Volumetric modulation arc radiotherapy with flattening filter-free beams compared with conventional beams for nasopharyngeal carcinoma:a feasibility study

There is increasing interest in the clinical use of flattening filter-free(FFF) beams.In this study,we aimed to investigate the dosimetric characteristics of volumetric modulated arc radiotherapy(VMAT) with FFF beams for nasopharyngeal carcinoma(NPC).Ten NPC patients were randomly selected to undergo a RapidArc plan with either FFF beams(RA-FFF) or conventional beams(RA-C).The doses to the planning target volumes(PTVs),organs at risk(OARs),and normal tissues were compared.The technical delivery parameters for RapidArc plans were also assessed to compare the characteristics of FFF and conventional beams.Both techniques delivered adequate doses to PTVs.For PTVs,RA-C delivered lower maximum and mean doses and improved conformity and homogeneity compared with RA-FFF.Both techniques provided similar maximum doses to the optic nerves and lenses.For the brain stem,spinal cord,larynx,parotid glands,oral cavity,and skin,RA-FFF showed significant dose increases compared to RA-C.The dose to normal tissue was lower in RA-FFF.The monitor units(MUs) were(536 ± 46) MU for RA-FFF and(501± 25) MU for RA-C.The treatment duration did not significantly differbetween plans.Although both treatment plans could meet clinical needs,RA-C is dosimetrically superior to RA-FFF for NPC radiotherapy.

Dosimetry Comparison between Volumetric Modulated Arc Therapy with RapidArc and Fixed Field Dynamic IMRT for Local-Regionally Advanced Nasopharyngeal Carcinoma

Objective: A dosimetric study was performed to evaluate the performance of volumetric modulated arc radiotherapy with RapidArc on locally advanced nasopharyngeal carcinoma (NPC). Methods: The CT scan data sets of 20 patients of locally advanced NPC were selected randomly. The plans were managed using volumetric modulated arc with RapidArc and fixed nine-field coplanar dynamic intensity-modulated radiotherapy (IMRT) for these patients. The dosimetry of the planning target volumes (PTV), the organs at risk (OARs) and the healthy tissue were evaluated. The dose prescription was set to 70 Gy to the primary tumor and 60 Gy to the clinical target volumes (CTV) in 33 fractions. Each fraction applied daily, five fractions per week. The monitor unit (MU) values and the delivery time were scored to evaluate the expected treatment efficiency. Results: Both techniques had reached clinical treatment’s requirement. The mean dose (Dmean), maximum dose (Dmax) and minimum dose (Dmin) in RapidArc and fixed field IMRT for PTV were 68.4±0.6 Gy, 74.8±0.9 Gy and 56.8±1.1 Gy; and 67.6±0.6 Gy, 73.8±0.4 Gy and 57.5±0.6 Gy (P<0.05), respectively. Homogeneity index was 78.85±1.29 in RapidArc and 80.34±0.54 (P<0.05) in IMRT. The conformity index (CI: 95%) was 0.78±0.01 for both techniques (P>0.05). Compared to IMRT, RapidArc allowed a reduction of Dmean to the brain stem, mandible and optic nerves of 14.1% (P<0.05), 5.6% (P<0.05) and 12.2% (P<0.05), respectively. For the healthy tissue and the whole absorbed dose, Dmean of RapidArc was reduced by 3.6% (P<0.05), and 3.7% (P<0.05), respectively. The Dmean to the parotids, the spinal cord and the lens had no statistical difference among them. The mean MU values of RapidArc and IMRT were 550 and 1,379. The mean treatment time of RapidArc and IMRT was 165 s and 447 s. Compared to IMRT, the delivery time and the MU values of RapidArc were reduced by 63% and 60%, respectively. Conclusion: For locally advanced NPC, both RapidArc and IMRT reached the clinic requirement. The target volume coverage was similar for the different techniques. The RapidArc technique showed some improvements in OARs and other tissue sparing while using reduced MUs and delivery time.

