外挂式多叶准直器对准直器散射因子的影响

目的　用电离室测量外挂式多叶准直器 (MLC)对准直器散射因子 (Sc)的影响 ,并用双源模型对结果进行分析。方法　测量MLC形成的 2个不规则射野序列 ,并与等效方野的测量值进行了比较 ,应用双源模型得出MLC对Sc产生影响时叶片所处的位置公式。结果　当MLC叶片位置离中心足够近时 ,叶片将对准直器散射因子产生影响 ;产生影响时叶片位置计算值与测量结果相符。结论　基于双源模型的MLC位置公式较好地描述了当外挂式准直器 (MLC或铅块 )形成的射野小于公式给出值时 ,准直器散射因子将受其影响。     

应用位移技术改善多叶准直器射野的矩齿状边缘

[目的]探讨HD-270MLCTM位移技术对不规则射野边缘的改善程度.[方法]设计一个由3条不同斜度的靶区轮廓边缘形成的三角形射野并选择一实际鼻咽癌病人的面颈联合野-分别由西门子MLC 1cm宽度叶片、HD-270技术的3种虚拟叶片宽度5mm、3mm、2mm和低熔点铅整体挡铅形成多个射野,用柯达感光胶片在加速器下拍片并读出相对等剂量曲线分布图,用有效半影和等剂量曲线波动度来评价剂量分布和射野适形度.[结果]与单纯MLC射野的矩齿状剂量分布相比,3种虚拟叶片宽度的HD-270射野的等剂量线分布明显光滑,剂量波动和有效半影显著降低,深度dmax处有效半影的平均值由单纯MLC射野的10.5mm降低到叶片虚拟宽度2mm的HD-270射野的6.3mm.[结论]HD-270技术能有效降低剂量波动和有效半影,实现等中心叶片宽度<1cm的虚拟mini-MLC.     

调强放疗计划系统的剂量学特性测试方法

目的建立治疗计划系统调强放疗(IMRT)功能的剂量学特性测试方法,以期确定系统计算IMRT照射野或计划的剂量准确性。方法多叶准直器(MLC)调强是IMRT的主要实现方式,针对MLC特点设计一组测试例,测试这些特点对IMRT射野剂量分布的影响。与传统铅门相比, MLC设计的特点和带来的影响包括:(1)MLC叶片末端可能采用弧形端面设计,引起叶片末端效应; (2)MLC叶片侧面采用凸凹槽咬合设计,引起凸凹槽效应;(3)MLC叶片厚度通常比铅门簿,因此对原射线的衰减有差别;(4)IMRT照射野多个子野叠加照射形成的剂量分布将体现前述三个特点的综合效果。结果所有测试例的绝对剂量误差都较小,只有1个>2%。除了T1b和在10 cm深度时的T2外,其他测试例在3%/3 mm时的通过率都>95%。T1b和在10 cm深度时的T2位置处的计算剂量都偏高。除了对MLC凸凹槽的模拟稍差之外,经调整后的机器模型可计算得到相对准确的剂量分布,模型的各个参数基本已是最优值。结论实验结果显示该方法可准确反映MLC的设计特点对剂量的独立影响和综合影响,设计的测试方法适合于计划系统IMRT功能的验收测试。     

基于EPID和EBT3胶片剂量计对动态MLC叶片到位精度检测研究

目的 建立一种使用EPID和EBT3胶片剂量计进行动态MLC叶片到位精度的快速准确检测方法。方法 美国瓦里安6 MV加速器的固定机架角和准直器角度为0°,共设计11个MLC以滑窗方式运行的射野,每个射野由一组相同宽度的窄条野组成,窄条野的宽度为1~10 mm,窄条野之间的间距为2 cm。使用EPID、EBT3胶片剂量计作为测量工具,刻度设计窄条野宽度(带宽)与测量带宽的半高宽的关系。以同样方式设计一带宽为5 mm射野,并在不同位置设计几处MLC叶片偏差,通过EPID、EBT3分析MLC叶片到位精度。结果 当设计带宽>4 mm时,可很好地线性拟合设计带宽与实测带宽的半高宽。EPID检测带宽、峰值间距、MLC叶片位置的精度分别为±0.2、±0.1、±0.1 mm,EBT3检测的分别为±0.3、±0.2、±0.2 mm。结论 提供了一种使用EPID或EBT3胶片剂量计快速检测MLC实际到位精度的方法,为MLC的QA提供帮助。     

