6MV与15MVX线在肺癌调强放疗中的剂量学比较

目的：分析、比较用于治疗非小细胞肺癌（NSCLC）的6MV和15MVX线调强放疗（IMRT）计划。方法：随机选择10例NSCLC患者，采用6MV和15MVX射线对每例NSCLC进行IMRT的计划设计，并用ADAC Pinnacle3计划系统提供的卷积／迭加（convolution／superposition）算法对两种能量条件下相同布野方案的IMRT计划进行剂量计算，比较靶区及危及器官的剂量分布、DVH等指标。结果：6MV与15MV放疗计划的等剂量线和DVH相近，6MV计划的靶区剂量均匀性优于15MV计划．而15MV计划高剂量覆盖靶区的程度略优于6MV计划，食管、心脏、脊髓等危及器官的受量基本相同。结论：对于NSCLC，剂量计算应采用能够精确修正组织不均匀性影响的卷积／迭加等算法，调强放疗时应首选6MV X射线。     

蒙卡剂量算法(XVMC)在胸部肿瘤调强放射治疗计划设计中的临床价值

目的:比较蒙卡剂量算法(Monte Carlo)和笔形束剂量算法(Finite Site Pencil Beam)在胸部肿瘤调强放射治疗计划设计中对计划结果的影响。方法:在MONACO(CMS)治疗计划系统中,分别使用其内嵌的光子蒙卡(XVMC)剂量算法和笔形束剂量算法,对5例胸部肿瘤病例比较其靶区和危及器官的剂量。结果:蒙卡方法得到的结果和笔形束算法的结果相差较大。结论:对于组织密度差异较大的胸部肿瘤病例,特别是使用调强放射治疗技术时,用XVMC剂量算法评估放射治疗计划更准确。     

不同能量X线胸段食管癌调强放疗计划的剂量学研究

目的:研究不同能量X射线治疗胸段食管癌调强放疗(IMRT)计划的剂量学差异。方法:选择l2例胸段食管癌患者,在ADAC Pinnacle3三维治疗计划系统(TPS)中分别采用6 MV、10 MV和15 MV X线给每位患者设计三个调强放疗计划,在规定计划靶区(PTV)至少达到95%处方剂量的前提下,根据剂量体积直方图(DVH)比较三种计划的靶区剂量分布及脊髓、肺、心脏等正常组织受照射剂量的差异。结果:三种计划中靶区的最大剂量、最小剂量、平均剂量及靶区适形度指数、均匀性指数均无明显差异,但15 MV计划高剂量覆盖程度大于6 MV和10 MV计划,脊髓、双肺及心脏受照剂量都在可耐受的范围内,差异也无统计学意义(P>0.05)。结论:6 MV、10 MV、15 MV X射线都能满足胸段食管癌临床调强放疗需求。     

PBC算法与AAA算法在肺癌调强放疗中的剂量学比较

目的:分析、比较笔形束卷积算法(PBC)和各向异性解析算法(AAA)在非小细胞肺癌(NSCLC)调强放疗计划设计中的剂量学差异。方法:随机选择7例NSCLC患者,采用Eclipse version 7.3.10计划系统提供的PBC算法和AAA算法对每例NSCLC进行IMRT的计划设计,比较靶区及危及器官的剂量分布、DVH等指标。结果:两种算法获得治疗计划的靶区剂量均匀性和适形度均无明显差别,食管、心脏、脊髓等危及器官的受量也基本相同。结论:对于NSCLC,剂量计算应采用受呼吸时相影响更小的AAA算法。     

