Journal of the National Cancer Institute Advance Access originally published online on August 26, 2008
JNCI Journal of the National Cancer Institute 2008 100(17):1264; doi:10.1093/jnci/djn237
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© The Author 2008. Published by Oxford University Press.
CORRESPONDENCE |
Re: Intensity-Modulated Radiation Therapy Dose Prescription, Recording, and Delivery: Patterns of Variability Among Institutions and Treatment Planning Systems
Affiliations of authors: Department of Radiation Oncology, Thomas Jefferson University, Philadelphia, PA (JMG, YX); Department of Radiation Oncology, Emory University, Atlanta, GA (WJC)
Correspondence to: James M. Galvin, DSc, Department of Radiation Oncology, Thomas Jefferson University Hospital, 111 South 11th St, Philadelphia, PA (e-mail: james.galvin{at}jeffersonhospital.org).
Das et al. (1) assert that their results "suggest that it may not be meaningful to compare clinical outcomes among intensity-modulated radiation therapy (IMRT) patients treated at different institutions." The research missions of the Radiation Therapy Oncology Group (RTOG) and other multicenter research organizations rely on the validity of such comparisons, and we, as representatives of the RTOG, believe that such comparisons can be made when investigators from different institutions follow the specific guidelines of carefully designed clinical trials. It is not clear to us that the institutions involved in providing the data for the Das et al. report worked under the type of guidelines for dose specifications, planning, and reporting that are provided for RTOG protocols. Our concern is that the radiation oncology community might misinterpret the conclusions of this report to mean that clinical trial groups such as the RTOG are still struggling to bring IMRT under control. This is an interpretation that we would like to strongly refute.
We agree with Das et al. that IMRT is a complex technology. However, we believe that their report overly emphasizes the maximum to minimum dose difference in order to make the point that IMRT produces increased dose heterogeneity relative to three-dimensional conformal radiation therapy (3D-CRT). It is generally accepted that the use of IMRT to bend isodose lines around critical structures will degrade a radiation dose distribution. It is not clear that the information presented by Das et al. properly separates this inherent feature of IMRT from other effects that are not unique to this planning and delivery technique. We do not agree that the dose heterogeneities found among patients treated with IMRT are so different from those found among patients treated with earlier techniques that the characterization that "such a large deviation from prescription in 3D-CRT would have been reported as a misadministration" is warranted. This statement can only be verified by adding a second arm to the study in which patients are treated with 3D-CRT.
In addition, RTOG protocols that use IMRT determine the maximum and minimum radiation dose limits for protocol compliance by assigning a sampling volume for the high- or low-dose regions. The RTOG uses this approach to avoid reporting of single-voxel anomalies that could give exaggerated dose heterogeneity values. It is possible that Das et al. used the technique of standardizing the sampling volume for the upper and lower dose limits to present the data in their report, but this cannot be determined from the information provided in the manuscript.
In conjunction with the National Cancer Institute–funded Advanced Technology Consortium (ATC), the RTOG has developed the guidelines and procedures necessary to move forward with meaningful clinical trials that use or study IMRT. We do agree with Das et al. that there should be national guidelines for the use of IMRT, but we are surprised that they did not mention that the RTOG and ATC have been actively working to ensure that such guidelines are an integral part of clinical trials.
REFERENCES
1. Das IJ, Cheng C-W, Chopra KL, et al. Intensity-modulated radiation therapy dose prescription, recording, and delivery: patterns of variability among institutions and treatment planning systems. J Natl Cancer Inst. (2008) 100(5):300–307.
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J Natl Cancer Inst 2008 100: 1265-1266.
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