Planning target volume-to-skin proximity for head-and-neck intensity modulated radiation therapy treatment planning

Robert A. Price; Sion Koren; Iavor Veltchev; Murshed Hossain; Mu Han Lin; Thomas Galloway; Patrice Flanagan; Jonah Haber; Chang Ming Ma

doi:10.1016/j.prro.2013.04.002

Planning target volume-to-skin proximity for head-and-neck intensity modulated radiation therapy treatment planning

Robert A. Price, Sion Koren, Iavor Veltchev, Murshed Hossain, Mu Han Lin, Thomas Galloway, Patrice Flanagan, Jonah Haber, Chang Ming Ma

Fox Chase Cancer Center

Research output: Contribution to journal › Article › peer-review

9 Scopus citations

Abstract

Purpose: The goal of this work is to evaluate planning target volume (PTV)-to-skin proximity versus plan quality as well as the effects of calculation voxel size on dose uncertainty in the surface region. Methods and Materials: A right-sided clinical target volume with the lateral border 5 mm from the surface was delineated on the computed tomographic data of a head-and-neck phantom. A 5-mm PTV expansion was generated except laterally where distances of 0-5 mm were used. A 7-field intensity modulated radiation therapy plan was generated using the Eclipse treatment planning system. Optimization was performed where 95% of the PTV receives the prescription dose using a voxel size of 2 mm³. Dose calculations were repeated for voxel sizes of 1, 3, and 5 mm³. For each plan, 9 point dose values were obtained just inside the phantom surface, corresponding to a 2 cm × 2 cm grid near the central target region. Nine ultrathin thermoluminescent dosimeters were placed on the phantom surface corresponding to the grid. Measured and calculated dose values were compared. Conformality, homogeneity, and target coverage were compared as well. This process was repeated for volumetric modulated arc therapy (VMAT) calculated with a 2-mm³ voxel size. Results: Surface dose is overestimated by the treatment planning system (TPS) by approximately 21% and 9.5% for 5- and 3-mm³ voxels, respectively, and is accurately predicted for 2-mm³ voxels. A voxel size of 1 mm³ results in underestimation by 11%. Conformality improves with increasing PTV-to-skin distance and a conformality index of unity is obtained for grid sizes between 1 and 3 mm³ and PTV-to-skin distances of 4-4.5 mm. Hot spot also improves and falls below 110% at 4-mm PTV-to-skin distance. Underdosage worsens as the PTV approaches the skin. All of the above appear to hold for volumetric modulated arc therapy. Conclusions: For decreasing PTV-to-skin distance with this TPS, isodose conformality decreases, "hot spot" increases, and target coverage degrades. Surface dose is overestimated when voxel sizes greater than 2 mm³ are chosen, and underestimated for smaller voxels.

Original language	English
Pages (from-to)	e21-e29
Journal	Practical Radiation Oncology
Volume	4
Issue number	1
DOIs	https://doi.org/10.1016/j.prro.2013.04.002
State	Published - Jan 2014
Externally published	Yes

Bibliographical note

Funding Information:
Sources of support: This publication was supported by grant number P30 CA006927 from the National Cancer Institute, National Institutes of Health. Its contents are solely the responsibility of the authors and do not necessarily represent the official views of the National Cancer Institute or the National Institutes of Health.

Funding

Sources of support: This publication was supported by grant number P30 CA006927 from the National Cancer Institute, National Institutes of Health. Its contents are solely the responsibility of the authors and do not necessarily represent the official views of the National Cancer Institute or the National Institutes of Health.

Funders	Funder number
National Institutes of Health
National Cancer Institute	P30CA006927

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10.1016/j.prro.2013.04.002

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title = "Planning target volume-to-skin proximity for head-and-neck intensity modulated radiation therapy treatment planning",

abstract = "Purpose: The goal of this work is to evaluate planning target volume (PTV)-to-skin proximity versus plan quality as well as the effects of calculation voxel size on dose uncertainty in the surface region. Methods and Materials: A right-sided clinical target volume with the lateral border 5 mm from the surface was delineated on the computed tomographic data of a head-and-neck phantom. A 5-mm PTV expansion was generated except laterally where distances of 0-5 mm were used. A 7-field intensity modulated radiation therapy plan was generated using the Eclipse treatment planning system. Optimization was performed where 95% of the PTV receives the prescription dose using a voxel size of 2 mm3. Dose calculations were repeated for voxel sizes of 1, 3, and 5 mm3. For each plan, 9 point dose values were obtained just inside the phantom surface, corresponding to a 2 cm × 2 cm grid near the central target region. Nine ultrathin thermoluminescent dosimeters were placed on the phantom surface corresponding to the grid. Measured and calculated dose values were compared. Conformality, homogeneity, and target coverage were compared as well. This process was repeated for volumetric modulated arc therapy (VMAT) calculated with a 2-mm3 voxel size. Results: Surface dose is overestimated by the treatment planning system (TPS) by approximately 21% and 9.5% for 5- and 3-mm3 voxels, respectively, and is accurately predicted for 2-mm3 voxels. A voxel size of 1 mm3 results in underestimation by 11%. Conformality improves with increasing PTV-to-skin distance and a conformality index of unity is obtained for grid sizes between 1 and 3 mm3 and PTV-to-skin distances of 4-4.5 mm. Hot spot also improves and falls below 110% at 4-mm PTV-to-skin distance. Underdosage worsens as the PTV approaches the skin. All of the above appear to hold for volumetric modulated arc therapy. Conclusions: For decreasing PTV-to-skin distance with this TPS, isodose conformality decreases, {"}hot spot{"} increases, and target coverage degrades. Surface dose is overestimated when voxel sizes greater than 2 mm3 are chosen, and underestimated for smaller voxels.",

