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

Abstract

A small proportion of nasopharyngeal carcinoma (NPC) patients show resistance to induction chemotherapy (IC). This study sought to investigate the impact of tumor volume enlargement after IC on the dosimetric parameters of subsequent radiotherapy. The records of a total of 240 locally advanced NPC patients who received IC followed by concurrent chemoradiotherapy were retrospectively reviewed. Patients with a tumor volume enlargement of ≥10% and patients with a tumor volume reduction of ≥10% after induction chemotherapy were classified as the enlargement group and the control group, respectively. The dosimetric parameters of the planning target volumes (PTVs) and the organs at risk (OARs) were compared between the matched groups after propensity score matching (PSM). For the gross tumor volume of nasopharynx (GTVnx), 21 patients and 127 patients were classified as the enlargement group and the control group, respectively. After matching, 20 sub-pairs of 40 patients were generated in the post-PSM cohort. The GTVnx enlargement group exhibited no significant disadvantages in all of the dosimetric parameters, except in the planning organ-at-risk volume (PRV) of contralateral lens (Dmax, 722 cGy vs. 634 cGy, p = 0.041). For the gross tumor volume of lymph nodes (GTVnd), 44 patients and 144 patients were classified as the enlargement group and the control group, respectively. After matching, 39 sub-pairs of 78 patients were generated in the post-PSM cohort. The GTVnd enlargement group exhibited no significant disadvantages in all of the dosimetric parameters. Univariate and multivariate analyses showed that the enlargement of GTVnx and the enlargement of GTVnd were not independently associated with any of the dosimetric parameters. A tumor volume enlargement of ≥10% in GTVnx or GTVnd after induction chemotherapy has no significant impact on the dosimetric parameters of subsequent radiotherapy in locally advanced NPC.

Keywords: dosimetry; induction chemotherapy; nasopharyngeal carcinoma; propensity score matching; tumor volume.

FIGURE 1

A typical case of GTVnx enlargement (left) and its matched control case(right) in the post‐PSM cohort. The red lines represent the contours of GTVnx before induction chemotherapy. The purple lines represent the contours of GTVnx after induction chemotherapy. (GTVnx = the gross tumor volume of nasopharynx)

FIGURE 2

A typical case of GTVnd enlargement (left) and its matched control case(right) in the post‐PSM cohort. The red lines represent the contours of GTVnd before induction chemotherapy. The purple lines represent the contours of GTVnd after induction chemotherapy. (GTVnd =the gross tumor volume of lymph nodes)