1. A. Denker, C. Rethfeldt, J. Röhrich, Helmholtz-Zentrum Berlin, Protons for Therapy Reliability of the Facility for Proton Therapy of the Helmholtz-Zentrum Berlin

2. Hahn-Meitner-Institut (reactor, cyclotron, solar energy) = largest non- university research centre in Berlin BESSY (synchrotron) +

3. History 1977: start of cyclotron operation for nuclear physics (VICKSI) 1995 – 2006: Ionenstrahllabor ISL – laboratory for ion beam applications –internal and external (~ 70%) users –ion energy: eV < E ion < 800 MeV –research areas: materials modification and ion-solid-interaction materials analysis medical applications since 2007: accelerator operation for therapy purposes only

4. Accelerator Layout 2 x 14.5 GHz ECR sources on 150 kV platforms RFQ 5.5 MV Van-de-Graaff k = 132 16 dedicated target stations

5. Accelerator Performance cyclotron in operation since 1977 averaged downtime before 1995: 10 % start of therapy start of RFQ operation for users

6. Reduction of Downtime step by step process addressing all subsystems: sources, injectors, beam lines, cyclotron, control system preventive maintenance increased redundancy modernisation improved diagnosis reduction of elements

7. Preventive Maintenance regular belt change of Van-de-Graaff service of rotating parts cyclic change of spare power supplies used on HV terminal drying of SF 6 gas cleaning of isolators service on vacuum pumps: oil, bearings replacement of water tubes

8. Modernisation new computers for control system replacement of old dipole power supplies exchange of shunt against transducer regulation in quadrupole power supplies (gain in stability: factor 10) discrete rectifiers replaced by complete 3-phase modules replacement of main coil power supply of cyclotron side effect: less energy consumption

9. Redundancy / Reduction of elements smaller variety of pumps, vacuum gauges, power supplies…. whenever possible: spare parts for quick exchange low intensity proton beams: no pre-bunching no water cooling of deflector plates in beam line dipoles

10. Improved Diagnostics display of accelerator status

11. Improved Diagnostics display of accelerator status 24 h charts start of main magnet overshoot procedure

12. Improved Diagnostics display of accelerator status 24 h charts beam stability programme

13. ISL Protons for Therapy (PT) 11/04: decision to close ISL at the end of 2006 – Post-Docs and technical staff on temporary positions left – people were transferred to other departments – stop of investments 9/06: start of planning operation solely for PT –reduced man-power (less beam-time) –reduction of beam lines, cables… –this step: almost completed nevertheless: maintain reliability

14. Accelerator Performance small number of beam time hours: major events have huge impact on statistics ~ 4500 hours/year ~ 1750 hours/year

15. changing ion species and energies ~ 15 target stations varying requirements on focusing 34 weeks/year 3 shifts a day (24/24) H, 68 MeV –cyclotron fixed frequency –one NMR-probe/dipole 2 target stations, identical focusing –1/4 of existing beam line system 12 therapy weeks/year 2 shift operation (6:00 -22:00) Thursday: start up and tuning Friday: quality control of accelerator weekend: standby* Monday-Friday: Therapy ISL PT: Operation Comparison * exceptions on weekends: - experiments - infants, requiring more than 4 sessions

16. PT: Reliability availability 95 % in 2007 2/3 of downtime due to one major event: electrostatic injection – preventive maintenance – replacement of Ta shields by Ti (good experience in ECR source) – after one week: failure – fault of new ceramics ? – Ti shields (now Ta again) – delay of 2 days uptime 2008: 98 % worst case: failure in electricity supply at 6:00 am – delay of 2 hours

17. Accelerator Operation: Reliability uptime 2009: 95 % 1/3 of downtime again due to one major event: water leak in RF –interruption of therapy week for the first time since 1998 (110 therapy weeks) availability 2010: 95 % frequent drops in RF error difficult to find: isolator problems on tube socket of anode power supply

18. Lessons Learned turbo pumps on 60 % of rotational speed (standby mode) increases service intervals about factor 5 analysis of residual gas for water logging of electricity for failure analysis cryo pumps on cryo pumps off

19. Wish List Uninteruptable Power supplies: –overall solution: too expensive in investment and man power –thus only for computers of control system counter on frequently moved Faraday cups

20. ISL PT: Installation of a Tandetron further shortening of beam lines less rooms reduction of radiation safety easy and reliable operation: – no moving parts – source on ground potential installation: Apr. 07:purchased from BAM, start of dismantling Oct. 07:transfer to HMI, installation starts Sep. 08:first beam from source Oct. 08: first beam through tandetron Mar. 09: first beam through cyclotron Aug. 10: acceptance test finished, applied for licence Dec. 10: licence granted Jan. 11: first therapy with tandetron as injector

21. ISL PT: Installation of a Tandetron start of tandetron beam tests: perfect short term stability measured on FC behind cyclotron

22. ISL PT: Installation of a Tandetron start of tandetron beam tests: perfect short term stability but long term stability unsatisfactory

23. ISL PT: Installation of a Tandetron start of tandetron beam tests: long term stability unsatisfactory now: short and long term stability better than 5 %

24. 12 therapy weeks per year past years: uptime at least 95 % 85% choroidal melanomas 97% tumour control iris melanomas and haemangiomas: no recidives Conclusion

25. 12 therapy weeks per year past years: uptime at least 95 % but: the finest hardware is useless without dedicated personnel sincere thanks to all the people involved Thank you for your attention!