Elekta立体定位体架对靶区吸收剂量的影响

目的:研究立体定向放射治疗中Elekta立体定位体架(ESBF)对靶区吸收剂量的影响。方法:将小水箱放入ESBF内做CT扫描,图像传至PrecisePlan计划系统三维重建数字化体模。计算6MV、15MVX线存在和不存在立体定位体架时靶区吸收剂量的差别,并与水箱中的测量值进行比较。结果:TPS计算结果显示对于两侧野,当等中心坐标Y150mm时吸收剂量的差别为5.4%～5.7%;当Y150mm时为9.0%～9.3%。利用后野照射时靶点吸收剂量差别为2.2%～2.4%,后斜野为2.6%～2.9%。两档能量X线计算值无明显差异。水箱测量结果显示,当两侧野Y150mm时剂量差别没有明显变大;两后斜野215°野的差别大于145°野;且15MV的差别均小于6MV。结论:射线经过Elekta立体定位体架时由于衰减会对靶区的吸收剂量造成影响。PrecisePlan剂量计算算法能够根据坐标值对体架影响做出修正,但与测量值存在偏差,实际照射时需要根据测量结果进行修正。     

肺癌肺内肿瘤不同能量三维适形放疗的比较

目的:研究6 MV和15 MV X射线对肺癌肺内肿瘤三维适形放疗肿瘤组织、危及器官及正常组织剂量的影响。方法:选择11例肺癌肺内肿瘤患者,对每例患者分别采用6 MV和15 MV X射线进行三维适形放疗计划设计,同一患者的两个计划均使用相同的布野方案和剂量体积约束。比较两组计划的计划靶区、危及器官及正常组织的剂量分布。结果:6MV和15 MV两种能量X线三维适形放疗计划计划靶区的剂量分布、均匀性、适形度的差异无显著性意义(P>0.05),危及器官脊髓、食管、心脏,正常组织肺的剂量分布无显著性意义(P>0.05)。结论:肺癌肺内肿瘤6 MV、15 MV三维适形放疗剂量分布无明显差异,三维适形放疗能量用6 MV,不主张用15 MV。     

CollapsedCone光子束剂量计算方法研究

剂量计算是放射治疗计划系统的核心,与常用的笔形束剂量计算方法相比,collapsed cone卷积/叠加剂量计算方法具有更高的计算精度,为此我们研究了collapsed cone卷积/叠加剂量计算方法及加速算法,开发了一套基于collapsed cone卷积/叠加剂量计算方法的光子束放射治疗计划系统,并运用蒙特卡罗方法...     

基于共轭梯度法的调强算法的实现

目的：研究调强放射治疗（IMRT）的具体实现与约束条件的表述。材料与方法：在每个射野方向上，利用真实的笔形束剂量分布数据，并加入机头散射、组织补偿等因素，计算得到单位剂量笔形束在特定位置形成的剂量分布。在优化过程中，以此笔形束剂量分布为依据进行剂量计算。用Visual C＋＋6．0编写基于共轭梯度法的IMRT的算法实现，并考虑多种约束条件。最后求解优化的射野笔形束权重，并加以分析。结果：在TPS软件中集成IMRT功能，并进行模拟病例的优化，获得了高适形度的剂量分布，满足DVH约束。结论：结合特定的约束条件，共轭梯度法能有效的优化射野笔形束权重，并且有较快的计算速度，有广阔的应用前景。     

6 MV和10 MVX线宫颈癌经典适形照射治疗计划比较分析

目的 研究不同身高、体质量宫颈癌术后患者不同能量6 MV和10 MVX线经典适形四野照射治疗计划的剂量分布,指导临床照射能量的选择.方法 选取21例患者,按体质指数(BMI)分为肥胖组和非肥胖组并进行6 MV和10 MV X线箱式照射治疗的计划设计,统计分析治疗计划相关的剂量学参数.结果 采用10 MV X线的治疗计划:①2组均能降低计划靶区(PTV)的最大剂量(Dmax)、最小剂量(Dmax)、提高适形指数(CI)和不均匀性指数(HI);不能降低平均剂量(Dmax);非肥胖组中位剂量(D50)有变化;肥胖组患者更能有效地降低Dmax和提高HI.②能降低靶区周围危及器官(OAR)的剂量.③更能有效地减少患者中低受量体积.④更能有效地减少机器跳数(MU).结论 对于肥胖宫颈癌患者,采用10 MV X线治疗计划具有优势.     

