多发脑转移瘤容积旋转调强立体定向放射外科计划对比

【摘要】目的:通过调整容积旋转调强（VMAT）计划等中心数目及其共面条件,研究其在多发性脑转移瘤治疗中的剂量学特征,为其临床应用提供指导。方法:收集2019年在湖北省肿瘤医院治疗的多发性脑转移瘤1例,分别设计1个等中心4个非共面弧、5个等中心5个共面弧以及5个等中心5个非共面弧计划,要求处方剂量（24 Gy/3次）覆盖95%靶体积。计划评价参数包括靶区适形度指数、梯度指数、脑部放射坏死指标（V12）和低剂量区（V5）体积覆盖率。结果:VMAT单等中心非共面弧计划对比多等中心计划有着更好的靶区适形度和更小的V12,且在小体积肿瘤的治疗中有着更好的剂量跌落。结论:VMAT单等中心非共面弧计划比多等中心共面或非共面计划更适合多发性脑转移瘤。     

Experimental verification of IMPT treatment plans in an anthropomorphic phantom in the presence of delivery uncertainties

Clinically relevant intensity modulated proton therapy (IMPT) treatment plans were measured in a newly developed anthropomorphic phantom (i) to assess plan accuracy in the presence of high heterogeneity and (ii) to measure plan robustness in the case of treatment uncertainties (range and spatial). The new phantom consists of five different tissue substitute materials simulating different tissue types and was cut into sagittal planes so as to facilitate the verification of co-planar proton fields. GafChromic films were positioned in the different planes of the phantom, and 3D-IMPT and distal edge tracking (DET) plans were delivered to a volume simulating a skull base chordoma. In addition, treatments planned on CTs of the phantom with HU units modified were delivered to simulate systematic range uncertainties (range-error treatments). Finally, plans were delivered with the phantom rotated to simulate spatial errors. Results show excellent agreement between the calculated and the measured dose distribution: >99% and 98% of points with a gamma value <1 (3%/3 mm) for the 3D-IMPT and the DET plan, respectively. For both range and spatial errors, the 3D-IMPT plan was more robust than the DET plan. Both plans were more robust to range than to the spatial uncertainties. Finally, for range error treatments, measured distributions were compared to a model for predicting delivery errors in the treatment planning system. Good agreement has been found between the model and the measurements for both types of IMPT plan.     

Dosimetric evaluation of partially overlapping intensity modulated beams using dynamic mini-multileaf collimation

The dose distribution resulting from partially overlapping intensity modulated beams (IMBs) assigned to different isocenters for the treatment of the same planning target volume (PTV) was evaluated. These partially overlapping IMBs are used in static intensity modulated radiation therapy (IMRT) treatments with the Novalis system using the mini-MultiLeaf Collimator (mini-MLC) in Dynamic MultiLeaf Collimation (DMLC) mode. The resultant dose distribution was verified dosimetrically for a cylindrical target defined in a homogeneous cubic phantom. The phantom positioning can introduce dose nonuniformities in the resultant dose distribution by nonperfect positioning of the isocenters in accordance with each other. The dose inhomogeneities are quantified mathematically by summation of the dose profiles of the used IMBs and experimentally by measurement of the resulting dose profiles with radiographic film and thermoluminescent detectors (TLD). The mathematical estimation of the resulting dose profile of the treatment with a perfect positioning of the isocenters showed a good agreement with the planned dose profile. The magnitude of the maximum dose inhomogeneities introduced by the simulated supplementary shifts between the isocenters decreases by -8.54% mm(-1) as the shift changes from -0.30 +/- 0.10 cm to +0.30 +/- 0.10 cm. The TLD measurements showed a similar variation of the magnitude of the maximum dose inhomogeneities: -8.77% mm(-1). The amount of dose variation was underestimated with the radiographic film measurements, which showed a variation of -7.17% mm(-1). The film measurements demonstrated that the magnitude of the introduced maximum dose inhomogeneities did not alter significantly throughout the PTV. The approach of using partially overlapping IMBs assigned to different isocenters to enlarge the treatment region introduces smaller dose inhomogeneities in the resultant dose distribution than when abutting treatment fields are used. The resultant dose distribution of this treatment technique is less sensitive to positioning errors of the used treatment isocenters.     

