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Journal of Thoracic Oncology:
doi: 10.1097/01.JTO.0000283425.74391.cb
Poster Discussion Abstracts: Session PD3 and PD5 PD -Thursday, September 6: Session PD5: Thursday, September 6 Technical Advances on Radiation Therapy: Technical Advances on Radiation Therapy, Thu, 12:30 - 14:15

Time trends in nodal CT volume and nodal motion during radiotherapy for patients with stage III non-small cell lung cancer: PD5-1-7

Bosmans, Geert; van Baardwijk, Angela; Dekker, Andre; Wanders, Stofferinus; Boersma, Liesbeth; Lambin, Philippe; De Ruysscher, Dirk

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Department of Radiation Oncology (MAASTRO), GROW, University Hospital, Maastricht, The Netherlands

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Background:

Knowledge of changes in volume and motion of either tumor or involved lymph nodes during a course of radiotherapy is necessary to improve the treatment (adaptive radiotherapy). These changes for the primary tumor were already reported (Bosmans et al, Int J Radiat Oncol Biol Phys, 2006). The purpose of this study is describing the time trends in nodal CT volume and nodal motion, for patients with locally advanced non-small cell lung cancer.

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Methods:

Eleven patients, with a total of 21 nodes, from a prospective clinical trial underwent CT-PET scans prior to treatment, which was repeated in the first and second week following the start of radiotherapy. For 20 nodes, the motion could be measured based on a respiration correlated CT (RCCT) scan. Moreover, repeated RCCT scans were available for 11 nodes to evaluate the change in motion. Patients were treated with an accelerated fractionation schedule, 1.8 Gy BID, with a total tumor dose depending on pre-set dose constraints for the lungs and the spinal cord.

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Results:

A heterogeneity of nodal volume changes was observed at all time points similar to the tumor volume changes. In some patients the nodal volume increased > 50% (4/21) in others the volume decreased > 50% (1/21) but for the majority of nodal areas (16/21) the volume only changed slightly (< 50%). The initial absolute nodal volume was 4.5 cc ± 4.3 cc, therefore large volume changes were observed and the delineation of small volumes is sensitive to intra-observer variability. On average the nodal volume did not change significantly (4.5, 4.9 and 4.3 cc prior to treatment, 1 and 2 weeks after the start of treatment respectively). The 3D vector motion, which is the quadratic sum of the orthogonal movements, of the nodal areas was initially 5.7 mm ± 2.9 mm, which was somewhat smaller than the tumor motion (7.8 mm ± 4.8 mm). The motion of the lymph nodes decreased during therapy (5.8 mm after 1 week and 5.3 mm after 2 weeks) but was not statistically significant different. No difference in motion and motion changes was observed between the locations of the lymph nodal areas.

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Conclusion:

A large variability of changes in nodal volume between the patients was observed, but is not clinically relevant since the volumes and hence the volume changes are small. The motion of the nodal areas is smaller than the tumor motion and does not change during therapy. Therefore smaller internal margins can be applied for the nodal areas compared to the internal margin for the primary tumor.

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Copyright © 2007 by the European Lung Cancer Conference and the International Association for the Study of Lung Cancer.

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