Dosimetric comparison between Intensity Modulated Radiation Therapy (IMRT) vs dual arc Volumetric Arc Therapy (VMAT) for nasopharyngeal cancer (NPC): Systematic review and meta-analysis

Background and Purpose: Previous non-randomised studies com-paring dosimetric outcomes between advanced techniques such as IMRT and VMAT reported conflicting findings. We thus sought to perform a systematic review and meta-analysis to consolidate the find-ings of these studies. Materials and Methods: We searched PUBMED and EMBASE for eligible studies from their time of inception to 10 March 2022. A ran-dom effects model was used to estimate the pooled mean differences (MDs) and their 95% confidence intervals(CIs) for target volume cov-erage, organ-at-risk(OAR) doses, monitor units(MUs) and treatment delivery times. We also performed a subgroup analysis to evaluate if different treatment planning systems (TPS) (Eclipse, Monaco and Pin-nacle) used affected the pooled mean differences. Results: A total of 17 studies (383 patients) were eligible to be included. The pooled results showed that dual arc VMAT re-duced D2% of PTV (MD = 0.71Gy,95%CI= 0.14-1.27,P = 0.01), mean left cochlea dose (MD = 2.6Gy,95%CI= 0.03-5.16,P = 0.05), mean right cochlea dose (MD = 3.4Gy,95%CI= 0.7-6.1,P = 0.01), MUs (MD = 554.9,95%CI = 245.8-863.9,P = 0.0004), treatment de-livery times (MD = 6.7mins,95%CI= 4.5-8.9,P < 0.0001) and in-tegral dose (MD = 0.97Gy,95%CI= 0.28-1.67,P = 0.006). None of the other indices were significantly better for the IMRT plans. The subgroup analysis showed that the integral dose was sig-nificantly lower only for Eclipse (MD = 0.88Gy, 95%CI = 0.14-1.63, P = 0.02). The total MUs was significantly lower only for Eclipse (MD = 1035.2, 95%CI= 624.6-1445.9, P < 0.0001) and Pin-nacle (MD = 293, 95%CI= 15.6-570.5, P = 0.04). Similarly, delivery time was also significantly lower only for Eclipse (MD = 6.1mins, 95%CI= 5.7-6.5, P < 0.0001) and Pinnacle (MD = 4.9mins, 95%CI= 2.6-7.2, P < 0.0001). The subgroup analysis however showed that target coverage was superior for the IMRT plans for both Pin-nacle (MD = 0.48Gy, 95%CI= 0.31-0.66, P < 0.0001) and Monaco (MD = 0.12Gy, 95%CI = 0.07-0.17, P < 0.0001). Conclusion: Dual-arc VMAT plans improved OAR doses, MUs and treatment times as compared to IMRT plans. The different TPS used may modify dosimetric outcomes.