Helical tomotherapy and volumetric modulated arc therapy:New therapeutic arms in the breast cancer radiotherapy

AIM To analyse clinical and dosimetric results of helical tomotherapy(HT) and volumetric modulated arc therapy(VMAT) in complex adjuvant breast and nodes irradiation.METHODS Seventy-three patients were included(31 HT and 42 VMAT). Dose were 63.8 Gy(HT) and 63.2 Gy(VMAT) in the tumour bed, 52.2 Gy in the breast, 50.4 Gy in supraclavicular nodes(SCN) and internal mammary chain(IMC) with HT and 52.2 Gy and 49.3 Gy in IMC and SCN with VMAT in 29 fractions. Margins to particle tracking velocimetry were greater in the VMAT cohort(7 mm vs 5 mm).RESULTS For the HT cohort, the coverage of clinical target volumes was as follows: Tumour bed: 99.4% ± 2.4%; breast: 98.4% ± 4.3%; SCN: 99.5% ± 1.2%; IMC:96.5% ± 13.9%. For the VMAT cohort, the coverage was as follows: Tumour bed: 99.7% ± 0.5%, breast: 99.3% ± 0.7%; SCN: 99.6% ± 1.4%; IMC: 99.3% ± 3%. For ipsilateral lung, Dmean and V20 were 13.6 ± 1.2 Gy, 21.1% ± 5%(HT) and 13.6 ± 1.4 Gy, 20.1% ± 3.2%(VMAT). Dmean and V30 of the heart were 7.4 ± 1.4 Gy, 1% ± 1%(HT) and 10.3 ± 4.2 Gy, 2.5% ± 3.9%(VMAT). For controlateral breast Dmean was 3.6 ± 0.2 Gy(HT) and 4.6 ± 0.9 Gy(VMAT). Acute skin toxicity grade 3 was 5% in the two cohorts.CONCLUSION HT and VMAT in complex adjuvant breast irradiation allow a good coverage of target volumes with an acceptable acute tolerance. A longer follow-up is needed to assess the impact of low doses to healthy tissues.

Partial and Full Arc Volumetric Modulated Arc Therapy in Lung Cancer Stereotactic Body Radiotherapy with Different Definitions of Internal Target Volume Based on 4D CT

Purpose: To investigate the feasibility of partial arc volumetric modulated arc therapy (VMAT) in lung cancer stereotactic body radiotherapy (SBRT), as well the volumetric and dosimetric effects of different internal target volume (ITV) definitions with 4D CT. Methods: Fourteen patients with primary and metastatic lung cancer underwent SBRT were enrolled. Full and partial arc VMAT plans were generated with four different ITVs: ITVall, ITVMIP, ITVAIP and ITV2phases, representing ITVs generated from all 10 respiratory phases, maximum intensity projection (MIP), average intensity projection (AIP), and 2 extreme respiratory phases. Volumetric and dosimetric differences, as well as MU and delivery time were investigated. Results: Partial arc VMAT irradiated more dose at 2 cm away from planning target volume (PTV) (P = 0.002), however, it achieved better protection on mean lung dose , lung V5, spinal cord, heart and esophagus compared with full arc VMAT. The average MU and delivery time of partial arc VMAT were 240 and 1.6 min less than those of full arc VMAT. There were no significant differences on target coverage and organ at risks (OARs) sparing among four ITVs. The average percent volume differences of ITVMIP, ITVAIP and ITV2phases to ITVall were 8.6%, 13.4%, and 25.2%, respectively. Conclusions: Although partial arc VMAT delivered more dose 2 cm out of PTV, it decreases the dose to lung, spinal cord, and esophagus, as well decreased the total MU and delivery time compared with full arc VMAT without sacrificing target coverage. Partial arc VMAT was feasible and more efficient for lung SBRT.

