THERAPY OPERATION AT GSI
U.Scheeler, D.Wilms
Gesellschaft fuer Schwerionenforschung, 64291 Darmstadt, Germany
Abstract
GSI is the heavy ion research center in Germany
operating the three accelerators UNILAC (linac), SIS(synchrotron) and ESR (storage ring). Experiments are
made on the fields of nuclear and atomic physics, plasmaphysics, nuclear chemistry, material research andbiophysics. The most important program of thebiophysics group is the study of the advantage of Carbon
ions for cancer irradiation. The developed raster-scanningtechnique allows the direct 3D irradiation of irregular

first beam time took place in December 1997 without any
time sharing with other experiments. Figure 2 displays thenumber of patients treated in the beam periods since1997. During the following years per year 3 beam periods
for patient treatment of about 32 days length took place,in parallel physics experiments were performed, but undercertain restrictions during daytime. One of theserestrictions is the limited beam energy for parallel
experiments due to the influence of saturation effects of
the SIS quadrupole magnet fields, that leads to a
deterioration of the spill structure. Therefore the magnetic
rigidity for parallel experiments was limited to 10 Tm(normal operation value up to 18 Tm). Due to safety
aspects no fast extracted beam and no electron cooledbeam is available for experiments behind the SIS.
1500
beam at experiment target
beam for therapy
hours

1000

500

1 OVERVIEW
Within the last 5 years about 160 people suffering fromtumors mostly in the head region have been treated. TheFigure 2: Number of patients per therapy beam period.
181614121086420

number of patients

2002 jun

2002 nov2002 apr

2001 nov

2001 apr

2001 aug

2000 jul

2000 nov

2000 feb

1999 jun

1998 oct1999 feb

1997 dec

shaped tumor and minimizes the dose in healthy tissue[1],[2]. This method requires the reliable request of alarge variety of beam parameters (energy, intensity,beam-spot diameter) for sequential synchrotron cycles.
Certain restrictions to the physics experimental program
have to be considered during the treatment sessions. To
deliver excellent conditions for the other experiments,
these restrictions had to be kept as small as possible.

1998 aug01999 aug

Figure 1: 3D irradiation systemtherapy beam period

Figure 3: Target time for therapy and parallel
experiments during therapy periods.
In Figure 3 the target time for the therapy and theparallel experiments is given. The about 500h available
target time corresponds to 16 hours therapy operation
time per day. The number of target hours for the otherexperiments varies due to the beam time scheduling. Up
to the year 2000 a lot of physics experiments which usedcarbon beam took place. The request of having an
additional isotope available at the SIS is in contradiction
with requests of the UNILAC low energy experiments.
Therefore the target time for the physics experiments isdecreased after 2000.

Nov. 2002

Apr. 2002

Jun. 2002

Aug. 2001

therapy beam period

Nov. 2001

Apr. 2001

Jul. 2000

Nov. 2000

Feb. 2000

Jun. 1999

Aug. 1999

Oct. 1998

Feb. 1999

Aug. 1998

Dec. 1997

number2 ACCELERATOR SETUP
For the raster scanning technique the beam parameters oftable 1 have to be available by request of the scanningsystem. The isotope is provided by the ECR- ion source atthe High Charge State Injector, the intensity steps are
performed by a rf-chopper system at the HLI, the energy
steps are provided by the synchrotron SIS. The different
beam diameters are produced by changing the setting of

the last quadrupole doublet in the beam line to thetreatment place CAVE M.
Table 1: Beam parameters at the isocenter CAVE M.
rangesteprel. variation
12 6+
isotopeCbeam energy 80-430 MeV/u 255
Fixedintensity
2*106-2*108
15-50% +30%
focus
4-10 mm725%
position hor. 5.0 mm
25% of focus
position vert. 3.7 mm
25% of focus
All settings are stored in nonvolatile storage chips, theaccess to the settings is made directly by the device
control system. The setting for the UNILAC is done byusing proofed operation data. In principle, the settings forthe high energy part of the beam line ( SIS and beam line
to treatment place) are produced by scaling the data of thetheoretical accelerator model. To reach the required
values for position, the settings of various steering
magnets are obtained by measuring and correcting thebeam position behind the SIS and in front of the treatment
place. The same procedure is done with the device
settings responsible for focus and intensity variation. Theirradiation sessions are performed within a special timesharing mode. When the irradiation starts, the request of
all other beam cycles is disabled. The therapy supercycleis activated from the treatment control system, startingwith the lowest requested energy up to the highest one.
This means, that up to 30 minutes the activation ofparallel experiments is prohibited [3].

