阅读说明：本技术 基于统计过程控制的针对影像引导放疗设备定位精度的性能评估方法 (Performance evaluation method for positioning precision of image-guided radiotherapy equipment based on statistical process control ) 是由 李光俊 李治斌 段炼 陈黎 肖青 白龙 柏森 于 2021-07-26 设计创作，主要内容包括：本发明提供了一种基于统计过程控制的针对影像引导放疗设备定位精度的性能评估方法,属于影像引导放疗设备定位精度领域。所述方法包括以下步骤：步骤1、定位误差数据采集；步骤2、绘制Shewhart控制图；步骤3、异常检查；步骤4、排除异常数据。该方法基于统计过程控制技术,对临床使用的影像引导放疗设备的定位精度进行系统综合的评估,评估内容包括系统的定位精度及定位精度随时间而发生的系统偏移,以及系统在多大程度上能够满足既定的定位精度要求。运用本发明的方法,可以快速高效的查找到对影像引导放疗设备定位精度产生影响的因素,据此制定改进措施,进一步规范工作流程,提高该设备在临床运用中的定位精度。(The invention provides a performance evaluation method for positioning accuracy of image-guided radiotherapy equipment based on statistical process control, and belongs to the field of positioning accuracy of image-guided radiotherapy equipment. The method comprises the following steps: step 1, collecting positioning error data; step 2, drawing a Shewhart control chart; step 3, checking the abnormity; and 4, eliminating abnormal data. The method is based on a statistical process control technology, and carries out systematic comprehensive evaluation on the positioning precision of the clinically used image-guided radiotherapy equipment, wherein the evaluation content comprises the positioning precision of the system, the system deviation of the positioning precision along with time, and the degree of the system which can meet the set positioning precision requirement. By using the method, the factors influencing the positioning accuracy of the image-guided radiotherapy equipment can be quickly and efficiently searched, and the improvement measures are made according to the factors, so that the working process is further standardized, and the positioning accuracy of the equipment in clinical application is improved.)

1. A performance evaluation method aiming at positioning accuracy of image-guided radiotherapy equipment based on statistical process control is characterized in that: the method comprises the following steps:

step 1, positioning error data acquisition:

positioning each time of radiotherapy of a patient by using the image guide radiotherapy equipment to be evaluated, positioning each time of radiotherapy of the patient by using a gold standard method, and calculating each time of positioning error of the image guide radiotherapy equipment to be evaluated; positioning error = difference between positioning data of the image guided radiotherapy apparatus to be evaluated and positioning data using the gold standard method; the fraction number of the radiotherapy is more than or equal to 2;

step 2, drawing a Shewhart control chart:

drawing a line drawing by taking the positioning error of the image guide radiotherapy equipment to be evaluated, which is calculated in the step 1, for each time as a data source, then adding a center line CL, an upper control limit UCL and a lower control limit LCL, and drawing a Shewhart control chart;

step 3, abnormal inspection:

checking the Shewhart control chart drawn in the step 2, and marking the positioning error exceeding the upper control limit UCL or the lower control limit LCL as abnormal data;

step 4, eliminating abnormal data:

eliminating abnormal data in the step 3, taking the residual positioning errors as data sources, repeating the steps 2-3, and finding out all abnormal data until the positioning errors exceeding the upper control limit UCL or the lower control limit LCL do not appear; and (4) checking the fractionated radiotherapy corresponding to the abnormal data, and searching for abnormal reasons.

2. The performance evaluation method according to claim 1, characterized in that: in step 1, the image-guided radiotherapy equipment to be evaluated is an optical surface guiding device, an electronic portal image system, an orthogonal projection X-ray imaging system, an ultrasonic image guiding system, a Warrian real-time position management system and a respiratory gating scanning module, and the gold standard method is a method for positioning by using cone beam CT as an image guiding device;

and/or the positioning error comprises one or more of head and foot direction positioning error, front and back direction positioning error and left and right direction positioning error;

and/or, the patient is a cancer patient, preferably a head and neck tumor patient or a breast tumor patient.

