Cone-beam computed tomography (CBCT) is widely used in dentistry, surgery, radiotherapy and other medical fields. However, repeated CBCT scans expose patients to additional radiation doses, increasing the risk of secondary malignant tumors. Low-dose CBCT image reconstruction technology, which employs advanced algorithms to reduce radiation dose while enhancing image quality, has emerged as a focal point of recent research. This review systematically examined deep learning-based methods for low-dose CBCT reconstruction. It compared different network architectures in terms of noise reduction, artifact removal, detail preservation, and computational efficiency, covering three approaches: image-domain, projection-domain, and dual-domain techniques. The review also explored how emerging technologies like multimodal fusion and self-supervised learning could enhance these methods. By summarizing the strengths and weaknesses of current approaches, this work provides insights to optimize low-dose CBCT algorithms and support their clinical adoption.
【摘要】 目的 研究使用Bowtie濾線器（F1）后，保證加速器CBCT患者掃描圖像質量前提下，如何合理設置掃描條件，盡量降低輻射劑量。 方法 使用Piranha輻射測量儀測量CBCT在使用F1與未使用F1時射線的半價層。設定不同的掃描模式，使用直徑30 cm的有機玻璃模體測量掃描劑量，并使用XVI附帶的Catphan503模體測量客觀圖像質量。在此基礎上，研究掃描劑量以及圖像質量與掃描條件的關系，提出了適合臨床患者的胸部與腹部不同的掃描條件。 結果 使用F1后射束的半價層增加了0.77～0.92 mmAl，掃描劑量明顯減少，中心點減少了22%~29%，邊緣點減少了41%~45%，皮膚劑量減少顯著。圖像質量隨著掃描劑量的增大而提高。空間分辨力受FOV影響較大，但一般能識別1～2 mm的物體，完全能夠滿足分辨細小骨結構與標記點的臨床要求。圖像偽影在使用L20時的大mAs下明顯。胸部低劑量的CBCT圖像如100 kV，M20，0.5 mAs的掃描條件亦可滿足臨床要求。腹部則需要使用較大劑量的掃描模式，CBCT圖像才達到進行配準的要求。 結論 F1的使用在改善圖像質量的前提下降低了掃描劑量，使用新的掃描序列能平衡二者的關系。【Abstract】 Objective To explore the influence of bowtie filtration on absorb dose and half-value layer inaluminum (Al) of cone-beam CT, estimate the image dose under different scan protocol, and establish the relationship between the image quality and the scan protocol after using F1. Methods Piranha was used to measure the HVL. Dose measurements were performed with an 0.6 cc Farmer type ionization chamber with a 30 cm-diam cylindrical shaped water phantoms in 100 and 120 kV with a series of mAs and FOV. CNR, noise and uniformity were measured on the Catphan503 images. Results HVL increased 0.77-0.92 mmAl where XVI generally had more penetrating beams at the similar kV settings. Scanning dose significantly reduced, the center point decreased 22%-29%, the edge with a decrease of 41%-45% which meant a very significant reduction in skin dose. Image quality improved with mAs increase. The spatial resolution mainly changed with FOV. But generally can identify 1-2 mm-diam objects, fully meet the clinical requirements of identify small bone structure and marker. Through this clinical investigation, low-dose CBCT images in chest, such as 100 kV, M20, and 0.5 mAs scanning protocol appeared to be an optimal settings. Abdomen image needed a higher dose to reach the requirements of registration. Conclusion Using F1 under the premise of improving the image quality then reducing the scanning dose and using a new scanning sequence can balance the image quality and scanning dose.
