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

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.

Long-term outcomes of replanning during intensity-modulated radiation therapy in patients with nasopharyngeal carcinoma: An updated and expanded retrospective analysis

“…Previous studies had demonstrated that the volumetric changes and spatial variability were significant during the course of IMRT due to the weight loss and tumor shrinkage, which usually resulted in dose distribution variations 7,12,[22][23][24] . Wang et al performed a study in 28 patients with NPC receiving IMRT 9 , in which all patients underwent a repeat CT simulation scan and replanning at the 25th fraction of IMRT.…”

Assessing the need for adaptive radiotherapy in head and neck cancer patients using an automatic planning tool

“…A recent review by Morgan et al [3] reported median shrinkage rates of the primary tumour ranging from 3% to 16% in the end of the second week of treatment (2 studies), 7% to 48% by the end of week 4 (2 studies) and of 6% to 66% by the end of week 7 (14 studies), with the involved nodes presenting similar results. These volumetric variations have been associated with dosimetric consequences, such as reduction of the minimum delivered dose and loss of homogeneity in the dose distribution on the target volumes [11][12][13]. Conversely, some studies report that, despite the existence of volume reduction, dosimetric coverage of target volumes tends to be robust to anatomical changes [14][15][16].…”

Impact of tumor volume enlargement after induction chemotherapy on subsequent radiotherapy in locally advanced nasopharyngeal carcinoma: A propensity‐score matching analysis

“…Due to the complicated anatomical location, the tumor size of NPC has a significant influence on the dosimetric parameters of radiotherapy. [12][13][14] Tumor volume enlargement after IC has been observed in a small proportion of NPC patients despite the high chemotherapy sensitivity of the cancer, 6 but its influence on the subsequent radiotherapy plan has not yet been investigated. To the best of our knowledge, the current study is the first to address this problem.…”