3. The performance evaluation method according to claim 1, characterized in that: in step 2, the line graph is formed by drawing the data source according to the time sequence of the radiotherapy;

the calculation formulas of the center line CL, the upper control limit UCL and the lower control limit LCL are as follows:

wherein x is the positioning error of the image guided radiotherapy equipment to be evaluated each time,is the average value of x and is,is the average of the MRs, the MRs are very poor moving,，for radiation treatment fractions, d2= 1.128.

4. The performance evaluation method according to any one of claims 1 to 3, characterized in that: the method further comprises the steps of: calculating a process capability index:

calculating a procedure capability index C for positioning a patient using an image-guided radiotherapy device to be evaluated _pk ：

Wherein u is the mean value of the positioning errors of the image guided radiotherapy equipment to be evaluated every time,for the standard deviation of the positioning error of each time of the image guided radiotherapy equipment to be evaluated, the USL is a set upper specification limit, and the LSL is a set lower specification limit.

5. The performance evaluation method according to claim 4, characterized in that: USL =5mm, LSL = -5 mm.

6. The performance evaluation method according to any one of claims 1 to 3, characterized in that: the method further comprises the steps of: drawing an EWMA control chart to observe whether the positioning accuracy of the image-guided radiotherapy equipment to be evaluated drifts over time:

and (3) converting the positioning error of the image guide radiotherapy equipment to be evaluated, which is calculated in the step (1), every time, drawing the converted data into a line graph according to the time sequence of radiotherapy, and then adding a center line CL, an upper control limit UCL 'and a lower control limit LCL' to draw an EWMA control chart.

7. The performance evaluation method according to claim 6, characterized in that: the calculation formula of the upper control limit UCL 'and the lower control limit LCL' is as follows:

wherein the content of the first and second substances,the number of fractions of the radiation treatment is indicated,is as followsThe error of the positioning in the order of time,is as followsThe data after the conversion is divided into a plurality of times,the mean value of the positioning errors of the radiotherapy equipment is guided for the image to be evaluated each time,λ = 0.05 and L = 2.492, as standard deviation of the positioning error of each time of the image-guided radiotherapy apparatus to be evaluated.

8. The performance evaluation method according to any one of claims 1 to 7, characterized in that: the method further comprises the steps of: and (3) improving the system:

and (4) corresponding measures are made according to the abnormal data and the abnormal reasons found in the steps, the flow is standardized, and the positioning precision of the image-guided radiotherapy equipment to be evaluated is improved.

9. Use of the method of any one of claims 1 to 8 for assessing the positioning accuracy of an image-guided radiotherapy apparatus.

10. A computer equipment for assessing image guide radiotherapy equipment positioning accuracy, characterized in that: the computer device comprises a memory, a processor and a computer program stored on the memory and executable on the processor, the processor implementing the steps of any of claims 1 to 8 when executing the computer program.

Technical Field

The invention belongs to the field of positioning precision of image-guided radiotherapy equipment, and particularly relates to a performance evaluation method for positioning precision of image-guided radiotherapy equipment based on statistical process control.

Background

The image guidance technology is a key technology for realizing precise radiation in radiotherapy. Because the human body has the non-rigid structural characteristics, the relation between the tumor in the body of the patient and the body surface mark is not completely consistent, and in the treatment process of the patient, the accurate positioning of the tumor is also interfered by the change of the anatomical structure in the body, the respiratory movement of the patient and other physiological movements. The body position of the patient is fixed by means of the current technology, the tumor position of the patient is determined only according to the body surface markers, accurate irradiation is difficult to achieve, and accurate positioning needs to be achieved by means of an image guiding technology.

At present, there are many kinds of image-guided radiotherapy devices, including cone beam ct (cbct), electronic portal imaging system (EPID), orthogonal projection X-ray imaging system, optical body surface imaging system, ultrasound image guidance system, RPM, RGSC, and the like. Different image-guided radiotherapy devices have different positioning accuracy due to differences in imaging principles and implementation details. In clinical work, in order to efficiently and accurately implement an image guidance technology, an image guidance workflow often needs to be established to coordinate and well match a plurality of image guidance devices. In addition, all equipment used in clinics needs to implement certain quality control measures to ensure that the equipment works normally, and serious adverse effects on clinics caused by the problems of the equipment or the use process of the equipment are avoided. However, for a new radiotherapy apparatus, the characteristics of the apparatus need to be fully understood before a quality control scheme can be developed. For the above reasons, it is necessary to evaluate the positioning accuracy of various image-guided radiotherapy devices.