3 BEAM TIME SCHEDULEof the treatment plans. The nights are generally used forphysics experiments. During the commissioning time of
the accelerator (first 5 days) the carrying out of otherexperiments between 6:00 and 22:00 makes no sense. But
when the patient treatment is started, there are breaks of
20 to 30 minutes between the irradiation times for
positioning the next patient. These times are mostly used
for physics experiments. The fraction of beam time forphysics experiments is about 40-60%. The data for atypical day are displayed in table 3. They are extracted
from the pulse to pulse logging of the SIS intensity, which
are displayed at the GSI controls group web page [4].
Table 3: Time sharing operation (28 of Nov. 2002).
Acc
therapy
exp1
exp2
exp3
sumPulses
3963
504
2321
3100
9888

ratio (%)
41
523
31

beam time (h)
4:37
2:17
1:58
4:26
13:18

4 ACCELERATOR OPERATION
Besidestheaccelerator
tuningduring
thecommissioning phase a lot of hardware checks have to bedone to ensure a reliable and safe operation. For theoptimization of the beam parameters expert systems areused. To provide the requested beam quality for thepatient treatment a system to check the beam parameters
Figure 4: Calculated horizontal beam position at thetreatment place for different beam diameters.

Every therapy beam time has a duration of about 32days. Before the beam time starts 2 days are necessary forthe preparation of the ion source. We need about 2 days
for performing the various checks and the tuning of theaccelerator-sections. 4 to 5 days are reserved for thecommissioning of the treatment installations and theirradiation control system, e.g. checking the actions ofthose components, that switch off the beam on request
within a few milliseconds. Furthermore, time is needed
for test irradiations and for the verification of treatment
plans. The next 22 days are filled with patients treatment.
The corresponding schedule is given in table 2.
Table2: Daily schedule.
Time
Event
6:30
7:00
9:00

accelerator protocols
check of beam quality and safety systempatient irradiation (in parallel to physics
experiments)
18:30
verification of irradiation plans, biologicalexperiments
21:30
accelerator protocols
22:00
physics experiments
2 days are reserved for the case of longer unexpected
breakdowns of any component and for development. The
start and end times are not completely determined, theydepend on the number of the patients and the complexity

has been established. Every day at 6:30 and 21:30 a data
protocol is made. The operators have to start preparedbeam cycles and measured values of beam parameters aretaken automatically. For example, Figure 4 displays thecalculated horizontal beam position for different energies
and different beam diameters at the treatment place,
derived from measured beam diagnostic data. The
calculation is based on measured positions at two beam

profile grids in front of Cave M. Similar data are collected
for the 15 intensity steps and for a special selection ofdevice values.
For the therapy cycles the device values are measured
and stored in special files. These data can be easily
compared to reference values by graphical means. Figure
5 displays the relative deviation between set value andmeasured value of the current of the power supplies for
all quadrupoles. The empty symbols corresponds to one
measurement, the filled characters corresponds to anotherone.
Figure 5: Relative deviation of the current for
quadrupole power
supplies.

component is out of order. The boxes at the top switchfrom grey to red colour if a component of thecorresponding beam line breaks down. The dark red box
indicates that the irradiation is running and turns to grey
when it has finished. The green lines beneath show thestatus of several interlock functions concerning the safetysystem. This is connected to the disabled access to theaccelerator components. In the large window at the lower
left side information about the actual beam cycle (time,count, energy step, focus step, intensity step, themeasured beam intensity) is displayed. On the right handside information concerning the central pulse generator isdisplayed. The lowest box displays information about thetherapy control system.

5 CONCLUSION

Due to the fact, that the irradiation is not controlledfrom the main control room (the therapy has its own
control room near Cave M) the organization ofcommunication between both places is important.
Furthermore, the access to all accelerator components
connected to the beam for therapy is disabled during theirradiation-time because of safety reasons. To reduce thedirect communication (phone calls etc.) to a minimum
level, both sides need to know what the other one is doingat the moment. For this purpose the computer program
THINFO is providing the actual status information. ForThe patient treatment program has a great influence on
the accelerator operation at GSI. Due to the requested
beam quality additional installations and upgrades ofmany accelerator components had to be made. The
reliability of the accelerator sections could be increased,
and a better knowledge of the accelerator behavior in thetime sharing mode was achieved. The improved scaling
procedures of the settings reduce the tune up times forother experiments as well. The development of beamalignment and focusing procedures is concerned withtherapy. A lot of smaller technical problems (jitter, ripple)
were solved. Over the years for the operators someroutine is developed, because the therapy requests keeps
constant. Due to the restricted time regime theorganization of the time sharing operation mode isdifficult. The tune up times for the physics experiments
have to be scheduled carefully. They are shifted mostly tothe late evening, which is not the best time if any problem
occurs. A compromise has to be found between stable
therapy conditions and tune up possibilities and times forthe other experiments. In principle, long range
experiments have to be scheduled preferably. For theexperiment scheduling the long carbon runs makes thistask difficult. For difficult physics experiments weinterrupt the patient treatment for one day to enable theaccelerator tuning.
For the technical personal the support of all features fortherapy operation parallel to the global upgrade of theaccelerator is not easy. The checking everything works
well needs 2 to 3 commissioning days in every beamtime.

6 REFERENCES

the accelerator operators the information about the statusof the irradiation is interesting. The therapy crew wants toknow, whether the accelerator is working well or any[1]http://www-aix.gsi.de/~bio/home.html[2] Haberer, Th. et al. , “Magnetic scanning system forheavy ion therapy,” Nucl. Intr. Meth. A330 (1993)
p. 296[3] H. Eickhoff et al. ‘Accelerator Control for the GSICancer Therapy Project’, EPAC 1998[4]http://bel.gsi.de/acc/Online/online.html