Purpose/Objective(s): Image guided radiotherapy (IGRT) via cone-beam computerized tomography (CBCT) could improve the geometric accuracy for head and neck cancer radiotherapy. However, there is lacking data of this technique influence the treatment results. This retrospective study aimed to evaluate the impact of IGRT and other risk factors in nasopharyngeal cancer (NPC) patients received intensity modulated radiotherapy (IMRT).

Materials/Methods: From January 2012 to June 2017, there were 207 patients diagnosed of NPC. This study enrolled 197 patients without metastasis and previous malignant disease. All patients received IMRT with or without IGRT technique by CBCT method. Most of them received concurrent chemoradiotherapy (CCRT) (87.8%, 173/197) with or without induction and adjuvant chemotherapy. Risk factors of age, gender, T4, N3, Stage IV, treatment time, IGRT and kinds of chemotherapy were examined. The survival rates were calculated by Kaplan-Meier method and the risk factors were evaluated by Log-rank test. The multivariate analysis was evaluated by Cox regression model.

Results: The calculated five-year survival rate was 79.3% for the whole population. Using univariate analysis, the factors of long treatment time (>56 days, p=0.046), Stage IV disease (p=0.009), N3 status (p=0.007) and non-IGRT technique (p=0.02) significantly impaired the survival rates. By multivariate analysis, the non-IGRT technique (p=0.031) and N3 status (p=0.012) were the independent risk factors.

Conclusion: In the CCRT and IMRT era, the factors of long treatment time, Stage IV, N3 and non-IGRT technique were the risk factors for NPC patients. Among them, the N3 and non-IGRT technique were the independent risk factors. Table 1. Prognostic factors evaluated by univariate and multivariate analysis (n=197)

Variables	Number of cases	5-yrs OS rates	Univariate	Multivariate
Age <52 y/o	102	81.5%
>52 y/o	95	76.7%	p=0.479
Gender Female	45	79.2%
Male	152	79.5%	p=0.979
T-stage* T1~3	150	80.8%
T4	47	74.3%	p=0.220
N-Stage* N0~2	157	84.3%
N3	40	53.4%	p=0.007	p=0.012
Stage* I~III	121	86.2%
IV	76	67.3%	p=0.009	p=0.072
RT time <56 days	174	82.7%
>56 days	23	61.2%	p=0.046	p=0.153
IGRT IGRT	87	91.8%
Non-IGRT	110	74.3%	p=0.020	p=0.031
Chemotherapy CCRT alone	125	84.4%
CCRT+IC or AC	48	78.2%	p=0.175

Abbreviation: OS=overall survival; IGRT=image guided radiotherapy; CCRT= concurrent chemoradiotherapy; IC= induction chemotherapy; AC= adjuvant chemotherapy.* According to the 7^th AJCC staging system.