At present, the positioning accuracy of the image-guided radiotherapy equipment is evaluated mainly by a direct and simple evaluation method, specifically, the detection positions of the image-guided radiotherapy equipment for multiple times of a plurality of patients are collected and compared with a gold standard to obtain the positioning error detected by the image-guided radiotherapy equipment. And calculating the average value, the standard deviation, the quartile and the like of the collected results of all the times by a simple and direct statistical method so as to evaluate the positioning accuracy of the image guide equipment. However, the existing evaluation method only performs simple statistics on all positioning results, and cannot identify whether a single-time positioning result is an abnormal result, so that the method is easily influenced by abnormal values; moreover, the existing evaluation method can not bring time factors into analysis, and can not detect the system deviation of the positioning accuracy of the image guiding device along with the time; in addition, the existing evaluation method cannot evaluate how much the image guide device can meet the specified precision requirement, and further improves and improves the positioning precision of the image guide device.

Statistical Process Control (SPC) refers to analyzing a Process and its output using Statistical techniques such as Control charts and Process capability indices, and achieves and maintains Process stability through appropriate measures, thereby achieving the purpose of improving and ensuring product quality. The control chart is a means for judging whether the production process is in a control state. In 1924, doctor houhart (w.a. shewhart) who was a master of quality in the united states first invented a control chart method to control the process so as to stabilize the quality of the production process and achieve the purpose of prevention. SPC is self-created and is popularized and applied in industries such as industry and service. However, no report on the use of statistical process control techniques for evaluating the positioning accuracy of image-guided radiotherapy devices is known.

Disclosure of Invention

The technical problem to be solved by the invention is as follows: the performance evaluation method for the positioning accuracy of the image-guided radiotherapy equipment based on statistical process control is provided.

The invention provides a performance evaluation method for positioning accuracy of image-guided radiotherapy equipment based on statistical process control, which comprises the following steps of:

step 1, positioning error data acquisition:

positioning each time of radiotherapy of a patient by using the image guide radiotherapy equipment to be evaluated, positioning each time of radiotherapy of the patient by using a gold standard method, and calculating each time of positioning error of the image guide radiotherapy equipment to be evaluated; positioning error = difference between positioning data of the image guided radiotherapy apparatus to be evaluated and positioning data using the gold standard method; the fraction number of the radiotherapy is more than or equal to 2;

step 2, drawing a Shewhart control chart:

drawing a line drawing by taking the positioning error of the image guide radiotherapy equipment to be evaluated, which is calculated in the step 1, for each time as a data source, then adding a center line CL, an upper control limit UCL and a lower control limit LCL, and drawing a Shewhart control chart;

step 3, abnormal inspection:

checking the Shewhart control chart drawn in the step 2, and marking the positioning error exceeding the upper control limit UCL or the lower control limit LCL as abnormal data;

step 4, eliminating abnormal data:

eliminating abnormal data in the step 3, taking the residual positioning errors as data sources, repeating the steps 2-3, and finding out all abnormal data until the positioning errors exceeding the upper control limit UCL or the lower control limit LCL do not appear; and (4) checking the fractionated radiotherapy corresponding to the abnormal data, and searching for abnormal reasons.

Further, in step 1, the image-guided radiotherapy device to be evaluated is an optical surface guiding device, an electronic portal image system, an orthogonal projection X-ray imaging system, an ultrasound image guiding system, a warrior real-time position management system (RPM), and a respiratory gating scanning module (RGSC), and the gold standard method is a method for positioning by using cone beam CT as an image guiding device;

and/or the positioning error comprises one or more of head and foot direction positioning error, front and back direction positioning error and left and right direction positioning error;

and/or, the patient is a cancer patient, preferably a head and neck tumor patient or a breast tumor patient.

Further, in step 2, the line graph is drawn by the data source according to the time sequence of the radiation therapy;

the calculation formulas of the center line CL, the upper control limit UCL and the lower control limit LCL are as follows:

wherein x is the positioning error of the image guided radiotherapy equipment to be evaluated each time,is the average value of x and is,is the average of the MRs, the MRs are very poor moving,，for radiation treatment fractions, d2= 1.128.