A prospective trial of volumetric intensity-modulated arc therapy vs conventional intensity modulated radiation therapy in advanced head and neck cancer

AIM: To prospectively compare volumetric intensitymodulated arc therapy(VMAT) and conventional intensity-modulated radiation therapy(IMRT) in coverage of planning target volumes and avoidance of multiple organs at risk(OARs) in patients undergoing definitive chemoradiotherapy for advanced(stage Ⅲ or Ⅳ)squamous cell cancer of the head and neck. METHODS: Computed tomography scans of 20 patients with advanced tumors of the larynx, naso-, oroand hypopharynx were prospectively planned using IMRT(7 field) and VMAT using two arcs. Calculated doses to planning target volume(PTV) and OAR were compared between IMRT and VMAT plans. Dose-volume histograms(DVH) were utilized to obtain calculated doses to PTV and OAR, including parotids, cochlea,spinal cord, brainstem, anterior tongue, pituitary and brachial plexus. DVH's for all structures were compared between IMRT and VMAT plans. In addition the planswere compared for dose conformity and homogeneity. The final treatment plan was chosen by the treating radiation oncologist. RESULTS: VMAT was chosen as the ultimate plan in 18 of 20 patients(90%) because the plans were thought to be otherwise clinically equivalent. The IMRT plan was chosen in 2 of 20 patients because the VMAT plan produced concentric irradiation of the cord which was not overcome even with an avoidance structure. For all patients, VMAT plans had a lower number of average monitor units on average(MU = 542.85) than IMRT plans(MU = 1612.58)(P < 0.001). Using the conformity index(CI), defined as the 95% isodose volume divided by the PTV, the IMRT plan was more conformal with a lower conformity index(CI = 1.61) than the VMAT plan(CI = 2.00)(P = 0.003). Dose homogeneity, as measured by average standard deviation of dose distribution over the PTV, was not different with VMAT(1.45 Gy) or IMRT(1.73 Gy)(P = 0.069). There were no differences in sparing organs at risk.CONCLUSION: In this prospective study, VMAT plans were chosen over IMRT 90% of the time. Compared to IMRT, VMAT plans used only one third of the MUs, had shorter treatment times, and similar sparing of OAR. Overall, VMAT provided similar dose homogeneity but less conformity in PTV irradiation compared to IMRT. This difference in conformity was not clinically significant.

A dosimetric evaluation of flattening filter-free volumetric modulated arc therapy for postoperative treatment of cervical cancer

Objective The aim of the study was to compare flattening filter-free(FFF) beams and conventional flattening filter(FF) beams in volumetric modulated arc therapy(VMAT) for cervical cancer after surgery, through a retrospective planning study.Methods VMAT plans of FFF beams and normal FF beams were designed for a cohort of 15 patients. The prescribed dose was 45 Gy to 1.8 Gy per fraction, and at least 95% of the planning target volume received this dose. Doses were computed with a commercially available treatment planning system using a Monte Carlo(MC) algorithm. Plans were compared according to dose-volume histogram analysis in terms of planning target volume homogeneity and conformity indices(HI and CI), as well as organs at risk(OAR) dose and volume parameters. Results FFF-VMAT was similar to FF-VMAT in terms of CI, but inferior to FF-VMAT considering HI. No statistically differences were observed between FFF-VMAT and FF-VMAT in following organ at risks including pelvic bone marrow, small bowel, bladder, rectum, and normal tissue(NT)..Conclusion For patients with cervical cancer after hysterectomy, the FFF beam achieved target and OAR dose distribution similar to that of the FF beam. Reduction of beam-on time in cervical cancer is beneficial.

