YY/T 0798-2010Radiotherapy treatment planning system—Guidelines for quality assurance (English PDF)

3.1 Three-dimensional conformal radiotherapy

While minimizing the amount of normal tissue received, the high-dose area and the target area are conformed in three-dimensional space (three-dimensional images and three-dimensional agents are required). Amount calculation).

3.2 Absolute dose

Radiation dose, the unit is Gy or cGy.

3.3 Acceptance

The user confirms that the system can meet the purchase agreement and specifications.

3.4 Acceptance test

A test to confirm that the system can meet the procurement specifications.

3.5 Algorithm

A method used for calculation; contains specific steps for calculation.

4.1 Common errors in radiotherapy

Applying complex radiotherapy techniques to clinical practice, if these techniques are not implemented and managed well and carefully, there will be In potential danger. Looking back at the findings of recent radiotherapy accidents, full-time personnel should be very careful in giving prescriptions, calculations, and implementation of radiotherapy.

Be careful and careful. The IAEA recently released a report on 92 radiotherapy accidents [10]. There are many lessons to be considered. Table 1 summary 26 cases of exposure accidents caused by problems in the treatment planning process were reported. The purpose of listing these in detail is to cause everyone to be It is vigilant and emphasizes the importance of proper debugging and QA process.

The International Commission for Radiological Protection (ICRP) issued a report on the prevention of accidental exposure of patients undergoing radiotherapy. This newspaper The report described and analyzed the causes and consequences of a series of serious accidents, and provided suggested methods to avoid and prevent these problems from occurring.

The main causes of accidents related to RTPS are as follows.

a) Lack of understanding of RTPS;

b) Lack of suitable debugging (no comprehensive testing);

c) Lack of independent calculation and verification.

4.1.1 Education

As far as the use of RTPS is concerned, education is needed at both the technical level and/or professional level; as for institutional policies and procedures, education is The organizational level is also needed. A very important aspect of education is that it has a very important impact on the functions and limitations of RTPS software.

Ok, I understand. In particular, the normalization program for dose calculation, the comparison of the treatment setting parameters used by the computer and the actual treatment machine parameters, The calculation method of occasional MU and the correction of non-uniform tissue. Any small misunderstanding of these calculation procedures will potentially This resulted in a very serious treatment accident. In brachytherapy, the most important issue to consider is how to use radioactive source activity specifications and algorithms. Use this specification.

4.1.2 Verification

Among the reported errors, nearly 60% are related to the lack of auxiliary independent accounting for treatment planning or dose calculation.

4.1.3 Documentation

Each patient's treatment plan, departmental rules and regulations, and documentation are required to be clear.

4.1.4 Communication

Since everyone's majors are different during the treatment process, the entire treatment team should fully communicate in all aspects of treatment. flow. The key factor in some of the medical incidents in the report is the lack of communication.

4.2 The need for quality assurance (QA)

QA refers to. all plans and systematic behaviors, committed to providing the confidence that the quality requirements of any equipment or steps will be met Ren. When mentioning the necessity of QA, the first two points to consider. The first point is the accuracy in the radiotherapy process; the second point is to avoid Avoid mistakes in treatment.

4.2.1 The accuracy of radiotherapy

As we all know, the biological effects of radiation on tumors and normal tissues all follow an S-shaped dose-response relationship curve. Clinical dose The response curve is very steep. In the steepest part, the typical value is about 5% of the dose change, and there can be 10% to 30% of the biological effect.

. The degree of accuracy required for radiotherapy depends on the steepness of the dose response curve and the actual accuracy that can be achieved during radiotherapy.

The accuracy is caused by different links in the whole process of radiotherapy. Based on this consideration, the International Radiation Units and Metrology Committee The ICRU recommends that the total dose error received by patients during radiotherapy should not exceed 5%. Further uncertainty about radiotherapy Qualitative analysis found that when the error of radiation therapy is 3% of the accuracy of dose calculation, the accuracy of patient dose is 5%. In practice, this The recommendation means that the responsibility of the medical physicist is to ensure that the accuracy of the RTPS in the dose calculation should be within 3%.

4.2.2 Wrong avoidance in treatment

Errors made during radiotherapy can cause huge differences in the results of patients after treatment, and the degree of the difference depends on the magnitude of the error. small. Examples of these errors are described in 4.1.

The QA core of RTPS is to establish a process to ensure that each patient receives the best treatment consistent with the plan, and There will be no errors in the use of RTPS and the execution of the treatment plan.

4.2.3 Debug

According to the context of this standard, "debugging" is the pre-clinical preparation of RTPS. In order to debug RTPS, users need Enter the relevant parameters of the machine and the measurement data required by the dose calculation algorithm. Therefore, the debugging process includes inputting the test The measurement data also includes the output data of RTPS using these measurement data and the manufacturer's algorithm.

