A dosimetric study of helical tomotherapy for nasopharyngeal carcinoma / 中华放射肿瘤学杂志

Objective To use helical tomotherapy ( HT ) for determining the difference between actual doses and planning doses to the target volume and organs at risk ( OARs ) in patients with nasopharyngeal carcinoma receiving radiotherapy, and to provide guidance for the clinical treatment. Methods Localization and delineation of the target volume and OARs were performed by computed tomography ( CT) in 21 patients with nasopharyngeal carcinoma receiving radical radiotherapy using HT. All patients underwent megavoltage CT ( MVCT) scan prior to treatment. The obtained MVCT images were used for dose reconstruction in the adaptive module of HT, in which the actual dose was obtained and the non?image?guided dose was simulated. Each single dose distribution and the corresponding CT image were sent to software MIM6. 0 for superimposition, and the overall dose was obtained. The initial plan, image?guided plan, and non?image?guided plan were named Plan?1, 2, and 3, respectively. The dose distribution in the target volume and OARs was compared between the three plans with t ? test or wilcoxon test . Results Compared with those in Plan?1, the D98 values for the planning gross tumor volume ( PGTV) and planning target volume ( PTV) in Plan?2 were significantly reduced by 1. 16% and 2. 3%, respectively ( P=0. 025;P=0. 043);the volumes of the left and right parotids in Plan?2 were significantly reduced by 46. 0% and 46. 5% on average, respectively ( P=0. 000);the distances between the midline and the center?of?mass for left and right parotids were significantly reduced by 6. 9% and 6. 5%, respectively ( P=0. 000);the V26 and Dmean for both parotid glands were significantly elevated by 32. 8% and 25. 2%, respectively ( P=0. 000) . Compared with those in Plan?1, the D98 values for PGTV, PTV?1, and PTV?2 in Plan?3 were significantly reduced by 2. 0%, 1. 9%, and 2. 4%, respectively ( P=0. 001;P=0. 007;P=0. 036);the V26 and Dmean for both parotid glands in Plan?3 were significantly elevated by 33. 6% and 25. 3%, respectively ( P=0. 000);Dmax to the spinal cord was significantly increased by 6. 9%( P=0. 005) . There was no significant difference in D2 to the spinal cord between Plan?2 and Plan?1( P=0. 392) . Conclusions The doses to both parotid glands increase during HT for nasopharyngeal carcinoma, which is closely associated with the shift of the parotid glands toward the midline. Image?guided radiotherapy does not enhance the dose to the target volume, but reduces the dose to the spinal cord.

Dosimetry study of volumetric-modulated arc therapy for single brain metastasis / 中华放射肿瘤学杂志

Objective To evaluate the plan quality of volumetric modulated arc therapy (VMAT) in single brain metastasis compared with the stereotactic arc therapy (S_ARC).Methods 31 patients were replanned using VMAT and S_ARC technique.Prescription dose is 40 Gy delivered in 4 fractions covering at least 95％ of the target volume while keeping minimum doses to the volume of normal brain tissue.The plans were assessed and compared using the conformity indexes (CI),gradient indexes (GI),the mean dose of normal brain tissue,the volumes of normal brain tissue receiving 4 Gy doses,the number of monitor unit and treatment times.A paired t test or non-parametric Wilcoxon signed rank test was performed to analyze the difference between these two plans.Results VMAT plans increased dose conformity,but not dose gradient,compared with S_ARC plans.The median dose conformity index values were 0.815,0.818,and 0.779 (P =0.000,0.000),and the median dose gradient score index values were 5.865,5.706,and 3.133(P =0.000,0.000,0.000),in single arc,double arc VMAT plans and S_ARC plans,respectively.The mean dose of normal brain tissue was higher in VMAT plans.And the volume of the normal brain tissue receiving doses of 4 Gy in VMAT plans was significantly larger than the volume in S_ARC plans.The VMAT plans got higher MU number (P =0.000,0.000).And the mean treatment times were (2.7 ± 0.1) min,(2.8 ± 0.1) min,and (7.6 ± 0.2) min in single arc,double arc VMAT plans and S_ ARC plans,respectively (P =0.000,0.000).Conclusions The dosimetry of VMAT plan can meet the requirements of clinical,and is recommended in the treatment of big volume single brain metastasis or single brain metastasis in cerebellum.

