先进外照射光子剂量算法与笔形束卷积算法在鼻咽癌旋转容积调强放疗剂量学分布中的应用

摘 要：［目的］ 对比分析先进外照射光子剂量算法（advanced external photon dose algorithm，Acuros XB算法）与笔形束卷积算法（pen-shaped beam convolution algorithm，PBC算法）在鼻咽癌患者旋转容积调强放疗（rotational volume adjustment of intensive radiotherapy，RapidArc）剂量学分布中的应用价值。［方法］ 选取2020年6月至2020年12月于攀枝花市中西医结合医院肿瘤科行RapidArc放疗治疗的40例鼻咽癌患者作为研究对象，对比分析Acuros XB算法和PBC算法在鼻咽癌患者RapidArc放疗中的剂量学分布。［结果］ 两种算法在靶区Dmean、D5、D95上对比差异无统计学意义（P均>0.05）。与PBC算法相比，Acuros XB算法在靶区适合度指数上对比更高，均匀性指数上对比更低（（P均<0.05）。与PBC算法相比，Acuros XB算法在视神经、晶体、脑干、脊髓等危及器官的最大剂量值更低（P均<0.05）。Delta4验证结果显示，PBC算法和Acuros XB算法的γ通过率均高于90%，两组算法对比差异无统计学意义。两种算法点剂量误差均符合临床要求。［结论］ 与PBC算法相比，Acuros XB算法在鼻咽癌RapidArc放疗中所获得的靶区和危及器官剂量学参数总体上较优。     

两种调强治疗计划系统的Axesse加速器光子束模型验收测试

目的 研究Monaco、Oncentra TPS的Axesse加速器光子束模型的验收测试,以期确定两者同时验收的完整方法。方法 验收前考虑两TPS相矛盾的参数,将加速器对应参数调至两TPS的交集部分;验收分为点、面、MLC特性模拟测试,MLC特性测试包括凹凸槽、穿射、“offset”、“Gain”值等。     

对于光子外照射治疗报告的建议

针对光子外照射治疗报告的规范化及格式化，国际辐射单位及测量委员会(ICRU)相继颁布了50号报告和62号报告。本文对ICRU50号报告和ICRU62号报告中关于各种靶体积和剂量报告的建议分别进行介绍和对比，同时做了进一步的分析和讨论。     

三维治疗计划系统的剂量学验证

目的验证Pinnacle三维治疗计划系统数学模型拟和参数的剂量计算精度。方法比较治疗计划系统计算与实验测量的输出因子,同时根据荷兰辐射剂量测量委员会的推荐设计了12项测试项目,通过相对偏差及置信限度验证剂量计算的精度。结果目前所确立的Pinnacle系统模型参数有良好的计算精度,全部开野输出囚子计算值偏差均＜1%,楔形野除1个(15cm×40cm,60°楔形角)外计算偏差均＜3%,其余12项测试的最大平均偏差均＜1%,符合NCS的推荐标准,总体精度优于文献报道的其他三维TPS。结论TPS投入临床使用前必须进行剂量验证。笔者所用Pinnacle系统可投入临床使用。     

鼻咽癌外照射方案三维治疗计划系统剂量学评价

[目的]对面颈联合野为基础的鼻咽癌外照射治疗方案进行剂量学评价。[方法]采用ACQSim &ACQPlan(CT模拟及三维计划系统) ,根据不同的外照射方案 ,评价不同层面的三维剂量分布及正常组织的DVH。[结果]①各种方案的90%～100%的等剂量曲线包纳鼻咽原发灶、颅底、咽旁间隙、口咽及颈部区域 ,剂量分布均匀 ,脑干及上颈脊平均剂量分别为12.2Gy～19Gy及46.4Gy～49.3Gy。②垂体保护或将上界定于蝶窦顶 ,垂体平均剂量由60.3Gy分别下降至29.2Gy及14.7Gy;加用鼻前野 ,减少了颞颌关节、中耳、腮腺的受量。③射野后界定于斜坡上、下端后0.75cm及1.5cm ,95%的等剂量曲线包纳整个颅底 ,剂量达66.5Gy～70Gy。④采用全程面颈联合野 +β 线照射颈后三角野方案 ,咽旁间隙、口咽及上颈部分布一个100%～105 %的等剂量曲线。[结论]以面颈联合野为基础的各种鼻咽癌外照射治疗方案满足肿瘤靶区照射的剂量学要求 ,但是 ,正常组织如颞颌关节、中耳、腮腺、视交叉亦受到不同程度高剂量的照射 ,3D CRT及IMRT是鼻咽癌放射治疗发展的趋势 ,在设备完善及有良好QC和QA肿瘤中心 ,可开展此技术的运用。针对病人不同的临床分期 ,提出选择不同鼻咽癌外照射治疗方案的原则。     