多叶准直器透射对调强放疗剂量计算准确性影响观察

目的 探讨多叶准直器透射及其对调强放疗剂量计算准确性的影响。方法 使用电离室分别测量瓦里安Trilogy直线加速器多叶准直器(MLC)叶片平均透射和叶片剂量学间距(DLG),并使用电子射野影像装置测量MLC叶片内透射和叶片间透射。通过 10例肿瘤调强放疗患者资料评价计划系统使用实际测量结果模拟MLC透射计算剂量准确性。结果 6、10 MV X射线MLC叶片平均透射值分别为1.6%、1.8%,透射值随射野增大而增加、随深度增加而增加、离轴位置稍低于中心轴;叶片内透射值分别为 0.8%~1.2%、1.1%~1.6%;叶片间透射值分别为 1.3%~1.9%、1.6%~2.5%。计划系统使用实际测量结果模拟MLC的透射值具有很好一致性。3%3 mmγ通过率 2例鼻咽癌患者分别为93.6%和94.5%,其余 8例患者均>95%。结论 调强放疗中MLC透射直接影响靶区剂量准确性,MLC叶片透射与测量深度、射野大小和离轴位置有关。     

应用EPID代替胶片法对MLC的质控研究

目的 研究EPID代替胶片对加速器MLC的质控方法并探讨其在任意机架角度下的可行性。方法 采用RIT113软件对EPID影像和EBT3胶片影像数据进行分析。以EBT3胶片射野边缘50%等剂量曲线位置定义MLC叶片实际位置,在同一射野条件下EPID影像数据中找到MLC叶片实际位置所对应百分剂量值,从而完成EPID到EBT3胶片的替代过程。结果 加速器机架角0°时,以EBT3胶片确定的MLC叶片位置处EPID影像对应的期望百分剂量值为44%,最大MLC位置误差为0.12 mm。任意机架角度时,EPID影像数据通过与0°结果做距离一致性分析比对,半径为0.5 mm时所有像素点均通过。结论 采用EPID代替胶片对加速器MLC叶片到位质控方法可行,且其精度满足临床要求并适用于任意机架角的测量,具有广泛推广和借鉴意义。     

BL-3型模拟机图像采集制作不规则铅模或MLC文件

常规二维放射治疗中不规则铅模或MLC文件的制作,通常先行模拟机拍摄射野定位片,由定位片勾画出不规则靶区,再至数字化仪制作出铅模或MLC文件;另一种方法是由全数字化模拟机采集BEV图像,在电脑上勾画出不规则靶区,直接由相应的软件生成铅模切割文件或MLC文件。我院购置的北京BL-     

乳腺癌保乳术后全乳野中野适形调强放射治疗技术

目的：探讨乳腺癌保乳术后全乳野中野适形调强照射技术方法,并与常规全乳切线野照射技术进行剂量学对比。方法：选取22例早期乳腺癌保乳术后患者在CT模拟机下对乳腺部位行薄层定位扫描,将定位图像传输至治疗计划系统进行全乳野中野计划设计：在全乳两切线适形野的基础上挡去高剂量区部分,另设计2—4个小跳数射野以降低靶区最高剂量和调整高剂量区的范围及所在位置。处方剂量50Gy／25次,要求95％的靶区接受处方剂量;然后利用其CT模拟定位资料按照常规切线野射野方法在治疗计划上模拟常规切线野治疗计划,对野中野计划和常规射野计划进行靶区适形性、靶区均匀性和危及器官受量的比较。结果：野中野适形调强放射治疗技术的适形度、均匀性优于常规切线野照射,靶区内超过110％处方剂量的体积明显小于常规切线野技术。减少了肺组织V20的体积,降低了心脏的平均剂量和受照体积。结论：乳腺癌保乳术后全乳野中野适形调强放射治疗技术是一种有益的全乳照射技术。     

乳腺癌保乳术后全乳野中野适形调强放射治疗技术

目的:探讨乳腺癌保乳术后全乳野中野适形调强照射技术方法,并与常规全乳切线野照射技术进行剂量学对比.方法:选取22例早期乳腺癌保乳术后患者在CT模拟机下对乳腺部位行薄层定位扫描,将定位图像传输至治疗计划系统进行全乳野中野计划设计:在全乳两切线适形野的基础上挡去高剂量区部分,另设计2-4个小跳数射野以降低靶区最高剂量和调整高剂量区的范围及所在位置.处方剂量50Gy/25次,要求95%的靶区接受处方剂量;然后利用其CT模拟定位资料按照常规切线野射野方法在治疗计划上模拟常规切线野治疗计划,对野中野计划和常规射野计划进行靶区适形性、靶区均匀性和危及器官受量的比较.结果:野中野适形调强放射治疗技术的适形度、均匀性优于常规切线野照射,靶区内超过110%处方剂量的体积明显小于常规切线野技术.减少了肺组织V20的体积,降低了心脏的平均剂量和受照体积.结论:乳腺癌保乳术后全乳野中野适形调强放射治疗技术是一种有益的全乳照射技术.     