DICOM-RT Plan Complexity Verification for Volumetric Modulated Arc Therapy

The purpose of this study was to investigate the relationship between plan parameters verified with DICOM-RT and dosimetric results for volumetric modulated arc therapy (VMAT). We investigated three treatment locations: prostate cancer (ten cases), maxillary sinus cancer (four cases), and malignant pleura mesothelioma (four cases) with treatment plans generated by a MonacoTM treatment planning system (TPS), and delivered with an Elekta SynergyTM linear accelerator. We calculated plan parameters, including gantry and multileaf collimator (MLC) positions, Monitor Units (MU), and millimeters of MLC motion per degree of gantry rotation (mm/degree), and performed quality assurance (QA) with a DICOM-RT plan verification system. We measured the VMAT dose with a two-dimensional diode array detector. The average gamma passing rate with percent dose acceptance criteria and distance to agreement criteria of 2 mm and 2% (2 mm/2%) were 97.4%, 97.8% and 92.0% for prostate cancer, maxillary sinus cancer, and malignant pleural mesothelioma, respectively. The mean 95th percentile value for DICOM-calculated mm/degree was 4.0, 5.2, and 11.1 for prostate cancer, maxillary sinus cancer, and malignant pleural mesothelioma, respectively. The gamma passing rate showed a correlation with calculated mm/degree, with a coefficient of determination (R2) of 0.60. Higher calculated mm/degree values led to increased dosimetric errors. We conclude that dose distribution calculated by a TPS is more reliable at smaller mm/degree.

Dosimetric comparison of different multileaf collimators in volumetric modulated arc therapy for malignant pleural mesothelioma

Objective The aiom of the study was to compare the impacts of two types of multileaf collimators （MLC） [standard MLC with a width of 10 mm （sMLC） and micro-MLC with a width of 5 mm （mMLC）] on volumetric modulated arc therapy （VMAT） planning for malignant pleural mesothelioma. Methods VMAT for ten patients with inoperable malignant pleural mesotheliomas was retrospectively planned with the sMLC and mMLC. Histogram-based dose-volume parameters of the planning target vol- ume （PTV） [conformity index （CI） and homogeneous index （HI）] and organs-at-risk were compared for VMAT plans with sMLC （sMLC-VMAT） and mMLC （mMLC-VMAT）. Results The mMLC-VMAT plans were more efficient （average delivery time： 2.67±1.49 min） than the sMLC-VMAT plans （average delivery time： 4.21 ± 2.03 min; P 〈 0.05）. Moreover, compared to the sMLC plans, the mMLC plans demonstrated advantages in the dose coverage of the PTV （CI 0.75 ± 0.08 vs 0.73± 0.09; HI 1.09 ±0.02 vs 1.10± 0.02）, although the difference was not statistically significant （P 〉 0.05）. In addition, significant dose sparing in the fraction of the ipsilateral lung volume receiving 〉 20 Gy （V20; 54.72± 27.08 vs 58.52 ± 29.30） and 〉 30 Gy （V30; 42.74 ± 27.86 vs 46.86± 31.49） radiation, respectively, was observed for the mMLC plans （P 〈 0.05）. Conclusion Comparing sMLC-VMAT and mMLC-VMAT not only demonstrated the higher efficiency and better optimal target coverage of mMLC-VMAT, but also considerably improved the dose sparing of the ipsilateral lung in the VMAT plans for mali qnant pleural mesothelioma.

Benefits and Limitations of Volumetric Modulated Arc Therapy in Treating Bilateral Breast Cancer with Regional Lymph Nodes

Purpose: The study was performed comparing dosimetric characteristics of volumetric modulated arc therapy (VMAT) and field-in-field (FiF) techniques on a patient with synchronous bilateral breast carcinoma. Methods: The patients with bilateral breast cancer treatment were included in this study. A total dose of 40.05 Gy in 15 fractions was prescribed to the Planning Target Volume (PTV) of the whole bilateral breast cancer with the supraclavicular and infraclavicular nodes, with a complementary boost of 10 Gy in 4 fractions to the surgical bed (PTVboost). For both radiotherapy techniques, several VxGy parameters were analyzed for the PTVs, together with the Conformity index (CI), the Homogeneity index (HI) and the critical organs at risk (OARs), lungs and heart. Results: The patient was treated by the VMAT technique and the daily treatment time was less than 20 minutes with daily CBCT imaging. In the VMAT plan, the PTV 95% dose covered 38.89 ± 0.81 Gy, compared to 37.26 ± 1.02 Gy in the FiF technique. The VMAT plan improved the dose homogeneity index and lower dose in lung towards high dose region. Conclusion: The study demonstrates the viability of the VMAT technique in the treatment of bilateral breast cancer. The introduced single isocentric VMAT technique is fast to deliver and it increases the dose homogeneity of the target volume with some limitations. The treatment was well tolerated, without interruption of the treatment courses caused by treatment-related toxicities.

