the reading is taken directly perpendicular to the film, while others argue that you can get bleedover from adjacent sections of the light bar. Both the Epson and the Vidar have been used successfully at many institutions around the country, so people just use whichever one they are more comfortable with.
IBA WP1D Water Phantom
This is a water phantom with 1-dimensional ion chamber movement. It can be used with an ion chamber for TG-51 calibration.
[forgot to take a pic]
Custom-made Water Phantom
Our machine shop put this tank together. It is the tank that is most often used for patient-specific QA along with the PPC05 or other ion chamber.
IBA Blue Phantom2
This thing is huge and weighs over 600 lbs when fully loaded. It has extremely fine-controlled positioning motors that can move an ion chamber or other device in three dimensions inside the tank. It is used in the commissioning process for a treatment room. It can run through patterns of movement automatically and it can automatically pause if it detects a beam interruption.
The idea behind this is great. It’s a 1D phantom that has a slot to insert a MatriXX ion chamber array or other similar device. It can motor back and forth to take measurements in 3D. Unfortunately, hooking it up is a reputed to be a nightmare, so it doesn’t get used as much as it should.
In the beam line
Multi layer faraday cup
This measures the beam energy coming out of the snout, before it hits the apertures, compensators, and other apparatus. It verifies that the cyclotron is sending the correct energy to the treatment room.
[no pic possible]
This counts the monitor units delivered to the patient.
[no pic possible]
Ok, that was more than I realized. Thanks for reading all the way through!