电子射野影像装置在容积调强旋转放疗多叶准直器到位精度质控中的应用

目的 研究利用电子射野影像装置（electronic portal imaging device,EPID）检测容积调强旋转放疗（volumetric-modulated arc therapy,VMAT）执行过程中多叶准直器（multileaf collimator,MLC）到位精度的方法。方法 随机选取了8例鼻咽癌患者的放疗计划进行分析,通过二维电离室矩阵进行剂量学验证,得到剂量验证通过率。借助Heimann Imaging Software拍摄软件和医科达Synergy直线加速器机载EPID,获取VMAT计划执行过程中MLC的到位信息,通过梯度检测算法获取MLC实际位置,并与VMAT计划中规定的MLC位置进行比较,得到MLC的位置误差,计算计划通过率。结果 8例鼻咽癌患者的放疗计划在评价标准为3%/3 mm时,剂量验证通过率是（94.8±2.1）%;当叶片到位误差允许值为1 mm时,叶片验证的通过率是（91.1±4.0）%。结论 8例VMAT计划全部通过了剂量验证,但仍存在不同程度的叶片到位误差,因此只对VMAT计划进行剂量验证是不够的,对VMAT计划剂量的验证需要对MLC进行专门的质量控制。通过EPID进行MLC到位精度的检测能够提供更详细、更深入的质控信息,为VMAT技术的开展提供更多的保障。     

Incorporating leaf transmission and head scatter corrections into step-and-shoot leaf sequences for IMRT

PURPOSE: Leaf transmission and head scatter are two important factors that influence intensity-modulated radiation therapy (IMRT) delivery and should be correctly taken into account when generating multileaf collimator (MLC) sequences. Significant discrepancies between the desired and delivered intensity profiles could otherwise result. The purpose of this article is to propose a reliable algorithm to minimize the dosimetric effects caused by the two factors in step-and-shoot mode. MATERIALS AND METHODS: The goal of the algorithm is to minimize the difference between the desired fluence map and the fluence map actually delivered. For this purpose, an error function, defined as the least-square difference between the desired and the delivered fluence maps, is introduced. The effects of transmission and head scatter are minimized by adjusting the fractional monitor units (MUs) in the initial MLC sequences, created by using the desired fluence map without inclusion of the contributions from the two factors. Computationally, a downhill simplex optimization method is used to minimize the error function with respect to the fractional MUs. A three-source model is used to evaluate the relative head scatter distribution for each segment at the beginning of the calculation. The algorithm has been assessed by comparing the dose distributions delivered by the corrected leaf sequence files and the theoretic predication, calculated by Monte Carlo simulation using the desired fluence maps, for an intuitive test field and several clinical IMRT cases. RESULTS: The deviations between the desired fluence maps and those calculated using the corrected leaf sequence files are <0.3% of the maximum MU for the test field and <1.0% for the clinical IMRT cases. The experimental data show that both absolute and relative dose distributions delivered by the corrected leaf sequences agree with the desired ones within 2.5% of the maximum dose or 2 mm in high-dose gradient regions. Compared with the results obtained by using the leaf sequences in which only the transmission or none of the two effects is corrected, significant improvements in the fluence and dose distributions have been observed. CONCLUSIONS: Transmission and head scatter play important roles in the dosimetric behavior of IMRT delivery. A larger error may result if only one factor is considered because of the opposite effects of the two factors. We noted that the influence of the two effects is more pronounced in absolute dose than in the relative dose. The algorithm proposed in this work accurately corrects for these two effects in step-and-shoot delivery and provides a reliable tool for clinical IMRT application.     

