Emery, R

Jacky, J

Reid, D D

Risler, R

CERN Document Server

 A VME/X-WINDOWS BASED CONTROL SYSTEM FOR ACLINICAL NEUTRON MACHINEDavid D. Reid, Jon Jacky, Ruedi Risler, Robert EmeryUniversity Of Washington Medical Center1959 NE Pacific Street, Seattle, WA 98195AbstractA control program has been developed for use with anexisting radiation therapy machine used to treat cancerpatients with neutrons. The system is safety-critical,multitasking, meets real-time deadlines and replacesexisting control system hardware and software in use since1984.  The program allows therapists to treat patients in asafe and timely manner.  The system controls variouswedges, filters, and a collimator that shape the therapybeam dose distribution.  It checks the actual machine stateagainst a database of prescribed machine setups, andrecords accumulating dose for each patient across multipletreatment sessions, and updates logs used for patientrecord keeping and machine quality assurance.Development involved both formal and traditionalmethods, including extensive use of the Z formalspecification language. Since the therapy equipment is indaily clinical use with the original control system, accessto real machine hardware is very limited.  This limitedaccess necessitated the use of portable components such asX windows and ANSI C to allow for most developmentand testing to be done on a general purpose workstationand operating system. The program was written only inANSI C using minimal support (X Windows, the realtime operating system, and ANSI C libraries) to reducethe dependence on other third party products and software.This was done to ensure stability over the lifespan of thesystem and for quality control of safety critical functions.Experiences with testing the program and actual clinicaluse is reported.1  INTRODUCTIONThe University of Washington ClinicalCyclotron is a Scanditronix MC50 with an isocentricneutron therapy gantry, various wedges and filters,  amulti-leaf collimator, and a movable therapy couch.Using these components together allow the therapists todeliver the correct dose and shaped beam to the target.The original therapy control system consisted of a DigitalEquipment Corporation PDP-11 and a VT-100 terminal.The cyclotron has been in routine operation since 1984.[1]The decision was made that the old controlsystem needed to be replaced to allow for more efficienttreatment cycles, safer treatment, and less reliance on outdated equipment.[2]It was decided to take advantage of the newesttechnology and use a VME based single board computerto replace the PDP-11 and an X-Windows terminal for theoperator interface.  This decision was made to allow foreasier migration as newer technologies become available.2  CONTROL SYSTEM HARDWARE2.1Existing HardwareThe old control system was comprised of a DECPDP-11 communicating over 4 RS-232 serialcommunication lines to stand alone controllers.  Thesecontrollers are :1)Therapy Motion Controller (TMC)This runs the all of the motions in the treatmentroom including the gantry, wedges, filters, and the roomdoor.2)Leaf Collimator Controller (LCC)This runs the multi leaf collimator which shapesthe neutron beam to match the tumor shape.3)Dose Monitor Controller(DMC)This monitors the amount of dose delivered onthe target and terminates the treatment.4)Modicon PLCThis monitors all the of the digital I/O points onthe system, including door switches, push buttons, andbeamline components.Because of the specialized functions of theScanditronix controllers (the TMC, DMC, LCC), thedecision was made to continue to use these devices.2.2 New HardwareThe PDP-11 has been replaced by a MotorolaMVME 167 single board computer residing in a VMEcrate communicating with the local network via ethernet.The serial communication ports available via theMotorola transition board are used for the RS-232communications to the various controllers.3  CONTROL SYSTEM SOFTWARE3.1  Existing SoftwareThe only software that is carried over from theold control system is the Modicon PLC programming.  International Conference on Accelerator and Large Experimental Physics Control Systems152International Conference  Accel rator and L rge Experim ntal Physics Control Systems, 1999, Trieste, Italy3.2  New SoftwareExtensive use of the Z formal specificationlanguage allowed for both formal and traditional modelingtechniques.[3]The new program was written only in ANSI Cusing minimal support applications such as X Windows,the real time operating system VxWorks from WindRiver, and the ANSI C libraries. This reduces thedependence on third party products and software. Thisinsures the reliability of safety critical functions and thestability of the system over the life of the project.The operator interface runs on a Tektronix Xwindows terminal that is not running a window managersystem.  