ObjectiveCompare the two-degrade collimator (MLC) angle selection's impact on plan quality and operational efficiency for volumetric intensity-modulated radiotherapy (VMAT) in the treatment planning system, and to explore the scheme for treatment plan optimization. MethodsTwenty patients with nasopharyngeal carcinoma underwent the treatment between March and December 2013 were randomly selected and planned for SIBVMAT treatment with different parameters set in the range of 0-60°with 15°interval for collimator angles. Planned dose distribution to the target volumes, organs at risk, and monitor units were compared. ResultsAs the MLC angle increased, target conformal index and homogeneity index had a trend to became deteriorated. The optimal plans were 0°and 15°, while 45°and 60°plans gave poor protection for the organ at risk compare to other angle plans and the monitor units were significantly increased. ConclusionChange the MLC angle had visible impact on treatment plans,there was a trend to deteriorate with the MLC angle increased, but small changes in MLC angle range can theoretically reduce the influence from leakage radiation on the human body.
Objective To investigate the consistency of regions of interest (ROI) volume among different radiological treatment planning systems (TPS) for the same group of patient data, and analyze the tendency and degree of differences caused by data transfer. Methods Between October 2010 and December 2013, the data of 10 nasopharyngeal carcinoma patients treated in West China Hospital were transferred from Monaco TPS into various other treatment planning systems. Based on different ROI volumes, they were divided into 8 groups. We counted the volume differences between these TPS and Monaco TPS, and carried out the statistical analysis. Results For small ROI volume, the calculated difference reached up to 65% in our study. As a general trend, differences became less and less with the increasing of volumes. But for single ROI, the volume difference was likely to vary randomly. The percentage of ROI volumes which were smaller than that of Monaco TPS was 70% for Raystation TPS, 38.75% for Pinnacle TPS, 88.75% for Eclipse TPS, 97.5% for Masterplan TPS, and 83.13% for iPlan TPS. Conclusions ROI volume differences exist generally among different treatment planning systems when ROIs are transferred among them by DICOM protocol. The volume variations may be affected by multiple factors. The volume consistency should be evaluated before any direct comparison of dose volu me histogram parameters which are done between different systems.
While radiation treatment to patients with tumors in thorax and abdomen is being performed, further improvement of radiation accuracy is restricted by the tumor intra-fractional motion due to respiration. Real-time tumor tracking radiation is an optimal solution to tumor intra-fractional motion. A review of the progress of real-time dynamic multi-leaf collimator (DMLC) tracking is provided in the present review, including DMLC tracking method, time lag of DMLC tracking system, and dosimetric verification.
【摘要】 目的 研究Monaco治疗计划系统中不同参数设置对容积旋转调强放射治疗(VMAT)计划质量的影响，得出更合理的治疗计划参数设置以提高VMAT治疗质量。 方法 2010年1-5月间治疗3例患者，为食管癌、宫颈癌和鼻咽癌各1例，分别设置不同的计划参数进行容积旋转调强计划优化，通过多种评估指标比较各VMAT计划质量的差异，得出临床所需的MSC、MSS、SSF、Sm、MMS和MDR共6个治疗计划参数对VMAT治疗质量的影响。 结果 MSC、MSS和SSF的3个参数对VMAT治疗质量不产生影响，有影响的Sm、MMS和MDR参数中，随着Sm和MMS值的增大，VMAT计划的剂量分布逐渐变差，但控制点数、机器跳数和照射时间均逐渐减小；随着MDR值增大，VMAT治疗的剂量分布先逐渐变差后不变，控制点数和机器跳数均是先增大后不变，而照射时间是先减小后不变。 结论 Sm、MMS和MDR 3个参数对VMAT计划质量有较大影响，对不同的患者，设置合适的Sm、MMS和MDR值对提高计划质量非常重要。【Abstract】 Objective To investigate the impacts of parameter settings on the quality of plans for the volumetric modulated arc therapy (VMAT) with Monaco treatment planning system. Methods Three patients who underwent VMAT from January to May 2010 were selected. The planning optimizations were processed by setting different planning parameters, including MSC, MSS, SSF, Sm, MMS and MDR, respectively. Then the quality of each plan with a certain set of parameters was evaluated by various evaluation indexes. The differences of quality among different plans were analyzed by comparing these indexes. Results There was no influence on the quality of VMAT planning for the parameter MSC, MSS and SSF to be set with different values. However, the other three parameters, MSC, MSS and SSF , affected the quality of VMAT planning with different values. Along with the aggrandizement of Sm and MMS value, the dose distribution of VMAT plans gradually became bad, while the number of control points, machine monitor units and irradiation time were gradually reduced. And along with the aggrandizement of MDR value, the dose distribution of VMAT plans became bad gradually until a constant state was reached, and both the number of control points and machine monitor units increased at first and then kept constant, while irradiation time decreased at first and then kept constant. Conclusion The selections of parameter Sm, MMS and MDR impact the quality of VMAT planning greatly. It is very important to set the suitable value of Sm, MMS and MDR to get the best planning quality for patients with different complexity.