CM治疗计划系统照射野剂量计算的验证

目的　对美国CMS公司生产的肿瘤治疗计划系统 (TPS)计算结果值与实际测量值进行比较。方法　按照测量条件下的带有Farmer型电离室的固体水模在螺旋CT下进行扫描 ,图像通过网络数字传输系统传入TPS中 ,分别进行 10cm× 10cm规则野与不规则野、均匀组织与不均匀组织(分别含骨和肺 )、源轴距 10 0cm中心轴上深度 6和 10cm、野内任意点、机架角 30°、楔形板、MLC、铅挡、源皮距 90和 12 0cm条件下 6和 15MVX线计划设计并采用卷积和叠加两种算法计算 ,再与加速器治疗机上实际测量结果进行比较。结果　对于均匀组织和含骨的不均匀组织卷积和叠加算法的计算结果值具有良好的一致性 ,两种计算方法的结果偏差在 0 .5 %以内。多数实测值与计算值偏差在2 .5 %以内 ,个别计算与实测结果偏差在 3%以内 ,含肺的不均匀组织做不均匀组织校准后卷积算法与实测偏差较大 ,6MVX线为 7.8% ,15MVX线为 4 .5 % ,而叠加算法与实测偏差在 1.5 %以内。结论　除了卷积算法不能用于含肺组织或含气空腔剂量计算以外 ,卷积和叠加算法均可用于剂量计算 ,且偏差符合临床要求。     

螺旋断层治疗计划系统升级前后验证结果及叶片打开时间对比研究

目的 比较4.0.4、4.2.3版本螺旋断层治疗计划系统叶片打开时间参数和γ通过率差别及改进状况。方法 用4.0.4、4.2.3版本治疗计划系统各选择 345例计划进行回顾性比较。从患者备份计划文件提取出Sinogram并计算叶片打开时间参数进行评估分析,包含最大叶片打开时间、叶片平均打开时间、打开时间<100 ms的叶片数比例、打开时间在最大时间5ms范围内叶片数比例及出束总时间。对升级前后计划的γ通过率(分析标准为3mm/3%、10%Threshold和全局误差)及叶片打开时间参数对比采用独立t检验分析,采用多元线性回归评估叶片打开时间参数与γ通过率之间相关性。结果 4.0.4版本的γ通过率低于4.2.3版本(97.86%∶98.6%,P<0.001),4.2.3版本的最大时间与投影时间的间隔低于4.0.4版本(1 ms∶11ms,P<0.001)。多元线性回归显示4.0.4版本最大打开时间附近5ms范围内的叶片数比例和出束总时间与γ通过率呈显著负相关(P<0.001),而4.2.3版本仅出束总时间与γ通过率呈显著负相关(P<0.001)。结论 螺旋断层治疗系统升级到4.2.3版本后提高了计划验证的γ通过率,且有效修复了旧版系统在最大叶片打开时间附近的叶片可能会导致γ通过率下降的问题。     