Planning evaluation of radiotherapy for complex lung cancer cases using helical tomotherapy

Lung cancer treatment is one of the most challenging fields in radiotherapy. The aim of the present study was to investigate what role helical tomotherapy (HT), a novel approach to the delivery of highly conformal dose distributions using intensity-modulated radiation fan beams, can play in difficult cases with large target volumes typical for many of these patients. Tomotherapy plans were developed for 15 patients with stage III inoperable non-small-cell lung cancer. While not necessarily clinically indicated, elective nodal irradiation was included for all cases to create the most challenging scenarios with large target volumes. A 2 cm margin was used around the gross tumour volume (GTV) to generate primary planning target volume (PTV2) and 1 cm margin around elective nodes for secondary planning target volume (PTV1) resulting in PTV1 volumes larger than 1000 cm3 in 13 of the 15 patients. Tomotherapy plans were created using an inverse treatment planning system (TomoTherapy Inc.) based on superposition/convolution dose calculation for a fan beam thickness of 25 mm and a pitch factor between 0.3 and 0.8. For comparison, plans were created using an intensity-modulated radiation therapy (IMRT) approach planned on a commercial treatment planning system (TheraplanPlus, Nucletron). Tomotherapy delivery times for the large target volumes were estimated to be between 4 and 19 min. Using a prescribed dose of 60 Gy to PTV2 and 46 Gy to PTV1, the mean lung dose was 23.8+/-4.6 Gy. A 'dose quality factor' was introduced to correlate the plan outcome with patient specific parameters. A good correlation was found between the quality of the HT plans and the IMRT plans with HT being slightly better in most cases. The overlap between lung and PTV was found to be a good indicator of plan quality for HT. The mean lung dose was found to increase by approximately 0.9 Gy per percent overlap volume. Helical tomotherapy planning resulted in highly conformal dose distributions. It allowed easy achievement of two different dose levels in the target simultaneously. As the overlap between PTV and lung volume is a major predictor of mean lung dose, future work will be directed to control of margins. Work is underway to investigate the possibility of breath-hold techniques for tomotherapy delivery to facilitate this aim.     

Dose-volume considerations with linear programming optimization.

A method of incorporating dose-volume considerations within the framework of conventional linear programming is presented. This method is suitable for the optimization of beam weights and angles using a conformal treatment philosophy (i.e., tailoring the high-dose region to the target volume only). Dose-volume constraints are introduced using the concept that volumes of normal tissue nearer the target volume will be allowed higher dose constraints than volumes of normal tissue distal to the target volume. Each involved normal structure is divided into high-dose and low-dose volumes. These two volume partitions are represented by constraint points with either high-dose or low-dose constraints, respectively. Optimized treatment plans for three clinical sites demonstrate that this technique meets or surpasses the original dose-volume constraints for a conformal-type treatment plan using straightforward linear programming in a time frame that is comparable to other linear programming problems.     

Estimation of the delivered patient dose in lung IMRT treatment based on deformable registration of 4D-CT data and Monte Carlo simulations

The purpose of this study is to accurately estimate the difference between the planned and the delivered dose due to respiratory motion and free breathing helical CT artefacts for lung IMRT treatments, and to estimate the impact of this difference on clinical outcome. Six patients with representative tumour motion, size and position were selected for this retrospective study. For each patient, we had acquired both a free breathing helical CT and a ten-phase 4D-CT scan. A commercial treatment planning system was used to create four IMRT plans for each patient. The first two plans were based on the GTV as contoured on the free breathing helical CT set, with a GTV to PTV expansion of 1.5 cm and 2.0 cm, respectively. The third plan was based on the ITV, a composite volume formed by the union of the CTV volumes contoured on free breathing helical CT, end-of-inhale (EOI) and end-of-exhale (EOE) 4D-CT. The fourth plan was based on GTV contoured on the EOE 4D-CT. The prescribed dose was 60 Gy for all four plans. Fluence maps and beam setup parameters of the IMRT plans were used by the Monte Carlo dose calculation engine MCSIM for absolute dose calculation on both the free breathing CT and 4D-CT data. CT deformable registration between the breathing phases was performed to estimate the motion trajectory for both the tumour and healthy tissue. Then, a composite dose distribution over the whole breathing cycle was calculated as a final estimate of the delivered dose. EUD values were computed on the basis of the composite dose for all four plans. For the patient with the largest motion effect, the difference in the EUD of CTV between the planed and the delivered doses was 33, 11, 1 and 0 Gy for the first, second, third and fourth plan, respectively. The number of breathing phases required for accurate dose prediction was also investigated. With the advent of 4D-CT, deformable registration and Monte Carlo simulations, it is feasible to perform an accurate calculation of the delivered dose, and compare our delivered dose with doses estimated using prior techniques.     

