a bi-monthly peer-reviewed research journal
TCRT August 2010
Volume 9No. 4 (317-430) August 2010 ISSN 1533-0338
Open Access Letter to the Editor (317-318)To the Editor – We read with interest the article by Schoonbeek et al (TCRT Vol 9(3), 279-289) on treatment planning comparisons of various intracranial radiosurgery modalities.We would like to point out that in the analysis of the volumes of different structures such as brainstem, optic chiasm, and normal brain receiving ≥10 Gy, etc., there can be significant discrepancies in absolute volumes computed by different treatment planning systems as noted in our similar study (Sahgal et al, Radiosurgery Vol 7, 366-377). We have noticed that even for identical sets of contours exported via the Dicom-RT protocol, Gamma Knife calculations result in as much as 5-35% less volume than Cyberknife calculations, and as much as 5-15% less volume than Novalis calculations due to different sampling resolution and volume-rendering algorithms. Therefore, the absolute volumes presented in Figures 2-3 of the article may not be comparable.
Open Access Article Lijun Ma, Ph.D
University of California San Francisco Department of Radiation Oncology San Francisco, CA 94143 Arjun Sahgal, M.D Princess Margaret Hospital Sunnybrook Health Sciences Center University of Toronto, Toronto, Canada David Larson, M.D, Ph.D University of California San Francisco Department of Radiation Oncology San Francisco, CA 94143
Response from the Author – We realize that there are severe problems with the delineation of the volumes, especially when they are small, as is common in radiosurgery. As remarked in the Patients and Methods section it was not always possible to import and export the contours, adding an additional uncertainty to the measurements. To verify the integrity of the (manual) delineation on the different systems, a comparison was made between the different PTV volumes that were delineated on the different systems. We found that especially for the small volumes the differences could amount to 10 to 20% of the volume. This factor, which includes the systematic effect that you describe, probably has limited influence on the brainstem measurements (figures 2.1 and 3.1) but could influence the results of the chiasm and pituitary gland measurements up to 20%. This should be noted when interpreting these figures. However, we believe that it does not significantly change the conclusions of our article.
Richard van der Maazen
University Nijmegen Medical Center Department of Oncology Nijmengen, The Netherlands |
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