原发性肝癌靶体积对立体定向放射治疗计划设计的影响分析

目的:分析原发性肝癌靶体积对γ射线立体定向放射治疗计划设计的影响。方法:2008.05～2010.03采用γ射线立体定向放射治疗139例原发性肝癌患者,共146个靶区,以计划靶区体积(Vptv)大小分成三组:A组41个,Vptv<150cm3;B组77个,150 cm3≤Vptv<300 cm3;C组28个,Vptv≥300 cm3。比较分析各组立体定向放射治疗计划。结果:146个靶区均50%～90%等剂量线覆盖。靶体积越小,覆盖靶区的等剂量线越高;A组等中心数最少,C组最多,B组次之;A组剂量均匀性最好,B、C无明显差别。结论:靶体积大小影响原发性肝癌立体定向放射治疗计划设计,靶体积越小,所需的等中心数更少,靶区均匀性越好,覆盖靶区的等剂量线越高。     

The influence of lateral electronic disequilibrium on the radiation treatment planning for lung cancer irradiation

Using higher energy photons can obtain better target dose uniformity and skin sparing for treating deep lesions, but the effect of lacking lateral scattering in the low-density lung may degrade the target coverage. To analyze the influence of lateral electronic disequilibrium on the radiation treatment planning for lung cancer, three dimension conformal treatment (3D-CRT) plans of using 6 MV and 18 MV X-ray respectively for a lung cancer case have been worked out by using pencil beam algorithm and collapsed cone algorithm provided by Helax-TMS treatment planning system for the same radiation field arrangement for both energies. Dose volume histogram (DVH) in target and organs at risk (OARs) are used for comparison of different plans. The study shows that using pencil beam algorithm, the target DVH are similar for 6 MV and 18 MV plan. However, using collapsed cone algorithm that can make account of lateral electron scattering, the target is underdosed. The change is even more pronounced for 18 MV plan. The doses for lung and spinal cord are similar for these two energies and two algorithms. Therefore, for lung cancer, dose calculation algorithm should have the ability of handling accurately the effect of the tissue density heterogeneity. It is better to use the lower-energy photons (6 MV) than to use the higher-energy photons (18 MV).     

Experimental verification of convolution/superposition photon dose calculations for radiotherapy treatment planning

This work describes an experimental verification of the two-photon dose calculation engines available on the Helax-TMS (version 6.1) commercial radiotherapy treatment planning system. The performance of the pencil beam convolution and the collapsed cone superposition algorithms was examined for 4, 6, 15 MV beams, under a range of clinically relevant irradiation geometries. Comparisons against measurements were carried out in terms of absolute dose, thus assessment of the accuracy of monitor unit (MU) calculations was also carried out. Results show that both algorithms agree with measurement to acceptable tolerance levels in most cases in homogeneous water-equivalent media irradiated under full scatter conditions. The collapsed cone algorithm slightly overestimates the penumbra width and this is mainly due to discretization effects of the fluence matrix. The accuracy of this algorithm strongly depends on the resolution of the patient density matrix. It is recommended that the density matrix voxel size used for dose calculations is less than 5 x 5 x 5 mm3. The dose in media irradiated under missing tissue geometry, or in the presence of low or high-density heterogeneities, is modelled best with the collapsed cone algorithm. This is of particular clinical interest in treatment planning of the breast and of the thorax. For these treatment sites, a retrospective study of treatment plans indicated in certain cases significant overestimation of the dose to the planning target volume when using the pencil beam convolution model.     

