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Medical Physics / Volume 37 / Issue 6 / RADIATION THERAPY PHYSICS

Med. Phys. 37, 2441 (2010); http://dx.doi.org/10.1118/1.3426001 (4 pages)

Dose correction strategy for the optimization of volumetric modulated arc therapy a

a Conflict of interest: Memorial Sloan-Kettering Cancer Center has a research agreement with Varian Medical Systems.
Pengpeng Zhang, Jie Yang, Margie Hunt, and Gig Mageras

Department of Medical Physics, Memorial Sloan-Kettering Cancer Center, New York, New York 10021

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(Received 21 December 2009; accepted 12 April 2010; revised 30 March 2010; published online 6 May 2010)

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Purpose: Dose calculation during optimization of volumetric modulated arc therapy (VMAT) is necessarily simplified to keep computation time manageably low; however the approximations used in the scatter dose calculation lead to discrepancy with more accurate dose calculation following optimization. The purpose of this study is to develop a dose correction strategy in optimization that can minimize the disagreement.
Methods: VMAT delivery is modeled using a number of static equispaced beams. Dose correction factors (Cij) are associated with each beam i and point j inside the region of interest. Cij is calculated as the ratio of dose obtained from the full scatter dose calculation over that from the partial scatter dose calculation in optimization. VMAT optimization algorithm is a multiple resolution approach. The dose correction factors are calculated at the beginning of each resolution and applied as multiplicative corrections to the partial scatter dose during optimization. Clinical cases for brain, prostate, paraspinal, and esophagus are utilized to evaluate the method. Treatment plans created with and without the correction scheme are normalized such that the complication rates of organs at risk (OARs) are comparable. The resulting planning target volume (PTV) mean doses are used to compare plan quality.
Results: The difference between the dose calculated at the end of optimization and at the end of the final forward dose calculation is reduced from 7% and 5% for the PTV and OAR mean doses without correction to approximately 1% with correction. Applying dose correction during optimization saves planners 2–4 h in average in treatment planning, and has a positive impact on plan quality, evidenced by a noticeably higher PTV mean dose: 2.1%, 2.4%, 0.5%, and 9.3% of the corresponding prescription dose in the brain, esophagus, prostate, and paraspinal cases, respectively.
Conclusions: When dose correction is applied during optimization, dose discrepancies between optimization and full dose calculation are reduced. Integrating dose correction in VMAT optimization allows planners to adjust the optimization constraints more easily and confidently during optimization and has the potential to improve plan quality.

© 2010 American Association of Physicists in Medicine

ACKNOWLEDGMENTS

The authors would like to thank Yves Archimbault from Varian Medical Systems, Palo Alto, CA for his help and discussion regarding Varian’s implementation of RapidArc.

Article Outline

  1. INTRODUCTION
  2. METHOD AND MATERIALS
    1. Dose correction factor
    2. Dose correction: When and how often?
    3. Testing and evaluation
  3. RESULTS AND DISCUSSION
  4. CONCLUSION
Digital Object Identifier
http://dx.doi.org/10.1118/1.3426001

KEYWORDS and PACS

Keywords

biological organs, dosimetry, optimisation, radiation therapy, volumetric arc modulated therapy, treatment planning, dose calculation

PACS

  • 87.55.dk

    Dose-volume analysis

  • 87.53.Jw

    Therapeutic applications, including brachytherapy

PUBLICATION DATA

ISSN

0094-2405 (print)  

Publisher

$abstract.society.value is a Member of CrossRef American Association of Physicists in Medicine

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