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

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

Rep Pract Oncol Radiother. 2020 Jan-Feb;25(1):41-45. doi: 10.1016/j.rpor.2019.12.012. Epub 2019 Dec 16.

Authors

Wafa Mnejja^{1

2}, Hend Daoud^{1

2}, Nejla Fourati^{1

2}, Tarek Sahnoun¹, Wicem Siala^{1

2}, Leila Farhat¹, Jamel Daoud^{1

2}

Affiliations

¹ Radiotherapy Department, Habib Bourguiba Hospital, Sfax, Tunisia.
² Faculty of Medicine Sfax University, Sfax, Tunisia.

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 38 Gy. 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 (1.4 Gy for PTV H, p = 0.007; 0.3 Gy for PTV I, p = 0.03 and 1.15 Gy 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: Anatomic changes; CI, Conformity Indice; CTV (H), High Risk Clinical Target Volume; CTV (I), Intermediate Risk Clinical Target Volume; CTV (L), Low Risk Clinical Target Volume; CTV, Clinical Target Volume; CTint, Initial CT; CTmi, Mid-treatment CT; Dose distribution.; GTV, Gross Tumor Volume; HI, Homogeneity Indice; ID, Dice Index; IMRT, Intensity Modulated Radiation Therapy; Intensity modulated radiotherapy; NPC, Nasopharyngeal Carcinoma; Nasopharyngeal carcinoma; OAR, Organs At Risk; PTV (H), High Risk Planning Target Volume; PTV (I), Intermediate Risk Planning Target Volume; PTV (L), Low Risk Planning Target Volume; PTV, Planning Target Volume; Vi, Initial Volume; Vm, Mid-treatment Volume.