Differential dosing of prostate and seminal vesicles using dynamic multileaf collimation

Purpose: We have investigated the potential of applying different doses to the prostate (PTV2) and prostate/seminal vesicles (PTV1) using multileaf collimation (MLC) for intensity modulated radiation therapy (IMRT). Current dose-escalation studies call for treatment of the PTV1 to 54 Gy in 27 fractions followed by 20 Gy minimum to the PTV2. A daily minimum PTV dose of 2 Gy using a 7-field technique (4 obliques, opposed laterals, and an ant-post field) is delivered. This requires monitor unit calculations, paper and electronic chart entry, and quality assurance for a total of 14 fields. The goal of MLC IMRT is to improve efficiency and deliver superior dose distributions. Acceptance testing and commissioning of the dynamic MLC (DMLC) option on a dual-energy accelerator was accomplished. Most of the testing was performed using segmental MLC (SMLC) IMRT with stop-and-shoot sequences built within the dynamic mode of the DMLC.

Methods and Materials: The MLC IMRT fields were forward planned using a three-dimensional treatment planning system. The 14 fields were condensed to 7 SMLC IMRT fields with two segments each. In this process, steps were created by moving the leaves to the reduced field positions. No dose (<0.01%) was delivered during this motion. The monitor units were proportioned according to the planned treatment weights. Film and ionization chamber dosimetry were used to analyze leaf positional accuracy and speed, output, and depth-dose characteristics. A geometric phantom was used for absolute and relative measurements. We obtained a volumetric computerized tomography (CT) scan of the phantom, performed 3D planning, and then delivered a single treatment fraction.

Results: The acceptance testing and commissioning demonstrated that the leaves move to programmed positions accurately and in a timely manner. We did find an 1 mm offset of the set leaf position and radiation edge (50%) due to the curved-end nature and calibration limitations. The 7-field SMLC IMRT treatment duplicated the 14-field static plan dose distribution with variations no greater than 1.5%.

Conclusions: The MLC IMRT approach will improve efficiency because the number of electronic and chart entries has decreased by a factor of 2. Portal images are able to capture the initial and final MLC segments. The question of differential daily dose to the prostate and seminal vesicles remains.     

Resolution and sensitivity of a two-dimensional ionisation chamber array (PTW type 10024)

The two-dimensional verification of intensity-modulated radiation plans is one of the major requirements for the safe application of this technique. The present study examines the resolution and sensitivity of a two-dimensional ionisation-chamber array (PTW2D-Array, type 10024), which can be used for plan verification instead of films. According to the Shannon-Nyquist theorem, the resolution of the 2D-Array is sufficient for dose distributions with a minimal field size of 2 cm x 2 cm. The minimal field size can be reduced to 1 cm x 1 cm by shifting the array 5 mm in the direction of the MLC movement and by repeating the measurements. The high sensitivity against a monitor decalibration for a single field of a sequence is demonstrated on the basis of an individual case. The minimal threshold for MLC misalignment detected by a chamber of the array is less than 1 mm. Therefore, the resolution capabilities of the 2D-Array are sufficient for most intensity-modulated radiation therapy (IMRT)fields.     

Monitor units are not predictive of neutron dose for high-energy IMRT

ABSTRACT: BACKGROUND: Due to the substantial increase in beam-on time of high energy intensity-modulated radiotherapy (>10 MV) techniques to deliver the same target dose compared to conventional treatment techniques, an increased dose of scatter radiation, including neutrons, is delivered to the patient. As a consequence, an increase in second malignancies may be expected in the future with the application of intensity-modulated radiotherapy. It is commonly assumed that the neutron dose equivalent scales with the number of monitor units. METHODS: Measurements of neutron dose equivalent were performed for an open and an intensity-modulated field at four positions: inside and outside of the treatment field at 0.2 cm and 15 cm depth, respectively. RESULTS: It was shown that the neutron dose equivalent, which a patient receives during an intensity-modulated radiotherapy treatment, does not scale with the ratio of applied monitor units relative to an open field irradiation. Outside the treatment volume at larger depth 35% less neutron dose equivalent is delivered than expected. CONCLUSIONS: The predicted increase of second cancer induction rates from intensity-modulated treatment techniques can be overestimated when the neutron dose is simply scaled with monitor units.     

Comparison of two dose calculation methods applied to extracranial stereotactic radiotherapy treatment planning.

