Dose Distribution Verifications of IMRT for NPC

In order to explore a dose distribution verification procedure of intensity modulated radiation therapy （IMRT） for nasopharyngeal carcinoma （NPC） and establish its evaluation criteria, we performed 35 two-dimensional （2D） patient-specific IMRT verifications over the year i006. The percent of pixels passing 7 and the normalized agreement test （NAT） index were mainly used to represent the agreement between the measured and computed dose distributions with three criteria （2%/2 mm, 3%/3 mm and 5%/3 mm） as recommended in the literature. The results were that all cases passed through verifications with three criteria except that the NAT index of one case was beyond the limitation, and the three tolerance levels of 2%/2mm, 3%/3 mm and 5%/3 mm produced similar clinical verification results but led to different percent of pixels passing Y and NAT index. Our data showed that the percent of pixels passing y and the NAT index were complementary to evaluate future IMRT verifications as two significant metrics. Due to the influence of the noise and the trait of the software, we considered an IMRT plan as acceptable in case of the percent ofpixels passing y 〉95% and the NAT index 〈5 with the 5%/3 mm criteria for IMRT patient-specific quality assurance （QA）.

Application of Statistical Process Control for Setting Action Thresholds as Quality Assurance of Dose Verifications in External Beam Radiotherapy

Purpose: To test the concept of Statistical Process Control (SPC) as a Quality Assurance (QA) procedure for dose verifications in external beam radiation therapy in conventional and 3D Conformal Radiotherapy (3D-CRT) treatment of cervical cancer. Materials and Methods: A study of QA verification of target doses of 198 cervical cancer patients undergoing External Beam Radiotherapy (EBRT) treatments at two different cancer treatment centers in Kenya was conducted. The target doses were determined from measured entrance doses by the diode in vivo dosimetry. Process Behavior Charts (PBC) developed by SPC were applied for setting Action Thresholds (AT) on the target doses. The AT set was then proposed as QA limits for acceptance or rejection of verified target doses overtime of the EBRT process. Result and Discussion: Target doses for the 198 patients were calculated and SPC applied to test whether the action limits set by the Process Behavior Charts could be applied as QA for verified doses in EBRT. Results for the two sub-groups of n = 3 and n = 4 that were tested produced action thresholds which are within clinical dose specifications for both conventional AP/PA and 3D-CRT EBRT treatment techniques for cervical cancer. Conclusion: Action thresholds set by SPC were within the clinical dose specification of ±5% uncertainty for both conventional AP/PA and 3D-CRT EBRT treatment techniques for cervical cancer. So the concept of SPC could be applied in setting QA action limits for dose verifications in EBRT.

Delivered Dose Verification for Lung Cancer Stereotactic Body Radiotherapy Using Cone-Beam CT

Purpose: Verified the delivered dose distribution of lung cancer Stereotactic Body Radiotherapy (SBRT) using the cone-beam CT images. Methods: Twenty lung cancer patients who underwent SBRT with 100 CBCT images were enrolled in this study. Delivered dose distributions were recalculated on CBCT images with the deformed and non-deformed methods, respectively. The planned and delivered dose distributions were compared using the dose-volume histograms. Results: The delivered target coverage (V100) per patient inside target volume deviated on average were 0.83% ± 0.86% and 1.38% ± 1.40% for Pct vs. Pcbct and Pct vs. Pdcbct, respectively. The Conformity Index (CI) and Gradient Index (GI) showed a good agreement among the plans. For the critical organs, only minor differences were observed between the planned dose and the delivered dose. Conclusions: CBCT images were a useful tool for setup and dose delivery verification for lung cancer patients who underwent SBRT.

