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Objective To study the feasibility of helical tomoterapy (HT) at prescription dose escalation for nasopharyngeal carcinoma (NPC).Methods Static-IMRT (sIMRT) and HT plans were designed for 10 nasopharyngeal carcinoma patients which were treated by sIMRT and HT treatment plan.Prescription dose was escalated for each plan until any organs at risk (OARs) reached the quantitative analysis of normal tissue effects within the clinical threshold.Dosimetric factors of target and OARs were analyzed for both sIMRT and HT plans.Results Compared with sIMRT plan, prescribed dose of HT plans increased 42.6％ (t =6.373, P ＜ 0.01), and the homogeneity index was also improved (t =-2.288, P＜0.05);the conformity index decreased (P ＞ 0.05).The limits of HT prescribed dose escalation were spinal cord (2 cases), optic nerve (5 cases) and brainstem (3 cases).The limits of sIMRT prescribed dose escalation were lens (1 case), spinal cord (1 case) and parotid (8 cases).Conclusions HT could improve prescription dose of nasopharyngeal carcinoma while keeping the OARs safe.Compared with sIMRT, HT technology might be used at high dose NPC radiotherapy.
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Objective To investigate the difference of lung and target volume and dosimetry characteristics features of deep inhalation breathing holding-active breathing control (ABC) and the four dimensional CT (4D-CT) free breathing in stereotactic body radiation therapy (SBRT) technology for patients with lung cancer.Methods 10 patients with pulmonary malignant tumor who were proposed SBRT treatment were selected,and received CT under free breath (FB-CT),4D-CT scan under quiet respiration (4D-CT) and active breathing control CT scan (ABC-CT),respectively.With SBRT technology under the same condition designed four corresponding plans,FB-CT,ABC-CT,4D-CT and 4D-CT0 which was the end inspiratory phase of 4D-CT respectively.The lung volume(V),PTV,V5,V20,mean lung dose(MLD) and normal tissue complication probability(NTCP) of four treatment programs were counted and compared.Results Compared with FB-CT,V,PTV,V5,V20,MLD and NTCP of ABC-CT were 51.48％,-65.34％,-42.64％,-56.62％,-40.22％ and-98.53％ (t=-7.14 to6.16,P＜0.05);PTV,V5,V20,MLD and NTCP of 4D-CT were-40.14％,-16.90％,-37.16％,-17.85％ and-90.96％ (t =0.54 to 3.22,P＜0.05);PTV,V5,V20,MLD and NTCP of 4D-CT0 were-68.98％,-30.21％,-48.49％,-37.45％ and-95.82％ (t=1.32 to 5.46,P＜0.05),respectively.Compared with FB-CT,the lung volume of 4D-CT and 4D-CT0 had no statistical difference (P ＞ 0.05).Conclusions ABC-CT methods have ideal clinical characteristics,with larger double lung volume,smaller artifacts of image,and higher target matching precision.ABC-CT methods reduce the dose of normal lung tissues significantly.
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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 (PGTVnx) 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 PGTVnx,PCTV1,and D100,D98,D95,D50,D2and D0 were calculated,respectively.The homogeneity index (HI) and deviation between D95 and D50 of PGTVnx and PCTV1 were calculated,respectively.The differentiation of grouping results were analyzed with grouped t-test method.Results The HI of PGTVnx 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 PGTVnx 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 D550,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 instand of D95,the prescription dose of PGTVnx and PCTV1 should increase 5％ and 11％,respectively.