Further, the method further comprises the steps of: calculating a process capability index:

calculating a procedure capability index C for positioning a patient using an image-guided radiotherapy device to be evaluated _pk ：

Wherein u is the mean value of the positioning errors of the image guided radiotherapy equipment to be evaluated every time,is an image to be evaluatedAnd guiding the standard deviation of the positioning error of the radiotherapy equipment every time, wherein the USL is a set upper specification limit, and the LSL is a set lower specification limit.

Further, USL =5mm, LSL = -5 mm.

Further, the method for checking the abnormality in step 3 may also adopt an abnormal value checking method.

Further, the method further comprises the steps of: drawing an EWMA control chart to observe whether the positioning accuracy of the image-guided radiotherapy equipment to be evaluated drifts over time:

and (3) converting the positioning error of the image guide radiotherapy equipment to be evaluated, which is calculated in the step (1), every time, drawing the converted data into a line graph according to the time sequence of radiotherapy, and then adding a center line CL, an upper control limit UCL 'and a lower control limit LCL' to draw an EWMA control chart.

Further, the calculation formula of the upper control limit UCL 'and the lower control limit LCL' is as follows:

wherein the content of the first and second substances,the number of fractions of the radiation treatment is indicated,is as followsThe error of the positioning in the order of time,is as followsThe data after the conversion is divided into a plurality of times,the mean value of the positioning errors of the radiotherapy equipment is guided for the image to be evaluated each time,λ = 0.05 and L = 2.492, as standard deviation of the positioning error of each time of the image-guided radiotherapy apparatus to be evaluated.

Further, in the method of the present invention, in addition to the EWMA control chart, a CUSUM control chart may be drawn.

Further, the method further comprises the steps of: and (3) improving the system:

and (4) corresponding measures are made according to the abnormal data and the abnormal reasons found in the steps, the flow is standardized, and the positioning precision of the image-guided radiotherapy equipment to be evaluated is improved.

Furthermore, in the method of the present invention, the systematic improvement method may further search, through Failure Mode and Effect Analysis (FMEA), for factors that may affect the positioning accuracy of the image-guided radiotherapy apparatus during use, so as to make a corresponding strategy to improve the positioning accuracy.

The invention also provides application of the method in evaluating the positioning accuracy of the image-guided radiotherapy equipment.

The invention also provides computer equipment for evaluating the positioning accuracy of the image-guided radiotherapy equipment, which is characterized in that: the computer device comprises a memory, a processor and a computer program stored on the memory and executable on the processor, the processor implementing the above steps when executing the computer program.

Definitions of terms used in connection with the present invention: the initial definitions provided for by terms herein apply to that term throughout the specification unless otherwise indicated; for terms not specifically defined herein, the meanings that would be given to them by a person skilled in the art are to be given in light of the disclosure and the context.

The image-guided radiotherapy equipment is as follows: before and during treatment of a patient, the device is used for monitoring the tumor and normal organs, and the treatment position, treatment conditions and the like are adjusted according to the monitored positions of the organs, so that the irradiation field is accurately aligned to a treatment target area.

Optical surface guidance devices refer to: based on the optical imaging principle, before and during the treatment of a patient, the body surface of the patient is imaged and used for positioning the patient and guiding the radiation treatment to be accurately performed.

Compared with the prior art, the performance evaluation method for the positioning accuracy of the image-guided radiotherapy equipment based on statistical process control, provided by the invention, has the following beneficial effects:

the method provided by the invention is based on a statistical process control technology, carries out systematic comprehensive evaluation on the positioning precision of the image-guided radiotherapy equipment used clinically, and provides theoretical basic support for establishing an image-guided radiotherapy working flow and a quality assurance scheme of the image-guided radiotherapy equipment in clinic, wherein the evaluation content comprises the positioning precision of the system, the system deviation of the positioning precision along with time, and the degree of the system which can meet the set positioning precision requirement.

By using the method, the factors influencing the positioning accuracy of the image-guided radiotherapy equipment can be quickly and efficiently searched, and the improvement measures are made according to the factors to further standardize the working process so as to improve the positioning accuracy of the equipment in clinical application.