自动IMRT计划在宫颈癌术后放疗中的可行性

目的:通过比较自动IMRT计划与人工IMRT计划的剂量学差异,探讨自动计划在宫颈癌术后IMRT计划设计中的可行性。 方法:使用飞利浦Pinnacle3 9.10计划系统的自动IMRT和人工IMRT方法分别对25例宫颈癌术后患者进行计划设计,比较2种计划得到的靶区和危及器官的剂量学参数、机器跳数、调试次数及计划设计时间。结果:自动和人工IMRT计划靶区的Dmean、D95、CI及HI等参数均无明显差异（P>0.05）;自动IMRT计划得到的危及器官剂量学参数均优于人工IMRT计划,其中膀胱V40减少2.5%（P<0.05）,直肠V40减少0.9%（P<0.05）,骨V35减少2.8%（P<0.05）,小肠V30减少4.2%（P<0.05）,左侧股骨头V30减少5.2%（P<0.05）以及右侧股骨头V30减少5.5%（P<0.05）;并且自动计划明显减少了计划调试次数,将人工IMRT计划的平均调试次数由3次减少到平均2次,计划设计时间由人工IMRT的69.5 min减少到42.7 min;但自动计划的平均跳数（1 042 MU）高于人工计划（931 MU）。结论:基于Pinnacle3的自动IMRT计划质量可以达到人工IMRT计划水平的同时,明显提高了计划设计效率,在宫颈癌术后的IMRT计划设计中具有可行性。     

Point dose calculations using an analytical pencil beam kernel for IMRT plan checking

A method to verify the monitor units for a treatment plan is to calculate point doses, possibly at the isocentre, by using a simple calculation method. This verification is recommended to find mistakes in the treatment plan. Treatment plans for intensity modulated radiation therapy are no exception. The method should employ a simple physical model and a dose calculation algorithm, which is different from the method used for the treatment plan. Our approach uses a convolution algorithm and an analytical pencil beam kernel with eight parameters. The model is intuitive and simple. At the same time, the method is so general that it can be applied to both step-and-shoot and sliding-window techniques. The results of applications to actual treatment plans show that the calculated total isocentre doses are accurate within +/-2% of planned doses for six-field prostate plans when calculation points are in a uniform dose region. Head and neck cases show a slightly larger difference than prostate cases. When calculation points are located in a region of high dose gradient, however, the difference could be greater than 5%.     

胃癌调强放疗中多叶光栅3种状态的剂量学比较

目的:通过比较胃癌调强放疗中多叶光栅（MLC）3种不同状态下放疗计划的剂量学差异,为临床放疗方案的选择提供参考依据。 方法:选取10例胃癌患者分别制定9野的锁野调强、分野调强和旋转小机头分野调强的治疗计划,比较机器跳数,靶区适形度、均匀性、Dmax、Dmean、V45,以及body、肝脏、小肠、脊髓和肾脏V5、V10、V20、V30、V40、V45、Dmax、Dmean等参数的剂量学差异。 结果:3种计划均可满足临床需求。锁野计划相比分野和旋转小机头分野调强计划在body的V5、V10、V20、V30均显著降低且差异具有统计学意义,同时对于肾脏、肝脏和小肠在某些低剂量区均有一定的降低且有统计学差异。对于body（计划靶区）的Dmax参数,分野计划稍微低于锁野和旋转小机头分野调强计划且差异具有统计学意义。 结论:锁野计划可以更好地保护危及器官,同时减少低剂量区。     

