Effect of accounting for interfractional CTV shape variations in PTV margins on prostate cancer radiation treatment plans

Taka aki Hirose, Hidetaka Arimura, Yusuke Shibayama, Jun ichi Fukunaga, Ohga Saiji

Research output: Contribution to journalArticle

Abstract

Purpose: The aim of this study was to account for interfractional clinical target volume (CTV) shape variation and apply this to the planning target volume (PTV) margin for prostate cancer radiation treatment plans. Methods: Interfractional CTV shape variations were estimated from weekly cone-beam computed tomography (CBCT) images using statistical point distribution models. The interfractional CTV shape variation was taken into account in the van Herk's margin formula. The PTV margins without and with the CTV shape variation, i.e., standard (PTV ori ) and new (PTV shape ) margins, were applied to 10 clinical cases that had weekly CBCT images acquired during their treatment sessions. Each patient was replanned for low-, intermediate-, and high-risk CTVs, using both margins. The dose indices (D98 and V70) of treatment plans with the two margins were compared on weekly pseudo-planning computed tomography (PCT) images, which were defined as PCT images registered using a deformable image registration technique with weekly CBCT images, including contours of the CTV, rectum, and bladder. Results: The percentage of treatment fractions of patients who received CTV D98 greater than 95% of a prescribed dose increased from 80.3 (PTV ori ) to 81.8% (PTV shape ) for low-risk CTVs, 78.8 (PTV ori ) to 87.9% (PTV shape ) for intermediate-risk CTVs, and 80.3 (PTV ori ) to 87.9% (PTV shape ) for high-risk CTVs. In most cases, the dose indices of the rectum and bladder were acceptable in clinical practice. Conclusion: The results of this study suggest that interfractional CTV shape variations should be taken into account when determining PTV margins to increase CTV coverages.

Original languageEnglish
Pages (from-to)66-76
Number of pages11
JournalPhysica Medica
Volume54
DOIs
Publication statusPublished - Oct 1 2018

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Cone-Beam Computed Tomography
planning
margins
Prostatic Neoplasms
cancer
Radiation
radiation
Rectum
Urinary Bladder
Tomography
Statistical Distributions
Therapeutics
tomography
rectum
cones
bladder
dosage

All Science Journal Classification (ASJC) codes

  • Biophysics
  • Radiology Nuclear Medicine and imaging
  • Physics and Astronomy(all)

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Effect of accounting for interfractional CTV shape variations in PTV margins on prostate cancer radiation treatment plans. / Hirose, Taka aki; Arimura, Hidetaka; Shibayama, Yusuke; Fukunaga, Jun ichi; Saiji, Ohga.

In: Physica Medica, Vol. 54, 01.10.2018, p. 66-76.

Research output: Contribution to journalArticle

Hirose, Taka aki ; Arimura, Hidetaka ; Shibayama, Yusuke ; Fukunaga, Jun ichi ; Saiji, Ohga. / Effect of accounting for interfractional CTV shape variations in PTV margins on prostate cancer radiation treatment plans. In: Physica Medica. 2018 ; Vol. 54. pp. 66-76.
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abstract = "Purpose: The aim of this study was to account for interfractional clinical target volume (CTV) shape variation and apply this to the planning target volume (PTV) margin for prostate cancer radiation treatment plans. Methods: Interfractional CTV shape variations were estimated from weekly cone-beam computed tomography (CBCT) images using statistical point distribution models. The interfractional CTV shape variation was taken into account in the van Herk's margin formula. The PTV margins without and with the CTV shape variation, i.e., standard (PTV ori ) and new (PTV shape ) margins, were applied to 10 clinical cases that had weekly CBCT images acquired during their treatment sessions. Each patient was replanned for low-, intermediate-, and high-risk CTVs, using both margins. The dose indices (D98 and V70) of treatment plans with the two margins were compared on weekly pseudo-planning computed tomography (PCT) images, which were defined as PCT images registered using a deformable image registration technique with weekly CBCT images, including contours of the CTV, rectum, and bladder. Results: The percentage of treatment fractions of patients who received CTV D98 greater than 95{\%} of a prescribed dose increased from 80.3 (PTV ori ) to 81.8{\%} (PTV shape ) for low-risk CTVs, 78.8 (PTV ori ) to 87.9{\%} (PTV shape ) for intermediate-risk CTVs, and 80.3 (PTV ori ) to 87.9{\%} (PTV shape ) for high-risk CTVs. In most cases, the dose indices of the rectum and bladder were acceptable in clinical practice. Conclusion: The results of this study suggest that interfractional CTV shape variations should be taken into account when determining PTV margins to increase CTV coverages.",
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