A. Denker, C. Rethfeldt, J. Röhrich, Helmholtz-Zentrum Berlin, Protons for Therapy Reliability of...
-
Upload
braiden-marling -
Category
Documents
-
view
220 -
download
0
Transcript of A. Denker, C. Rethfeldt, J. Röhrich, Helmholtz-Zentrum Berlin, Protons for Therapy Reliability of...
A. Denker, C. Rethfeldt, J. Röhrich,
Helmholtz-Zentrum Berlin, Protons for Therapy
Reliability of the Facility for Proton Therapy of the Helmholtz-Zentrum Berlin
Hahn-Meitner-Institut
(reactor, cyclotron,
solar energy)
=
largest non-university research centre in Berlin
BESSY (synchrotron)
+
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
2 x 14.5 GHz ECR sources on 150 kV platforms
RFQ 5.5 MV Van-de-Graaff
k = 132
16 dedicated target stations
95 96 97 98 99 00 01 02 03 04 05 06 07 08 09 100
5
10
15
Do
wn
tim
e (
%)
Accelerator Performance
cyclotron in operation since 1977averaged 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 systempreventive maintenanceincreased redundancymodernisation improved diagnosisreduction 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
95 96 97 98 99 00 01 02 03 04 05 06 07 08 09 100
5
10
15
Do
wn
tim
e (
%) ~ 4500 hours/year
~ 1750 hours/year
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
PT: Reliability
availability 95 % in 20072/3 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 RFerror 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
14:47:12.00 14:47:12.50 14:47:13.00 14:47:13.50
140
150
160
170
180
190
200
210
220
230
240
Vo
ltag
e [V
]
time
V1 V2 V3
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 dismantlingOct. 07:transfer to HMI, installation startsSep. 08: first beam from sourceOct. 08: first beam through tandetronMar. 09: first beam through cyclotronAug. 10: acceptance test finished, applied for licenceDec. 10: licence grantedJan. 11: first therapy with tandetron as injector
ISL PT: Installation of a Tandetron
start of tandetron beam tests: perfect short term stabilitymeasured on FC behind cyclotron
14:35 14:36 14:37 14:38 14:39 14:400
1
2
3
4
5
15
20
25
30
Std
. D
ev.
(%)
I F
CZ
1 (n
A)
14:45 14:50 14:55 15:00 15:05 15:10 15:1514.0
14.5
15.0
15.5
16.0
16.5
17.0
I F
C (
nA
) ISL PT: Installation of a Tandetron
start of tandetron beam tests: perfect short term stabilitybut 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 %
21:00 01:00 05:00
1.95
2.00
2.05
2.10
stability_QS1!plot110407 JR 08.04.2011
I cu
p (
µA
)
Time (start 7. Apr. 2011)
12 therapy weeks per year past years: uptime at least 95 %
85% choroidal melanomas 97% tumour controliris melanomas and haemangiomas: no recidives
98 99 00 01 02 03 04 05 06 07 08 09 10 11
3
0
1
05
1
66
2
34
3
17
4
37
5
36
6
77
8
29
10
14
12
27
14
37
16
61
0
25
50
75
100
125
150
175
200
225
Pa
tie
nts
pe
r Y
ea
r Conclusion
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!