In Reply to Dr. Jenkins

In Reply to Dr. Jenkins

644 I. J. Radiation Oncology d Biology d Physics Volume 71, Number 2, 2008 IN REGARD TO SHER ET AL.: QUANTIFICATION OF MEDIASTINAL AND HILAR LYMPH ...

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I. J. Radiation Oncology d Biology d Physics

Volume 71, Number 2, 2008

IN REGARD TO SHER ET AL.: QUANTIFICATION OF MEDIASTINAL AND HILAR LYMPH NODE MOVEMENT USING FOUR-DIMENSIONAL COMPUTED TOMOGRAPHY SCAN: IMPLICATIONS FOR RADIATION TREATMENT PLANNING (INT J RADIAT ONCOL BIOL PHYS 2007;69:1402–1408) To the Editor: Sher et al. have quantified the movement of mediastinal lymph nodes with respiration using four-dimensional computed tomography (4D-CT) scans (1). The authors are to be congratulated for the meticulous data collection needed to complete this important study. It appears that lymph node motion with ventilation is greatest in the craniocaudal direction, presumably related to the forces exerted on the mediastinum by contraction of the diaphragm. I note with interest that their results and conclusions are very similar to those of our earlier report (2), using fluoroscopic assessment of calcified mediastinal lymph nodes (Fig. 1). Many centers have yet to commission 4D-CT planning and, consequently, are unable to measure the lymph node motion of individual patients. I would, therefore, be interested in the authors’ response to the following two points, which might help to define the internal margin when 4D-CT is unavailable. First, was the lymph node motion they observed correlated with the movement of the diaphragm or carina? If this was the case, the movement of these fluoroscopically visible structures could be used as a surrogate for that of the lymph nodes. Second, in contrast to our more limited analysis, 14 patients in their study had movement measured in more than one node. However, the correlation of the peak excursions for the separate lymph node stations is not stated in their report. Unless the movement seen in the different lymph nodes is similar, little option exists other than to measure motion on a caseby-case basis using 4D-CT technology.

PETER JENKINS, PH.D., M.R.C.P., F.R.C.R. Gloucestershire Oncology Centre Cheltenham, United Kingdom doi:10.1016/j.ijrobp.2008.02.020 1. Sher DJ, Wolfgang JA, Niemierko A, et al. Quantification of mediastinal and hilar lymph node movement using four-dimensional computed tomography scan: Implications for radiation treatment planning. Int J Radiat Oncol Biol Phys 2007;69:1402–1408. 2. Jenkins P, Salmon C, Mannion C. Analysis of the movement of calcified lymph nodes during breathing. Int J Radiat Oncol Biol Phys 2005;61: 329–334.

IN REPLY TO DR. JENKINS To the Editor: We appreciate the comments from Dr. Jenkins and agree that our findings are consistent with his group’s previous work. We also agree that correlating the carinal and/or diaphragmatic motion with nodal movement could potentially obviate (or, at least, reduce) the need for fourdimensional computed tomography planning if either structure could serve as an accurate surrogate for nodal motion. Unfortunately, we did not record these data, so we will not be able to perform this analysis. With respect to the correlations between nodal stations, Dr. Jenkins makes a valuable suggestion. We have obtained Spearman correlation coefficients between each nodal station for peak-to-peak motion in three dimensions (Table 1). Although the sample size was small, the most striking findings were the correlations in the craniocaudal and lateral motion between the subcarinal and hilar lymph nodes; a significant relationship was also found between the movement of the paratracheal nodes in the same patient. The remainder of the correlation coefficients did not reach statistical significance, but there do appear to be several moderately strong correlations between the motion of different stations. A larger sample might be able to clarify this question.

Table 1. Spearman correlation coefficients Station–Station n Superorinferior Right–left Anteroposterior Paratracheal vs. paratracheal Paratracheal vs. subcarinal Paratracheal vs. hilar Subcarinal vs. hilar

Fig. 1. Computed tomography scan reconstructed in paracoronal plane showing calcified right hilar and subcarinal lymph nodes in patient with non–small-cell lung cancer.

5 9 7 4

0.89 p = 0.04 0.60 p = 0.09 0.62 p = 0.14 1.0 p \ 0.0001

0.08 p = 0.90 0.48 p = 0.19 0.0 p = 1.0 0.95 p = 0.05

0.92 p = 0.03 0.54 p = 0.13 0.64 p = 0.12 0.32 p = 0.68

DAVID J. SHER, M.D., M.P.H. JOHN A. WOLFGANG, PH.D. ANDRZEJ NIEMIERKO, PH.D. NOAH C. CHOI, M.D. Department of Radiation Oncology Massachusetts General Hospital Harvard Medical School Boston, MA doi:10.1016/j.ijrobp.2008.02.019