Data analysis of dose map verification for IMRT

In this paper we analyze the results of dose map verifications for patient’s IMRT (Intensity-modulated radiation therapy) plans and study the factors that may influence the accuracy of verification. MapCHECK, a two-dimensional diode array, was used to measure the dose maps for 1242 plans (14540 fields) from May 2004 to August 2008. The plans were designed with Pinnacle3 planning system. The passing rate of beams was determined when the acceptance criterion was 2%/2 mm, 3%/3 mm and 4%/4 mm. And the data with 3%/3 mm criteria was analyzed in more detail. The considered factors were beam modeling, optimization mode and treatment site. The median passing rate of total fields was 93.5%, 98.8%, and 100% when the acceptance criterion was 2%/2 mm, 3%/3 mm and 4%/4 mm, and the interquartile range were 11.1%, 3.8%, and 1.3%, respectively. The results of direct machine parameter optimization (DMPO) planning mode was better than those of multiple-step mode and beam modeling of new accelerators was better than that of old accelerators. These indicate that beam modeling is the key point of improving passing rate of IMRT verification and the influence of treatment site was little. The factors, the total number of segments, minimum area of segments and minimum monitor unit (MU) of segments, also influence the dosimetric accuracy of IMRT plan verification.

Research Progress of Two-d imensional Matrix Detectors in IMRT Dose Verification

With the continuous development of science and technolog ies in China,radiotherapy technology in medical field has been very significant ly developing,and intensity modulated radiation therapy(IMRT)technology has been the most widely used.This paper first introduces the components and types of two-dimensional matrix detector,two-dimensional ionization chamber matrix detector and two-dimensional semiconductor matrix detector,then analyzes the dosimetric characteristics of the two-dimensional matrix detector.In the end,the various applications of the two-dimensional matrix detector are analyzed and discussed in detail.The paper aims to promote the two-dimensional matrix detector’s development in the field of radiotherapy in China.

Verification of Dosimetric and Positional Accuracy of Dynamic Tumor Tracking Intensity Modulated Radiation Therapy

Purpose: We performed both, dosimetric and positional accuracy verification of dynamic tumor tracking (DTT) intensity modulated radiation therapy (IMRT), with the Vero4DRT system using a moving phantom (QUASAR respiratory motion platform;QUASAR phantom) and system log files. Methods: The QUASAR phantom was placed on a treatment couch. Measurement of the point dose and dose distribution was performed for conventional IMRT, with the QUASAR phantom static and moving;for DTT IMRT, this was performed with the phantom moving for pyramid shaped, prostate, paranasal sinus, and pancreas targets. The QUASAR phantom was driven by a sinusoidal signal in the superior-inferior direction. Furthermore, predicted positional errors induced by the Vero4DRT system and mechanical positional errors of the gimbal head, were calculated using the system log files. Results and Conclusion: For DTT IMRT, the dose at the evaluation point was within 3% compared with the verification plan, and the dose distribution in the passing rates of γ was 97.9%, with the criteria of 3% dose and 3 mm distance to agreement. The position error calculated from the log files was within 2 mm, suggesting the feasibility of employing DTT IMRT with high accuracy using the Vero4DRT system.

A preliminary study of a new high-resolution detector matrix applied to three-dimensional dose verification in intensity-modulated radiotherapy

Objective:To test the basic dosimetry characteristics of a new high-resolution matrix and to perform a preliminary study on the three-dimensional(3D)dose verification of intensity-modulated treatment(IMRT).Methods:The dosimetry characteristics of the new matrix were investigated,including repeatability,dose-rate response,and dose linearity.Twenty cases of nasopharyngeal carcinoma(NPC)and 20 cases with lung cancer were randomly selected for IMRT plans,and the novel matrix was employed for 3D dose verification.The measured results were evaluated using the gamma passing rate(GPR)and dose volume histogram(DVH).The action limit(AL)and tolerance limit(TL)of the target volume and each organ at risk(OAR)were calculated with reference to the American Association of Physicists in Medicine(AAPM)TG218 report.Results:The matrix performed well for all dosimetry characteristic tests,with a deviation of<1%.The average GPRs of the body were(99.32±0.32)%,(98.36±0.59)%,and(96.27±1.20)%for NPC,and(99.17±0.74)%,(98.09±1.33)%,and(95.83±2.22)%for lung cancer at the gamma standards of 3%/3 mm,3%/2 mm,and 2%/2 mm.The average GPRs difference between the head-neck and thorax-abdomen plans were<1%for the same gamma standard.For both the target volumes and OARs,the average GPRs were>90%under the relatively strict standard of 2%/2 mm.The DVH showed that the measurement results of D_(98) and D_(95) for the target volumes were slightly lower and D_(2) were higher than those of treatment planning system(TPS)(P<0.01).In addition,with the same standard,there may be significant differences in the values of AL and TL between different structures for target volumes and OARs,especially small-volume OARs such as the chiasma and optic nerve-L.Conclusions:The new matrix showed good dosimetry characteristics and can be effectively applied to the treatment planning dose verification of the head-neck and lung cancer.Further research is needed to establish how to analyze the GPR and DVH of the target volume and OARs,and to determine more precise dose verification standards combined with the parameters of AL and TL to better guide 3D dose verification in clinic.