【摘要】 目的 研究千伏级锥形束CT（kV-cone beam CT，kV-CBCT）影像用于鼻咽癌调强放射治疗计划剂量计算的可行性和精确度。 方法 2010年7-9月7例鼻咽癌患者 ，获取每例患者的第1天放射治疗时的kV-CBCT影像。用CIRS062密度模体和患者自身特定区域亨氏单位值（hounsfield unit，HU）映射的两种方法重新刻度亨氏单位值-相对电子密度（HU-RED）表，分别进行剂量计算，并与在传统扇形束CT（FBCT）影像上的原放射治疗计划结果进行对比，包括辐射剂量分布、靶区和危及器官的剂量体积直方图（DVH）。 结果 kV-CBCT影像的治疗计划和原治疗计划在剂量分布和DVH上有较好的一致性。在剂量分布的比较上采用了γ分析（2%/2 mm标准的通过率），用基于模体的HU-RED表得到的治疗计划与原治疗计划对比，在经过等中心冠状面、矢状面和横断面的通过率分别为92.7%±3.5%、95.1%±3.1%和95.7%±3.4%，用基于患者的HU-RED表得到治疗计划与原治疗计划对比的通过率分别为94.8%±2.7%、96.6%±2.9%和97.4%±2.7%。DVH的统计数据表明，两种方法得到的kV-CBCT治疗计划和原治疗计划相比较，靶区和危及器官剂量偏差大多数在2%以内。有1例因在横断面发生了明显的旋转误差，导致在横断面的通过率很低，DVH统计数据较原计划偏差较大。 结论 kV-CBCT影像可以用来做辐射剂量计算，基于患者自身影像生成的HU-RED表的治疗计划较原治疗计划有更高的符合度。【Abstract】 Objective To evaluate the feasibility and accuracy of dose calculation based on cone beam CT (CBCT) data sets for intensity modulated radiation therapy (IMRT) planning of nasopharyngeal cancer (NPC). Methods Seven NPC patients were selected. The kV-CBCT images for each patient were acquired on the first treatment day. Two correction strategies were used to generate the cone beam HU value vs relative electron density calibration tables which named CIRS062 phantom based HU-RED tables and patient specific HU-RED tables respectively for dose calculation. The dose distributions and dose volume histograms (DVHs) of the target and organs at risk (OAR) based on kV-CBCT images were compared to the plans based on the fan-beam CT (FBCT). Results The DVH and dose distribution comparison between plans based on the FBCT and those on the CBCT showed good agreements. The γ analysis with a criterion of 2 mm/2% was used for the comparison of dose distribution at the coronal plane, sagital plane and cross plane through the isocenter point. The passing rate from phantom based HU-RED tables were (92.7±3.5) %, (95.1±3.1) %, and (95.7±3.4)%, respectively. The passing rates from the patient specific HU-RED tables were (94.8±2.7) %, (96.6±2.9) %, and (97.4±2.7) %, respectively. The dose difference between plans based on CBCT and those based on FBCT was within 2% at most patients by analyzing DVH based parameters. Only one patient who had significant rotation setup error resulted in the low passing rate and disagreement in DVH. Conclusion The CBCT images can be used to do dose calculation in IMRT planning of NPC. The differences between plans based on HU-RED tables generated by specific patient and the original plans are less than those between plans based on CIRS062 phantom based HU-RED tables and the original plans.
To investigate the impact of respiratory movement to determine the target volume on cone beam CT (CBCT) for lung tumor,we used CIRS dynamic thorax phantom (Model-CIRS008) to simulate the sinusoidal motion of lung tumor. With a constant amplitude, the ratio of the time of near-end-expiratory and near-end- inspiratory (E/I) changed when it was scanned with CBCT. We analyzed the contrast changes of target by extracting the CT value of each pixel on the center line of the target movement direction. The targets were contoured with region growing method and compared with the motion volume generated by the tumor trajectory method. The result showed that the contrast of near-end-expiratory increased and the contrast of near-end-inspiratory decreased with increasing E/I. The contoured volume generated by region growing method decreased with increasing E/I. When E/I=4, the amplitude A=1 cm, diameter of 1 cm and 3 cm target volumes were reduced by 48.2% and 22.7%.The study showed that CBCT was not suitable to be used to accurately determine the range of lung tumor movement. The internal target volume (ITV) may be underestimated in CBCT images.
Patient-specific volumetric modulated arc therapy (VMAT) quality assurance (QA) process is an important component of the implementation process of clinical radiotherapy. The tolerance limit and action limit of discrepancies between the calculated dose and the delivered radiation dose are the key parts of the VMAT QA processes as recognized by the AAPM TG-218 report, however, there is no unified standard for these two values among radiotherapy centers. In this study, based on the operational recommendations given in the AAPM TG-218 report, treatment site-specific tolerance limits and action limits of gamma pass rate in VMAT QA processes when using ArcCHECK for dose verification were established by statistical process control (SPC) methodology. The tolerance limit and action limit were calculated based on the first 25 in-control VMAT QA for each site. The individual control charts were drawn to continuously monitor the VMAT QA process with 287 VMAT plans and analyze the causes of VMAT QA out of control. The tolerance limits for brain, head and neck, abdomen and pelvic VMAT QA processes were 94.56%, 94.68%, 94.34%, and 92.97%, respectively, and the action limits were 93.82%, 92.54%, 93.23%, and 90.29%, respectively. Except for pelvic, the tolerance limits for the brain, head and neck, and abdomen were close to the universal tolerance limit of TG-218 (95%), and the action limits for all sites were higher than the universal action limit of TG-218 (90%). The out-of-control VMAT QAs were detected by the individual control chart, including one case of head and neck, two of the abdomen and two of the pelvic site. Four of them were affected by the setup error, and one was affected by the calibration of ArcCHECK. The results show that the SPC methodology can effectively monitor the IMRT/VMAT QA processes. Setting treatment site-specific tolerance limits is helpful to investigate the cause of out-of-control VMAT QA.