商用质子治疗计划系统射程计算精度的验证北大核心CSCD

目的测量并验证商用质子治疗计划系统RayStation V10的计算精度及质子射程的计算精度,为该系统的临床运用提供参考。方法在上海瑞金医院质子治疗装置上,使用仿真头部模体验证RayStation的计算精度,扫描获取模体的CT数据并导入计划系统,追加设置水箱使其紧贴于模体后,在水箱适当深度设置一个立方体靶区,设计处方剂量为200 cGy(相对生物效应)且束流垂直穿过模体的单野验证计划,实施照射后,比较测量结果和计划系统计算结果。结果使用RayStation默认设置制订验证计划时,测量得到的纵向剂量分布相比计算结果往深的方向移动约4 mm,表明RayStation过高估计了模体中组织等效材料的水等效厚度。为研究该误差来源,用实际束流测量模体中软组织等效材料的水等效厚度,根据测量结果,微调RayStation默认设置,发现纵向扩展布拉格峰测量结果和计算结果的误差可以缩小到2 mm。结论使用RayStation默认设置计算仿真模体的阻止本领,可能带来较大射程误差。使用组织分割和实测模体的组织水等效厚度相结合的方法,可改善治疗计划系统在仿真模体上的射程计算精度。此方法有望成为减小此类剂量算法误差的有效手段之一。     

早期鼻咽癌三维适形和常规外照射计划的剂量学评价

目的利用三维治疗计划系统对早期鼻咽癌常规和三维适形放疗（3D CRT）计划作剂量学比较,评估不同照射方法剂量分布的差异,为今后指导临床治疗提供剂量学的依据。方法选择22例早期鼻咽癌患者,用三维治疗计划系统对每例患者分别作出常规和3D CRT计划设计,然后根据靶区覆盖率（V95）、正常组织受量（D50,D33和D5等）和正常组织并发症发生率（NTCP）比较这两种计划。结果剂量学比较表明,常规和3D CRT的PTVnx70、PTVnd160、PTVnx60、PTVnx50的V95分别为98．22％和99.98％（P=0.06）、98.41％和99．63％（P=1．00）、98．22％和99．98％（P=0．03）、98．85％和99．63％（P=0．02）。保护正常组织方面：在3D CRT和常规计划中,单侧腮腺的D50分别为51．91Gy和64．30Gy（P=0.00）,单侧颞颌关节D50,49．98Gy和64．47Gy（P=0.00）,脊髓D1cc,44.98Gy和48．09Gy（P=0．00）。结论3DCRT在亚临床靶区比常规方法有稍好的靶区覆盖率,3D CBT治疗早期鼻咽癌的优势在于给予靶区相似剂量分布的前提下。可以比常规方法减少某些正常组织器官如腮腺、颞颌关节等照射剂量,减少它们的NTCP。     

调强放射治疗笔形束算法研究

目的：探讨笔形束算法的原理应用于调强放射治疗计划的临床物理数据，参数修正方法。方法i对有限元笔形束算法的计算模型进行分析利用蒙特卡罗算法对利用大野数据推导的有限元笔形束算法数据进行对照分析，采用有限元笔形束算法的计算误差进行验证。结果：有限元笔形束算法模型得到的数据与测量数据对比，PDD数据有很好匹配，误差〈2％；Profiles数据在半影区域和射野边缘区域最大达到4％。利用大野线性关系得到的小射野输出因子与MonteCarlo算法得到的输出因子具很好的一致性。结论：以有限元笔形束算法模型为基础的调强放射治疗计划系统在临床剂量计算中能得到较好的精度，可提高计算速度。利用大野数据推导的小野输出因子，可以代替用Monte Carlo算法得到的射野输出因子。     

Retinoblastoma--comparative analysis of external radiotherapy techniques, including an IMRT technique

