On the radiobiological impact of metal artifacts in head-and-neck IMRT in terms of tumor control probability (TCP) and normal tissue complication probability (NTCP)

Abstract

To investigate the effects of distorted head-and-neck (H&N) intensity-modulated radiation therapy (IMRT) dose distributions (hot and cold spots) on normal tissue complication probability (NTCP) and tumor control probability (TCP) due to dental-metal artifacts. Five patients' IMRT treatment plans have been analyzed, employing five different planning image data-sets: (a) uncorrected (UC); (b) homogeneous uncorrected (HUC); (c) sinogram completion corrected (SCC); (d) minimum-value-corrected (MVC); and (e) streak-artifact-reduction including minimum-value-correction (SAR-MVC), which has been taken as the reference data-set. The effects on NTCP and TCP were evaluated using the Lyman-NTCP model and the Logistic-TCP model, respectively. When compared to the predicted NTCP obtained using the reference data-set, the treatment plan based on the original CT data-set (UC) yielded an increase in NTCP of 3.2 and 2.0% for the spared parotid gland and the spinal cord, respectively. While for the treatment plans based on the MVC CT data-set the NTCP increased by a 1.1% and a 0.1% for the spared parotid glands and the spinal cord, respectively. In addition, the MVC correction method showed a reduction in TCP for target volumes (MVC: delta TCP = -0.6% vs. UC: delta TCP = -1.9%) with respect to that of the reference CT data-set. Our results indicate that the presence of dental-metal-artifacts in H&N planning CT data-sets has an impact on the estimates of TCP and NTCP. In particular dental-metal-artifacts lead to an increase in NTCP for the spared parotid glands and a slight decrease in TCP for target volumes.

MR‐based CT metal artifact reduction for head‐and‐neck photon, electron, and proton radiotherapy

“…Our study thus suggests that override of different structures by a single HU value can introduce errors on the order of 3 mm for (worst case) proton dose planning. These are of the same order of magnitude as the errors from metal artifacts reported in the literature …”

“…Errors in these estimates directly translate to errors in, for example, the calculated water equivalent thickness (WET) and particle range. The CT additionally provides image material for organ and lesion delineation, whose accuracy could be reduced by the artifacts …”

The impact of low-Z and high-Z metal implants in IMRT: A Monte Carlo study of dose inaccuracies in commercial dose algorithms

“…In a subsequent study, they also demonstrated that the tumor control probability (TCP) decreases as well as normal tissues complication probability (NTCP) increases in regions where metal artifacts have a relevant impact on image quality. 10 Balazova et al 9 found errors up to 25% in a phantom filled with steel inserts and irradiated with 6 MV photon beam and 20% dose discrepancies in a prostate patient treated with 18 MV. Moreover, a phantom study in 2007 (Ref.…”

“…Other authors have addressed this topic, pointing out the importance of MAR algorithm for accurate photon dosimetry. [4][5][6][7][8][9][10] However, no investigation on the effect of different metal materials with respect to image quality and dose calculation accuracy was performed. Our hypothesis was that, due to the chemical and physical characteristics of metals, such as atomic number, atomic mass, and mass density, the interaction of photon beams with implants differs thus significantly affecting the magnitude of (1) CT image artifacts and (2) dose inaccuracies.…”

“…4 The resulting image degradation impacts radiotherapy planning at different levels: disease diagnoses and staging, region of interest identification and delineation, and incorrect tissue density prediction for dose calculation purposes. [4][5][6][7][8][9][10] Metal artifact reduction (MAR) in CT images has been studied by many researchers and a number of MAR algorithms is available. However, relatively little work has been done to assess its clinical relevance for dose computation purposes.…”