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

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

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 < Eion< 800 MeV research areas: materials modification and ion-solid-interaction materials analysis medical applications since 2007: accelerator operation for therapy purposes only

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

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

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

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 SF6 gas cleaning of isolators service on vacuum pumps: oil, bearings replacement of water tubes

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

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

Improved Diagnostics display of accelerator status

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

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

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

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

ISL  PT: Operation Comparison 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 exceptions on weekends: - experiments - infants, requiring more than 4 sessions

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

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

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

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

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

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

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

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

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

Thank you for your attention! Conclusion 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!