author = "Price, {Robert A.} and Sion Koren and Iavor Veltchev and Murshed Hossain and Lin, {Mu Han} and Thomas Galloway and Patrice Flanagan and Jonah Haber and Ma, {Chang Ming}",

note = "Funding Information: Sources of support: This publication was supported by grant number P30 CA006927 from the National Cancer Institute, National Institutes of Health. Its contents are solely the responsibility of the authors and do not necessarily represent the official views of the National Cancer Institute or the National Institutes of Health. ",

year = "2014",

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doi = "10.1016/j.prro.2013.04.002",

language = "אנגלית",

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T1 - Planning target volume-to-skin proximity for head-and-neck intensity modulated radiation therapy treatment planning

AU - Price, Robert A.

AU - Koren, Sion

AU - Veltchev, Iavor

AU - Hossain, Murshed

AU - Lin, Mu Han

AU - Galloway, Thomas

AU - Flanagan, Patrice

AU - Haber, Jonah

AU - Ma, Chang Ming

N1 - Funding Information: Sources of support: This publication was supported by grant number P30 CA006927 from the National Cancer Institute, National Institutes of Health. Its contents are solely the responsibility of the authors and do not necessarily represent the official views of the National Cancer Institute or the National Institutes of Health.

PY - 2014/1

Y1 - 2014/1

N2 - Purpose: The goal of this work is to evaluate planning target volume (PTV)-to-skin proximity versus plan quality as well as the effects of calculation voxel size on dose uncertainty in the surface region. Methods and Materials: A right-sided clinical target volume with the lateral border 5 mm from the surface was delineated on the computed tomographic data of a head-and-neck phantom. A 5-mm PTV expansion was generated except laterally where distances of 0-5 mm were used. A 7-field intensity modulated radiation therapy plan was generated using the Eclipse treatment planning system. Optimization was performed where 95% of the PTV receives the prescription dose using a voxel size of 2 mm3. Dose calculations were repeated for voxel sizes of 1, 3, and 5 mm3. For each plan, 9 point dose values were obtained just inside the phantom surface, corresponding to a 2 cm × 2 cm grid near the central target region. Nine ultrathin thermoluminescent dosimeters were placed on the phantom surface corresponding to the grid. Measured and calculated dose values were compared. Conformality, homogeneity, and target coverage were compared as well. This process was repeated for volumetric modulated arc therapy (VMAT) calculated with a 2-mm3 voxel size. Results: Surface dose is overestimated by the treatment planning system (TPS) by approximately 21% and 9.5% for 5- and 3-mm3 voxels, respectively, and is accurately predicted for 2-mm3 voxels. A voxel size of 1 mm3 results in underestimation by 11%. Conformality improves with increasing PTV-to-skin distance and a conformality index of unity is obtained for grid sizes between 1 and 3 mm3 and PTV-to-skin distances of 4-4.5 mm. Hot spot also improves and falls below 110% at 4-mm PTV-to-skin distance. Underdosage worsens as the PTV approaches the skin. All of the above appear to hold for volumetric modulated arc therapy. Conclusions: For decreasing PTV-to-skin distance with this TPS, isodose conformality decreases, "hot spot" increases, and target coverage degrades. Surface dose is overestimated when voxel sizes greater than 2 mm3 are chosen, and underestimated for smaller voxels.

AB - Purpose: The goal of this work is to evaluate planning target volume (PTV)-to-skin proximity versus plan quality as well as the effects of calculation voxel size on dose uncertainty in the surface region. Methods and Materials: A right-sided clinical target volume with the lateral border 5 mm from the surface was delineated on the computed tomographic data of a head-and-neck phantom. A 5-mm PTV expansion was generated except laterally where distances of 0-5 mm were used. A 7-field intensity modulated radiation therapy plan was generated using the Eclipse treatment planning system. Optimization was performed where 95% of the PTV receives the prescription dose using a voxel size of 2 mm3. Dose calculations were repeated for voxel sizes of 1, 3, and 5 mm3. For each plan, 9 point dose values were obtained just inside the phantom surface, corresponding to a 2 cm × 2 cm grid near the central target region. Nine ultrathin thermoluminescent dosimeters were placed on the phantom surface corresponding to the grid. Measured and calculated dose values were compared. Conformality, homogeneity, and target coverage were compared as well. This process was repeated for volumetric modulated arc therapy (VMAT) calculated with a 2-mm3 voxel size. Results: Surface dose is overestimated by the treatment planning system (TPS) by approximately 21% and 9.5% for 5- and 3-mm3 voxels, respectively, and is accurately predicted for 2-mm3 voxels. A voxel size of 1 mm3 results in underestimation by 11%. Conformality improves with increasing PTV-to-skin distance and a conformality index of unity is obtained for grid sizes between 1 and 3 mm3 and PTV-to-skin distances of 4-4.5 mm. Hot spot also improves and falls below 110% at 4-mm PTV-to-skin distance. Underdosage worsens as the PTV approaches the skin. All of the above appear to hold for volumetric modulated arc therapy. Conclusions: For decreasing PTV-to-skin distance with this TPS, isodose conformality decreases, "hot spot" increases, and target coverage degrades. Surface dose is overestimated when voxel sizes greater than 2 mm3 are chosen, and underestimated for smaller voxels.

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Planning target volume-to-skin proximity for head-and-neck intensity modulated radiation therapy treatment planning

Abstract

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