SRS MapCHECK与EDOSE在立体定向放疗计划剂量验证中的对比

目的:使用SRS MapCHECK和EDOSE对立体定向放疗(SRT)计划进行剂量验证,并比较它们的验证结果。方法:首先比较两种系统在不同方野(2 cm×2 cm、4 cm×4 cm、6 cm×6 cm、10 cm×10 cm)的γ通过率(3%/3 mm),然后选择29例SRT计划,分析两种系统在不同γ标准下的绝对剂量通过率,最后分析EDOSE建立的4种不同物理模型对SRT计划剂量验证的影响。结果:SRS MapCHECK在所有方野和29例SRT计划的绝对剂量γ通过率均高于EDOSE,两者的验证结果有统计学差异(P<0.05);SRS MapCHECK及EDOSE在29例SRT计划的γ通过率(2%/2 mm)分别是为98.60%±2.14%和96.53%±2.41%。基于EDOSE的不同物理模型验证结果有统计学差异,平均γ通过率(2%/2 mm)偏差为1.8%~5.1%。结论:SRS MapCHECK和EDOSE系统均满足SRT计划剂量验证的要求,且SRS MapCHECK的剂量验证通过率优于EDOSE;不同的EDOSE物理模型对SRT计划剂量验证有影响。

Dose reconstruction with Compton camera during proton therapy via subset-driven origin ensemble and double evolutionary algorithm

Compton camera-based prompt gamma(PG) imaging has been proposed for range verification during proton therapy. However, a deviation between the PG and dose distributions, as well as the difference between the reconstructed PG and exact values, limit the effectiveness of the approach in accurate range monitoring during clinical applications. The aim of the study was to realize a PG-based dose reconstruction with a Compton camera, thereby further improving the prediction accuracy of in vivo range verification and providing a novel method for beam monitoring during proton therapy. In this paper, we present an approach based on a subset-driven origin ensemble with resolution recovery and a double evolutionary algorithm to reconstruct the dose depth profile(DDP) from the gamma events obtained by a cadmium-zinc-telluride Compton camera with limited position and energy resolution. Simulations of proton pencil beams with clinical particle rate irradiating phantoms made of different materials and the CT-based thoracic phantom were used to evaluate the feasibility of the proposed method. The results show that for the monoenergetic proton pencil beam irradiating homogeneous-material box phantom,the accuracy of the reconstructed DDP was within 0.3 mm for range prediction and within 5.2% for dose prediction. In particular, for 1.6-Gy irradiation in the therapy simulation of thoracic tumors, the range deviation of the reconstructed spreadout Bragg peak was within 0.8 mm, and the relative dose deviation in the peak area was less than 7% compared to the exact values. The results demonstrate the potential and feasibility of the proposed method in future Compton-based accurate dose reconstruction and range verification during proton therapy.