PURPOSE: To compare the numerous external radiotherapy (RT) techniques for the treatment of retinoblastoma, as well as an intensity-modulated RT (IMRT) technique. The latter was elaborated to evaluate the potential dose reduction in the surrounding tissue, as well as the potential avoidance of subdosage in the ora serrata retinae. METHODS AND MATERIALS: A 2-year-old patient with unilateral retinoblastoma underwent CT. With the aid of an ophthalmologist, the ocular structures were delimited, and 13 techniques described in published reports were reproduced on three-dimensional planning software and identified according to their authors. A technique with four noncoplanar fields using IMRT was also elaborated. These techniques were compared according to the dose to the ora serrata retinae, lens, orbit (volume that received a dose of >or=20 Gy), vitreous, optic nerve, lacrimal gland (volume that received a dose of >or=34 Gy), and cornea and according to their ease of reproducibility. RESULTS: The techniques that attained the therapeutic dose to the ora serrata retinae were the IMRT technique and the techniques of Haye, Cassady, Cormack, and al-Beteri. The Cormack technique had the lowest volume that received a dose of >or=20 Gy in the orbit, followed by the IMRT technique. The IMRT technique also achieved the lowest volume that received a dose of >or=34 Gy (14%) in the lacrimal gland. The Abramson/McCormick/Blach, Cassady, Reese, and Schipper techniques were the easiest to reproduce and the Chin the most complex. CONCLUSION: Retinoblastoma treatment with IMRT has an advantage over the other techniques, because it allows for the greatest reduction of dose to the orbit and lacrimal gland, while maintaining the therapeutic dose to the ora serrata retinae and vitreous.     

Performance evaluation of computerized treatment planning systems for radiotherapy: external photon beams

A program for verifying the accuracy of any computerized treatment planning system for radiotherapy requires the use of suitable tests. A representative protocol for performing such an evaluation for external photon beams is given. Data are presented documenting the need for such a protocol. An important benefit of carrying out a verification protocol as outlined is that the user appreciates the limitations of the system as well as the most appropriate ways in which to operate the system to insure accurate data in unusual geometries.     

光子刀治疗恶性肿瘤207例临床研究

目的：观察分析光子刀在肿瘤放疗中的应用情况及技术特点,以进一步指导临床实践。方法：总结207例光子刀治疗的恶性肿瘤患者的靶区部位、治疗方针、治疗计划设计（计划靶体积、剂量分割、照射方式）、实施方法及不良反应。结果：照射部位：头颈部49例、体部158例。靶区分布前三位分别是：肺（24.6%）、颅脑（14.5%）和肝（13.5%）。治疗方针：单纯放疗190例（根治103例、姑息87例）和缩野推量17例。治疗计划：计划靶体积（PTV）：1～246.5cm^3,中位值66.7cm^3。射野数目：2～11个,中位数目6个。照射剂量：单次分割剂量1.2～9.56Gy,中位剂量6Gy;总量12～70Gy,中位剂量48Gy。分割方式：每周5次190例,每周（5次17例;分割次数：3～30次,中位数9次。不良反应：全组共发生16例1～2级放射不良反应（RTOG/EORCT标准）,占7.7%,无3级以上不良反应发生。结论：高精度、高剂量、高疗效和低损伤是光子刀治疗的临床优势,“小而精”的剂量学特点是优势形成的关键因素,推荐计划靶体积（PTV）≤216cm^3,临床以单放和常规分割照射为主的方式较为常用且安全,应用范围广并可望成为胰腺癌新的治疗选择,但摆位误差等问题亟待解决。     

基于双源光子模型的准直器散射因子新算法

目的　建立一种简单准确适合于临床应用的准直器散射因子(Sc)的计算模型。方法　建立双源光子束模型,将到达计算点的射线分成原射线和机头散射线两部分,原射线由位于靶点的点源产生,散射线由位于焦点外具有轴对称性的面源产生。并用一个反向散射修正因子对次级准直器的反向散射进行修正。结果　(1) 对于4 cm ×4cm ～40cm ×40 cm 的方野、长短轴比最大为10 的矩形野以及挡铅形成的不规则野,Sc 的计算结果与测量结果的最大偏差<0 .6 % 。(2) 等中心处射野设为10cm ×10cm ,源—电离室距(SCD)从75.5cm 到140 .0cm 变化时,Sc 的计算结果与测量结果的最大偏差< 0.4 % 。结论　该算法可用于准确计算不同SCD处的方野、对称和不对称矩形野、挡铅或多叶光栏(MLC) 形成的不规则野的Sc,是一种适合于临床应用的简单准确的计算Sc 方法     

MRI-based simulation of treatment plans for ion radiotherapy in the brain region

Purpose

To test the potential of MRI-based treatment plan simulation for ion radiotherapy in the brain region.