【摘要】 目的 調強放射治療（IMRT）能較好的保護危及器官并給予腫瘤足夠的致死劑量，基于多葉準直器（MLC）分步照射的IMRT技術對復雜病例需要更多子野。研究對直腸癌術后放射治療使用不同子野數目的IMRT計劃進行比對，選擇合理的子野數。 方法 選取2010年4-8月入院的直腸癌術后患者10例，保持射野入射角度及優化目標參數相同，僅改變MLC子野數目，設計不同IMRT對每一患者治療計劃的靶區適形指數（CI）、均勻性指數、最大劑量、最小劑量、平均劑量，危及器官關注體積的受照劑量，機器跳數及治療時間進行分析。 結果 所有治療計劃中靶區及危及器官的劑量學評估指標無統計學意義（Pgt;0.05），只有亞臨床計劃靶區（PTV）CI在15個子野的方案中（0.74±0.06）明顯差于25個子野方案（0.82±0.03）、40個子野方案（0.81±0.06）及60個子野方案（0.84±0.03），有統計學意義（Plt;0.05）；治療機器跳數（MU）隨子野數目增多明顯增大，15、20、40及60個子野方案所需MU分別為（458±56）、（559±62）、（614±74）、（622±82），有統計學意義（Plt;0.05），但40個子野方案與60個子野方案間無統計學意義。治療時間明顯隨子野數增加而增大。 結論 直腸癌術后IMRT計劃使用25個子野能滿足臨床劑量要求，同時能有效降低治療時間，可作為臨床應用參考值。【Abstract】 Objective The intensity modulated radiotherapy (IMRT) can deliver tumor enough doses and protect risk organs as much as possible at the same time. The MLC-based step and shoot IMRT(sIMRT) plan needs much more segment member to meet clinical aims. In this study, several sIMRT plans using different segment number for postoperative rectal cancer were compared to find out the most reasonable segment number setting. Methods Ten patients with rectal carcinoma underwent postoperative adjuvant radiotherapy for rectal cancer from April to August 2010 were selected. For each patient, the angle of field, the prescription expected and the physical parameters optimized were kept the same, while only the number of segments was changed in sIMRT plans. The dose volume histogram-based parameters [conformity index (CI) and homogeneous index (HI)] and other parameters concerned were compared and analyzed. Results The indexes of dosimetry associated with the targets and risk organs showed no significant statistical difference among the 4 sIMRT plans with different segment numbers. The index CI of PTV in the sIMRT plan with 15 segments (CI 0.74±0.06) was less than that in the sIMRT plan with 25 segments (CI 0.82±0.03), the sIMRT plan with 40 segments plan (CI 0.81±0.06), and the sIMRT plan with 60 segments (CI 0.84±0.03) (Plt;0.05). There were significant differences in MU among the sIMRT plans with 15 segments (average MU: 458±56) , with 25 segments (average MU: 559±62 ), and with 40 segments (average MU: 614±74)or with the 60 segments (average MU: 622±82 (Plt;0.05). The more segments meant more MU and more irradiation time. Conclusion The sIMRT plan for patients of rectal cancer to receive postoperative adjuvant radiotherapy may require at least 25 segments to balance the accepted dose results and efficient delivering.
ObjectiveTo compare the dosimetric differences among flattening filter free intensity modulated radiotherapy (3FIMRT), flattening filter free volumetric modulated arc therapy (3FVMAT), filter free intensity modulated radiotherapy (IMRT), and filter free volumetric modulated arc therapy (VMAT) for hyperthyroidism exophthalmus patients.MethodsComputed tomography (CT) scans of 29 patients, who were diagnosed with hyperthyroidism exophthalmus and treated with radiation therapy between September 2016 and September 2017, were selected for study. Four treatment plans with the same dose prescription and objective constrains were designed for each patient based on their images, consisting of IMRT, VMAT, 3FIMRT, and 3FVMAT. The target dosimetric distribution, normal tissue radiation dose, monitor units, and treatment time of each plan were evaluated.ResultsFour types of plans were all able to satisfy the clinical treatment requirements, and there were no significant differences in maximum dose, mean dose (Dmean), homogeneity index of the targets (P>0.05). For the parameters minimum dose, V50%, conformity index (CI), gradient index of the targets, statistically significant differences were observed among the four kinds of technologies (F=10.920, 35.860, 11.320, 17.790; P<0.05). The CI of IMRT and 3FIMRT were superior to those of VMAT and 3FVMAT, but there was no significant difference between IMRT and 3FIMRT. In terms of Lens Dmean and Brain Dmean, statistically significant differences were observed among the four kinds of technologies (F=5.054, 83.780; P<0.05). For Lens Dmean and Brain Dmean, 3FVMAT achieved better sparing effects when compared with the other three plans. The total monitor units and treatment time did not significantly differ between 3FVMAT and VMAT. The mean monitor units of 3FVMAT were 65.07% and 70.22% less than that of IMRT and 3FIMRT respectively. The mean treatment time of 3FVMAT were 48.1% and 35.24% less than that of IMRT and 3FIMRT respectively.Conclusion3FVMAT can bring more dosimetric advantages for hyperthyroidism exophthalmus radiation therapy when compared with IMRT, 3FIMRT, and VMAT.
While radiation treatment to patients with tumors in thorax and abdomen is being performed, further improvement of radiation accuracy is restricted by the tumor intra-fractional motion due to respiration. Real-time tumor tracking radiation is an optimal solution to tumor intra-fractional motion. A review of the progress of real-time dynamic multi-leaf collimator (DMLC) tracking is provided in the present review, including DMLC tracking method, time lag of DMLC tracking system, and dosimetric verification.