Collapsed cone convolution and analytical anisotropic algorithm dose calculations compared to VMC++ Monte Carlo simulations in clinical cases

The purpose of this work was to study and quantify the differences in dose distributions computed with some of the newest dose calculation algorithms available in commercial planning systems. The study was done for clinical cases originally calculated with pencil beam convolution (PBC) where large density inhomogeneities were present. Three other dose algorithms were used: a pencil beam like algorithm, the anisotropic analytic algorithm (AAA), a convolution superposition algorithm, collapsed cone convolution (CCC), and a Monte Carlo program, voxel Monte Carlo (VMC++). The dose calculation algorithms were compared under static field irradiations at 6 MV and 15 MV using multileaf collimators and hard wedges where necessary. Five clinical cases were studied: three lung and two breast cases. We found that, in terms of accuracy, the CCC algorithm performed better overall than AAA compared to VMC++, but AAA remains an attractive option for routine use in the clinic due to its short computation times. Dose differences between the different algorithms and VMC++ for the median value of the planning target volume (PTV) were typically 0.4% (range: 0.0 to 1.4%) in the lung and -1.3% (range: -2.1 to -0.6%) in the breast for the few cases we analysed. As expected, PTV coverage and dose homogeneity turned out to be more critical in the lung than in the breast cases with respect to the accuracy of the dose calculation. This was observed in the dose volume histograms obtained from the Monte Carlo simulations.     

各向异性分析算法和光子笔形束卷积算法在食管癌放射治疗中的剂量学比较

目的比较食管癌调强放射治疗各向异性分析算法（AAA）与光子笔形束卷积（PBC）算法的剂量学差异。方法选取9例食管癌患者,其中男性6例,女性3例;年龄54-68岁,平均年龄61岁。用瓦里安Eclipse 8.6治疗计划系统设计5野均分逆向调强计划,分别用AAA和PBC算法模型计算并利用COMPASS进行剂量验证。利用剂量体积直方图比较靶区、肺、心脏和脊髓照射剂量和体积。数据应用SPSS15.0进行配对t检验分析。结果大体肿瘤区（GTV）的均匀性指数（HI）、适合度指数（CI）、Dmean及计划靶区（PTV）的HI,AAA结果均优于PBC算法,差异均有统计学意义（P〈0.05）。AAA双肺各指标差值为-0.02%～-1.87%,即低估了肺2%以内的受量。PBC算法双肺各指标差值为-3.95%～1.05%,低剂量区（V5～15）低估了肺4%以内的受量,高剂量区（V20～30）则稍高估。对于脊髓,AAA和PBC算法分别高估了1.57%、4.49%。两种算法都低估了心脏的受量,但AAA相对准确。结论食管癌放射治疗中采用AAA优于PBC算法。     

Dose perturbation in the presence of metallic implants: treatment planning system versus Monte Carlo simulations

An increasing number of patients receiving radiation therapy have metallic implants such as hip prostheses. Therefore, beams are normally set up to avoid irradiation through the implant; however, this cannot always be accomplished. In such situations, knowledge of the accuracy of the used treatment planning system (TPS) is required. Two algorithms, the pencil beam (PB) and the collapsed cone (CC), are implemented in the studied TPS. Comparisons are made with Monte Carlo simulations for 6 and 18 MV. The studied materials are steel, CoCrMo, Orthinox, TiAlV and Ti. Monte Carlo simulated depth dose curves and dose profiles are compared to CC and PB calculated data. The CC algorithm shows overall a better agreement with Monte Carlo than the PB algorithm. Thus, it is recommended to use the CC algorithm to get the most accurate dose calculation both for the planning target volume and for tissues adjacent to the implants when beams are set up to pass through implants.     