Position modification and actual radiation dose in parotids for head and neck cancers treated with TomoTherapy / 中华放射医学与防护杂志

Objective To analyze the impact of parotid's position and volume changing on radiation dose for head and neck cancer treated with TomoTherapy.Methods Totally 12 patients with head and neck cancer were treated with TomoTherapy.Before the treatment,the dose distribution was recalculated with MVCT images,which would obtain the parameters of position,volume and actual radiation dose for parotids.Results The volume of parotids in Plan2 was significantly lower than in Plan1,and the percentage reduction was 29.06％ and 31.78％ for left and right parotid,respectively (Z =6.77,3.06,P ＜ 0.05).Distance between the COM (center of mass) of parotids and the midline of body was significantly smaller in Plan2 than in Plan1,and the percentage reduction was 6.72％ and 6.19％ (t =5.14,5.80,P ＜ 0.05) at left and right side,respectively.Average dose and V26 for both parotids were higher than those in Plan1,increasing by an average of 37.74％,25.08％ (Z =-6.03,-5.31,P ＜ 0.05) for left parotid and 30.45％,19.33％ (Z =-5.43,-3.26,P ＜0.05) for right parotid,respectively.Conclusions The actual radiation dose to parotids was significantly increased during the radiation therapy for patients with head and neck cancer.There was a linear correlation between the decrease of distance between the COM of parotids and the midline of body and the percentage increase of parotids' radiation dose.No correlation between the reduction of parotids' volume and dose to parotids.In order to reduce the parotids' radiation dose,modification of treatment plan at the appropriate time is essential.

Delta three-dimensional semiconductor array verification for intensity modulated planning of helical tomotherapy / 中华放射肿瘤学杂志

Objective To investigate the feasibility of dose verification of intensity modulated planning of helical tomotherapy (HT) using three-dimensional semiconductor array (Delta4) and find a more time-consuming and accurate method to validate the delivery dose.Methods Delta4 detector array was used to verify the HT plan dose distribution of 10 patients.The precise setup of detector array was guided and registered by MVCT imaging.After the implementation of delivery,the measured dose distributions on the corresponding planes were compared with those calculated by the treatment planning system (TPS).According to the different acceptance criteria combination of dose difference or distance to agreement at different threshold level including 3％/2 mm,3％/3 mm,3％/4 mm,3％/5 mm at TH5,TH10,TH20,TH30,TH70,TH90,the γ analysis method was utilized to evaluate the dose verification.Results The dose distribution measured by the Delta4 was well consistent with that calculated by the TPS.The mean γpassing rates were all above 94.89％.Conclusions Delta4 detector array can get satisfying results when used in HT plan dose verification and is a viable tool to replace traditional film dosimetry system in clinical quality assurance work.

Effects of edaravone on oxidative stress response during one-lung ventilation / 中华麻醉学杂志

ObjectiveTo investigate the effects of ederavone on oxidative stress response during one-lung ventilation (OLV).MetihodsThirty ASAⅠ or Ⅱ patients of both sexes aged40-64 yr,weighing50-85 kg undergoing elective esophageal cancer resection were randomly divided into 2 groups ( n =15 each):control group (group C) and edaravone group (group E).In group E edavavone was infused immediately after tracheal intubation at 60.0 mg/h for 30 min.Then the infusion rate was reduced to7.5 mg/h and maintained until the end of operation.In group C equal volume of normal saline was infused instead of edaravone.Arterial and venous blood samplea were taken immediately before skin incision,at 30 min of OLV and 30 min after re-expansion of the collapsed lung for blood gas analysis and determination of serum MDA and 8-iso-PGF2a concentrations.PaO2/FiO2,PA-aDO2 and respiratory index (RI) (RI =PA-aDO2/PaO2 ) were calculated.ResultsPA-a DO2,RI and serum concentrations of MDA and 8-iso-PGF2a were significantly lower at 30 min after re-expansion of the collapsed lung in group E than in group C( P ＜ 0.05).ConclusionEdaravone can attenuate oxidative stress response during OLV.