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. 2010 Jan;37(1):154-63.
doi: 10.1118/1.3259742.

Commissioning of the discrete spot scanning proton beam delivery system at the University of Texas M.D. Anderson Cancer Center, Proton Therapy Center, Houston

Michael T Gillin  1 , Narayan Sahoo, Martin Bues, George Ciangaru, Gabriel Sawakuchi, Falk Poenisch, Bijan Arjomandy, Craig Martin, Uwe Titt, Kazumichi Suzuki, Alfred R Smith, X Ronald Zhu
Affiliations

Commissioning of the discrete spot scanning proton beam delivery system at the University of Texas M.D. Anderson Cancer Center, Proton Therapy Center, Houston

Michael T Gillin et al. Med Phys. 2010 Jan.

Abstract

Purpose: To describe a summary of the clinical commissioning of the discrete spot scanning proton beam at the Proton Therapy Center, Houston (PTC-H).

Methods: Discrete spot scanning system is composed of a delivery system (Hitachi ProBeat), an electronic medical record (Mosaiq V 1.5), and a treatment planning system (TPS) (Eclipse V 8.1). Discrete proton pencil beams (spots) are used to deposit dose spot by spot and layer by layer for the proton distal ranges spanning from 4.0 to 30.6 g/cm2 and over a maximum scan area at the isocenter of 30 x 30 cm2. An arbitrarily chosen reference calibration condition has been selected to define the monitor units (MUs). Using radiochromic film and ion chambers, the authors have measured spot positions, the spot sizes in air, depth dose curves, and profiles for proton beams with various energies in water, and studied the linearity of the dose monitors. In addition to dosimetric measurements and TPS modeling, significant efforts were spent in testing information flow and recovery of the delivery system from treatment interruptions.

Results: The main dose monitors have been adjusted such that a specific amount of charge is collected in the monitor chamber corresponding to a single MU, following the IAEA TRS 398 protocol under a specific reference condition. The dose monitor calibration method is based on the absolute dose per MU, which is equivalent to the absolute dose per particle, the approach used by other scanning beam institutions. The full width at half maximum for the spot size in air varies from approximately 1.2 cm for 221.8 MeV to 3.4 cm for 72.5 MeV. The measured versus requested 90% depth dose in water agrees to within 1 mm over ranges of 4.0-30.6 cm. The beam delivery interlocks perform as expected, guarantying the safe and accurate delivery of the planned dose.

Conclusions: The dosimetric parameters of the discrete spot scanning proton beam have been measured as part of the clinical commissioning program, and the machine is found to function in a safe manner, making it suitable for patient treatment.

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Figures

Figure 1
Figure 1
A spot, defined as a burst of monoenergetic protons in a short time segment, deposits dose nonuniformly in a narrow region.
Figure 2
Figure 2
Data flow for patient treatments using discrete spot scanning proton beam at PTC‐H.
Figure 3
Figure 3
Schematic of the scanning proton beam nozzle of the Hitachi ProBeat machine at PTC‐H.
Figure 4
Figure 4
Selected pristine Bragg peaks measured in water using a point by point approach.
Figure 5
Figure 5
Integral doses in Gymm2∕MU at the depth of 2cm as a function of energy. Circles are measured integral doses; squares are corrected integral doses; and dashed line is the correction factors.
Figure 6
Figure 6
Linearity of the response of the main dose monitor over the range of MUs permitted by the system for 221.8 and 72.5MeV proton beams with range of 30.6 and 4.0cm in water, respectively.
Figure 7
Figure 7
FWHM of lateral profiles in air of single pencil beams at the isocenter plane as function of proton nominal energy E.
Figure 8
Figure 8
In‐plane half lateral profiles of single pencil beams at isocenter plane in air for 72.5, 148.8, and 221.8MeV energies. Measurements were performed with a cylindrical ionization chamber (model 31014, PTW‐Freiburg, Freiburg, Germany).
Figure 9
Figure 9
In‐plane half lateral profile of single pencil beams measured in water for 72.5, 148.8, and 221.8MeV. The surface of the water was placed at the isocenter plane.
Figure 10
Figure 10
Example of spot position measurements using radiochromic films.
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