Design of a Synchrotron Control System with DPO Series
for Advanced Therapy Operations*N. Araki, E. Takada, A. Itano, K. Noda, M. Kumada, M. Kanazawa, *H. Nakagawa,*T. Nakamura, *K. Kohigashi and *E. Hishitani.
National Institute of Radiological Sciences, Chiba 263, Japan.
*Hitachizosen Corp., Osaka 554, Japan.
Abstract
Therapeutical use of heavy ion synchrotrons ischaracterized by a frequent change of energy (range) andintensity (dose) to perform irradiation for individual cases.
Reducing the switching time is more important in case ofthree dimensional irradiation, where a successive switch ofenergy is necessary during few-minutes treatment times.
The DPO series, that is developed to meet the abovementioned requirement, is a group of VME modules with apowerful microprocessor unit and dual port memory(DPRAM). It has several functions such as multiple paged
memory, calculation algorithms and regulation synchronousto other modules. (A synchrotron control system adopting
the DPO series is designed as an upgrade version of presentcontrol system.)This paper reports a system design by utilizing DPO series
and a method of control for variable energy operations.
1 Introduction
The HIMAC (Heavy Ion Medical Accelerator in Chiba)
accelerator at NIRS, that has been in operation since 1993,is used for clinical treatment of several kinds of tumor. At
the HIMAC energy change is carried out within 15 or 20minutes, which includes the initializing excitation of themain magnets. Reducing the energy switching time forindividual patients is necessary to increase the number ofpatients. The dynamic pattern output module (DPO), thatwas specified with increased pattern memory to solve theseproblems, has been developed by collaboration with NIRS
and Hitachizosen[1].
The irradiation synchronous to breathing has beensuccessfully carried out since February 1996, which covers
a tumor moving along with the breathing of a patient[2]. In
this scheme, the precise concentration of the dose to tumor
is possible. A series of experiments of three dimensional
irradiation by utilizing a range-shifter is tried to shape thedepth dose distribution[3].
Another method, to shape the depth dose distribution is byswitching the energy of synchrotron operation. An energy
shift is effective to prevent fragmentation produced in therange-shifter material. This method is realized to increase or
decrease the flat-top (FT) on the excitation of the main
magnets and the acceleration frequency of the rf cavity atspill by spill simultaneously. It is essential to synchronize
all devices during the repetitive operation. The energychange per patient is presently carried out by switching two
memories on the pattern memory board, however, it is
impossible to be successively synchronous at spill by spill;
it is necessary to increase the memory. A pattern memoryboard development is required for the method of variableenergy operation.
In the heavy ion medical accelerator project, by Hyogo
Prefectural Government, it is also planned to use 3-dirradiation by extraction energy switching[4].
2 Specifics of the DPO series
2.1 Firmware
The firmware of the DPO series is loaded in a flush ROM
on the board. A DPO operation is carried out according tothe command from the software and the external control
code. The software control code is shown in table 1, which
is simply coded to the function. To send a command to theDPO series, the software control code sets the ID number tothe command port in DPRAM. DPO application software
can be developed without driver software.
When the DPO power on starts, the boot program checks
the DRAM, SRAM and the look up tables (LUT). The
firmware is duplicated to the SRAM area for the sake ofhandling speed of the program. The pattern data is tagged
by an ID number because of managing a pattern memoryarea in DRAM. Therefore, the pattern is switched by
selecting an ID number only. The pattern memories of theDPO provide 128k counts (128k long words) and 128 pages
at maximum within the DRAM volume, of which 32 pages
are selected to switch by the external control code.
Arithmetic functions of the DPO include the digital filter,
the spline fit, the linear fit, the four rules in arithmetics andthe Boolean operation. These can be real-time calculations
and off-line modes. Real-time mode is carried out within
the data sampling cycle. Another mode calculates thepattern off-line, which helps pattern edition.
The spill by spill energy switch necessitates that the hostCPU understands the DPO status exactly. It is informed byan interrupt request from the external control code. Thusthe host CPU is able to manage the real-time handling byusing interrupt services of the VME architecture.
The firmware procedure is executed by interrupt to thecommand handling. When the DPO is not receiving acommand, the firmware runs a RAS and status watchingtask. The part of subroutine is carried out by utilizing a
direct memory access controller (DMAC) due to handling
speed.
2.2 Performance
The DPO series uses the high performance RISC microprocessor, SH-2 (SH-7604). The operating frequency andcalculation capability are 28.7MHz and 25MIPS. The SHseries, in which fast calculation is possible under low power
operation, is adopted widely in home game machines. The
SH-2 microprocessor is characterized as follows :(1) Versatile mnemonics helps increase the handling speedof the calculation. In particular, integral multiplication andsum mnemonic, as used in DSP, enables real-time operationof the filtering and feed-back operations.
(2) Interrupt priority is precisely set. The priority has 15levels. The interrupt is assigned for the external control
code, clock and software control code.
(3) The microprocessor is accompanied with peripheraldevices, such as watch dog timer, direct memory access
controller, clocks and bus arbitrator.
The DPO's microprocessor was tested for handling
performance. The result of output data synchronizing Tclock is shown in fig. 1. The test result was compared withthe calculated execution time of a microprocessor
instruction; it is about 3µs. The difference of both times iscaused by the handling time in the field programmable gatearray circuit (FPGA). The result of the test is satisfactory forthe performance of DPO's external clock (T-clock), of
which the frequency is higher than 50kHz.