BACKGROUND AND PURPOSE: Lung tissue is a special challenge for a dose calculation algorithm, especially in the case of extracranial stereotactic radiotherapy (ESRT) due to small field sizes in combination with large variations in tissue density. The present study investigates the choice of dose calculation algorithm for 18 patients with a single lung tumor and 8 patients with a single liver tumor. The dose calculation is performed with both the pencil beam convolution algorithm and the collapsed cone convolution algorithm with the same number of monitor units in both cases. In addition, the dose calculation with the collapsed cone convolution algorithm is also performed with modified field sizes in order to match the Planning Target Volume (PTV) peripheral dose of the pencil beam based treatment. RESULTS: For liver tumors, the mean Clinical Target Volume (CTV) dose calculated by the collapsed cone convolution algorithm and the pencil beam convolution algorithm is almost identical. For lung tumors, the mean CTV dose determined by the collapsed cone convolution algorithm differs up to 20%. Plans obtained by the two algorithms have field sizes which differ up to 8mm for the same number of monitor units and minimum dose to the lung PTV. CONCLUSIONS: The choice of dose calculation algorithm can have a large influence on a treatment plan for ESRT of the lungs.     

Room shielding for intensity-modulated radiation therapy treatment facilities

PURPOSE: The traditional assumptions used in room-shielding calculations are reassessed for intensity-modulated radiation therapy (IMRT). IMRT makes relatively inefficient use of monitor units (MUs) when compared to conventional radiation therapy, affecting the assumptions used in room-shielding calculations. For the same single-fraction tumor dose delivered, the total number of MUs for IMRT is much greater than for a conventional treatment. Therefore, the exposure contribution from the linear accelerator head leakage will be significantly greater than with conventional treatments. METHODS AND MATERIALS: We propose a shielding calculation model that decouples the concepts of workload, MUs, and target dose when determining primary and secondary barrier thicknesses. The workload for primary barrier calculations for conventional multileaf collimator (MLC) IMRT treatments is determined according to patient tumor doses. The same calculation for accelerator-based serial tomotherapy IMRT requires scaling by the average number of treatment slices. However, rotational therapy yields a small use factor that compensates for this increase. We further define a series of efficiency factors to account for the small field sizes employed in IMRT. For secondary barrier calculations, the patient-scattered radiation is assumed to be the same for all IMRT modalities as for conventional therapy. The accelerator head leakage contribution is proportional to the number of MUs. Knowledge of the average number of MUs per patient is required to estimate the head leakage contribution. We used a 6-MV linear accelerator photon beam to guide the development of this technique and to evaluate the adequacy of conventional barriers for IMRT. Average weekly IMRT workload estimates were made based on our experience with 180 serial tomotherapy patients and published data for both "step and shoot" and dynamic MLC delivered treatments. RESULTS: We found that conventional primary barriers are adequate for both dynamic MLC and serial tomotherapy IMRT. However, the excessive head leakage produced by these modalities requires an increase in secondary barrier shielding.Conclusion: When designing shielding for an IMRT facility, increases in accelerator head leakage must be taken into account for secondary shielding. Adequacy of secondary shielding will depend on the IMRT patient load. For conventional facilities that are being assessed for IMRT therapy, existing primary barriers will typically prove adequate.     

Field Shaping for Three-Dimensional Conformal Radiation Therapy and Multileaf Collimation

Three-dimensional (3-D) conformal treatments are complex and involve many fields, virtually all of which are irregularly shaped and, in the not too distant future, may be intensity-modulated arbitrarily. The multileaf collimator (MLC) is an essential tool for making the delivery of these treatments practical. The characteristics of MLCs of different manufacturers vary significantly, which has an impact on the resulting dose distributions and their clinical applicability. The jagged edges of the fields shaped with MLCs has raised concern about the dose distributions. To study the dosimetric consequences of the jagged boundary, accurate methods of predicting dose distributions are necessary. Preliminary dosimetric and clinical studies show that, for a vast majority of sites and techniques, the MLC is an appropriate replacement for continuous alloy blocks and that the uneasiness about the MLC-shaped boundaries is unwarranted. To fully realize the efficiency possible with a MLC, it is important that it be integrated into the 3-D conformal treatment planning system. Schemes and criteria for positioning leaves relative to the continuous boundary are being studied and often depend on the treatment site, the surrounding normal critical structures, and the treatment technique. Optimum use of the MLC for the efficient delivery of complex 3-D conformal treatments is possible only when treatments are delivered under computer control. Computer-controlled radiation therapy with the MLC is evolving rapidly. Currently, only boundaries are shaped automatically. It is expected that in the near future intensity-modulated treatments will also become practical. General quality assurance and safety requirements of a treatment machine. In many ways, MLCs are more precise and safer than conventional field-shaping devices. However, it is important that the MLC configuration for each field be verified by a record and verify system to ensure that the correct field shape has been selected for treatment.     