Predicting Delivery Error Using a DICOM-RT Plan for Volumetric Modulated Arc Therapy

The purpose of this study was to investigate the prediction of mechanical error using DICOM-RT plan parameters for volumetric modulated arc therapy (VMAT). We created plans for gantry rotation arcs of 360° and 180° (full-arc and half-arc VMAT) for six maxillary sinus cancer cases using a Monaco treatment planning system, and delivered the doses with a linear accelerator. We calculated DICOM-RT plan parameters, including gantry, multileaf collimator (MLC) positions and Monitor Units (MU). We compared plans with regard to gantry angle per MU (degrees/MU) and MLC travel per MU (mm/MU) for each segment. Calculated gantry angle/MLC position speeds and errors were evaluated by comparison with the log file. On average, the half-arc VMAT plan resulted in 47% and 35% fewer degrees/MU and mm/MU than the full-arc VMAT plan, respectively. The root mean square (r.m.s.) gantry and MLC speeds showed a linear relationship with calculated degrees/MU and mm/MU, with coefficients of determination (R2) of 0.86 and 0.72, respectively. The r.m.s. gantry angle and MLC position errors showed a linear relationship with calculated degrees/MU and mm/MU with R2 of 0.63 and 0.76, respectively. Deviations from plan parameters were related to mechanical error for VMAT, and provided quantitative information without the need for VMAT delivery. These parameters can be used in the selection of treatment planning.

Dosimetric Comparative Analysis of Volumetric Modulated Arc Therapy and Intensity-Modulated Radiation Therapy in Cervical Cancer

Objective:To carry out dosimetric comparison between volumetric modulated arc therapy(VMAT)and intensity-modulated radiation therapy(IMRT)in cervical cancer.Methods:50 postoperative cervical cancer patients were included in this study.The patients were admitted for treatment from January 2021 to January 2022.VMAT and IMRT plans were designed for each patient to analyze the dose distribution in the target area of the two treatment techniques.Results:Comparing the monitor unit for single treatment(638.21±116.21 MU)and time of single treatment(143.21±23.14 s)in the observation group and the monitor unit for single treatment(932.14±74.11 MU)and time of single treatment(223.14±17.26 s)in the control group,there was significant difference(P<0.05);there was also significant difference(P<0.05)between the normal tissue(bladder and rectum)of the observation group and that(bladder and rectum)of the control group.Conclusion:VMAT is more effective in cervical cancer,and it has a certain protective effect on normal tissues in patients and can reduce the radiation dose.

ArcCHECK Machine QA工具在医用直线加速器质量保证中的应用效果

目的探讨ArcCHECK Machine QA工具在医用直线加速器质量保证中的应用效果。方法利用ArcCHECK Machine QA工具和ArcCHECK体模对医用直线加速器进行性能测试,项目包括机架角度、机架旋转速度、机架旋转中心、多叶准直器和铅门位置的一致性、机架旋转出束时的平坦度和对称性,评估该工具在医用直线加速器质量保证中的应用效果。结果旋转模式下机架平均旋转速度为3.6 deg/s,最大偏差约0.5 deg/s;机架旋转等中心形成的平均半径为0.4 mm,多叶准直器与铅门的最大距离正、负差异平均值分别为0.7 mm、-0.7 mm;旋转出束模式下Y方向的平坦度为1.8%,Y方向的对称性为1.1%,X方向的对称性为4.3%。结论ArcCHECK Machine QA工具可用于医用直线加速器常规及容积调强出束性能质量保证。