This way the control system cannot beminimized or hidden anywhere on the screen.4 CONTROL SYSTEM OPERATIONS4.1 Program Startup and InitializationThe VxWorks boot parameters are set so that thecontrol system will start up automatically.  Upon startupthe program loads many constants and factors into residentmemory.  These factors are in multiple text files thatreside on the Hewlett Packard UNIX machines that areclustered on the department network.  If there is an errorwith reading any of these files, the program will alert theoperator and will not be able to deliver any dose.The program also reads files that define thekeypad keys for operational use.  Because a windowmanager is not used, there is no mouse available.  In orderto change windows and enter information, the keypad keysare mapped to functions to bring up different windows andchange settings.Upon startup, the program also reads in font andcolor values and defines X window graphics contexts andsaves them in memory.  This allows for faster operationand redrawing of X window items.4.2  Operational StartupBefore the system is ready to treat patients it isnecessary for the cyclotron operator to setup the systemfor the day.  To do this, the operator is required to loginto the control system and enter in the temperature andair pressure, which is read by hand in the therapy room.These readings are then used by the program to generatethe daily calibration reading, which is used to monitor thedose delivered.  This number is used to correct the ionchamber readings, which determine the dose and which arepressure and temperature dependent.  Once the number hasbeen calculated, the cyclotron operator logs off and thesystem is ready for treatment of patients.  The programwill not allow treatment unless the numbers entered arewithin a specific range.  The program also monitors thetemperature and pressure during the treatments and willgive an error if they drift out of a specified range.4.3  Therapy SequenceThe therapists each log in under their own loginnames.  This allows for easier record keeping and lets usto know which therapists treat which patients.Once logged in, the therapists see a listing of thecurrent patients.  This list is loading from the HP clusterand is generated by the therapists using a treatmentplanning program developed in house called PRISM.This program creates the treatment prescription andgenerates the settings needed by the therapy machine todeliver the correct dosage.  Each patient is identified byname and patient I.D. number.  Once a patient is selected, the therapists thengoes to the SELECT_FIELD screen.  This shows a list ofthe prescribed fields and give the therapists the status ofeach field.  It shows the number of treatments that havebeen given to date and the total number of treatments, andthe dose per treatment and the total number of dosedelivered to date.  Both the patients name, I.D. number,and selected field are always present at the top of thedisplay.After a field is chosen, the therapist is then freeto begin making machine subsystems ready for treatment.These subsystems consist of gantry/couch, filter/wedge,leaf collimator, dosimetry, room interlocks, and protonbeam.  These are represented along the top of the display,above the field and patient display, with boxes whichdisplay either red, green, or yellow.  Green means that thesubsystem has been cleared and is ready for treatment.Red means that the subsystem has not been cleared andmust be cleared before treatment can start.  Yellow meansthat the subsystem has been overridden.  As a generalrule, the machine is not to run with settings overridden.To clear the various subsystems, the therapistmust select the appropriate subsystem display.  Once thedisplay is selected, the therapist can hit theAUTO_SETUP key to start the serial communications tothe controllers to clear the subsystem.  Some of thecontrol points must be set by hand by the therapists.These include the gantry angle, the collimator angle, andthe opening and closing of the therapy room door.  For the DMC, the AUTO_SETUP commandwill begin sending the string of RS-232 commands thatwill load the dose numbers into the DMC.  For the LCC, the AUTO_SETUP will load  thecalibration factors into the LCC, and then will move theleafs to match the field prescription.  