Evaluation of inhomogeneity correction factors for 6 MV flattening filter-free beams with brass compensators

被引:2
|
作者
Robinson, Joshua [1 ,2 ]
Opp, Daniel [1 ]
Zhang, Geoffrey [1 ]
Feygelman, Vladimir [1 ]
机构
[1] H Lee Moffitt Canc Ctr & Res Inst, Dept Radiat Oncol, Tampa, FL 33612 USA
[2] Univ S Florida, Dept Phys, Tampa, FL 33620 USA
来源
关键词
flattening filter-free; compensator; inhomogeneity correction factor; dose calculation accuracy; lung; MANAGEMENT; ACCURACY; DELIVERY; MOTION;
D O I
10.1120/jacmp.v14i3.3990
中图分类号
R8 [特种医学]; R445 [影像诊断学];
学科分类号
1002 ; 100207 ; 1009 ;
摘要
The 6 MV flattening filter-free (FFF) beam has been commissioned for use with compensators at our institution. This novel combination promises advantages in mitigating tumor motion due to the reduced treatment time made possible by the greatly increased dose rate of the FFF beam. Given the different energy spectrum of the FFF beam and the beam hardening effect of the compensator, the accuracy of the treatment planning system (TPS) model in the presence of low-density heterogeneities cannot be assumed. Therefore, inhomogeneity correction factors (ICF) for an FFF beam attenuated by brass slabs were measured and compared to the TPS calculations in this work. The ICF is the ratio of the point dose in the presence of inhomogeneity to the dose in the same point in a homogeneous medium. The ICFs were measured with an ion chamber at a number of points in a flat water-equivalent slab phantom containing a 7.5 cm deep heterogeneity (air or 0.27 g/cm(3) wood). Comparisons for the FFF beam were carried out for the field sizes from 5 x 5 to 20 x 20 cm(2) with the brass slabs ranging from 0 to 5 cm in thickness. For a low-density wood heterogeneity in a slab phantom, with the exception of the point 1 cm beyond the proximal buildup interface, the TPS handles the inhomogeneity correction with the brass-filtered 6 MV FFF beam at the requisite 2% error level. The combinations of field sizes and compensator thicknesses when the error exceeds 2% (2.6% maximum) are not likely to be experienced in clinical practice. In terms of heterogeneity corrections, the beam model is adequate for clinical use.
引用
收藏
页码:226 / 231
页数:6
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