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Evaluation of plan optimisers in prostate VMAT using the dose distribution index

Published online by Cambridge University Press:  29 April 2019

James C. L. Chow Open the ORCID record for James C. L. Chow [Opens in a new window] ,
Runqing Jiang  and
Lu Xu
James C. L. Chow*
Affiliation:
Radiation Medicine Program, Princess Margaret Cancer Centre, University Health Network, Toronto, Canada Department of Radiation Oncology, University of Toronto, Toronto, Canada
Runqing Jiang
Affiliation:
Medical Physics Department, Grand River Regional Cancer Centre, Kitchener, Canada Department of Physics, University of Waterloo, Waterloo, Canada
Lu Xu
Affiliation:
Medical Physics Department, Grand River Regional Cancer Centre, Kitchener, Canada Department of Physics, University of Waterloo, Waterloo, Canada
*
Author for correspondence: Dr James Chow, Department of Medical Physics, Princess Margaret Cancer Centre/UHN, 7/F, 700 University Avenue, Toronto, ON, Canada M5G 1X6. Tel: 416 946 4501. Fax: 416 946 6566. E-mail: james.chow@rmp.uhn.ca
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Abstract

Purpose:

Dose distribution index (DDI) is a treatment planning evaluation parameter, reflecting dosimetric information of target coverage that can help to spare organs at risk (OARs) and remaining volume at risk (RVR). The index has been used to evaluate and compare prostate volumetric modulated arc therapy (VMAT) plans using two different plan optimisers, namely photon optimisation (PO) and its predecessor, progressive resolution optimisation (PRO).

Materials and methods:

Twenty prostate VMAT treatment plans were created using the PO and PRO in this retrospective study. The 6 MV photon beams and a dose prescription of 78 Gy/39 fractions were used in plans with the same dose–volume criteria for plan optimisation. Dose–volume histograms (DVHs) of the planning target volume (PTV), as well as of OARs such as the rectum, bladder, left and right femur were determined in each plan. DDIs were calculated and compared for plans created by the PO and PRO based on DVHs of the PTV and all OARs.

Results:

The mean DDI values were 0·784 and 0·810 for prostate VMAT plans created by the PO and PRO, respectively. It was found that the DDI of the PRO plan was about 3·3% larger than the PO plan, which means that the dose distribution of the target coverage and sparing of OARs in the PRO plan was slightly better. Changing the weighting factors in different OARs would vary the DDI value by ∼7%. However, for plan comparison based on the same set of dose–volume criteria, the effect of weighting factor can be neglected because they were the same in the PO and PRO.

Conclusions:

Based on the very similar DDI values calculated from the PO and PRO plans, with the DDI value in the PRO plan slightly larger than that of the PO, it may be concluded that the PRO can create a prostate VMAT plan with slightly better dose distribution regarding the target coverage and sparing of OARs. Moreover, we found that the DDI is a simple and comprehensive dose–volume parameter for plan evaluation considering the target, OARs and RVR.

Keywords

dose distribution indexplan optimisationprostate radiotherapytreatment planning evaluationVMAT
Type
Original Article
Information
Journal of Radiotherapy in Practice , Volume 18 , Issue 4 , December 2019 , pp. 323 - 328
Copyright
© Cambridge University Press 2019 

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