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Assessment of three-dimensional set-up errors in conventional head and neck radiotherapy using electronic portal imaging device.

Gupta T, Chopra S, Kadam A, Agarwal JP, Devi PR, Ghosh-Laskar S, Dinshaw KA - Radiat Oncol (2007)

Bottom Line: Using van Herk's formula, the clinical target volume to planning target volume margins were 3.76, 3.83 and 4.74 mm in AP, ML and SI direction respectively.The set-up margins were <5 mm in all directions.Caution is warranted against adopting generic margin recipes as different margin generating recipes lead to a different probability of target volume coverage.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Radiation Oncology, Advanced Centre for Treatment Research & Education in Cancer, Tata Memorial Centre, Kharghar, Navi Mumbai, India. tejpalgupta@rediffmail.com

ABSTRACT

Background: Set-up errors are an inherent part of radiation treatment process. Coverage of target volume is a direct function of set-up margins, which should be optimized to prevent inadvertent irradiation of adjacent normal tissues. The aim of this study was to evaluate three-dimensional (3D) set-up errors and propose optimum margins for target volume coverage in head and neck radiotherapy.

Methods: The dataset consisted of 93 pairs of orthogonal simulator and corresponding portal images on which 558 point positions were measured to calculate translational displacement in 25 patients undergoing conventional head and neck radiotherapy with antero-lateral wedge pair technique. Mean displacements, population systematic (Sigma) and random (sigma) errors and 3D vector of displacement was calculated. Set-up margins were calculated using published margin recipes.

Results: The mean displacement in antero-posterior (AP), medio-lateral (ML) and supero-inferior (SI) direction was -0.25 mm (-6.50 to +7.70 mm), -0.48 mm (-5.50 to +7.80 mm) and +0.45 mm (-7.30 to +7.40 mm) respectively. Ninety three percent of the displacements were within 5 mm in all three cardinal directions. Population systematic (Sigma) and random errors (sigma) were 0.96, 0.98 and 1.20 mm and 1.94, 1.97 and 2.48 mm in AP, ML and SI direction respectively. The mean 3D vector of displacement was 3.84 cm. Using van Herk's formula, the clinical target volume to planning target volume margins were 3.76, 3.83 and 4.74 mm in AP, ML and SI direction respectively.

Conclusion: The present study report compares well with published set-up error data relevant to head and neck radiotherapy practice. The set-up margins were <5 mm in all directions. Caution is warranted against adopting generic margin recipes as different margin generating recipes lead to a different probability of target volume coverage.

No MeSH data available.


Histogram of translational displacements in all three directions including mean and standard deviation.
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Figure 3: Histogram of translational displacements in all three directions including mean and standard deviation.

Mentions: Translational displacements were measured in 186 (93 anterior and 93 lateral) portal images and assessed over 558-point positions in antero-posterior (AP), medio-lateral (ML) and supero-inferior (SI) direction. The mean displacement in AP; ML; and SI direction was -0.25 mm (range -6.50 to +7.70 mm); -0.48 mm (range -5.50 to +7.80 mm); and +0.45 mm (range -7.30 to +7.40 mm) respectively (Fig. 1,2 and 3). The set-up errors in AP and ML direction were normally distributed (skewness ≤ 2 × standard error of skewness), whereas they were skewed inferiorly in the SI direction. Ninety three percent of the set-up deviations were within 5 mm in all three directions.


Assessment of three-dimensional set-up errors in conventional head and neck radiotherapy using electronic portal imaging device.

Gupta T, Chopra S, Kadam A, Agarwal JP, Devi PR, Ghosh-Laskar S, Dinshaw KA - Radiat Oncol (2007)

Histogram of translational displacements in all three directions including mean and standard deviation.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC2238756&req=5

Figure 3: Histogram of translational displacements in all three directions including mean and standard deviation.
Mentions: Translational displacements were measured in 186 (93 anterior and 93 lateral) portal images and assessed over 558-point positions in antero-posterior (AP), medio-lateral (ML) and supero-inferior (SI) direction. The mean displacement in AP; ML; and SI direction was -0.25 mm (range -6.50 to +7.70 mm); -0.48 mm (range -5.50 to +7.80 mm); and +0.45 mm (range -7.30 to +7.40 mm) respectively (Fig. 1,2 and 3). The set-up errors in AP and ML direction were normally distributed (skewness ≤ 2 × standard error of skewness), whereas they were skewed inferiorly in the SI direction. Ninety three percent of the set-up deviations were within 5 mm in all three directions.

Bottom Line: Using van Herk's formula, the clinical target volume to planning target volume margins were 3.76, 3.83 and 4.74 mm in AP, ML and SI direction respectively.The set-up margins were <5 mm in all directions.Caution is warranted against adopting generic margin recipes as different margin generating recipes lead to a different probability of target volume coverage.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Radiation Oncology, Advanced Centre for Treatment Research & Education in Cancer, Tata Memorial Centre, Kharghar, Navi Mumbai, India. tejpalgupta@rediffmail.com

ABSTRACT

Background: Set-up errors are an inherent part of radiation treatment process. Coverage of target volume is a direct function of set-up margins, which should be optimized to prevent inadvertent irradiation of adjacent normal tissues. The aim of this study was to evaluate three-dimensional (3D) set-up errors and propose optimum margins for target volume coverage in head and neck radiotherapy.

Methods: The dataset consisted of 93 pairs of orthogonal simulator and corresponding portal images on which 558 point positions were measured to calculate translational displacement in 25 patients undergoing conventional head and neck radiotherapy with antero-lateral wedge pair technique. Mean displacements, population systematic (Sigma) and random (sigma) errors and 3D vector of displacement was calculated. Set-up margins were calculated using published margin recipes.

Results: The mean displacement in antero-posterior (AP), medio-lateral (ML) and supero-inferior (SI) direction was -0.25 mm (-6.50 to +7.70 mm), -0.48 mm (-5.50 to +7.80 mm) and +0.45 mm (-7.30 to +7.40 mm) respectively. Ninety three percent of the displacements were within 5 mm in all three cardinal directions. Population systematic (Sigma) and random errors (sigma) were 0.96, 0.98 and 1.20 mm and 1.94, 1.97 and 2.48 mm in AP, ML and SI direction respectively. The mean 3D vector of displacement was 3.84 cm. Using van Herk's formula, the clinical target volume to planning target volume margins were 3.76, 3.83 and 4.74 mm in AP, ML and SI direction respectively.

Conclusion: The present study report compares well with published set-up error data relevant to head and neck radiotherapy practice. The set-up margins were <5 mm in all directions. Caution is warranted against adopting generic margin recipes as different margin generating recipes lead to a different probability of target volume coverage.

No MeSH data available.