In this process, some issues need to be paid attention to. The first point. the software is more complicated and includes many functional modules. A simple test may only It is an application way to test the software, but does not necessarily represent a more general system use; second, with the rapid development of computer software and hardware Rapid development and transformation require QA testing when software and hardware are upgraded.

The QA process includes not only debugging and quality control (QC). It started when I started buying RTPS. QA tools The physical details will vary from hospital to hospital, depending on the size of the organization, computer and other technical conditions, and economic conditions.

4.3 Total Quality Management (TQM)

The TQM system focuses on superior management and clear division of labor. TQM includes the production of a clear organizational structure and subordinate system.

TQM needs to guide each employee to have a sense of teamwork.

The core idea of TQM is a management method and process. When a problem occurs, the error is no longer a person's problem, but the management The system has flaws. Therefore, constantly reviewing problems and improving the management system are the key to TQM.

TQM and a good quality system are very conducive to the implementation of tumor radiotherapy. In summary, including the following.

a) The quality system is used to ensure continuous quality improvement, especially when personnel or technology changes;

b) Introducing the quality system, not only the management should have an understanding of it, but all personnel should know and understand it. This will make all People, not just management, will respond positively to it;

c) The quality system is a management tool used to clarify the responsibilities of various positions and provide good training for these people;

d) Since all personnel are involved in quality management and have received better training, they can effectively mobilize everyone's enthusiasm;

e) Since the setting of goals is based on a summary of the actual situation in the past, the quality system has therefore become very efficient;

f) The quality system can reduce the possibility of medical accidents and errors;

g) Since errors occur less frequently, the possibility of prosecution can be effectively reduced.

5.1 Introduction

QA includes all plans and systematic actions, committed to providing the trust that the quality requirements of any equipment will be met. quality Control (QC) includes a process of comparing measured values with current standards, so the QC process includes the following steps.

a) Definition specifications;

b) Measure according to the specification;

c) Compare the measured value with the standard value;

d) Measures that may be taken when the measurement result exceeds the allowable range.

When formulating d), it is also necessary to determine the acceptable deviation range (tolerance) relative to the standard value. The following chapters mainly discuss measurement and quality evaluation Estimate, including uncertainty, tolerance, and error.

5.2 Uncertainty, deviation, tolerance and error

5.2.1 Uncertainty

In the process of radiotherapy, no measurement or operation is perfect, including dose calculation, every step will be correspondingly inaccurate Qualitative. The data obtained after repeated measurements with a specific measurement method are discretely distributed, and the uncertainty is used to describe the characteristics of the distribution.

Parameter [1], these data can be expressed in the form of statistical distribution [Figure 1a)], and can be described by specific statistical values, including average, population Uncertainty refers to the standard deviation (or its multiples). Understanding of the uncertainty in each step of the radiotherapy plan With knowledge, it is necessary to determine the uncertainty of the calculated dose distribution.

Usually the uncertainty of a measurement contains multiple aspects. The method used by the International Commission for Weights and Measures (CIPM) to assess data will be uncertain The degree is divided into two categories. Type A uncertainty, which is evaluated by statistical methods; Type B uncertainty, which is evaluated by other methods. In the past two categories A and B Classified as random or systematic uncertainty, it is now believed that these classifications are not always a purely corresponding relationship.

The radiotherapy literature still frequently uses the two uncertainties of "random" and "system". In fact, system uncertainty such as patient positioning It can be determined and corrected by statistical methods (for example, in the first few treatments, the field image is used for measurement).

Figure 1b) shows the distribution of two uncertainties, one of which contains systematic errors.

5.2.2 Deviation

The measured or calculated deviation refers to the difference between its value and the expected value obtained by other methods, and the expected value can be used as a reference value. use. In the dose calculation discussed below, the reference data is usually calculated by measurement or Monte Carlo.

Measurements usually have both Type A uncertainty and Type B uncertainty. Different from measurement (measurement errors are usually both random and systematic Poor), the calculation will only produce type B uncertainty in most cases. For example, when evaluating the calculated dose at a certain point, assume The calculation parameters are exactly the same (for example, the same calculation grid, the same geometric conditions, the same calculation points, the same calculation algorithm, etc.), you can send Now this calculation can be repeated. In the same position of the phantom, the results showed a certain distribution after multiple measurements. Therefore, the contrast is The random uncertainty in the calculation is 0, and the measurement has a significant statistical distribution. If the calculated value deviates significantly from the measured mean value, consider System error (see Figure 1). In some cases, if it is based on statistical methods (such as Monte Carlo calculation), the calculation may also have Type A uncertainty Degree, this algorithm uses a randomly generated starting point (seed) to generate random numbers.

In addition, you can also compare the results of many calculations (at different spatial positions, such as the percent depth dose on the central axis) with the same space Different measurement results on location. This requires statistical integration of isolated deviations to fully evaluate the quality of calculations.