Comparison of IMRT optimization based on a pencil beam and a superposition algorithm

To investigate the role of sophisticated dose calculation methods for treatment planning, we compared conventional pencil beam optimized 6 and 15 MV intensity-modulated treatment plans with optimizations based on the superposition technique. Five lung and five head and neck IMRT cases with spatial resolutions of bixels and dose voxels usually employed in clinical practice were considered for tumor volumes between 15 and 500 cm3. We investigated the systematic error of the pencil beam algorithm and the pencil beam induced error to the optimal solution of bixel weights. For the lung cases, the pencil beam overestimated the mean dose deposited inside the planning target volume (PTV) by about 8%, for small lung tumors even up to 20.6%. In the head and neck cases only a slight overestimation in mean PTV dose of 1.5% was observed. The optimization with the superposition method substantially improved the dose coverage of the considered radiation targets. Additionally, for the head and neck cases, the brainstem was significantly spared by about 4% mean PTV dose through the use of the superposition technique. Our studies showed that, in target regions with intricate tissue inhomogeneities, superposition or Monte Carlo techniques have to be used for the optimization and the final dose calculation of intensity-modulated treatment plans.     

Accuracy of patient dose calculation for lung IMRT: A comparison of Monte Carlo, convolution/superposition, and pencil beam computations

The accuracy of dose computation within the lungs depends strongly on the performance of the calculation algorithm in regions of electronic disequilibrium that arise near tissue inhomogeneities with large density variations. There is a lack of data evaluating the performance of highly developed analytical dose calculation algorithms compared to Monte Carlo computations in a clinical setting. We compared full Monte Carlo calculations (performed by our Monte Carlo dose engine MCDE) with two different commercial convolution/superposition (CS) implementations (Pinnacle-CS and Helax-TMS's collapsed cone model Helax-CC) and one pencil beam algorithm (Helax-TMS's pencil beam model Helax-PB) for 10 intensity modulated radiation therapy (IMRT) lung cancer patients. Treatment plans were created for two photon beam qualities (6 and 18 MV). For each dose calculation algorithm, patient, and beam quality, the following set of clinically relevant dose-volume values was reported: (i) minimal, median, and maximal dose (Dmin, D50, and Dmax) for the gross tumor and planning target volumes (GTV and PTV); (ii) the volume of the lungs (excluding the GTV) receiving at least 20 and 30 Gy (V20 and V30) and the mean lung dose; (iii) the 33rd percentile dose (D33) and Dmax delivered to the heart and the expanded esophagus; and (iv) Dmax for the expanded spinal cord. Statistical analysis was performed by means of one-way analysis of variance for repeated measurements and Tukey pairwise comparison of means. Pinnacle-CS showed an excellent agreement with MCDE within the target structures, whereas the best correspondence for the organs at risk (OARs) was found between Helax-CC and MCDE. Results from Helax-PB were unsatisfying for both targets and OARs. Additionally, individual patient results were analyzed. Within the target structures, deviations above 5% were found in one patient for the comparison of MCDE and Helax-CC, while all differences between MCDE and Pinnacle-CS were below 5%. For both Pinnacle-CS and Helax-CC, deviations from MCDE above 5% were found within the OARs: within the lungs for two (6 MV) and six (18 MV) patients for Pinnacle-CS, and within other OARs for two patients for Helax-CC (for Dmax of the heart and D33 of the expanded esophagus) but only for 6 MV. For one patient, all four algorithms were used to recompute the dose after replacing all computed tomography voxels within the patient's skin contour by water. This made all differences above 5% between MCDE and the other dose calculation algorithms disappear. Thus, the observed deviations mainly arose from differences in particle transport modeling within the lungs, and the commissioning of the algorithms was adequately performed (or the commissioning was less important for this type of treatment). In conclusion, not one pair of the dose calculation algorithms we investigated could provide results that were consistent within 5% for all 10 patients for the set of clinically relevant dose-volume indices studied. As the results from both CS algorithms differed significantly, care should be taken when evaluating treatment plans as the choice of dose calculation algorithm may influence clinical results. Full Monte Carlo provides a great benchmarking tool for evaluating the performance of other algorithms for patient dose computations.     

