Volume 71, Issue 5 , Pages 1537-1546, 1 August 2008
Underestimation of Low-Dose Radiation in Treatment Planning of Intensity-Modulated Radiotherapy
Purpose
To investigate potential dose calculation errors in the low-dose regions and identify causes of such errors for intensity-modulated radiotherapy (IMRT).
Methods and Materials
The IMRT treatment plans of 23 patients with lung cancer and mesothelioma were reviewed. Of these patients, 15 had severe pulmonary complications after radiotherapy. Two commercial treatment-planning systems (TPSs) and a Monte Carlo system were used to calculate and compare dose distributions and dose–volume parameters of the target volumes and critical structures. The effect of tissue heterogeneity, multileaf collimator (MLC) modeling, beam modeling, and other factors that could contribute to the differences in IMRT dose calculations were analyzed.
Results
In the commercial TPS-generated IMRT plans, dose calculation errors primarily occurred in the low-dose regions of IMRT plans (<50% of the radiation dose prescribed for the tumor). Although errors in the dose–volume histograms of the normal lung were small (<5%) above 10 Gy, underestimation of dose <10 Gy was found to be up to 25% in patients with mesothelioma or large target volumes. These errors were found to be caused by inadequate modeling of MLC transmission and leaf scatter in commercial TPSs. The degree of low-dose errors depends on the target volumes and the degree of intensity modulation.
Conclusions
Secondary radiation from MLCs contributes a significant portion of low dose in IMRT plans. Dose underestimation could occur in conventional IMRT dose calculations if such low-dose radiation is not properly accounted for.
IMRT dosimetry, Underestimation of low dose, Pulmonary complications, Monte Carlo simulation, Thoracic cancers
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Supported in part by National Cancer Institute grant R01-CA074043-08A2.
Presented at the 49th Annual Meeting of the American Association of Physicists in Medicine, July 22–26, 2007, Minneapolis, MN.
Conflict of interest: none.
PII: S0360-3016(08)00656-1
doi:10.1016/j.ijrobp.2008.04.014
© 2008 Elsevier Inc. All rights reserved.
Volume 71, Issue 5 , Pages 1537-1546, 1 August 2008