5.2.3 Tolerance

Tolerance is strictly defined as an acceptable range, beyond which correction is required. For example, when measuring, take the source skin distance as an example, the tolerance If the value is 5mm, the measurement of SSD exceeding ±5mm is not allowed (that is, it is unacceptable and needs to be corrected).However, as shown in 5.3, For RTPS, this situation is not so simple, and a looser definition is usually used.

The tolerance value can be determined based on the uncertainty of the reference data. The greater the uncertainty, the greater the tolerance, and more specialized requirements can also be used Or procedures to define. For example, radiosurgery has a smaller tolerance on dose and geometric conditions than palliative care. It should be noted that during radiotherapy The limited tolerance may depend on the clinical situation. Because stereotactic therapy is often given near normal tissues with very high radiation sensitivity.

The tolerance of stereotactic radiosurgery using Ono therapy is better than usual. Regulations or Ono exposure are much stricter.

5.2.4 Error

In this standard, error refers to a deviation in quantity caused by incorrect operation. Even if the result is within the tolerance range, there may still be errors. error. Of course, the influence of the error depends on whether the result is close to the tolerance value, and the influence is relatively small when it is close. If it is outside the tolerance, the result is obviously not accessible. Accept and pay more attention to it.

Random uncertainties from different sources usually overlap and cancel each other. However, if there is a system error, first consider eliminating it it. However, in some cases, although users know that there are system errors, they cannot eliminate them. For RTPS, a typical example is There is a repeatable deviation between the calculated value and the measured value at some specific points in the field (such as the penumbra area or near). In this way, even though The existence of repetitive differences may not be corrected by the user to avoid causing larger errors elsewhere.

If the RTPS error exceeds the tolerance, it should be reported to the supplier immediately. It is hoped that the supplier will provide appropriate software updates and eliminate Bed work has a significant impact on errors. During the period of the error, and RTPS is required, the user should ensure that the clinical treatment in this specific situation Planning errors are additionally compensated (for example, manual corrections).

5.3 Evaluate the quality standards, reference data, tolerances and methods of the treatment planning system

5.3.1 Quality standards

As mentioned in 5.1, if you want to formulate the QA procedures of RTPS, you need to implement the QC procedures-the standards need to be defined. The quality standard is Criteria that can be used to evaluate various behaviors. Standards can be defined in different forms, including those with double results. Therefore, for For RTPS, if the instructions indicate that there is a DVH function, then perform a functional evaluation (that is, whether it can be DVH scored).

Analysis?), to further evaluate the accuracy of the DVH analysis, does the calculation accuracy of the volume reach 0.5cm³ or the standard deviation is 1%?

Generally speaking, the quality assessment of RTPS requires reviewing all modules one by one, including qualitative analysis and quantitative analysis. 5.3.2~5.3.4 Mainly focus on the dose calculation function.

5.3.2 Reference data

The reference data used to evaluate the dose calculation should be consistent with the field data used for treatment. Therefore, in theory, it is The composition of the data measured at different positions under the piece. These data are used to evaluate the deviation of the calculated dose under similar conditions and serve as the field reference number according to. In addition to basic comparisons, especially for complex situations, some benchmark data can also be used. These data include.

Data from the literature, or data used in internal evaluations. The last type of reference data refers to the acquisition of field modeling and input as an algorithm.

A series of data into the data. Table 2 summarizes the different types of reference data.

However, when the technical specification describes a specific RTPS, it is often ambiguous; for example, when the supplier states "dose When the accuracy of the calculation algorithm can reach 2%", it means that the maximum error between the experimental data or Monte Carlo calculation value is 2%, or Means that the standard deviation of the difference is 2% (that is, the difference can be much greater than 2% at some specific points), or other statistical parameters? So the manufacturer The description of accuracy should include these statistical descriptions [2].

5.3.3 Tolerance for dose calculation

Tolerance settings should consider.

a) There is a difference between the measured value and the calculated value;

b) These differences depend on the position in the field and the patient's geometric conditions;

c) People cannot generalize about acceptable standards (tolerance). The accuracy of the dose calculation depends on the algorithm, the field area and The position in the patient's body, so we should analyze the deviation (and set the tolerance value) based on a full understanding of this;

d) A very effective way to compare calculated and measured values is to use statistical methods to analyze deviations. Although the comparison on individual points can be Given a specific tolerance value, but determining the overall acceptable range does not blindly follow the tolerance value at each point.

More reasonable is based on confidence limits or other similar standards. For example, some points may exceed the 2% tolerance, but if 95% of the points are within the range of 2%, this situation is acceptable;

e) Any ordinary tolerance or expected value table depends on the level of development of the dose calculation algorithm and the conditions considered (radio parameter Number, patient parameters) type. Different users will get different expectations and tolerance values based on the same type of information. Table 3 and The example in Table 4 describes two different ways of defining acceptance criteria.