The Related Research Of Protecting Organ At Risk In The Process Of Precise Radiotherapy

One of the cornerstones of radiation therapy is the delivery of therapeutic radiation doses to the target tissue, yet minimization of dose to surrounding normal tissue. In practice, there is always some dose delivered to surrounding normal tissue. Pure restriction of dose to the target volume, without any incidental irradiation of normal tissue, is physically impossible for most situations. The advantage of precise radiotherapy is that it may improve theraputic ratio. The methods to protect organ at risk may be as follows:(1) To reduce the PTV margin and decrease the radiation dose of surrounding normal tissue.(2)Accurate prescription dose report makes the OAR dose assessment more precise.(3)Using radiatonprotective agent may also reduce OAR damage. The first chapter: The feasibility research of using Sentinel? system for set-up verification instead of CBCT in the process of precise radiotherapy. Objective Accurate and fast positioning is a prerequisite for precise radiotherapy. The aim of this study is to investigate the accuracy of Sentinel? system for patient setup using rigid-body phantoms. At the same time, the relationship between Sentinel? system and CBCT were analyzed to evaluate that CBCT may be replaced by Sentinel? system to reduce the excess radiation dose. Methods A 002 LFC IMRT phantom was placed on Elekta Hexa POD? 6-degree couch using tattoo and the laser in the treatment room. When a well-know shift and rotation was moved, CBCT and Sentinel? system were scanned respectively, and the measuring errors of six dimensions were recorded. The absolute differences between applied and measuring errors were compared. And total 24 patients were scanned. Then the relationship between CBCT and Sentinel? system were analyzed. Results Total 15 well-know shifts were investigated. The stability of Sentinel? system was very good. The largest absolute difference was less than 0.9mm and 0.2°. At the same time, a good conformance between Sentinel? system and CBCT was displayed because the largest absolute difference between applied and measuring error was less than 0.9mm(shift, Z direction) and 0.2°(rotation). Conclusions Sentinel? system is fast, simple, non-invasive and seems to be reliable in detecting patient setup errors. It maybe hold potential to ensure precise patient positioning with reduced CBCT frequency in tumor locations with fixed relation to surface structures. The second chapter:The related research of dose prescription and reporting in the process of precise radiotherapyObjective To analyze the difference of prescription dose between ICRU report 83 and Chinese recommendation in the nasopharyngeal carcinoma when using intensity modulated radiation treatment.Methods Eighty-four NPC were treated using IMRT technology from Jan 1, 2010 to Apr 1, 2012. All DVH of the 84 IMRT plan were analyzed retrospectively. The target volume, minimum dose(D100%), maximum dose(D0%), Dnear-min(D98%)、D95%、D50% and Dnear-max(D2%) were recorded. The mean, medial, standard error, range, coefficient of variation(CV), homogeneity index(HI) and deviation between D95% and D50% were calculated using PASW Statistics 18, respectively.Results The HI of PGTVnx and PCTV1 were 0.1179±0.045 and 0.2723±0.037, respectively. The bigger target volume was, the worse HI was. The advanced T stage was, the worse HI was. 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±180c Gy(t=-19.4,p<0.001= and 741±140 c Gy(t=-48.7,p<0.001=.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 instand of D95%, the prescription dose of PGTVnx and PCTV1 should increase 5% and 11%, respectively. The third chapter: The feasibility research of hippocampal avoidance whole brain radiotherapy(HA-WBRT) Objective To analysis the feasibility of hippocampal avoidance prophylactic cranial irradiation for Non-small cell lung cancer. Methods The brain metastases and hippocampuses and SVZs of 56 cases of NSCLC were contoured on the T1W1-contrasted MRI. The relationship between the location of metastases and NSC including hippocampus and SVZ were analyzed. And a HA-PCI plan was designed to analyze the relationship between dose distribution and metastases. Results None of total 139 metastases involved hippocampus. There were 6 and 18 metastases in the range of 5mm and 10 mm outside of the hippocampus, respectively. Seven of total 139 metastases involved SVZ. There were 19 and 45 metastases in the range of 5mm and 10 mm outside of