title: Beam characteristics in two different proton uniform scanning systems: a side-by-side comparison.
abstract: OBJECTIVE
  To compare clinically relevant dosimetric characteristics of proton therapy fields produced by two uniform scanning systems that have a number of similar hardware components but employ different techniques of beam spreading.
  
  
  METHODS
  This work compares two technologically distinct systems implementing a method of uniform scanning and layer stacking that has been developed independently at Indiana University (IU) and by Ion Beam Applications, S. A. (IBA). Clinically relevant dosimetric characteristics of fields produced by these systems are studied, such as beam range control, peak-to-entrance ratio (PER), lateral penumbra, field flatness, effective source position, precision of dose delivery at different gantry angles, etc.
  
  
  RESULTS
  Under comparable conditions, both systems controlled beam range with an accuracy of 0.5 mm and a precision of 0.1 mm. Compared to IBA, the IU system produced pristine peaks with a slightly higher PER (3.23 and 3.45, respectively) and smaller, symmetrical, lateral in-air penumbra of 1 mm compared to about 1.9/2.4 mm in the inplane/crossplane (IP/CP) directions for IBA. Large field flatness results in the IP/CP directions were similar: 3.0/2.4% for IU and 2.9/2.4% for IBA. The IU system featured a longer virtual source-to-isocenter position, which was the same for the IP and CP directions (237 cm), as opposed to 212/192 cm (IP/CP) for IBA. Dose delivery precision at different gantry angles was higher in the IBA system (0.5%) than in the IU system (1%).
  
  
  CONCLUSIONS
  Each of the two uniform scanning systems considered in this work shows some attractive performance characteristics while having other features that can be further improved. Overall, radiation field characteristics of both systems meet their clinical specifications and show comparable results. Most of the differences observed between the two systems are clinically insignificant.
authors.affiliation: Indiana University Integrated Science and Accelerator Technology Hall, Bloomington, IN 47408, USA. nichipor@indiana.edu
authors.forename: Dmitri
authors.initials: D
authors.lastname: Nichiporov
authors.forename: Wen
authors.initials: W
authors.lastname: Hsi
authors.forename: Jonathan
authors.initials: J
authors.lastname: Farr
mesh_terms: D017785:Photons / Q000627:therapeutic use*; D011874:Radiometry / Q000379:methods*