916P - Reducing radiation-induced temporal lobe injury by changing tumor prescription dose in nasopharyngeal carcinoma

Background

Radiation-induced temporal lobe injury (TLI) is one of the most common radiation-induced toxicities in nasopharyngeal carcinoma (NPC) treated by intensity-modulated radiotherapy (IMRT), especially in patients with cavernous sinus invasion whose planning target volume of nasopharynx (PTVnx) and temporal lobe (TL) is often overlapped. We named the overlap area as the sub-volume of PTVnx and TL (PTVsv-TL) and gave it independent prescription dose, and investigated its efficacy and feasibility in this study.

Methods

From 2015 to 2020, T4 stage NPC patients with cavernous sinus invasion treated by independent prescription dose of PTVsv-TL (60-64Gy) were enrolled in study group, while T4 stage patients with cavernous sinus invasion treated by prescription dose recommended as international guidelines were enrolled in control group. The primary endpoint is the 3-year cumulative incidence of TLI, and secondary endpoints included dose parameters of TL, local recurrence rate and pattern, regional recurrence-free survival (RRFS), distant metastasis-free survival (DMFS) and overall survival (OS). SPSS 25.0 was used for statistical analysis.

Results

Totally, 137 and 357 patients were enrolled in the study group and control group, respectively. The median follow-up time was 33.0 months (inter-quartile range, 22.0-44.0 months). 17.6% patients (87/494) were diagnosed as TLI by MRI. The 3-year cumulative incidence of TLI in the study and control group were 15.3% and 28.5% (P=0.006). The dose parameters of TLs in two groups were as follows: D₂, D_0.5cc, D_1cc and D_2cc were 62.0 vs 70.5Gy, 66.1 vs 73.2Gy, 64.1 vs 72.1Gy, and 61.8 vs 70.0Gy (all P<0.001). The 3-year cumulative local recurrence rate were 6.2% and 10.4% in the study and control groups (P=0.170), with 2 cases of marginal failure in each group and none out-field failure. The 3-year PFS and OS rates were 87.8% vs 90.4% (P=0.275), 86.3% vs 88.2% (P=0.649), and 97.2% vs 97.3% (P=0.581).

Conclusions

Giving independent prescription dose to PTVsv-TL could significantly reduce the irradiated dose of TLs and decrease the incidence of TLI, meanwhile achieved satisfactory local control and long-term survival. Further prospective study is warranted.

Clinical trial identification

Editorial acknowledgement

Legal entity responsible for the study

Sun Yat-sen University.

Funding

Has not received any funding.

Disclosure

All authors have declared no conflicts of interest.