IN REPLY TO DR. JENKINS

To the Editor: We appreciate the comments from Dr. Jenkins and agreethat our findings are consistent with his group’s previous work. We alsoagree that correlating the carinal and/or diaphragmatic motion with nodalmovement could potentially obviate (or, at least, reduce) the need for four-dimensional computed tomography planning if either structure could serveas an accurate surrogate for nodal motion. Unfortunately, we did not recordthese data, so we will not be able to perform this analysis.

With respect to the correlations between nodal stations, Dr. Jenkins makesa valuable suggestion. We have obtained Spearman correlation coefficientsbetween each nodal station for peak-to-peak motion in three dimensions(Table 1). Although the sample size was small, the most striking findingswere the correlations in the craniocaudal and lateral motion between thesubcarinal and hilar lymph nodes; a significant relationship was also foundbetween the movement of the paratracheal nodes in the same patient. The re-mainder of the correlation coefficients did not reach statistical significance,but there do appear to be several moderately strong correlations betweenthe motion of different stations. A larger sample might be able to clarifythis question.

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 OncologyMassachusetts General HospitalHarvard Medical SchoolBoston, MA

doi:10.1016/j.ijrobp.2008.02.019

Table 1. Spearman correlation coefficients

Station–Station n Superorinferior Right–left Anteroposterior

Paratracheal vs.paratracheal

5 0.89 0.08 0.92p = 0.04 p = 0.90 p = 0.03

Paratracheal vs.subcarinal

9 0.60 0.48 0.54p = 0.09 p = 0.19 p = 0.13

Paratracheal vs.hilar

7 0.62 0.0 0.64p = 0.14 p = 1.0 p = 0.12

Subcarinal vs.hilar

4 1.0 0.95 0.32p \ 0.0001 p = 0.05 p = 0.68

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 NODE MOVEMENT

USING FOUR-DIMENSIONAL COMPUTED TOMOGRAPHY

SCAN: IMPLICATIONS FOR RADIATION TREATMENT

PLANNING (INT J RADIAT ONCOL BIOL PHYS2007;69:1402–1408)

To the Editor: Sher et al. have quantified the movement of mediastinallymph nodes with respiration using four-dimensional computed tomography(4D-CT) scans (1). The authors are to be congratulated for the meticulousdata collection needed to complete this important study. It appears that lymphnode motion with ventilation is greatest in the craniocaudal direction, pre-sumably related to the forces exerted on the mediastinum by contraction ofthe diaphragm. I note with interest that their results and conclusions arevery similar to those of our earlier report (2), using fluoroscopic assessmentof 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 move-ment of the diaphragm or carina? If this was the case, the movement of thesefluoroscopically visible structures could be used as a surrogate for that of thelymph nodes. Second, in contrast to our more limited analysis, 14 patients intheir study had movement measured in more than one node. However, thecorrelation of the peak excursions for the separate lymph node stations isnot stated in their report. Unless the movement seen in the different lymphnodes is similar, little option exists other than to measure motion on a case-by-case basis using 4D-CT technology.

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

PETER JENKINS, PH.D., M.R.C.P., F.R.C.R.Gloucestershire Oncology CentreCheltenham, United Kingdom

doi:10.1016/j.ijrobp.2008.02.020

1. Sher DJ, Wolfgang JA, Niemierko A, et al. Quantification of mediastinaland hilar lymph node movement using four-dimensional computed to-mography scan: Implications for radiation treatment planning. Int J RadiatOncol Biol Phys 2007;69:1402–1408.

2. Jenkins P, Salmon C, Mannion C. Analysis of the movement of calcifiedlymph nodes during breathing. Int J Radiat Oncol Biol Phys 2005;61:329–334.