The difference analysis of prescription dose between ICRU report 83 and Chinese recommendation in the nasopharyngeal carcinoma when using IMRT

Objective: To analyze the difference of prescription dose between ICRU report 83 and Chinese recommendation in the nasopharyngeal carcinoma (NPC) for intensity modulated radiation therapy (IMRT). Methods: Eighty-four NPC were treated using IMRT technology from Jan 1, 2010 to Apr 1, 2012. All dose volume histogram of the 84 IMRT plan were analyzed retrospectively. The target volumes of planning gross tumor volume of nasopharynx (PGTV_nx) or planning clinical target volume and high risk lymphatic drainage (PCTV₁) and doses of D₁₀₀, D₉₈, D₉₅, D₅₀, D₂ and D₀ were recorded. The mean, standard error, medial, range, coefficient of variation (CV) of PGTV_nx, PCTV₁, and D₁₀₀, D₉₈, D₉₅, D₅₀, D₂ and D₀ were calculated, respectively. The homogeneity index (HI) and deviation between D₉₅ and D₅₀ of PGTV_nx and PCTV₁ were calculated, respectively. The differentiation of grouping results were analyzed with grouped t-test method. Results: The HI of PGTV_nx and PCTV₁ were 0.118 ± 0.045 and 0.272 ± 0.037, respectively. It is the bigger target volume, the worse HI; and the advanced T stage, the worse HI. Either PGTV_nx or PCTV₁, D₉₅ were less than D₅₀. The average deviation was -5.15% and -10.97%, and the actual difference value was (382 ± 180) cGy (P = 0.000) and (741 ± 140) cGy (P = 0.000). Conclusions: D₅₀, which is the recommendation prescription dose of PTV in ICRU report 83, could evaluate accurately the IMRT plan with combining D₉₈ and D₂. When D₅₀ is used to instead of D₉₅, the prescription dose of PGTV_nx and PCTV₁ should increase 5% and 11%, respectively. (authors)