A method for direct conversion of EPID images to incident fluence for dose reconstruction

A direct incident fluence measurement method based on amorphous silicon electronic portal imaging device(a-Si EPID) has been developed for pretreatment verification of intensity-modulated radiation therapy(IMRT).The EPID-based incident fluence conversion method deconvolves EPID images to the primary response distribution based on measured lateral scatter kernels in the EPID detector using Conjugate Gradient algorithm.The primary response is converted to the incident fluence based on measured fluence conversion matrix which corrects for off-axis position dependence of the a-Si EPID response and the "horn" beam profile caused by flatting filter. To verify feasibility and accuracy of this method, square fields of various sizes and two IMRT plans were delivered. The dose distributions computed based on EPID-derived incident fluence were compared with the measurement data. For all square field sizes except the smallest field(2 cm), the mean dose differences in cross-line dose profiles were within 1% excluding the penumbra region, and gamma passing percentages with a 2%/2 mm criterion were about 99%. For two IMRT plans, the least gamma passing percentage for all eight IMRT fields was 98.14% with 2%/3 mm criteria. It can be concluded that our direct EPID-based incident fluence conversion method is accurate and capable of being applied to pretreatment dose verification in clinical routines.

基于Edose系统的鼻咽癌调强放疗三维剂量验证

目的:探讨Edose系统在鼻咽癌调强放疗三维剂量验证中的应用。方法:随机选取17例鼻咽癌患者的调强放疗计划,将计划传输至Edose系统中,使用Edose系统在CT中重建三维剂量分布并将剂量计算结果标记为R,Edose系统实测剂量标记为E,并计算绝对百分剂量偏差D%。统计各计划的计划靶区(planning target volume,PTV)和危及器官的R和E,并分析Gamma通过率。采用SPSS 22.0软件进行统计学分析。结果:各PTV的D%都在2%以内。危及器官的D%较PTV的差异大,最大的为小体积的晶体,为(12.47±7.43)%,其次是眼球,为(10.29±7.74)%,其余各危及器官的D%均在5%以内。3%/3 mm、3%/2 mm和2%/2 mm的Gamma通过率分别为(99.20±0.63)%、(98.61±0.86)%和(96.39±1.89)%,均符合临床要求。结论:仅依靠Edose系统的Gamma通过率比较有时并不能完全反映治疗计划是否符合临床治疗的要求,需要全面评估基于三维影像解剖结构的剂量误差对临床计划执行的影响,从而为临床放疗计划的三维剂量验证提供依据。

Inter-Fraction and Intra-Fraction Variation in the Absorbed-Dose Delivery during Interstitial High Dose Rate Brachytherapy—A Study Using MicroMOSFET <i>In-Vivo</i>Dosimeter

Background: The delivered dose has to be checked and verified with planned dose since precise and accurate dose delivery is essential in Brachytherapy. Sources of uncertainty during Brachytherapy are intra-fraction, inter-fraction and inter-application variations. In-vivo dosimetry is the direct method to monitor the radiation dose delivered to a patient during radiotherapy. In this study, assessment of the inter-fraction and intra-fraction variations in the interstitial Brachytherapy was done with microMOSFET. Aim: To analyze the inter-fraction variations in dose delivery during interstitial HDR Brachytherapy and to compare the measured point dose with the TPS-calculated point dose, intra-fraction variation, using the microMOSFET in-vivo dosimeter. Materials and Methods: From May 2014 to February 2016, 22 patients with Head and Neck cancers and 8 patients with Soft-Tissue Sarcomas (STS) were selected for this study. All these patients underwent CT imaging more than 24 hours after the application. Brachyvision 3DTPS and GammaMed Plus iX HDR unit were used for treatments. MicroMOSFET in-vivo dosimeter after calibration was used for the measurements of dose inside the treated volume. Intra & Inter-fraction variations were analyzed and reported. Results: The SD of inter-fraction variation among 22 Head & Neck patients ranges from 2.14% to 14.26%. Minimum & maximum dose variation with first fraction dose of patients ranged from -22.33% to +26.71% and the mean doses were -6.42% to +19.76%. Differences of TPS dose and microMOSFET measured first fraction dose, intra-fraction variation, ranged from -12.36% to +5.05%. The SD of inter-fraction variation for 8 STS patients was from 2.81% to 14.43%. Minimum and maximum doses vary from -38.72% to +25.74% and mean dose varies from -21.5% to +12.53%. Differences of point doses of TPS and measured, intra-fraction variation, were from -5.86% to 4.88%. Conclusions: MicroMOSFET has the potential to minimize the gross errors during multi-fractionated Interstitial Brachytherapy. Edema, applicator displacements and placement of microMOSFET are the main influencing factors for inter-fraction uncertainty in dose delivery. Re-planning with re-simulated images should be considered whenever the microMOSFET readings vary more than ±10% of the planned dose inside the CTV measured in two successive fractions.

