Vol 25, No 1 (2020)
Original research articles
Published online: 2020-01-01

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Dosimetric impact on changes in target volumes during intensity-modulated radiotherapy for nasopharyngeal carcinoma

Wafa Mnejja12, Hend Daoud12, Nejla Fourati12, Tarek Sahnoun1, Wicem Siala12, Leila Farhat1, Jamel Daoud12
DOI: 10.1016/j.rpor.2019.12.012
Rep Pract Oncol Radiother 2020;25(1):41-45.

Abstract

Background and purpose

To assess anatomic changes during intensity modulated radiotherapy (IMRT) for nasopharyngeal carcinoma (NPC) and to determine its dosimetric impact.

Patients and methods

Twenty patients treated with IMRT for NPC were enrolled in this study. A second CT was performed at 38Gy. Manual contouring of the macroscopic tumor volumes (GTV) and the planning target volumes (PTV) were done on the second CT. We recorded the volumes of the different structures, D98 %, the conformity, and the homogeneity indexes for each PTV. Volume percent changes were calculated.

Results

We observed a significant reduction in tumor volumes (58.56 % for the GTV N and 29.52 % for the GTV T). It was accompanied by a significant decrease in the D98 % for the 3 PTV (1.4Gy for PTV H, p=0.007; 0.3Gy for PTV I, p=0.03 and 1.15Gy for PTV L, p=0 0.0066). In addition, we observed a significant reduction in the conformity index in the order of 0.02 (p=0.001) and 0.01 (p=0.007) for PTV H and PTV I, respectively. The conformity variation was not significant for PTV L. Moreover, results showed a significant increase of the homogeneity index for PTV H (+ 0.03, p=0.04) and PTV L (+ 0.04, p=0.01).

Conclusion

Tumor volume reduction during the IMRT of NPC was accompanied by deterioration of the dosimetric coverage for the different target volumes. It is essential that a careful adaptation of the treatment plan be considered during therapy for selected patients.

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Reports of Practical Oncology and Radiotherapy