Technical Note: Validation of halo modeling for proton pencil beam spot scanning using a quality assurance test pattern.
Med Phys
; 42(9): 5138-43, 2015 Sep.
Article
en En
| MEDLINE
| ID: mdl-26328965
ABSTRACT
PURPOSE:
The purpose of this paper is to demonstrate the utility of a comprehensive test pattern in validating calculation models that include the halo component (low-dose tails) of proton pencil beam scanning (PBS) spots. Such a pattern has been used previously for quality assurance purposes to assess spot shape, position, and dose.METHODS:
In this study, a scintillation detector was used to measure the test pattern in air at isocenter for two proton beam energies (115 and 225 MeV) of two IBA universal nozzles (UN #1 and UN #2). Planar measurements were compared with calculated dose distributions based on the weighted superposition of location-independent (UN #1) or location-dependent (UN #2) spot profiles, previously measured using a pair-magnification method and between two nozzles.RESULTS:
Including the halo component below 1% of the central dose is shown to improve the gamma-map comparison between calculation and measurement from 94.9% to 98.4% using 2 mm/2% criteria for the 115 MeV proton beam of UN #1. In contrast, including the halo component below 1% of the central dose does not improve the gamma agreement for the 115 MeV proton beam of UN #2, due to the cutoff of the halo component at off-axis locations. When location-dependent spot profiles are used for calculation instead of spot profiles at central axis, the gamma agreement is improved from 98.0% to 99.5% using 2 mm/2% criteria. The two nozzles clearly have different characteristics, as a direct comparison of measured data shows a passing rate of 89.7% for the 115 MeV proton beam. At 225 MeV, the corresponding gamma comparisons agree better between measurement and calculation, and between measurements in the two nozzles.CONCLUSIONS:
In addition to confirming the primary component of individual PBS spot profiles, a comprehensive test pattern is useful for the validation of the halo component at off-axis locations, especially for low energy protons.
Texto completo:
1
Colección:
01-internacional
Base de datos:
MEDLINE
Asunto principal:
Garantía de la Calidad de Atención de Salud
/
Dosis de Radiación
/
Terapia de Protones
/
Modelos Biológicos
Tipo de estudio:
Prognostic_studies
Idioma:
En
Revista:
Med Phys
Año:
2015
Tipo del documento:
Article