The Impact of Air Cavity Correction on Optimization Convergence Error in Intensity-Modulated Radiation Therapy Planning for Nasopharyngeal Carcinoma

Objective To investigate the impact of air cavity correction(ACC) on optimization convergence error(OCE) in intensity-modulated radiation therapy(IMRT) planning for nasopharyngeal carcinoma(NPC), and to provide evidence-based insights for the implementation of precise radiotherapy in NPC patients.Methods A total of 20 NPC patients received IMRT were retrospectively enrolled. Two group plans were designed using Eclipse TPS for each patient: one with ACC enabled(ACCon) and the other with ACC disabled(ACCoff). For plan evaluation, the primary tumor gross target volume(PGTVnx) was subdivided into two sub-volumes based on the CT value threshold of -100HU: the air cavity target volume(PGTVcavity, CT<-100HU) and the tissue target volume (PGTVtissue,CT>-100HU). Dosimetric parameters of PGTVnx, PGTVcavity, and PGTVtissue were evaluated, including Dmin, Dmax, Dmean, D95%, V100%, homogeneity index(HI) and conformity index(CI). Meanwhile, the maximum dose(Dmax) of organs at risk(OARs) and plan complexity metrics, included elapsed time(ET), iteration(I), monitor units(MUs) were recorded. Additionally, the correlation between dosimetric change value of ACCon relative to ACCoff(Δx) and the volume proportion of air cavity in the PGTVnx (VPcavity) were analyzed.Results For the target, ACCon demonstrated superior dose coverage(Dmin, D95%, and V100%) for all three targets compared with ACCoff(P<0.05). Specifically, V100% of PGTVcavity was increased by 21.8% (85.0±5.0% vs. 69.8±8.0%, P=0.000); hotspots and dose homogeneity for PGTVnx and PGTVtissue also was improved(P<0.05), HI of PGTVtissue was decreased by 15.7% (0.102±0.027 vs. 0.086±0.006, P=0.014). For sparing of OARs and plan complexity, no significant differences were observed(P>0.05). Correlation analysis revealed that ΔDmin(r=0.693, P=0.001), ΔD95%(r=0.822, P=0.000), ΔV100%(r=0.661, P=0.001) of PGTVnx were strongly and positively correlated with VPcavity, while ΔHI(r=-0.503, P=0.024) exhibited a significantly negative correlation with VPcavity.Conclusions Enabling ACC in NPC IMRT planning optimization significantly reduces OCE, enhances dose delivery to air cavities, evelates the dose of PGTVnx, improves target dose uniformity, without compromising OAR sparing or increasing plan complexity.. Notably, the reduction effect of ACC on OCE becomes more pronounced with an increasing proportion of air cavity within PGTVnx.