Obviously, many modifications, substitutions, and variations are possible in light of the above teachings of the invention, without departing from the basic technical spirit of the invention, as defined by the following claims.

The present invention will be described in further detail with reference to the following examples. This should not be understood as limiting the scope of the above-described subject matter of the present invention to the following examples. All the technologies realized based on the above contents of the present invention belong to the scope of the present invention.

Drawings

Fig. 1 is a flowchart illustrating a performance evaluation method for positioning accuracy of an image-guided radiotherapy apparatus based on statistical process control according to the present invention.

Fig. 2 is a schematic diagram of shewhhart control chart and EWMA control chart, in which, a, b, and c are shewhhart control chart of data without system offset, with gradual small system offset, and with abrupt large system offset, respectively, and c, d, and e are EWMA control chart corresponding to data of a, b, and c, respectively.

Fig. 3 is a Shewhart control chart drawn after performing a location monitoring of 27 head and neck patients using an optical surface guided radiotherapy apparatus according to the method of embodiment 1 of the present invention.

Detailed Description

The raw materials and equipment used in the invention are known products and are obtained by purchasing commercial products.

Example 1: performance evaluation method for positioning precision of image-guided radiotherapy equipment based on statistical process control

The image guided radiotherapy device to be evaluated in this embodiment is an optical surface guided device (Catalyst), C-RAD AB, Uppsala, Sweden. The radiotherapy targets of the embodiment are 28 patients with head and neck tumor and 37 patients with breast tumor, the radiotherapy frequency of the head and neck patient is 25-33 times, and the radiotherapy frequency of the breast patient is 25 times. According to the disease parts, the patients with head and neck tumor and the patients with breast tumor are divided into two groups, and the performance of the positioning accuracy of the image-guided radiotherapy equipment is evaluated by adopting the method of the embodiment respectively. The specific evaluation method is as follows:

step 1: positioning error data acquisition

At the first treatment of each patient, the reference surface is acquired using an optical surface guidance device (Catalyst) after the patient setup is corrected using cone beam ct (cbct). During the setup phase of each subsequent fraction, the patient is monitored for position using both CBCT and optical surface guidance device (Catalyst). The CBCT is taken as a gold standard of the image guiding device, and the difference value of the readings of the CBCT and the gold standard represents the positioning error of the optical surface guiding device, wherein the positioning error comprises the following errors in three directions: the head and foot direction (SI direction), the front and rear direction (AP direction), and the left and right direction (LR direction).

Step 2: plotting Shewhart control chart

And (2) respectively drawing Shewhart control charts for the errors in each direction by taking the positioning errors of each treatment fraction collected in the step 1 as a data source, drawing all data points in the charts in a line chart mode according to the time sequence of radiotherapy implementation, and adding a Central Line (CL), an Upper Control Limit (UCL) and a Lower Control Limit (LCL). According to the statistical process control theory, the calculation formulas of CL, LCL and UCL are as follows:

where x is each data point (i.e., the monitored positioning error),is the average value of x, MR is the moving range, and the calculation mode is，The treatment is divided into a plurality of times for the radiation treatment,d2 is a constant value, 1.128, for the average MR value.

And step 3: anomaly checking

And (3) checking the Shewhart control chart drawn in the step 2, carefully checking the fractionated radiotherapy corresponding to all the data points exceeding the upper control limit or the lower control limit, searching for an abnormal reason, eliminating the data points exceeding the upper control limit or the lower control limit, and continuing to execute the next step.

And 4, step 4: exception rejection

And (3) after eliminating the data points exceeding the upper control limit or the lower control limit, repeating the step 2-3 by taking the rest data points as data sources, and searching all abnormal data exceeding the upper control limit or the lower control limit until no abnormal data appears.

And 5: calculating a process capability index

According to the unit work experience and requirementsThe ability of the procedure to position the patient using the optical surface guidance device was evaluated against a positioning error of 5mm, and it was evaluated whether the procedure achieved the desired positioning accuracy. According to the statistical process control theory, the process capability index C _pk The calculation formula of (a) is as follows:

where u is the mean of all raw data points (i.e., the positioning error for each treatment fraction collected in step 1),for the standard deviation of all the original data points, the USL and the LSL are respectively the upper specification limit and the lower specification limit, where USL =5mm and LSL = -5mm are selected in this embodiment.