Simultaneous optimization of sequential IMRT plans

Radiotherapy often comprises two phases, in which irradiation of a volume at risk for microscopic disease is followed by a sequential dose escalation to a smaller volume either at a higher risk for microscopic disease or containing only gross disease. This technique is difficult to implement with intensity modulated radiotherapy, as the tolerance doses of critical structures must be respected over the sum of the two plans. Techniques that include an integrated boost have been proposed to address this problem. However, clinical experience with such techniques is limited, and many clinicians are uncomfortable prescribing nonconventional fractionation schemes. To solve this problem, we developed an optimization technique that simultaneously generates sequential initial and boost IMRT plans. We have developed an optimization tool that uses a commercial treatment planning system (TPS) and a high level programming language for technical computing. The tool uses the TPS to calculate the dose deposition coefficients (DDCs) for optimization. The DDCs were imported into external software and the treatment ports duplicated to create the boost plan. The initial, boost, and tolerance doses were specified and used to construct cost functions. The initial and boost plans were optimized simultaneously using a gradient search technique. Following optimization, the fluence maps were exported to the TPS for dose calculation. Seven patients treated using sequential techniques were selected from our clinical database. The initial and boost plans used to treat these patients were developed independently of each other by dividing the tolerance doses proportionally between the initial and boost plans and then iteratively optimizing the plans until a summation that met the treatment goals was obtained. We used the simultaneous optimization technique to generate plans that met the original planning goals. The coverage of the initial and boost target volumes in the simultaneously optimized plans was equivalent to the independently optimized plans actually used for treatment. Tolerance doses of the critical structures were respected for the plan sum; however, the dose to critical structures for the individual initial and boost plans was different between the simultaneously optimized and the independently optimized plans. In conclusion, we have demonstrated a method for optimization of initial and boost plans that treat volume reductions using the same dose per fraction. The method is efficient, as it avoids the iterative approach necessitated by currently available TPSs, and is generalizable to more than two treatment phases. Comparison with clinical plans developed independently suggests that current manual techniques for planning sequential treatments may be suboptimal.     

基于预测剂量引导的宫颈癌自动计划研究

目的:使用机器学习方法建立宫颈癌计划剂量预测回归模型，并将预测剂量引导生成Monaco 计划系统（TPS）可调用 的优化模板文件，实现宫颈癌的自动计划设计。方法:对50例宫颈癌术后调强治疗计划中的危及器官采集基于重叠体积直 方图的几何特征值和基于剂量直方图的剂量目标值，建模后将模型预测剂量结果自动生成Monaco TPS模板文件，进而由TPS 调用优化。使用该方法对另外10例未参与模型训练的测试病例进行自动计划设计，并和人工设计的计划进行对比分析。 结果:自动计划比手动计划的平均设计时间减少了40 min（P<0.05），且平均调优次数降低了3次（P<0.05），剂量学指标和计 划执行效率上两者无明显差异（P>0.05）。结论:基于预测剂量引导的宫颈癌自动计划可以达到临床要求，并且提高了计划 设计效率。     

Stereotactic arc therapy for small elongated tumors using cones and collimator jaws; dosimetric and planning aspects

Stereotactic arc treatment of small intracranial tumors is usually performed with arcs collimated by circular cones, resulting in treatment volumes which are basically spherical. For nonspherical lesions this results in a suboptimal dose distribution. Multiple isocenters may improve the dose conformity for these lesions, at the cost of large overdosages in the target volume. To achieve improved dose conformity as well as dose homogeneity, the linac jaws (with a minimum distance of 1.0 cm to the central beam axis) can routinely be used to block part of the circular beams. The purpose of this study was to investigate the feasibility of blocking cones with diameters as small as 1.0 cm and a minimum distance between the jaw and the central beam axis of 0.3 cm. First, the reproducibility in jaw positioning and resulting dose delivery on the treatment unit were assessed. Second, the accuracy of the TPS dose calculation for these small fields was established. Finally, clinically applied treatment plans using nonblocked cones were compared with plans using the partially blocked cones for several treatment sites. The reproducibility in dose delivery on our Varian Clinac 2300 C/D machines on the central beam axis is 0.8% (1 SD). The accuracy of the treatment planning system dose calculation algorithm is critically dependent on the used fits for the penumbra and the phantom scatter. The average deviation of calculated from measured dose on the central beam axis is -1.0%+/-1.4% (1 SD), which is clinically acceptable. Partial cone blocking results in improved dose distributions for elongated tumors, such as vestibular schwannoma and uveal melanoma. Multiple isocenters may be avoided. The technique is easy to implement and requires no additional workload.     

Impact of the accuracy of automatic tumour functional volume delineation on radiotherapy treatment planning

Over the past few years several automatic and semi-automatic PET segmentation methods for target volume definition in radiotherapy have been proposed. The objective of this study is to compare different methods in terms of dosimetry. For such a comparison, a gold standard is needed. For this purpose, realistic GATE-simulated PET images were used. Three lung cases and three H&N cases were designed with various shapes, contrasts and heterogeneities. Four different segmentation approaches were compared: fixed and adaptive thresholds, a fuzzy C-mean and the fuzzy locally adaptive Bayesian method. For each of these target volumes, an IMRT treatment plan was defined. The different algorithms and resulting plans were compared in terms of segmentation errors and ground-truth volume coverage using different metrics (V(95), D(95), homogeneity index and conformity index). The major differences between the threshold-based methods and automatic methods occurred in the most heterogeneous cases. Within the two groups, the major differences occurred for low contrast cases. For homogeneous cases, equivalent ground-truth volume coverage was observed for all methods but for more heterogeneous cases, significantly lower coverage was observed for threshold-based methods. Our study demonstrates that significant dosimetry errors can be avoided by using more advanced image-segmentation methods.     

