More than 10 years experience of beam monitoring with the Gantry 1 spot scanning proton therapy facility at PSI.
OBJECTIVE
The beam monitoring equipments developed for the first PSI spot scanning proton therapy facility, Gantry 1, have been successfully used for more than 10 years. The purpose of this article is to summarize the author's experience in the beam monitoring technique for dynamic proton scanning.


METHODS
The spot dose delivery and verification use two independent beam monitoring and computer systems. In this article, the detector construction, electronic system, dosimetry, and quality assurance results are described in detail. The beam flux monitor is calibrated with a Faraday cup. The beam position monitoring is realized by measuring the magnetic fields of deflection magnets with Hall probes before applying the spot and by checking the beam position and width with an ionization strip chamber after the spot delivery.


RESULTS
The results of thimble ionization chamber dosimetry measurements are reproducible (with a mean deviation of less than 1% and a standard deviation of 1%). The resolution in the beam position measurement is of the order of a tenth of a millimeter. The tolerance of the beam position delivery and monitoring during scanning is less than 1.5 mm.


CONCLUSIONS
The experiences gained with the successful operation of Gantry 1 represent a unique and solid background for the development of a new system, Gantry 2, in order to perform new advanced scanning techniques.
Lin
Shixiong
S
Center for Proton Therapy, Paul Scherrer Institute, CH-5232 Villigen PSI, Switzerland. shixiong.lin@psi.ch
Boehringer
Terence
T
Coray
Adolf
A
Grossmann
Martin
M
Pedroni
Eros
E
D002138:Calibration; D004574:Electromagnetic Fields; D005160:Facility Design and Construction; D006801:Humans; D061766:Proton Therapy; D011785:Quality Assurance, Health Care; D011874:Radiometry / Q000295:instrumentation / Q000379:methods; D011879:Radiotherapy Dosage; D013997:Time Factors; D011522:Protons
D011522:Protons