(a)(b)

Table 1 Software control code (excerpt).

Fig. 1 Test result of DPO performance. (a) Turned on andoff LED of signal by triggered T-clock. LED is turned on
4.5µs later. (b) Output data by triggered 50kHz T-clock.
Data pulse width is about 7µs in 50kHz T-clock case.

2.3 DPI to DPO loop control
At HIMAC, the tracking control of the main magnetic
field was realized by utilizing an iterative control[4].
The iterative control algorithm is given by the equation:
Vset(n+1,m) = Vset(n,m) + G(m)Σ( W(k)∆I(K-k) )where, n : pattern number;
m: sample number;
G : control gain;
W : control weight;∆I : differential current;
K : filter tap number.

The renewal voltage setting pattern is given to minor-AVR
in the power supply of main magnets. After the optimized
voltage setting pattern is reproduced and stored into idle
memory by the algorithm, the iterative control switches
pattern in the power supply controller (PC).
The control system by the DPO series can perform theiterative control within the DPI-DPO loop. The dataexchange between DPO and DPI is independently done
through the VSB bus, which reduces any disturbance ofhandling on the VME bus. Thus the DPI-DPO loop can
carry out the iterative control algorithm in real-time withina sampling cycle of 833µs.
Such feed back control is of advantage to reduce theiterative time. At present, the iterative control is carriedout which 10 ~ 15 minutes. This time almost corresponds tothe time spent in the data swapping between the patternmemory and the host CPU. At last, the optimized voltage
setting pattern utilized by the iterative real-time control issaved to the database. Only optimized pattern controls areloaded to the power supply without the iterative control.
2.4 Dynamic event timing output (DTO)
The DTO is adopted as a component module of thepresent Timing System (TS) at HIMAC. The DTO uses 20

bits pattern data as 20 items event trigger. DTO hardware
was planned in common with the DPO. In order to regulate
synchronized DPO series, DTO generates, as a mastercontroller, the external control codes and clock signals (Tclock, B-clock). These are shown in fig. 2. The functions
are achieved by a new design of FPGA. These functions
are : (1) the master signal (MST), which controls therepetitive operation of the synchrotron, is generated from aU-phase upper zero crossing timing pulse of the 50 Hz
power line; (2) timing setting event is set to notch for 1 µs;(3) each timing setting event is interpolated during the pulse
to pulse of 24f0(1200Hz), which can be delayed bysynchronizing the 24f0 pulse with a digital counter circuit;(4) a pulse width of the timing event can be variably set on
the contiguous address of the same channel in the timing
memory (on DRAM).
DTO's functions are carried out by the commands of thesoftware control code from the host CPU.

