The effects of target size and tissue density on the minimum margin required for random errors

Abstract

The minimum margins required to compensate for random geometric uncertainties in the delivery of radiotherapy treatment were determined for a spherical Clinical Target Volume, using an analytic model for the cumulative dose. Margins were calculated such that the minimum dose in the target would be no less than 95% of the prescribed dose for 90% of the patients. The dose distribution model incorporated two Gaussians, and could accurately represent realistic dose profiles for various target sizes in lung and water. It was found that variations in target size and tissue density lead to significant changes in the minimum margin required for random errors. The random error margin increased with tissue density, and decreased with target size. The required margins were similar for dose distributions of spherical and cylindrical symmetry. Significant dose outside the spherical high dose region, as could result from multiple incident beams, lead to an increased margin for the larger targets. We could confirm that the previously proposed margin of 0.7 times the standard deviation of the random errors is safe for standard deviations up to 5 mm, except for very small targets in dense material.

A design of a DICOM‐RT‐based tool box for nonrigid 4D dose calculation

“…The results were found to be consistent with the literatures’ expectations. Studies 28 , 29 , 30 have suggested if the tumor is irradiated at its average position during the respiratory cycle, optimal dose coverage would be obtained even if the tumor is not fully within the high‐dose region for a small part of the breathing cycle due to the presence of the wide‐beam penumbra. Moreover, dose planning performed at the end‐exhale phase was also suggested to maximize the target coverage with the most stable or reproducible target position.…”

Sparing Healthy Tissue and Increasing Tumor Dose Using Bayesian Modeling of Geometric Uncertainties for Planning Target Volume Personalization

“…This work focuses specifically on margins necessitated by geometric considerations. Margin recipes compromise between wide margins, which risk overdosing surrounding healthy tissue, and narrow margins, which risk underdosing the CTV (1)(2)(3)(4)(5). Margins are commonly held constant throughout treatment for all patients.…”

Modelo de processamento de imagens mamográficas para detecção de agrupamentos de microcalcificações.

“…O fator densidade "mascara" tais estruturas, dificultando a sua localização. Além disso, a quantidade de ruídos presentes nas imagens cresce com a densidade dos tecidos (Witte et al, 2004;Zanetti-Dällenbach et al, 2008;Park et al, 2009).…”

“…Por fim, observando que o fator de risco de desenvolvimento de câncer de mama cresce acentuadamente de acordo com a densidade desse órgão (Boyd et al, 1995;Saha et al, 2001;Witte et al 2004;Malich et al, 2005) e que a reposição hormonal proporciona um incremento significativo na densidade do tecido mamário (Greemdale et al, 2003;Zanetti-Dällenbach et al, 2008;Yaffe, 2008), a performance dos esquemas CAD é efetivamente prejudicada por esses aspectos, que leva ao crescimento da taxa de detecção de falsos positivos (e, conseqüentemente, submissão desnecessária a processos invasivos, como biópsias).…”

“…Existem na literatura algumas classificações propostas para a determinação da densidade dos tecidos mamários, os quais em geral estratificam entre 4 a 6 classes de acordo com parâmetros histológicos (Wolfe, 1976;Jackson et al, 1993;Boyd et al, 1995;Gram et al, 1997;Kopans, 2000;Saha et al, 2001;Greemdale et al, 2003;Witte et al, 2004;Malich et al, 2005 (Kopans, 2000).…”