EDOSE在线剂量验证系统在宫颈癌患者容积旋转调强放射治疗三维剂量验证中的应用

目的探讨EDOSE在线剂量验证系统在宫颈癌患者容积旋转调强放射治疗(VMAT)三维剂量验证中的应用效果。方法随机选取2021年1—12月深圳市人民医院放疗科收治的20例宫颈癌术后患者,为其设计VMAT计划,并利用EDOSE在线剂量验证系统进行计划验证,分析所有患者计划验证的3%/3 mm和3%/2 mmγ通过率,比较放射治疗计划系统(TPS)计算剂量与EDOSE系统重建剂量的计划靶区D_(98)、D_(2)(Dx表示x%靶区体积所受到的照射剂量)以及危及器官小肠、膀胱、直肠、股骨头和骨髓V_(40)、V_(30)、V_(20)、V_(10)(Vx表示接受x Gy剂量照射的危及器官的体积百分比)等剂量学参数。结果20例患者计划验证的3%/3 mmγ通过率为(97.82±0.81)%,3%/2 mmγ通过率为(96.25±1.20)%。患者计划靶区D_(98),TPS计算值与EDOSE测量值比较,差异无统计学意义(P>0.05);患者计划靶区D_(2),TPS计算值与EDOSE测量值比较,差异有统计学意义(P<0.05),但偏差均小于3%,此差异临床可接受。关于小肠V_(40)、V_(30)、V_(20)、V_(10),直肠V_(40)、V_(30),右股骨头V_(20)、V_(10),左股骨头V_(20)、V_(10),以及骨髓V_(10),TPS计算值与EDOSE测量值比较,差异无统计学意义(P>0.05);关于膀胱V_(40)、V_(30),右股骨头V_(40)、V_(30),左股骨头V_(40)、V_(30),以及骨髓V_(40)、V_(30)、V_(20),TPS计算值与EDOSE测量值比较,差异有统计学意义(P<0.05)。结论将EDOSE在线剂量验证系统应用于宫颈癌患者VMAT三维剂量验证中可有效评估靶区和危及器官的TPS计算剂量和实际测量剂量三维剂量学参数误差,为验证计划提供更多的评价参数指标,提高放射治疗剂量验证的准确性。

EDose软件在锥筒计划剂量验证中的应用

通过使用软件Varian公司的Trilogy加速器自带的EPID配合EDose软件和德国IBA公司的RAROR Chamber以及与其配套的DOSE1剂量仪和RW-3固体水分别对12例锥筒计划进行绝对剂量验证,记录并分析使用EDose软件时在不同标准下绝对剂量γ通过率和使用电离室时的点剂量验证结果。发现采用γ(3%/3 mm)、(3%/2 mm)、(2%/2 mm)标准时,EDose软件验证的绝对剂量γ通过率分别为(99.59%±0.33%)、(96.96%±1.27%)、(95.48%±1.37%),等中心处绝对剂量偏差为0.27%±1.02%;电离室测量的等中心处绝对剂量偏差为-0.03%±1.20%,最大偏差是-1.82%。两种验证方法的验证结果均满足临床治疗的要求且无统计学差异。结果表明基于电子射野影像系统(EPID)的EDose软件可以用于锥筒计划的剂量验证,而且可以提供二维剂量分布,操作更加方便,同时可以节约科室成本。

Evaluation of photon beam dose calculation accuracy of treatment planning systems using in vivo dosimetry