selected pattern ID by the TS.
3.2 Spill by spill operations
The spill by spill energy switch is carried out by theexternal control code from TS (with master DTO). TS
sends the code to the DPO of PC when beam stopping
signal comes from the irradiation system for dose control.
The action of PC synchronizes the MST. The spill by spillenergy switch triggering is controlled by TS. Fig. 3.
Shows the beam control schematically. When the beamstopping signal is received during spill extraction, thesignal is directly sent to the extraction device without TS,
since the quick stopping is necessary, is shown in Fig. 3.
Then, TS switchs the energy pattern to synchronizing next
MST. Shaping the depth dose distribution in 3-d irradiation,
the stopping time is shorter than 1ms[6]. RF-KO extraction
technique satisfies this requirement[7].
3.3 beam adjusting and pattern edition.

3 System design
3.1 Reducing of energy switch time
The energy change is accompanied by the initializing
excitation of the main magnets. In the presently runningsystem at HIMAC, the main computer (CS) transfers an
initializing excitation pattern, in addition to the next current
setting pattern to the PC. In order to reduce the energychange time, it is necessary to reduce the initializing time,
because this time is dominant.
The system of DPO series is able to store the initializing
excitation pattern data with each DPO. The initializing
excitation pattern is transferred from CS to PC within theenergy change time. When the system starts, DPO series
stores itself with the initialized excitation pattern, inaddition to operational parameters ( e. g. the initializingtimes, the upper and lower limit to load and the deviation
value for warning).
Initializing of all magnets is carried out by setting a pre-The spill by spill energy change is prepared for beamadjusting from Eshallow to Edeep.(these pattern are P0, P1,P2,..,PN) of each energy pattern. The beam adjusting by
the DPO function is described in three cases as follows : (1)pattern is shifted by addition or subtraction of the very smallchanging quantities (∆E) to a basic pattern (P0) produced by
CS; (2) pattern is shifted by ∆E multiplied by P0; (3) all
patterns of P0 to PN are prepared in DPO. These aresynchronously switched by the TS.
Pattern editing for beam adjustment is enhanced to help
with synchrotron operation. Two ways of (1) and (2) areconsidered to attain a simple adjustment because the setting
pattern data in the DPO are enlarged by the information of∆E. The present control system provides the energy pattern
by CS editing. The operation on the CS is adjusting FT(move up or down). To reproduce the energy pattern and forthe real-time calculation by the DPO series, it is necessary
to reduce any disturbance of the network and CS handlingtime.

Fig 2 Schematic diagram of DTO to DPI/DPO control system.

4 Summary
In order to shape depth dose distribution without degrader,the summary of energy patterns are enough. Each energy
pattern produced by operator is expected to increase theadjusting and energy change time for individual patient'scase. DPO system will reduce these transactions by taking
over the function from CS and utilizing real-time iterativecontrol. The HIMAC synchrotron control system will beupgraded to meet increased requirement of energy change
operation of a pattern number and treatment time.
Acknowledgment
The authors would like to thank Dr. K. Kawachi and themembers of the Division of Accelerator Physics andEngineering at NIRS for helpful discussions. The authors

would like to thank Mr. Y. Hibi of Cosmotec Corp. for
helpful firmware development.
References[1] E. Takada et al., Proc. of ICALEPCS95, Chicago, USA,1995, vol. 2 pp1068-1073[2] HIMAC Annual Report, HIMAC-014[3] Y. Futami et al., Proc. of 10th SAST, Hitachi-Naka,Japan, 1995, pp442-444 (JAERI-Conf.95-021).
[4] A. Itano et al., Proc. of 10th SAST, Hitachi-Naka, Japan,
1995, pp398-400[5] N. Araki et al., Proc. of IWCSMSA96, Tsukuba, Japan,
1996, to be published.
[6] U. Krause and R. Steiner, Proc of ICALEPCS95,
Chicago, USA, 1995, vol. 1 pp14-19[7] K. Noda et al., NIM A 374, 1996, pp269-277

Fig. 3 Schematic diagram of beam stopping and energy change control.