A dynamic supraclavicular field-matching technique for head-and-neck cancer patients treated with IMRT

PURPOSE: The conventional single-isocenter and half-beam (SIHB) technique for matching supraclavicular fields with head-and-neck (HN) intensity-modulated radiotherapy (IMRT) fields is subject to substantial dose inhomogeneities from imperfect accelerator jaw/MLC calibration. It also limits the isocenter location and restricts the useful field size for IMRT. We propose a dynamic field-matching technique to overcome these limitations. METHODS AND MATERIALS: The proposed dynamic field-matching technique makes use of wedge junctions for the abutment of supraclavicular and HN IMRT fields. The supraclavicular field was shaped with a multileaf collimator (MLC), which was orientated such that the leaves traveled along the superoinferior direction. The leaves that defined the superior field border moved continuously during treatment from 1.5 cm below to 1.5 cm above the conventional match line to generate a 3-cm-wide wedge-shaped junction. The HN IMRT fields were optimized by taking into account the dose contribution from the supraclavicular field to the junction area, which generates a complementary wedge to produce a smooth junction in the abutment region. This technique was evaluated on a polystyrene phantom and 10 HN cancer patients. Treatment plans were generated for the phantom and the 10 patients. Dose profiles across the abutment region were measured in the phantom on films. For patient plans, dose profiles that passed through the center of the neck lymph nodes were calculated using the proposed technique and the SIHB technique, and dose uniformity in the abutment region was compared. Field mismatches of +/- 1 mm and +/- 2 mm because of imperfect jaw/MLC calibration were simulated, and the resulting dose inhomogeneities were studied for the two techniques with film measurements and patient plans. Three-dimensional volumetric doses were analyzed, and equivalent uniform doses (EUD) were computed. The effect of field mismatches on EUD was compared for the two match techniques. RESULTS: For a perfect jaw/MLC calibration, dose profiles for the 10 patients in the 3-cm match zone had an average inhomogeneity range of -1.6% to +1.6% using the dynamic-matching technique and -3.7% to +3.8% according to the SIHB technique. Measurements showed that dose inhomogeneities that resulted from 1-mm and 2-mm jaw/MLC calibration errors were reduced from as large as 27% and 45% with the SIHB technique to less than 2% and 5.7% with the dynamic technique, respectively. For -1-mm, -2-mm, +1-mm, and +2-mm jaw/MLC calibration errors, respectively, treatment plans for the 10 patients yielded average dose inhomogeneities of -5.9%, -3.0%, +2.7%, and +5.8% with the dynamic technique as compared to -22.8%, -11.1%, +9.8%, and +22.1% with the SIHB technique. Calculation based on a dose-volume histogram (DVH) showed that the SIHB technique resulted in larger changes in EUD of the PTV in the junction area than did the dynamic technique. CONCLUSION: Compared with the conventional SIHB technique, the dynamic field-matching technique provides superior dose homogeneity in the abutment region between the supraclavicular and HN IMRT fields. The dynamic feathering mechanism substantially reduces dose inhomogeneities that result from imperfect jaw/MLC calibration. In addition, isocenter location in the dynamic field-matching technique can be chosen for reproducible patient setup and for adequate IMRT field size rather than being dictated by the match position. It also allows angling of the supraclavicular field to reduce the volume of healthy lung irradiated, which is impractical with the SIHB technique. In principle, this technique should be applicable to any treatment site that requires the abutment of static and intensity-modulated fields.     

Current status and future prospects of 3D treatment planning in radiation therapy, focusing on IMRT]

The ultimate goal of radiation therapy is to confine a high dose to the target area while sparing the surrounding normal structures in order to increase the delivered dose and decrease the likelihood of organ injuries. In Japan, the rotational conformal technique, which is a combination of gantry rotation and dynamic movement of multi-leaf collimators (MLC), has been widely used as a standard method for high-precision radiation therapy. The non-coplanar technique in which radiation beams are given in three dimensions has the advantage of dose concentration as well as organ sparing. In intensity modulated radiotherapy (IMRT), an uneven intensity map within a beam is generated with various methods such as "sliding window technique" and "stop and shoot technique". Several intensity modulated beams are combined to create arbitrary dose distribution including concave distribution. Although a substantial number of proton therapy facilities are planned in this country, IMRT should be considered as a competitive rival from the viewpoint of cost-benefit analysis as well as clinical effectiveness.