Patient-specific volumetric modulated arc therapy (VMAT) quality assurance (QA) process is an important component of the implementation process of clinical radiotherapy. The tolerance limit and action limit of discrepancies between the calculated dose and the delivered radiation dose are the key parts of the VMAT QA processes as recognized by the AAPM TG-218 report, however, there is no unified standard for these two values among radiotherapy centers. In this study, based on the operational recommendations given in the AAPM TG-218 report, treatment site-specific tolerance limits and action limits of gamma pass rate in VMAT QA processes when using ArcCHECK for dose verification were established by statistical process control (SPC) methodology. The tolerance limit and action limit were calculated based on the first 25 in-control VMAT QA for each site. The individual control charts were drawn to continuously monitor the VMAT QA process with 287 VMAT plans and analyze the causes of VMAT QA out of control. The tolerance limits for brain, head and neck, abdomen and pelvic VMAT QA processes were 94.56%, 94.68%, 94.34%, and 92.97%, respectively, and the action limits were 93.82%, 92.54%, 93.23%, and 90.29%, respectively. Except for pelvic, the tolerance limits for the brain, head and neck, and abdomen were close to the universal tolerance limit of TG-218 (95%), and the action limits for all sites were higher than the universal action limit of TG-218 (90%). The out-of-control VMAT QAs were detected by the individual control chart, including one case of head and neck, two of the abdomen and two of the pelvic site. Four of them were affected by the setup error, and one was affected by the calibration of ArcCHECK. The results show that the SPC methodology can effectively monitor the IMRT/VMAT QA processes. Setting treatment site-specific tolerance limits is helpful to investigate the cause of out-of-control VMAT QA.
【摘要】 目的 研究千伏級錐形束CT（kV-cone beam CT，kV-CBCT）影像用于鼻咽癌調強放射治療計劃劑量計算的可行性和精確度。 方法 2010年7-9月7例鼻咽癌患者 ，獲取每例患者的第1天放射治療時的kV-CBCT影像。用CIRS062密度模體和患者自身特定區域亨氏單位值（hounsfield unit，HU）映射的兩種方法重新刻度亨氏單位值-相對電子密度（HU-RED）表，分別進行劑量計算，并與在傳統扇形束CT（FBCT）影像上的原放射治療計劃結果進行對比，包括輻射劑量分布、靶區和危及器官的劑量體積直方圖（DVH）。 結果 kV-CBCT影像的治療計劃和原治療計劃在劑量分布和DVH上有較好的一致性。在劑量分布的比較上采用了γ分析（2%/2 mm標準的通過率），用基于模體的HU-RED表得到的治療計劃與原治療計劃對比，在經過等中心冠狀面、矢狀面和橫斷面的通過率分別為92.7%±3.5%、95.1%±3.1%和95.7%±3.4%，用基于患者的HU-RED表得到治療計劃與原治療計劃對比的通過率分別為94.8%±2.7%、96.6%±2.9%和97.4%±2.7%。DVH的統計數據表明，兩種方法得到的kV-CBCT治療計劃和原治療計劃相比較，靶區和危及器官劑量偏差大多數在2%以內。有1例因在橫斷面發生了明顯的旋轉誤差，導致在橫斷面的通過率很低，DVH統計數據較原計劃偏差較大。 結論 kV-CBCT影像可以用來做輻射劑量計算，基于患者自身影像生成的HU-RED表的治療計劃較原治療計劃有更高的符合度。【Abstract】 Objective To evaluate the feasibility and accuracy of dose calculation based on cone beam CT (CBCT) data sets for intensity modulated radiation therapy (IMRT) planning of nasopharyngeal cancer (NPC). Methods Seven NPC patients were selected. The kV-CBCT images for each patient were acquired on the first treatment day. Two correction strategies were used to generate the cone beam HU value vs relative electron density calibration tables which named CIRS062 phantom based HU-RED tables and patient specific HU-RED tables respectively for dose calculation. The dose distributions and dose volume histograms (DVHs) of the target and organs at risk (OAR) based on kV-CBCT images were compared to the plans based on the fan-beam CT (FBCT). Results The DVH and dose distribution comparison between plans based on the FBCT and those on the CBCT showed good agreements. The γ analysis with a criterion of 2 mm/2% was used for the comparison of dose distribution at the coronal plane, sagital plane and cross plane through the isocenter point. The passing rate from phantom based HU-RED tables were (92.7±3.5) %, (95.1±3.1) %, and (95.7±3.4)%, respectively. The passing rates from the patient specific HU-RED tables were (94.8±2.7) %, (96.6±2.9) %, and (97.4±2.7) %, respectively. The dose difference between plans based on CBCT and those based on FBCT was within 2% at most patients by analyzing DVH based parameters. Only one patient who had significant rotation setup error resulted in the low passing rate and disagreement in DVH. Conclusion The CBCT images can be used to do dose calculation in IMRT planning of NPC. The differences between plans based on HU-RED tables generated by specific patient and the original plans are less than those between plans based on CIRS062 phantom based HU-RED tables and the original plans.