Comparative analysis of 60Co intensity-modulated radiation therapy

In this study, we perform a scientific comparative analysis of using (60)Co beams in intensity-modulated radiation therapy (IMRT). In particular, we evaluate the treatment plan quality obtained with (i) 6 MV, 18 MV and (60)Co IMRT; (ii) different numbers of static multileaf collimator (MLC) delivered (60)Co beams and (iii) a helical tomotherapy (60)Co beam geometry. We employ a convex fluence map optimization (FMO) model, which allows for the comparison of plan quality between different beam energies and configurations for a given case. A total of 25 clinical patient cases that each contain volumetric CT studies, primary and secondary delineated targets, and contoured structures were studied: 5 head-and-neck (H&N), 5 prostate, 5 central nervous system (CNS), 5 breast and 5 lung cases. The DICOM plan data were anonymized and exported to the University of Florida optimized radiation therapy (UFORT) treatment planning system. The FMO problem was solved for each case for 5-71 equidistant beams as well as a helical geometry for H&N, prostate, CNS and lung cases, and for 3-7 equidistant beams in the upper hemisphere for breast cases, all with 6 MV, 18 MV and (60)Co dose models. In all cases, 95% of the target volumes received at least the prescribed dose with clinical sparing criteria for critical organs being met for all structures that were not wholly or partially contained within the target volume. Improvements in critical organ sparing were found with an increasing number of equidistant (60)Co beams, yet were marginal above 9 beams for H&N, prostate, CNS and lung. Breast cases produced similar plans for 3-7 beams. A helical (60)Co beam geometry achieved similar plan quality as static plans with 11 equidistant (60)Co beams. Furthermore, 18 MV plans were initially found not to provide the same target coverage as 6 MV and (60)Co plans; however, adjusting the trade-offs in the optimization model allowed equivalent target coverage for 18 MV. For plans with comparable target coverage, critical structure sparing was best achieved with 6 MV beams followed closely by (60)Co beams, with 18 MV beams requiring significantly increased dose to critical structures. In this paper, we report in detail on a representative set of results from these experiments. The results of the investigation demonstrate the potential for IMRT radiotherapy employing commercially available (60)Co sources and a double-focused MLC. Increasing the number of equidistant beams beyond 9 was not observed to significantly improve target coverage or critical organ sparing and static plans were found to produce comparable plans to those obtained using a helical tomotherapy treatment delivery when optimized using the same well-tuned convex FMO model. While previous studies have shown that 18 MV plans are equivalent to 6 MV for prostate IMRT, we found that the 18 MV beams actually required more fluence to provide similar quality target coverage.     

Beam modeling and verification of a photon beam multisource model

Dose calculations for treatment planning of photon beam radiotherapy require a model of the beam to drive the dose calculation models. The beam shaping process involves scattering and filtering that yield radiation components which vary with collimator settings. The necessity to model these components has motivated the development of multisource beam models. We describe and evaluate clinical photon beam modeling based on multisource models, including lateral beam quality variations. The evaluation is based on user data for a pencil kernel algorithm and a point kernel algorithm (collapsed cone) used in the clinical treatment planning systems Helax-TMS and Nucletron-Oncentra. The pencil kernel implementations treat the beam spectrum as lateral invariant while the collapsed cone involves off axis softening of the spectrum. Both algorithms include modeling of head scatter components. The parameters of the beam model are derived from measured beam data in a semiautomatic process called RDH (radiation data handling) that, in sequential steps, minimizes the deviations in calculated dose versus the measured data. The RDH procedure is reviewed and the results of processing data from a large number of treatment units are analyzed for the two dose calculation algorithms. The results for both algorithms are similar, with slightly better results for the collapsed cone implementations. For open beams, 87% of the machines have maximum errors less than 2.5%. For wedged beams the errors were found to increase with increasing wedge angle. Internal, motorized wedges did yield slightly larger errors than external wedges. These results reflect the increased complexity, both experimentally and computationally, when wedges are used compared to open beams.