Antiproton Radiotherapy Experiments at CERN

In this moment we have a week of antiproton beam at CERN for radiobiology and dosimetry experiments. The main experiment is to measure the relative biological effectiveness (RBE) of antiprotons. As an endpoint we use clonogenic survival of V79 Chinese hamster cells (in vitro).

What makes this experiment so complicated, is :

• we only have narrow beam geometry available at CERN
• antiprotons are rare, we only get app. 1 Gy / hour
• beam is highly pulsed, i.e. a 500 nanosecond spill every 90 seconds.

Therefore, we invest a lot of effort in performing precise dosimetry with multiple redundant systems. This is a long story, which I will tell more about another time. Here, let me just show a few pictures...

The antiproton beam line with a water phantom for dosimetry.

The entire experiment is located in an experimental zone at the antiproton decelerator (AD) at CERN. We share our zone with the AEgIS people, who want to find out if antiprotons fly up or down in the gravitational field of the earth. :)

Franz-Joachim Kaiser messing with the water phantom. Behind him the AEgIS beam line.

Three ionization chambers (ICs) are visible here, from the left to the right: a custom made "Advanced Roos" chamber, a Markus chamber and the MicroLion liquid ionization chamber. All by PTW.

Gafchromic EBT film irradiated with antiprotons. Beam spot is about 1 cm FWHM. The narrow beam geometry makes us very vulnerable to positioning errors...

... and therefore we also monitor the beam from spill to spill with a Mimotera detector.

We are usually 2-4 people on a shift. Tonight I will do the night shift with Franz-Joachim (to the left). Stefan will leave soon. Usually, I would do night shifts with Roy Keyes, but he couldn't be here this year.

I build this little box for the experiment: it interfaces the antiproton decelerator with the printer port of our data acquisition computer. No need for expensive IO cards or fancy LabView. Basically it is just some TTL logic and optocouplers. On the server side, a daemon listens to the parallel port if a new spill of antiprotons is coming in.

Once triggered, the server takes care to read out all data systems, such as beam current transformers, ionization chamber and scintillators.

Client programs, here running on the laptop to the left, can connect to the server, and change various settings of the readout procedure.

Again, this is home-brew. Earlier, the data acquisition was some libncurses based stuff, this year is the first time we had a traditional GUI for the client and a clear client/server separation. I wrote the client in C++/QT4 and compiled it for linux and win32. Stefan did a package for mac. Server is pure C, linux only. Sometimes, I think the most valuable course I had when I was a student at our Physics department in Aarhus, was a C-programming course.  (And that course was only offered once! What a shame!)

Fiona from the Belfast QUB group is in charge of the film scans, and making sure there are enough sweets for all of us.

Entire experimental zone in the AD hall, seen from above, where our non-existant counting hut would be..

A bit off topic, but just over our heads, there is a positron beam line, which delivers the positrons to the anti-hydrogen "bottle" of ATRAP. Positrons go from the right side to the left.

Me, checking up on things... :-) I think this is the 8th or 9th time I am working at the ACE experiment.

Alanine is one of the most reliable solid state dosimeters for such exotic beams such as antiprotons. Here a stack of pellets is prepared for irradiation.

Once the pellets have been irradiated with antiprotons, they are shipped for read out to our collaborators at the National Physical Laboratory (NPL) in Teddington, UK.. (The NPL serves also as a primary standard lab for radiation quantities.)

Alright then.. :/

Recursively posting this blog entry.

More pictures here.