Evaluation of six TPS algorithms in computing entrance and exit doses

Abstract

Entrance and exit doses are commonly measured in in vivo dosimetry for comparison with expected values, usually generated by the treatment planning system (TPS), to verify accuracy of treatment delivery. This report aims to evaluate the accuracy of six TPS algorithms in computing entrance and exit doses for a 6 MV beam. The algorithms tested were: pencil beam convolution (Eclipse PBC), analytical anisotropic algorithm (Eclipse AAA), AcurosXB (Eclipse AXB), FFT convolution (XiO Convolution), multigrid superposition (XiO Superposition), and Monte Carlo photon (Monaco MC). Measurements with ionization chamber (IC) and diode detector in water phantoms were used as a reference. Comparisons were done in terms of central axis point dose, 1D relative profiles, and 2D absolute gamma analysis. Entrance doses computed by all TPS algorithms agreed to within 2% of the measured values. Exit doses computed by XiO Convolution, XiO Superposition, Eclipse AXB, and Monaco MC agreed with the IC measured doses to within 2%‐3%. Meanwhile, Eclipse PBC and Eclipse AAA computed exit doses were higher than the IC measured doses by up to 5.3% and 4.8%, respectively. Both algorithms assume that full backscatter exists even at the exit level, leading to an overestimation of exit doses. Despite good agreements at the central axis for Eclipse AXB and Monaco MC, 1D relative comparisons showed profiles mismatched at depths beyond 11.5 cm. Overall, the 2D absolute gamma (3%/3 mm) pass rates were better for Monaco MC, while Eclipse AXB failed mostly at the outer 20% of the field area. The findings of this study serve as a useful baseline for the implementation of entrance and exit in vivo dosimetry in clinical departments utilizing any of these six common TPS algorithms for reference comparison.PACS numbers: 87.55.‐x, 87.55.D‐, 87.55.N‐, 87.53.Bn

The accuracy of the Acuros XB algorithm in external beam radiotherapy – a comprehensive review

“…Additionally, there are two other studies, where the AXB algorithm has been used in conjunction with homogeneous water phantoms. In work by Tan et al 28 the AXB10 was compared with the PBC algorithm and the AAA implemented in Eclipse TPS and FFT convolution algorithm and multigrid superposition algorithm implemented in XiO TPS (Elekta AB, Stockholm, Sweden) and VMC fast MC algorithm implemented in Monaco TPS (Elekta AB). The algorithms were used to determine the entrance and exit doses to be used in in vivo dosimetry.…”

A dual two dimensional electronic portal imaging device transit dosimetry model based on an empirical quadratic formalism

“…Details of the experimental methods and series of BCF values as a function of field size, backscatter thickness and depth for the 6 MV beam investigated can be found in a previous publication. 29 Finally, before the IC dose planes were used to derive the A and B coefficients, all the M0 and M dose planes were scaled to the same reference level using inverse square distance correction. In this study, the isocentre (100 cm from source), which is also the mid-plane of the phantom, was chosen as the reference level.…”

“…While any disagreement is revealing a true discrepancy, the use of common gamma criterion, 3%/3 mm, is a problem especially when comparison is carried out at the exit level of the phantom, where the TPS-computed dose could be inaccurate. 29 Without correcting for the inaccuracy of TPS in computing exit doses, the gamma pass rate using 3%/3 mm criterion was as low as 29.4% (10 3 10 cm open field tested on heterogeneous phantom). However, when the TPS-computed exit doses were corrected based on IC-measured doses at the central axis, the pass rates were .96.…”

Measurement of image rotation angle in CT for radiotherapy treatment planning

“…A range of tests, methods, and tolerances is given in reports and guidelines published by competent bodies, such as the AAPM, ACR, and IAEA 1 , 2 , 3 . Nevertheless, several new methods of testing CT scanners have been recently discussed 4 , 5 , 6 , 7 . These include testing of parameters which have not been routinely controlled before, such as gantry rotation time, (4) table feed speed, (6) and gantry rotation overrun (7) .…”