ArcCheck模体与胶片在鼻咽癌VMAT剂量验证中的比较研究

比较研究ArcCheck与胶片在鼻咽癌容积弧形调强(VMAT)验证中的应用,探讨ArcCheck在VMAT剂量验证中的可行性。随机选取5例鼻咽癌病人的VMAT治疗计划,分别用ArcCheck和胶片两种方法进行剂量验证,比较两种方法的验证结果。ArcCheck验证的平均通过率为96.74±2.60,胶片验证的平均通过率是95.95±1.17,利用统计分析t检验,结果表明ArcCheck和胶片验证两种结果在剂量学上没有明显差异。ArcCheck分析软件可以直接获取三维合成的剂量分布,且操作过程较胶片验证简单,可以更为便捷的进行VMAT剂量验证。

ArcCheck系统在鼻咽癌容积旋转调强剂量验证中的应用

目的:研究ArcCheck验证系统在鼻咽癌容积旋转调强剂量验证中的应用。在病人接受放射治疗之前,进行容积调强计划的验证,使其满足计划设计要求。保证患者实际照射中接受到准确的剂量,确保治疗的安全。方法:选择34例鼻咽癌病例用热塑型体部网罩固定,CT扫描定位,将计划CT传到Pinnacle计划系统(9.2版本)中进行容积旋转调强治疗计划设计,然后将设计好的计划传输至MOSAIQ网络系统上。同时把治疗计划导入ArcCheck模体中重新新型剂量计算。在验证之前,对Arccheck系统进行本底校准,矩阵校准,绝对剂量校准。分析方法采用的是Gamma方法在ArcCHECK自带软件中对治疗计划系统中计算的结果和实际测量的结果二者的差异,阈值标准选择3%,3mm,10%。采用微软Excel2003数据统计软件。结果:Gamma分析方法相对量通过率97.9%,绝对量通过率为95.9%;实测剂量分布图与理论计算剂量分布图在高低剂量点分布上重合很好;另外X方向和Y方向的平坦度,实测结果与计算结果很接近。结论:ArcCheck验证系统在鼻咽癌容积旋转剂量验证中是可行的。它是一种方便快捷准确的旋转调强剂量验证方法。

A Systematic Approach to Patient-Specific Quality Assurance for Volumetric Modulated Arc Therapy

We developed the first non-commercial treatment planning system for volumetric modulated arc therapy(VMAT) in the United States. Because VMAT involves multi-parameter modulations, it is imperative to develop a comprehensive, rigorous and yet, practical procedure for routine patient-specific quality assurance(QA). In this paper, we presented our own approach as being currently implemented in our institution.Our patient-specific QA procedure involves multi-levels: pre-treatment QA,on-treatment QA, and posttreatment QA. The pre-treatment QA focuses on dosimetry verification, which is done with the commercial Map CHECK in Map PHAN mounted on an isocentric mounting fixture(IMF). This method is also referred to the fixed-gantry technique,i.e., the beams always remain perpendicular to the detector plane. The on-treatment QA involves in vivo optically stimulated luminescent dosimetry(OSLD).Prior to the treatment, two nano Dot TM OSLD dosimeters are placed on the patient abdomen under 1 cm bolus at the isocenter location. The irradiated dosimeters are then read by a nano Dot TM reader and the average reading of the two is calculated. The post-treatment QA involves the analysis of the Dyna Log and DLog files. The Dyna Log is a treatment log file that contains the planned and actual leaf positions at a given gantry angle. The DLog is a treatment log file that contains the planned segmented treatment table(STT) and the corresponding segment boundary samples, i.e., the actual delivered MU and gantry angle increment at each control point.