Objective The treatment planning system currently represents one of the basics of radiation therapy,because it is the only method to estimate patient dose delivery fast forward and accurately represent estimated tumor location of the tumor with the possibility of estimating densities in the tissue surrounding the tumor to overcome dose calculation defects but radial estimated the patient.Despite the flaws associated with the systems and calculates the dose of your programs in all programs currently existing in the world.Than necessary,to the existence of a review of the accuracy of accounts and how to confirm the radiation dose to the patient programs.Methods A total of 35 cancer patients were considered for this study,with 245 field measurements made with low-and high-energy diode detectors for brain and prostate cases.The treatments for all patients were planned using Eclipse Treatment Planning System version 13.6.Results Of the 105 field measurements made for the prostate cancer patients,16 included discrepancies outside the ±5% action level.Of the 145 measurements taken of the brain cases,there were four outside the ±5% action level.The results indicated a higher degree of accuracy.The study revealed that,for the prostate measurements,the higher discrepancy in the doses for the particular fields(exceeding the action level) may have been due to the isocenter being very close to the jaws and multi-leaf collimator of the linear accelerator machine.As a result,scatter from the jaws and the multi-leaf collimator could have contributed to the high dose delivered to the diode;hence,a probable higher discrepancy of the dose in more brain cases due highest quality of VMAT technique and fixation system.Conclusion A greater percentage of the observed discrepancies were well within the set tolerance level.However,it is recommended that the positioning of the diode on the patient's skin and the angular sensitivity of the diodes be reconsidered.It is also recommended that a more accurate calculation of expected diode values be performed,especially for fields that pass through the table.These efforts would achieve action levels of ±5%.

The impact of intensity modulated radiotherapy on the skin dose for deep seated tumors

Objective: The purpose of this study was to investigate the impact of intensity modulated radiotherapy (IMRT) on surface doses for brain, abdomen and pelvis deep located tumors treated with 6 MV photon and to evaluate the skin dose calculation accuracy of the XIO 4.04 treatment planning system. Methods: More investigations for the influences of IMRT on skin doses would increase its applications for many treatment sites. Measuring skin doses in real treatment situations would reduce the uncertainty of skin dose prediction. In this work a pediatric human phantom was covered by a layer of 1 mm bolus at three treatment sites and thermoluminescent dosimeter (TLD) chips were inserted into the bolus at each treatment site before CT scan. Two different treatment plans [three-dimensional conformal radiation therapy (3DCRT) and IMRT] for each treatment sites were performed on XIO 4.04 treatment planning system using superposition algorism. Results: The results showed that the surface doses for 3DCRT were higher than the surface doses in IMRT by 1.6%, 2.5% and 3.2% for brain, abdomen and pelvis sites respectively. There was good agreement between measured and calculated surface doses, where the calculated surface dose was 15.5% for brain tumor calculated with 3DCRT whereas the measured surface dose was 12.1%. For abdomen site the calculated surface dose for IMRT treatment plan was 16.5% whereas the measured surface dose was 12.6%. Conclusion: The skin dose in IMRT for deep seated tumors is lower than that in 3DCRT which is another advantage for the IMRT. The TLD readings showed that the difference between the calculated and measured point dose is negligible. The superposition calculation algorism of the XIO 4.04 treatment planning system modeled the superficial dose well.

Comparison of Different Reconstruction Algorithms for Decreasing the Exposure Dose during Digital Breast Tomosynthesis: A Phantom Study

We compared reconstruction algorithms [filtered back projection (FBP), maximum likelihood expectation maximization (MLEM), and the simultaneous iterative reconstruction technique (SIRT)] in terms of the radiation dose and image quality, for exploring the possibility of decreasing the radiation dose during digital breast tomosynthesis (DBT). The three algorithms were implemented using a DBT system and experimentally evaluated using measurements, such as signal difference-to-noise ratio (SDNR) and intensity profile, on a BR3D phantom (infocus plane image). The possible radiation dose reduction, contrast improvement, and artifact reduction in DBT were evaluated using different exposure levels and the three reconstruction techniques. We performed statistical analysis (one-way analysis of variance) of the SDNR data. The effectiveness of each technique for enhancing the visibility of the BR3D phantom was quantified with regard to SDNR (FBP versus MLEM, P < 0.05;FBP vs. SIRT, P < 0.05;MLEM vs. SIRT, P = 0.945);the artifact reduction was quantified with regard to the intensity profile. MLEM and SIRT produced reconstructed images with SDNR values indicative of low-contrast visibility. The SDNR value for the half-radiation dose MLEM and SIRT images was close to that of the FBP reference radiation dose image. Artifacts were decreased in the MLEM and SIRT images (in the infocus plane) according to the intensity profiles that we obtained. With MLEM and SIRT, the radiation dose may be decreased to half comparison with FBP.

