Individualization of clinical target volume delineation in eccentric nasopharyngeal carcinoma: a prospective comparative study

Abstract

Background: Clinical target volume (CTV) delineation is a major focus in radiotherapy for nasopharyngeal carcinoma (NPC) and currently lacks a universally accepted standard across treatment centers. We proposed an individualized CTV delineation method for eccentric NPC and evaluated its feasibility based on the eccentric distance of the primary lesion.

Materials and methods: Ninety patients with eccentric NPC were included. Each treatment plan was replanned using the individualized CTV method for dosimetric comparison with the conventional CTV, to evaluate coverage, homogeneity, and conformity of CTV and PTV, sparing of organs at risk (OARs) and radiotherapy technique. Paired sample t-tests and nonparametric rank-sum tests were used to compare target coverage, homogeneity, conformity, and OAR dose parameters between the two approaches. Correlation analysis is used to evaluate the correlation between eccentric distance of primary lesion and OARs dose changes. Subgroup analysis is used to compare the PTV and OARs dose parameters of individualized CTV at different T stages or radiotherapy techniques.

Results: Our results showed that compared with conventional CTV, the volume of CTV decreased significantly (P< 0.05) through individualizing delineation for eccentric NPC, especially CTV1 volume (95.81 cm³ vs. 57.57 cm³, P < 0.001). Individualized CTV reduced the doses delivered to OARs, including the brainstem, spinal cord, optic chiasm, optic nerves, and contralateral temporal lobe, inner ear and so on (all P< 0.05). When the eccentric distance of the primary lesion was between 1.4 and 2.1 cm, the individualized CTV approach provided significant advantages in organ protection, such as contralateral optic nerve, temporal lobe and parotid gland. Additionally, Subgroup analysis showed that the dose-sparing benefit of individualized CTV was more pronounced in patients treated with VMAT (volumetric modulated arc therapy).

Conclusion: This study demonstrates the dosimetric advantages of individualized CTV delineation based on eccentric distance. Our prospective trial is currently ongoing for further research (NCT06167109).

Keywords: clinical target volume; dosimetry; eccentric NPC; plan evaluation; radiotherapy techniques.

Figure 1

Comparison of conventional(up) and Individualized(down) CTV delineation. The images of (a), (c) and (e) represent the delineation of the GTV, CTV1 and CTV2, and the images of (b), (d) and(f) exhibit the delineation of PGTV, PTV1 and PTV2. The GTV and PGTV is in solid red, CTV1 and PTV1 is in solid green, and CTV2 and PTV2 is in solid orange.

Figure 2

Dose distribution comparison images of conventional (down) and Individualized (up) CTV delineation. (a), (b) and (c) are individualized cross-sectional dose distribution maps, while (d), (e), and (f) are conventional cross-sectional dose distribution maps. The PGTV is in solid red, PTV1 is in solid green, and PTV2 is in solid orange. The 95% dose line of 69.96Gy is yellow, the 95% dose line of 60.06Gy is brown, and the 95% dose line of 54.12Gy is purple. The light blue structure is the left temporal lobe, and the dark blue structure is the left inner ear.

Figure 3

Correlation between L and the dose difference of the contralateral structure. This figure was drawn using ChiPlot (https://www.chiplot.online/) (accessed on May 2024).