Process capability index C _pk The larger the scale, the more satisfactory the optical surface guidance device to be evaluated is to meet the desired accuracy.

Step 6: EWMA control chart is drawn to see if the positioning accuracy drifts over time

Converting all original data points (namely the positioning error of each treatment fraction collected in the step 1), drawing the converted data into a line graph according to the time sequence of radiotherapy implementation, and calculating and drawing an upper control limit and a lower control limit in the line graph to obtain an EWMA control chart. According to the statistical process control theory, the conversion formula of the original data, the calculation formulas of the upper control limit (UCL ') and the lower control limit (LCL') are as follows:

wherein the subscriptThe number of treatment fractions is indicated,is as followsThe error of the positioning in the order of time,is as followsThe data after the conversion is divided into a plurality of times,is the average of all the original data points,λ is a constant between 0-1, L is a constant, λ = 0.05, L = 2.492 used in this test, for the standard deviation of all raw data points.

And 7: system lift improvements

Corresponding measures are made aiming at the problems and the influencing factors found in the implementation process of the whole statistical process so as to standardize the process and improve the positioning precision of the optical surface guiding equipment in clinical application.

The result analysis of the performance evaluation method for the positioning accuracy of the image-guided radiotherapy equipment based on statistical process control in the embodiment is as follows:

1. in step 3, the number of times of abnormal positioning accuracy is found, the original data and the original image are carefully checked, and after inquiring an operator, the following factors are found to have influence on the positioning accuracy of the optical surface guiding device: the optical surface image acquisition is incomplete, the optical surface image range is too large (compared with the treatment part), the optical surface image comprises parts (such as arms and armpits) which are easy to change, the optical surface image acquisition range is large and small, the optical image acquisition comprises a fixing device such as a bed plate, a compensation film is included during the optical image acquisition, and the image of a wrong patient is acquired. The above factors all seriously affect the positioning accuracy of the optical surface guiding device, and in subsequent clinical application, a normative operation flow should be established according to the factors, so that the positioning accuracy of the optical surface guiding device in clinical application is improved.

2. By analyzing the Shewhart control chart and the EWMA control chart, the EWMA control chart can discover that the positioning accuracy of the device drifts over time. In addition, the positioning accuracy of different patients is different, and a system error of about 1mm exists, so the system error should be corrected in subsequent use.

3. From the process capability analysis it was found that the process capability of positioning different parts of the patient with the optical surface guidance device is different, wherein the process capability of positioning the head and neck is superior to the breast part.

In summary, the present invention uses a statistical process control technique to evaluate the positioning accuracy of the optical surface guidance device, finds that the positioning error is larger than other fractions, and performs backtracking inspection based on the above to find the factors affecting the positioning accuracy, which is helpful to improve the use flow of the device and improve the positioning accuracy of the optical surface guidance device. From the EWMA control chart it is found that the positioning accuracy of the optical surface guiding device differs for different patients, and it is therefore necessary to consider whether the patient is suitable for using the optical surface guiding device. Furthermore, the positioning accuracy of the optical surface guidance device may also vary gradually over time for some patients. From the process capability analysis, it was also found that the process capability of the optical surface guidance device for positioning the neck is superior to the positioning of breast patients.

In summary, the present invention provides a performance evaluation method for positioning accuracy of image-guided radiotherapy equipment based on statistical process control. The method is based on a statistical process control technology, carries out systematic comprehensive evaluation on the positioning precision of the image-guided radiotherapy equipment used clinically, and provides theoretical basic support for establishing an image-guided radiotherapy working flow and a quality assurance scheme of the image-guided radiotherapy equipment in clinic, wherein the evaluation content comprises the positioning precision of the system, system deviation of the positioning precision along with time, and the degree of the system which can meet the set positioning precision requirement. By using the method of the invention, various factors influencing the positioning accuracy of the image-guided radiotherapy equipment can be quickly and efficiently searched, and accordingly, improvement measures are made, and the working process is further standardized, so that the positioning accuracy of the equipment in clinical application is improved.