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

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

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

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 SF6 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. 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

16. PT: Reliability
availability 95 % in /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 (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. Conclusion 12 therapy weeks per year
past years: uptime at least 95 % 85% choroidal melanomas 97% tumour control iris melanomas and haemangiomas: no recidives

25. 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!