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Activity Distributions of Positron-Emitting-Isotopes Activated by Modulated Spot-Scanning Particle Beams

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W Hsi

W Hsi*, Y Deng , L Sun , Y Li , Z Huang , Y SHENG , J Zhao , and F Zhao, Shanghai Proton and Heavy Ion Center, Pudong, Shanghai, China


WE-EF-303-11 (Wednesday, July 15, 2015) 1:45 PM - 3:45 PM Room: 303

Purpose: To present the characteristics of positron-emitting-isotope (PEI) activity distributions on homogeneous and CIRS thorax phantoms irradiated by modulated spot-scanning carbon-ions and protons in Siemens IONTRIS system.

Methods and Materials: Cylindrical homogeneous wax was irradiated by carbon-ions and protons of 10cm uniform square field with single-energy-layer ranges of 7cm, 16cm and 29cm. Images of PEI distributions were acquired over a period of 30 minutes at 10 minutes after each irradiation. Optimized uniform biological-equivalent doses of carbon-ions over a 5.0cm spherical target was delivered to CIRS phantom. Doses with range shifts in depths from 1mm to 6mm were also calculated and delivered to evaluate the accuracy of measuring activated PEI distributions.

Results: Activated PEI distribution on homogeneous phantoms showed sharper peak near distal edge with flatter distribution toward proximal depth by carbon-ions than by protons. For depths near at Bragg-peak, penetration-depth spreading for energies from 10MeV/u to 60 MeV/u are from 0.4mm to 10.3mm, and 1.2mm to 30.4mm for projectile-fragments by carbon-ions and target-fragments by protons, respectively. For depths proximal to Bragg-peak, target-fragments for both carbon-ions and protons had minimal energy dependence in depth. For complex dose distributions delivered to CIRS thorax phantom, similar PEI peak-like distributions were still observed for carbon-ions. And, the changes at locations and edges of measured PEI peak were correlated within 0.5mm of shifted ranges. Mean activities over 5.0cm spherical target were similar for CISR phantom irradiated by doses with various range shifts.

Conclusions: Peak-like PEI distributions by carbon-ions with good correlation to distal edges in both homogeneous and CIRS thorax phantoms present the potential for the in-vivo range verification while additional efforts is needed for protons. Due to flat distributions for depths at 6mm proximal to distal edges, mean activity at target might be used for in-vivo dose verification of target.

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