非晶硅电子射野影像系统与ArcCHECK在直肠癌容积旋转调强剂量验证中的应用

目的:比较非晶硅电子射野影像系统(a-Si EPID)与旋转照射剂量验证仪器(Arc CHECK)在直肠癌容积旋转调强(VMAT)剂量验证中的应用。方法:随机选取20例直肠癌VMAT病例,分别设计a-Si EPID与Arc CHECK的验证计划,并在UNIQUE加速器上进行验证。采用γ分析方法(3 mm,3%)比较两种不同验证工具的相对剂量与绝对剂量通过率、X和Y方向的profile。结果:Arc CHECK的绝对剂量通过率为(97.73±1.98)%,相对剂量通过率为(96.96±2.34)%;aSi EPID的绝对剂量通过率为(97.58±1.88)%,相对剂量通过率为(98.13±1.47)%。X、Y方向的profile理论值与实测值很相近,理论剂量分布图与实测计算剂量分布图在高低剂量点分布上重合度较高。结论:Arc CHECK和a-Si EPID的验证结果在剂量学上没有明显差异,两者在直肠癌VMAT剂量验证中都是可行的,但a-Si EPID操作简单、使用方便、显示剂量即时,可以更便捷地进行VMAT剂量验证。

晚期鼻咽癌RapidArc与固定野调强放疗的比较研究

目的:近年RapidArc的临床应用已引起越来越多的关注,本研究比较RapidArc与固定野调强放射治疗(IMRT)两种放疗技术在晚期鼻咽癌治疗计划中的差异。方法:随机选取10例晚期鼻咽癌患者,采用RapidArc与IMRT两种技术进行计划设计与剂量验证,比较计划的靶区剂量、危及器官与正常组织剂量、机器跳数、治疗时间与剂量验证结果。结果:两种计划的剂量分布基本一致,均能提供足够的靶区剂量。RapidArc的PTVnx最小剂量,PTVnd、PTV60、喉、腮腺的平均剂量低于IMRT,PTV60的HI值高于IMRT,机器跳数比IMRT减少约58%,治疗时间减少约70%。以3%/3mm为界,RapidArc验证的γ指数通过率为(98.75±0.50)%,IMRT的通过率为(98.86±0.67)%。结论:两种放疗技术均能够满足临床治疗需要,剂量验证结果能够较好的符合计划计算结果。RapidArc比IMRT有着更多的优势,不仅可以减少机器跳数,缩短治疗时间,而且可以减少喉、腮腺的受照剂量。

运用ArcCHECK实施旋转调强全骨髓照射超长靶区的计划验证

探讨利用Arc CHECK对VMAT(Volumetric Modulated Arc Therapy)和HT(Helical Tomotherapy)全骨髓照射(TMI)超长靶区计划的验证方法。选取8例全身扫描患者,分别设计TMI计划。采用Arc CHECK对两组计划头颈、胸腹及盆腔三部位行验证分析。VMAT组采用模体Merge功能通过平移治疗床实现,HT组采用双计划(参考/执行)法得以完成,三部位验证通过率分别为98.9%±1.9%/94.3%±1.5%、98.4%±1.8%/96.5%±1.2%、97.4%±2.1%/94.1%±1.9%。表明利用Arc CHECK的Merge功能能较好地完成VMAT超长靶区的验证,采用双计划法实现了对HT超长靶区及远离中心部分靶区的验证。

