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Dosimetric impact on changes in target volumes during intensity-modulated radiotherapy for nasopharyngeal carcinoma
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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.
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 articleTitle
Dosimetric impact on changes in target volumes during intensity-modulated radiotherapy for nasopharyngeal carcinoma
Journal
Reports of Practical Oncology and Radiotherapy
Issue
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