【摘要】 目的 分析重力因素對二維探測器陣列驗證靜態調強計劃的影響，判斷機架角度歸為0°的測量方法是否安全可靠。 方法 在0°機架角和實際治療機架角分別測量靜態調強計劃的劑量分布，以3 mm范圍內偏差lt;3%(3% 3 mm)標準進行γ分析，獲得相對于參考劑量分布的通過率，分析通過率變化規律。分析兩種方法測量的等中心點絕對劑量的差異。 結果 通過率的變化呈隨機分布，96.9%的照射野偏差lt;2.5%。所有計劃的85.7%絕對劑量偏差lt;2%，最大偏差為4.75%。 結論 使用二維探測器陣列在0°角進行調強計劃的日常驗證是安全可靠的。【Abstract】 Objective To analyze impacts of gravity on the verification of IMRT plans with 2-Dimensional detector arrays and to evaluate the reliability of the measurements in vertical direction (gantry angle=0). Methods The dose distributions for each beam in IMRT plans were measured with 0 degree gantry angle and actual gantry angle respectively. The γ percentage pass rate (according to 3% 3 mm) for each beam under each angle condition was obtained by the comparison between the measured dose distribution and the calculated dose map from the treatment planning system which was treated as the reference distribution. Then the absolute dose at the isocenter for each plan was measured at each angle condition and was analyzed. Results The variations of γ percentage pass rates between the two types of measurements were randomly distributed, and the deviations for 96.9% beams were less than±2.5%. The differences between absolute doses for 85.7% beams were less than±2% and the biggest deviation was -4.75%. Conclusion Verification of IMRT plans for the radiotherapy quality assurance using 2-Dimensional detector arrays in 0 degree gantry angle is safe and reliable.
【摘要】 目的 利用不同匹配區域對錐形束CT（CBCT）與定位CT（FBCT）分別配準，測量出鼻咽癌放射治療中頸部的變形誤差。 方法 分析2007年4月-2008年12月收治鼻咽癌患者23例，調整治療床前198次CBCT掃描。將鼻咽部掃描CBCT圖像匹配區域分為上下兩個區域進行對比分析。其中上匹配區域為:上界為蝶竇上緣，下界為頸4下緣，側界包括下頜骨外輪廓，前界為上頜竇1/2，后界為平棘突后緣；下匹配區域為:上界約頸4下緣，下界約胸2-3下緣，側界包括椎體外輪廓，前界包括皮膚，后界平棘突后緣。匹配方式選擇骨，比較匹配結果差異。 結果 選擇上與下匹配區域結果除Y（頭腳）方向旋轉誤差無統計學差異外，余均有統計學差異（Plt;0.05） 。差值在X（左右）、Z（前后）、Y（頭腳）方向平移分別為（1.14±2.80）、（0.47±1.41）、（0.58±3.88） mm，旋轉誤差X、Y、Z方向分別為（0.90±1.98）、（0.80±2.03）、（0.68±1.90）°。 結論 鼻咽癌放射治療中頸部區域存在一定變形誤差，通過CBCT引導發現變形誤差并進行正確糾正是必須的，結合臨床實際及靶區與危及器官的變化為重新計劃提供依據。【Abstract】 Objective To investigate the rotation errors due to neck deformation in nasopharyngeal cancer (NPC) radiotherapy with different match areas to register conebeam CT(CBCT) from image guiding and fanbeam (FBCT) from simulation. Methods A total of 198 pre-correction CBCT data sets from 23 NPC patients from April 2007 to December 2008 were retrospectively analyzed. The matching areas in CBCT images were divided into up and down region of interest (ROI). For the up ROI, the superior, inferior, left and right, anterior, and posterior boundary were set parallel with sphenoid sinus up side, C4 down side, mandible outside, and 1/2 of maxillary air sinus and acanthi. For the down ROI, the lines were set parallel with C4 down side, T2-3 down side, neck outside, skin surface and acanthi respectively in all directions. All registrations were performed automatically by bony anatomy and the results were compared. Results The registration results by the up and the down ROI showed significant difference except Y direction for rotation. The translation error was (1.14±2.80),(0.47±1.41),and (0.58±3.88) mm, respectively; and the rotation error was (0.90±1.98),(0.80±2.03),and (0.68±1.90) ° in X, Y, and Z direction, respectively. 〖WTHZ〗Conclusions〖WTBZ〗There are some significant deformation errors at neck areas in NPC radiotherapy. It is important to find out the deformation and correct it with CBCT image guiding. This kind of error information may provide clues for re-planning in addition to clinical practice and the changes of clinical targets and involved organs.