the SVZ, respectively. In the HA-PCI plan, D50 and D2 of PTV were 25.6Gy and 27.1Gy, respectively. Dmean and D2 of hippocampus were 7.4Gy and 9.9Gy, respectively. D50 in the range of 0 to 5mm, 5 to 10 mm and 10 to 15 mm were 10.3Gy, 15.1Gy and 20.5Gy. When hippocampus and SVZ were avoided simultaneously, D50 and D98 in the range of 5 to 10 mm outside of SVZ were 18.6Gy and 10.4Gy, respectively. Conclusions It was impossible to protect SVZ because of nearly one third of metastases may be in the area of low dose distribution. However, hippocampal avoidance alone may be feasibility. The forth chapter: Comparison of two strategies to delineate the bowel for whole pelvis VMAT and the impact of oral contrast agents Objective Toevaluate the impact of oral contrast agents for radiation dose andcompare two different contouring approaches of the bowel including Bowel Bag and Small Bowel in the whole pelvis VMAT of post-surgery cervical carcinoma. Methods The target volumes and organs at risk were contoured in the simulation CT scans for the nine cases of post-surgery cervical carcinoma. Two radiation oncologists blindly used two different strategies including Bowel Bag and Small Bowel to contour the OARs of bowel, respectively. The average time expended in contouring and inter-observer variations were compared.One VMAT plans were designed for each case. Then re-calculating the radiation dose after changing the density of small bowel generated another plan. Plan A was conventional VMAT plan, and plan B specified the value of electron density of the small bowel equal to 1. Paired t test was select to compare the dose distribution between the two plans. Results The average time expended in contouring Bowel Bag and Small Bowel were 14.6±2.6min and 20.6±3.5min(t=7.675,p<0.001=, respectively. The average volume of Bowel Bag contoured by two radiation oncologists were 1632.5±287.0 cm3 and 1626.6±276.8 cm3(t=0.523, p=0.615), respectively. And The average volume of Small Bowel were 484.8±131.9 cm3 and 598.0±133.1 cm3(t=-3.580,p=0.007), respectively. The conformity index of volume were 0.904±0.057 and 0.653±0.128, respectively. The average electron density was 1.099±0.048(1.041~1.211), and the average CT value was 123.9±66.9(48~280)HU. The D98 and D50 of plan A and plan B were 4989.1±8.4 c Gy,5000.1±11.5 c Gy and 5208.6±22.7 c Gy,5191.6±25.5 c Gy, respectively. To achieve the same prescription dose, plan A and plan B needed 893.3±159.1MU and 865.8±153.5MU, respectively. Conclusions To contour the organ at risk of bowel, Bowel Bagis superior to Small Bag, because the former is less inter-observer variation and quicker over the latter. The CT value and electron density were increased due to the contrast agents in the small bowel. The actual radiation dose was increased about 3.2% compared with TPS calculated prescription dose, but showing no significant differences between groups. The fifth chapter: A randomized clinical trial of glutamine for the prevention and treatment of acute radiation-induced diarrhea Objectives The intestine is the dose-limited organ in patients receiving pelvic radiation treatment. Animal studies have strongly demonstrated that glutamine can promote repair of intestinal mucositis injury, and reduce the incidence of acute radiation-induced diarrhea. A prospective randomized clinical trial was administrated to investigate the protective and treatment effects of glutamine on radiation-induced diarrhea in pelvic radiotherapy.Methods Sixty-three patients suffered from cervical carcinoma or endometrial cancer were randomized divided into glutamine-treated and control groups. In the treatment group, 100 ml Dipeptiven® were administered intravenously every day in the last two weeks of the radiation period. The patients were evaluated for diarrhea grade according to the National Cancer Institute Common Toxicity Criteria version 3.0, frequency and dose of using antidiarrheal.Results There were no significant difference in overall diarrhea incidence(87.1%Vs90.6%, x2=0.198, p=0.656) and grade(x2=2.126, p=0.145) when the two groups were compared. The frequency(58.1%Vs81.3%, x2=4.019, p=0.045) and dose(27.98 mg Vs54.77 mg, t=2.416, p=0.019) of using antidiarrheic and number of stools per day in the fifth week(3.0 times/day Vs3.9 times/day, t=2.838, p=0.006) in the glutamine-treated group were less than those in the control group.Conclusions Glutamine may have treatment effect on radiation-induced diarrhea, but the protective effect need more clinical trial to be proven.