胰腺癌伽玛刀和加速器治疗计划剂量学比较

目的:比较分析OUR-QGD型γ刀和两种加速器治疗技术胰腺癌治疗计划的剂量学数据,为临床选择放疗技术提供参考。方法:选取20例胰腺癌病例,每例设计靶中靶(Target in Target,TIT)、调强(IMRT)和γ刀三种治疗计划。处方剂量为50 Gy包绕95%的PTV。计算比较三种计划的PTV靶区适形指数和均匀性指数,通过DVH计算靶区剂量和周围要害器官剂量。结果:IMRT计划的PTV靶区适形度最好,TIT计划次之,γ刀计划最差,均匀性指数γ刀计划也要劣于IMRT和TIT计划,但γ刀计划周围正常组织的剂量相对较低,而靶区剂量比TIT和IMRT计划要高得多。结论:根据物理剂量学数据,γ刀治疗胰腺癌可显著提高靶区剂量,同时很好地保护周围正常组织;TIT和IMRT也是治疗胰腺癌的有效方法。     

A comparative dosimetric study on tangential photon beams,intensity-modulated radiation therapy (IMRT) and modulated electron radiotherapy (MERT) for breast cancer treatment

Recently, energy- and intensity-modulated electron radiotherapy (MERT) has garnered a growing interest for the treatment of superficial targets. In this work. we carried out a comparative dosimetry study to evaluate MERT, photon beam intensity-modulated radiation therapy (IMRT) and conventional tangential photon beams for the treatment of breast cancer. A Monte Carlo based treatment planning system has been investigated, which consists of a set of software tools to perform accurate dose calculation, treatment optimization, leaf sequencing and plan analysis. We have compared breast treatment plans generated using this home-grown treatment optimization and dose calculation software forthese treatment techniques. The MERT plans were planned with up to two gantry angles and four nominal energies (6, 9, 12 and 16 MeV). The tangential photon treatment plans were planned with 6 MV wedged photon beams. The IMRT plans were planned using both multiple-gantry 6 MV photon beams or two 6 MV tangential beams. Our results show that tangential IMRT can reduce the dose to the lung, heart and contralateral breast compared to conventional tangential wedged beams (up to 50% reduction in high dose volume or 5 Gy in the maximum dose). MERT can reduce the maximum dose to the lung by up to 20 Gy and to the heart by up to 35 Gy compared to conventional tangential wedged beams. Multiple beam angle IMRT can significantly reduce the maximum dose to the lung and heart (up to 20 Gy) but it induces low and medium doses to a large volume of normal tissues including lung, heart and contralateral breast. It is concluded that MERT has superior capabilities to achieve dose conformity both laterally and in the depth direction, which will be well suited for treating superficial targets such as breast cancer.     

A feasibility study of using conventional jaws to deliver IMRT plans in the treatment of prostate cancer

The aim of this study is to investigate the feasibility of using conventional jaws to deliver inverse planned intensity-modulated radiotherapy (IMRT) plans for patients with prostate cancer. For ten patients, each had one three-dimensional conformal plan (3D plan) and seven inverse IMRT plans using direct aperture optimization. For IMRT plans using conventional jaws (JO plans), the number of apertures per beam angle was set from two to seven while three apertures per beam angle were set for the multi-leaf collimator (MLC) plans. To evaluate each planning method, we compared average dose volume histograms (DVH), the conformal index (COIN), total number of segments and total number of monitor units. Among the JO plans with the number of apertures per beam angle varying from two to seven, no difference was observed in the average DVHs, and the plan conformal index became saturated after four apertures per beam angle. Subsequently, JO plans with four apertures per beam angle (JO-4A) were compared with 3D and MLC plans. Based on the average DVHs, no difference was found among 3D, JO-4A and MLC plans with regard to the planning target volume and rectum, but the DVHs for the bladder and penile bulb were significantly better with inverse IMRT plans than those with 3D plans. When compared with the plan conformity, the average COIN values for 3D, JO-4A and MLC plans were 0.61 +/- 0.07, 0.73 +/- 0.05 and 0.83 +/- 0.05, respectively. In conclusion, inverse IMRT plans using conventional jaws are clinically feasible, achieving better plan quality than 3D-CRT plans.