Materials and methods

A classification-based tissue segmentation method based on discriminant analysis was employed to derive so-called pseudo CT numbers from MR images of three patients with lesions in the head region undergoing ion radiotherapy. Treatment plans for ions, and for comparison purposes also for photons, were subsequently optimized and simulated using both MRI-based pseudo CT and a standard X-ray-based reference CT.

Results

Pseudo CTs revealed mean absolute errors in CT number in the range of 141–165 HU. While soft tissue was in good agreement with reference CT values, large deviations appeared at air cavities and bones as well as at interfaces of different tissue types. In simulations of ion treatment plans, pseudo CT optimizations showed small underdosages of target volumes with deviations in the PTV mean dose of 0.4–2.0% in comparison to reference CT optimizations. In contrast, the PTV mean dose in photon treatment plans differed by no more than 0.2%.

Conclusions

The main challenge in deriving pseudo CT numbers from MRI was the correct assignment of air and compact bone. In this study, the impact of deviations on simulations of ion and photon treatment plans in the brain region was small, however for more complicated morphologies a further improvement of the classification method including MR imaging of compact bone is required.     

Haemostatic and antialgic effects of the 25 MV photon beam concentrated dose in the treatment of carcinoma of the cervix

The authors present the results of a preliminary study on the use of a concentrated dose of 13 Gy in 48 hours in the treatment of cancer of the cervix, especially for haemostatic and antialgic purposes and mostly as a first part of a split course of radiotherapy. In 13 patients with early stages of the disease, the method was used as an emergency treatment with good response in 84.6% of the cases without serious complications. In 43 patients with advanced disease, the concentrated dose was generally repeated for palliation and relieved symptoms in about 72% of the cases but with complications in 16.3%. The authors recommend this method only when absolutely necessary to stop severe haemorrhage and suggest that patients with good response to the first flash course should continue treatment with conventional fractionation, bearing in mind the tolerance of the normal tissues.     

The outcome differences of CT screening for lung cancer pre and post following an algorithm in Zhuhai, China

Purpose

To evaluate the change in outcomes from CT screening for lung cancer before and after collaboration with the International Early Lung Cancer Action Program (I-ELCAP) as well as changing from a single-row detector to a multi-row detector CT scanner (MDCT).

Methods and materials

All participants in the screening program were 40 years of age and older. From 1994 to 2002, a single slice spiral CT was used, the screening protocol was established empirically at our institution. From 2003 to 2009 a 16 slice MDCT was used and our institute became the first I-ELCAP site in China. Collaboration included use of the I-ELCAP protocol, image reading training, teaching files training and attendance at international conferences. The clinical and CT characteristics of participants and diagnosed lung cancers pre and post-collaboration were summarized. The outcomes before and after collaboration were compared, including nodule positive rate, lung cancer frequency, stage distribution, pathology, intervals between last routine screening and surgery, the rate of surgery for benign disease and survival rate.

Results

3348 participants were enrolled during 1994-2002 and 3582 participants during 2003-2009. Their age, gender, smoking and family cancer histories were comparable. The screening detection rate of lung cancer was 1.1% (36/3348) vs. 1.0% (34/3582) (P = 0.6), mean size was 18.6 mm vs. 15.6 mm (P = 0.04), stage I lung cancer was 67% vs. 91% (P = 0.38), median intervals between last routine screening and surgery was 213 days vs. 96 days (P < 0.001), 5-year survival rate due to lung cancer was 75% vs. 95% (P = 0.032) in pre- and post collaboration group respectively. The nodule positive rate was 6.2% (208/3348) vs. 9.8% (351/3582) (P < 0.001), the rate of surgery for benign disease was 18% (8/44) vs. 8% (3/37) (P = 0.4) in pre- and post collaboration group respectively.

Conclusion

Smaller lung cancer were detected, interval between last routine screening and surgery was shorter, surgery for benign disease decreased, and survival rate increased in CT screening for lung cancer in Zhuhai after the collaboration with I-ELCAP and with MDCT. Technology improvements along with a well defined protocol improved outcomes of CT screening for lung cancer in Zhuhai, China.