【摘要】 目的 分析重力因素对二维探测器阵列验证静态调强计划的影响，判断机架角度归为0°的测量方法是否安全可靠。 方法 在0°机架角和实际治疗机架角分别测量静态调强计划的剂量分布，以3 mm范围内偏差lt;3%(3% 3 mm)标准进行γ分析，获得相对于参考剂量分布的通过率，分析通过率变化规律。分析两种方法测量的等中心点绝对剂量的差异。 结果 通过率的变化呈随机分布，96.9%的照射野偏差lt;2.5%。所有计划的85.7%绝对剂量偏差lt;2%，最大偏差为4.75%。 结论 使用二维探测器阵列在0°角进行调强计划的日常验证是安全可靠的。【Abstract】 Objective To analyze impacts of gravity on the verification of IMRT plans with 2-Dimensional detector arrays and to evaluate the reliability of the measurements in vertical direction (gantry angle=0). Methods The dose distributions for each beam in IMRT plans were measured with 0 degree gantry angle and actual gantry angle respectively. The γ percentage pass rate (according to 3% 3 mm) for each beam under each angle condition was obtained by the comparison between the measured dose distribution and the calculated dose map from the treatment planning system which was treated as the reference distribution. Then the absolute dose at the isocenter for each plan was measured at each angle condition and was analyzed. Results The variations of γ percentage pass rates between the two types of measurements were randomly distributed, and the deviations for 96.9% beams were less than±2.5%. The differences between absolute doses for 85.7% beams were less than±2% and the biggest deviation was -4.75%. Conclusion Verification of IMRT plans for the radiotherapy quality assurance using 2-Dimensional detector arrays in 0 degree gantry angle is safe and reliable.
【摘要】 目的 调强放射治疗（IMRT）能较好的保护危及器官并给予肿瘤足够的致死剂量，基于多叶准直器（MLC）分步照射的IMRT技术对复杂病例需要更多子野。研究对直肠癌术后放射治疗使用不同子野数目的IMRT计划进行比对，选择合理的子野数。 方法 选取2010年4-8月入院的直肠癌术后患者10例，保持射野入射角度及优化目标参数相同，仅改变MLC子野数目，设计不同IMRT对每一患者治疗计划的靶区适形指数（CI）、均匀性指数、最大剂量、最小剂量、平均剂量，危及器官关注体积的受照剂量，机器跳数及治疗时间进行分析。 结果 所有治疗计划中靶区及危及器官的剂量学评估指标无统计学意义（Pgt;0.05），只有亚临床计划靶区（PTV）CI在15个子野的方案中（0.74±0.06）明显差于25个子野方案（0.82±0.03）、40个子野方案（0.81±0.06）及60个子野方案（0.84±0.03），有统计学意义（Plt;0.05）；治疗机器跳数（MU）随子野数目增多明显增大，15、20、40及60个子野方案所需MU分别为（458±56）、（559±62）、（614±74）、（622±82），有统计学意义（Plt;0.05），但40个子野方案与60个子野方案间无统计学意义。治疗时间明显随子野数增加而增大。 结论 直肠癌术后IMRT计划使用25个子野能满足临床剂量要求，同时能有效降低治疗时间，可作为临床应用参考值。【Abstract】 Objective The intensity modulated radiotherapy (IMRT) can deliver tumor enough doses and protect risk organs as much as possible at the same time. The MLC-based step and shoot IMRT(sIMRT) plan needs much more segment member to meet clinical aims. In this study, several sIMRT plans using different segment number for postoperative rectal cancer were compared to find out the most reasonable segment number setting. Methods Ten patients with rectal carcinoma underwent postoperative adjuvant radiotherapy for rectal cancer from April to August 2010 were selected. For each patient, the angle of field, the prescription expected and the physical parameters optimized were kept the same, while only the number of segments was changed in sIMRT plans. The dose volume histogram-based parameters [conformity index (CI) and homogeneous index (HI)] and other parameters concerned were compared and analyzed. Results The indexes of dosimetry associated with the targets and risk organs showed no significant statistical difference among the 4 sIMRT plans with different segment numbers. The index CI of PTV in the sIMRT plan with 15 segments (CI 0.74±0.06) was less than that in the sIMRT plan with 25 segments (CI 0.82±0.03), the sIMRT plan with 40 segments plan (CI 0.81±0.06), and the sIMRT plan with 60 segments (CI 0.84±0.03) (Plt;0.05). There were significant differences in MU among the sIMRT plans with 15 segments (average MU: 458±56) , with 25 segments (average MU: 559±62 ), and with 40 segments (average MU: 614±74)or with the 60 segments (average MU: 622±82 (Plt;0.05). The more segments meant more MU and more irradiation time. Conclusion The sIMRT plan for patients of rectal cancer to receive postoperative adjuvant radiotherapy may require at least 25 segments to balance the accepted dose results and efficient delivering.