CRT+ARC技术在肺癌“T”形靶区患者放射治疗中的剂量学研究

目的:探讨适形放疗(CRT)+容积旋转调强(ARC)在肺癌"T"形靶区放疗计划中的剂量学特点。方法:使用瓦里安计划系统(Eclipse 10.0)对随机选取的15例已行固定野调强放射治疗(FF-IMRT)治疗的肺癌"T"形靶区的患者,采用CRT和ARC设计CRT+ARC计划,采用CRT和FF-IMRT设计CRT+IMRT计划。在满足相同处方剂量要求的情况下,评价和比较两种治疗计划中计划靶区(PTV)的最小剂量(D_(min))、最大剂量(D_(max))、中位剂量、适形度指数(CI)、均匀性指数(HI)和危及器官受量(正常肺的V_5、V_(10)、V_(13)、V_(20)、V_(30)和平均剂量,脊髓D_(max),心脏V_(20)、V_(30)、V_(40)、V_(45)和平均剂量,食管V50、D_(max)),并比较两种治疗计划正常组织B-P受量和总机器跳数。结果:(1)PTV剂量学指标。CRT+ARC计划与CRT+IMRT计划相比,靶区中位值和V107略有升高,具有统计学意义(P=0.000、0.003),其它剂量学指标(PTV的D_(min)、D_(max)、CI、HI)均无统计学意义。(2)危及器官受量。CRT+ARC计划与CRT+IMRT计划相比,脊髓D_(max)有所降低,且具有统计学意义(P=0.000),正常肺的V13有所升高,但不具有统计学意义,正常肺的V_5、V_(10)、V_(20)、V_(30)和平均剂量有所降低,且V_(20)、V_(30)和平均值具有统计学意义(P=0.000、0.020、0.006);其它危及器官受量,食管V50和D_(max),心脏V_(20)、V_(30)、V_(40)、V_(45)和平均剂量,均无统计学意义。(3)正常组织B-P受量。CRT+ARC计划与CRT+IMRT计划相比,V10略有增高,且具有统计学意义(P=0.030);V_(15)、V_(20)、V_(25)和V_(30)有所降低,且具有统计学意义(P=0.000、0.000、0.000、0.001);其它剂量学指标(V_5、V_(35)、V_(40)、V_(45)和V_(50))无统计学意义。(4)机器跳数。CRT+ARC计划和CRT+IMRT计划单次计划中各射野机器跳数累加之和分别为460±59、1 561±180,两者有显著统计学意义(P=0.000)。结论:对于局部晚期或晚期具有"T"形(或"Y"形)靶区的肺癌患者,CRT+ARC计划比CRT+IMRT计划,在靶区剂量分布、保护肺和脊髓方面表现出了优势,明显减少了机器跳数,且肺和正常组织的低剂量受照体积受量未增加,还有一定程度的降低,这对于CRT+ARC技术在临床上应用,具有重要的指导意义。

RayArc在胸部旋转调强放射治疗计划设计中的应用

目的:利用RayStation计划系统提供的RayArc模块,在Varian公司的Trilogy加速器上进行胸部容积旋转调强(VMAT)计划设计,并对胸部VMAT和静态调强放射治疗(sIMRT)两种治疗计划的结果进行评价。方法:利用RayStation计划系统进行VMAT计划设计,需要对加速器参数和计划参数进行正确设置。计划设计使用直接子野优化算法,目标函数的选择遵循与sIMRT类似的标准。随机挑选10例胸部肿瘤(食管癌5例,肺癌5例)患者分别使用RayArc模块,制定VMAT计划,并与相应的sIMRT计划比较剂量分布、靶区适形度,以及危及器官剂量方面的差异情况。VMAT计划采用182°到178°的两个360°对偶治疗弧,sIMRT计划采用角度分别为182°、220°、310°、345°、15°、50°、150°的前后7个照射野,子野数为50,两者使用相同的逆向优化目标函数。结果:VMAT治疗计划经过多次优化,基本上可以在30min内完成,并达到放疗医师制定的临床目标。与前后7野sIMRT计划相比,356°双弧VMAT计划具有更好的靶区适形度,但是肺部的低剂量区(V_5)略高。另外,加速器运行VMAT计划治疗效率较高,可将治疗时间由sIMRT的6~8min缩短为2~3min。结论:使用RayStation计划系统的RayArc模块可以快速高效制定VMAT计划。RayArc制定出的胸部对偶双弧VMAT计划与常见的胸部7野sIMRT计划都可以满足放疗医师的临床目标要求,但是VMAT计划具有更好的靶区适形度和更高的治疗效率。