Rotational Angiography for 3D Roadmapping of Catheter Interventions in Congenital Heart Disease: Comparison of a Diagnostic and a Low Dose Program

Objectives: To compare the image quality, accuracy and effective dose of the default diagnostic pro-gram with the low dose program. Methods: The diagnostic and low dose programs of three-dimen-sional rotational angiography were compared considering their signal to noise ratio, their carrier to noise ratio and their actual radiation dose in μGy⋅m2/kg. An anthropomorphic phantom underwent both types of scans to evaluate the effective dose. Comparative measurements of vessel diameters were taken in the diagnostic and the low dose program and compared to the angiography as exact basis. The image quality of the scans using the different programs was rated by a specialist physician. Results: The low dose scan does use significantly less radiation and still provides images, which are adequate for 3D navigation of catheter-based interventions. Conclusion: Three-dimensional rotational angiography can be applied with the low dose program and is sufficient for 3D navigation.

基于标定和计算的电子射野影像系统剂量重建

提出了一种基于标定和计算的电子射野影像系统(EPID)剂量重建算法。首先,对连续采集模式的EPID原始数据进行暗场校正和增益校正,然后通过亮场灰度特征确定射野边界。其次,对EPID数据进行MU标定、离轴标定和射野大小标定,并根据标定后的叠加通量和加速器机头蒙特卡罗模型进行剂量重建。最后,选取9例IMRT计划,分别使用EPID和MapCheck对计划进行验证测量,并在不同γ标准下比较两种验证工具的通过率。针对选取的1例计划病例,两种标准下使用MapCheck对多个病例验证的通过率分别为99.02%±1.28%、90.84%±4.49%;使用EPID重建模型的平均通过率分别为98.86%±1.19%、91.39%±4.80%。本文提出的标定和剂量计算相结合的EPID重建算法,与主流剂量验证软件MapCheck相比,对IMRT计划的验证通过率没有统计学差异(P>0.05),符合剂量验证的临床要求。

PTW Detector7293种剂量验证方法在调强放射治疗中的对比研究

目的 :对比PTW Detector729 3种验证方法在调强放射治疗(intensity modulated radiation therapy,IMRT)剂量验证中的差异。方法:回顾性选取2022年1—12月于某院完成放射治疗的鼻咽癌、肺癌、乳腺癌、宫颈癌和全脑放射治疗患者共50例,使用PTW Detector729二维电离室矩阵配合PTW RW3固体水与PTW Ocavius 4D旋转模体对50例患者的IMRT计划分别进行归零机架角2D剂量验证、实际机架角2D剂量验证和实际机架角3D剂量验证。将剂量评估阈值设为10%,统计3种验证方法在3%/1 mm、2%/2 mm、3%/2 mm和3%/3 mm 4种评估标准下的γ通过率。采用SPSS 22.0统计学软件进行数据分析。结果:在10%剂量评估阈值标准下,归零机架角2D剂量验证的γ通过率最高,差异有统计学意义(P<0.05);实际机架角2D剂量验证的γ通过率高于实际机架角3D剂量验证,差异有统计学意义(P<0.05)。3种验证方法的γ通过率在3%/1 mm、2%/2 mm、3%/2 mm和3%/3 mm 4种标准下逐渐升高,且在3%/2 mm标准下均超过90%,结果满足临床放射治疗要求。结论:3种验证方法的验证结果均能达到IMRT剂量验证实践指南要求,根据IMRT开展情况选择合适的验证方法,对确保治疗方案安全、有效实施具有重要意义。