This is displayed tothe therapist by a graphical representation at the operator’sdisplay.Because of the multi-tasking aspects of thesystem, it is also possible for the therapists to select ascreen which shows a summary of the machine setup andstart the AUTO_SETUP.  Hitting AUTO_SETUP fromthis screen will cause the program to start the setupsequence for all non-ready subsystems.Once all the subsystems are cleared, the machine153is ready to deliver the dosage.  A prompt will appear atthe operators interface, instructing the therapists to pressthe START button.  This then starts a sequence in thePLC which will retract the faraday cup and allow forproton beam to hit the target and deliver neutrons to thepatient4.4  Safety InterlocksDuring the treatment sequence, there are multiplesafety interlocks that can interrupt the treatment.  Thesecan be internal interlocks in the program or externalinterlocks monitored by the PLC.  If an interlock is tripped during the treatment, thefaraday cup will interrupt the beam and stop the deliveryof dose to the patient. Interlocks override the software andact directly on the machine.  A message box will thenappear on the operator console and will alert the therapiststo the problem, and inform the therapists as to the stepsthat should be taken to remedy the situation.  Once theinterlock has been cleared, it is possible to for thetherapists to continue with the treatment.4.5  Record KeepingOne of the advantages of the new control systemis the easier tracking of patients records.  As a patientfinishes treatment for a specified field, a text filecontaining all pertinent data is written to the networkcomputers.  This allows for verification of patienttreatments.A text file is also written that notes all of thelog messages that have been written to the operatorscreen.  This allows for the review of the daily operationof the therapy machine.These files are both kept on a daily basis, whichlets us reconstruct the history of therapy treatments in thepast.There is also the option to write out files for theserial communications to the various machine controllers.These are not written out on a daily basis, but mustinstead be written by pressing the WRITE_FILE button.These files have proven to be very helpful introubleshooting any problems involving the controllers.5 OPERATIONAL EXPERIENCE5.1 System TestingMuch of the testing of the new control systemwas not done on the actual machine hardware.  Themachine is used 4 days a week for clinical use, with onemaintenance day scheduled per week.  Because of thisschedule, we made use of a testbed environment thatsimulated the serial communications to the variouscontrollers using UNIX text files.  This allowed us tohave testing procedures in place that let us make moreefficient use of our actual machine access time.5.2 Clinical UseThe new control system has been in clinicaloperation since June of 1999.  To date, there have beensome bugs discovered, most having to do with the readingand writing of files to the network computers.  However,these bugs have been quickly fixed and no down time hasresulted from them.  The therapists have been enthusiasticabout the ease of use of the new system, as well as thequickness with which they can treat patients.  Also, theextensive record keeping that is now being done hasallowed us to pinpoint some operational oddities with thecontrollers that were previously hidden by the old controlsystem.6 SUMMARYThe new control system for the University ofWashington Medical Center Clinical Cyclotron has beenoperational for 3 months.  By making use of low levelapplications and extensive formal and informal modeling,we were able to make a successful transition from the oldsystem to the new.  This transition has made for moreefficient patient treatments, without compromising onany safety concerns.7 ACKNOWLEDGEMENTSThe Authors would like to acknowledge the helpand support of Ira Kalet, James Kuan, Eric Dorman andthe radiation therapists at the UW Medical Center formaking this project successful.8 REFERENCES[1] R. Risler, R. Emery, J. Jacky, I. Kalet, and D. Reid“Present And Future Operation Of The SeattleClinical Cyclotron Facility”, Proceedings ofCyclotrons and Their Applications 1998[2] R. Risler, P. Wootton, F.Ziai, J. Jacky, S. Brossard,and I. Kalat, “Continued Operation Of The SeattleClinical Cyclotron Facility”, Proceedings ofCyclotrons and Their Applications 1992[3] J. Jacky and R. Risler, “Formal Specifications For ACyclotron Control System”, Proceedings ofCyclotrons and Their Applications 1992154

A VME/X-Windows Based Control System for a Clinical Neutron Machine

Abstract

Similar works

Full text

Available Versions

CERN Document Server