ObjectiveTo compare the dosimetric differences among the double-arc volumetric-modulated arc therapy (VMAT), 7 field intensity-modulated radiotherapy (IMRT) and 3-dimensional conformal radiotherapy (3D-CRT) techniques in treatment planning for cervical cancer as adjuvant radiotherapy. MethodFifteen patients who underwent adjuvant chemotherapy for cervical cancer between March 1st and September 30th, 2013 were chosen to be our study subjects through random sampling. Under Pinnacle 9.2 planning system, the same CT image was designed through three different techniques:VMAT, IMRT and 3D-CRT. We then compared target zone fitness index, evenness index, D98%, D2%, D50% among those different techniques. Monitor unit (MU) and treatment time were also analyzed. ResultsThree techniques showed similar target dose coverage. The IMRT and VMAT plans achieved better target dose conformity, which reduced the V20 of the pelvic, the V50 of the rectum and bladder, as well as the V40/50 of the small intestine (P<0.05). The VMAT technique showed few dosimetric advantages over the IMRT technique. VMAT technique had the advantages of less MU (P>0.05) and shorter overall treatment time (P<0.01) compared with IMRT technique. ConclusionsThe IMRT and VMAT plans achieve similar dose distribution to the target, and are superior to the 3D-CRT plans, in adjuvant radiotherapy for cervical cancer. VMAT technique has the advantages of less MU and shorter overall treatment time.
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.
In this paper, a method for dose calculation with pencil beam kernels constructed by point kernel superposition was proposed to accelerate the dose calculation during intensity optimization iteration. With this method, the direct aperture optimization method can be integrated in the planning system based on point kernel convolution/superposition model. The dose calculation time was also reduced during the iteration. From the result of the phantom and clinical patient data test, it was concluded that this method could be used for the intensity optimization of iteration dose calculation as the satisfied precision due to the optimization result coherence obtained. By implementing the method in the planning system product based on point kernel convolution/superposition model, a lot of additional research and development works for the pencil beam dose calculation model as well as the product maintenance cost can be avoided.
Intensity-modulated radiotherapy planning for nasopharyngeal carcinoma is very complex. The quality of plan is often closely linked to the experience of the treatment planner. In this study, 10 nasopharyngeal carcinoma patients at different stages were enrolled. Based on the scripting of Pinnacle3 9.2 treatment planning system, the computer program was used to set the basic parameters and objective parameters of the plans. At last, the nasopharyngeal carcinoma intensity-modulated radiotherapy plans were completed automatically. Then, the automatical and manual intensity-modulated radiotherapy plans were statistically compared and clinically evaluated. The results showed that there were no significant differences between those two kinds of plans with respect to the dosimetry parameters of most targets and organs at risk. The automatical nasopharyngeal carcinoma intensity-modulated radiotherapy plans can meet the requirements of clinical radiotherapy, significantly reduce planning time, and avoid the influence of human factors such as lack of experience to the quality of plan.
Nasopharyngeal carcinoma (NPC) is rather common in Southeast Asia and Southern China. The standard treatment for NPC is intensity-modulated radiotherapy (IMRT). A large number of the NPC survivors benefit from the IMRT, while some suffer from the late toxicities which can be life-threatening or significantly erode the patients’ quality of life and functional status, especially in the locally advanced NPC. Nowadays the late radiotherapy-related toxicities have been the most important concern for the radiotherapists and patients, who look forward to the better long-term tumor local control and overall survival. Therefore, we carried out a review about the late radiotherapy-related toxicities of the vital organs at risk after IMRT for NPC patients.
Aiming at the disadvantages of traditional direct aperture optimization (DAO) method, such as slow convergence rate, prone to stagnation and weak global searching ability, a gradient-based direct aperture optimization (GDAO) is proposed. In this work, two different optimization methods are used to optimize the shapes and the weights of the apertures. Firstly, in order to improve the validity of the aperture shapes optimization of each search, the traditional simulated annealing (SA) algorithm is improved, the gradient is introduced to the algorithm. The shapes of the apertures are optimized by the gradient based SA method. At the same time, the constraints between the leaves of multileaf collimator (MLC) have been fully considered, the optimized aperture shapes are meeting the requirements of clinical radiation therapy. After that, the weights of the apertures are optimized by the limited-memory BFGS for bound-constrained (L-BFGS-B) algorithm, which is simple in calculation, fast in convergence rate, and suitable for solving large scale constrained optimization. Compared with the traditional SA algorithm, the time cost of this program decreased by 15.90%; the minimum dose for the planning target volume was improved by 0.29%, the highest dose for the planning target volume was reduced by 0.45%; the highest dose for the bladder and rectum, which are the organs at risk, decreased by 0.25% and 0.09%, respectively. The results of experiment show that the new algorithm can produce highly efficient treatment planning a short time and can be used in clinical practice.