open access

Vol 25, No 1 (2020)
Original research articles
Published online: 2020-01-01
Submitted: 2019-07-18
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Dosimetric impact on changes in target volumes during intensity-modulated radiotherapy for nasopharyngeal carcinoma

Wafa Mnejja, Hend Daoud, Nejla Fourati, Tarek Sahnoun, Wicem Siala, Leila Farhat, Jamel Daoud
DOI: 10.1016/j.rpor.2019.12.012
·
Rep Pract Oncol Radiother 2020;25(1):41-45.

open access

Vol 25, No 1 (2020)
Original research articles
Published online: 2020-01-01
Submitted: 2019-07-18

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.

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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Keywords

Nasopharyngeal carcinoma; Intensity modulated radiotherapy; Anatomic changes; Dose distribution.; NPC; IMRT; OAR; CTint; GTV; CTV; PTV; CTV (H); CTV (I); CTV (L); PTV (H); PTV (I); PTV (L); CTmi; Vi; Vm; ID; CI; HI

About this article
Title

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

Journal

Reports of Practical Oncology and Radiotherapy

Issue

Vol 25, No 1 (2020)

Pages

41-45

Published online

2020-01-01

DOI

10.1016/j.rpor.2019.12.012

Bibliographic record

Rep Pract Oncol Radiother 2020;25(1):41-45.

Keywords

Nasopharyngeal carcinoma
Intensity modulated radiotherapy
Anatomic changes
Dose distribution.
NPC
IMRT
OAR
CTint
GTV
CTV
PTV
CTV (H)
CTV (I)
CTV (L)
PTV (H)
PTV (I)
PTV (L)
CTmi
Vi
Vm
ID
CI
HI

Authors

Wafa Mnejja
Hend Daoud
Nejla Fourati
Tarek Sahnoun
Wicem Siala
Leila Farhat
Jamel Daoud

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