Preliminary Research Of Re-planning During Radiation Therapy For Nasopharyngeal Carcinoma

Objective:To evaluate the anatomic and dosimetric changes of parotid glands during radiation therapy for nasopharyngeal carcinoma and to find out the factors affecting these changes.Methods:With HT, its planning system and adaptive software, weekly anatomic and dosimetric changes of parotid glands in patients with nasopharyngeal carcinoma were calculated. Anatomic and dosimetric parameters included parotid external borders, V1 and D50. The inter-fractional parameters and the factors affecting these changes were studied using analysis of variance methods for repeated measures.Results:The average parotid volume decreased by 29.47% (left) and 24.47% (right) at the end of radiation therapy in 35 patients. Inter-weekly parotid volume varied significantly (p<0.05). The rate of volume change reached the highest level at the 16th fraction. The average distance between external borders decreased by 7.5±3.85%, the average ratios of intra-target volume to extra-target volume of left parotid gland and right parotid gland increased by 102.3±80.05% and 86.43±122.1%, respectively. The average V1 increased by 32.2% (left) and 28.6% (right) and the average D50 increased by 33.9% (left) and 24.93% (right), repectively. The inter-weekly dosimetric parameters varied significantly in the second and the third week (p<0.05). The variation of parotid volume correlated with the initial volume (p=0.000) and treatment protocol (p=0.04), furthermore D50 variation trend correlated with treatment protocol (p=0.007), age (p=0.025), Dmean (p=0.000) and V30 (p=0.004) in the initial treatment plan.Conclusions:The volume and dose delivered to parotid glands vary significantly throughout radiotherapy process. These variations are affected by the initial parotid volume and parotid dose in the initial plan, treatment protocol, and age. The implementation of re-planning may have clinical benifits at the fourth week of treatment. Objective:Explore various factors impacting parotid volume changes in nasopharyngeal carcinoma patients during intensity modulated radiation therapy.Methods:Retrospectively analyze clinical data and planning parameters in 104 nasopharyngeal carcinoma patients. With HT system and its adaptive software, the profile of parotid gland was contoured to get parotid volume changes during treatment. Correlation between variety factors and parotid volume changes was analized by using Spearman correlation and Logistic regression model.Result:The average volume decreased by 6.69cm3 (25.51%) and 6.43cm3 (24.95%) in the left and right parotid gland at the 20th fraction, respectively. The absolute volume variation correlated with initial parotid volume, weight, treatment protocol, and the total volume of primary tumor and invaded lymph nodes. The relative volume variation correlated with tumor stage, treatment protocol, lymph node invasion and the total volume of primary tumor and invaded lymph nodes. With Logistic regression model, treatment protocol was detected as an independent prognostic factor for the absolute value and the relative value of parotid volume variation, respectively (p=0.009 and 0.007). The initial volume was detected as an independent prognostic factor for the absolute value of parotid volume variation (p=0.000).Conclusions:During intensity modulated radiation therapy for nasopharyngeal carcinoma, patients receiving concurrent chemotherapy or anti-EGFR targeted therapy, or with a large parotid volume should be under observation for timely re-planning. Objective:To find a variety of factors affecting xerostomia in NPC patients after intensity modulated radiation therapy.Methods:The 104 nasopharyngeal carcinoma patients mentioned in the PartⅡof this study were followed up with out-patient admissions and telephone communication. The xerostomia was evaluated according to RTOG/EORTC criteria. Correlations between the severity of xerostomia and various factors were evaluated with Spearman rank analysis.Results:Six to 12 months after the end of radiation therapy 17 cases (16.3%), 78 cases (75%) and 9 cases (8.6%) suffered from grade 0,1 and 2 xerostomia, respectively. The study failed to establish a correlation between the severity of xerostomia and re-planning during radiation therapy (p>0.05), however concurrent chemo-radiotherapy increased the severity of xerostomia (p=0.006) compared with radiotherapy alone or concurrently with anti-EGFR targeted therapy. Moreover, patients with large initial parotid volume suffered from more severe xerostomia (p= 0.024).Conclusions:A larger number of cases and a longer follow-up may be needed to evaluate the necessary of re-planning during radiation therapy to decreased the xerostomia. For patients with large initial parotid volume or concurrent chemo-radiotherapy, preventive measures should be practised.