DE102021107613A1 - Procedure for testing a medical gamma probe - Google Patents

Abstract

The invention relates to a method for testing a medical gamma probe, which includes both carrying out the acceptance test with regard to background and yield and the corresponding consistency tests. The radiation activity of the test source used is corrected on a daily basis. A corresponding gamma probe and a computer program for executing the method on the device and a corresponding computer-readable medium with the computer program are also specified.

Description

The invention relates to a method for testing a medical gamma probe.

Medical gamma probes are used, for example, during the surgical removal of breast cancer to determine whether it has already spread beyond a primary tumor into the lymphatic system. For this purpose, a protein-bound, radioactively marked substance is injected into the area surrounding the primary tumor. This substance is then quickly drained by the lymphatic system into the first lymph nodes, the so-called sentinel nodes, adjacent to the primary tumor. Using the gamma probe, the lymph nodes enriched with the radioactive substance can be located and surgically removed, which is known and established as a sentinel lymph node biopsy.

With such an application of medical gamma probes on and in the human body, legal requirements with regard to radiation protection must be observed, in particular quality assurance for all devices and equipment used in nuclear medicine. This required quality assurance includes, in particular, an acceptance test when the gamma probe is put into operation and a regular constancy test or quality test, which must be carried out and documented every working day, for example. The tests to be carried out include a so-called background test, in which the existing background noise is determined, and a yield test, in which the sensitivity of the gamma probe is checked using a suitable test source on this test source. Since gamma probes work as counting probes, the number of counts per unit of time is determined during the background test, for example during 30s ("counts/30s"), and the counts per second (cps) related to the radiation intensity of the test source used in kBq as the yield during the yield test given in "cps/kBq".

Quality assurance has so far been carried out manually for medical gamma probes, with the user checking the tests carried out as part of quality assurance, i. H. Acceptance test and constancy test, carried out manually in a corresponding test sequence and the measured values read from a control and display device connected to the gamma probe and manually recorded in a table and archived. This is time-consuming and error-prone, since reading and transmission errors can occur in particular. In addition, depending on the half-life of the isotope used, the test sources are subject to a continuous decrease in radiation intensity, which can lead to incorrect results.

The object of the invention is to propose a method for testing a medical gamma probe which can be carried out automatically and leads to a reproducible result while avoiding the disadvantages of the prior art.

In order to solve the stated problem, the embodiment of a method with the features of patent claim 1 is proposed according to the invention.

Advantageous configurations of the method according to the invention are the subject matter of dependent claims 2 to 5.

1. a) Ermittlung des aktuellen Datums und Durchführung einer Messreihe aus einer vorbestimmten Anzahl an einzelnen Strahlungsmessungen über ein vorbestimmtes Zeitintervall und Speicherung der zugehörigen Strahlungsmesswerte der Gammasonde pro Zeitintervall;
2. b) Berechnung des Mittelwertes sowie eines ersten und zweiten Toleranzwertes aus den gespeicherten Strahlungsmesswerten;
3. c) Speicherung des Mittelwertes und der ersten und zweiten Toleranzwerte aus Schritt b) als Bezugswerte für Untergrundprüfung mit dem aktuellen Datum;
4. d) Ermittlung des aktuellen Datums und Bereitstellung eines Gammastrahlung emittierenden Prüfstrahlers, wobei das Kalibrierdatum und die am Kalibrierdatum vorliegende Strahlungsaktivität des Prüfstrahlers erfasst werden und die Differenz zwischen dem aktuellen Datum und dem Kalibrierdatum des Prüfstrahlers berechnet und die Strahlungsaktivität des Prüfstrahlers nach Maßgabe der berechneten Differenz und der Halbwertszeit des Prüfstrahlers korrigiert wird;
5. e) Durchführung einer Messreihe aus einer vorbestimmten Anzahl an einzelnen Strahlungsmessungen über ein vorbestimmtes Zeitintervall, wobei die Strahlungsmessungen am Prüfstrahler vorgenommen werden und eine Berechnung der Ausbeute der Gammasonde pro Zeiteinheit aus dem Quotienten der Strahlungsmesswerte pro Zeitintervall und der korrigierten Strahlungsaktivität des Prüfstrahlers vorgenommen wird und Speicherung der berechneten Ausbeuten der Gammasonde pro Zeiteinheit;
6. f) Berechnung des Mittelwertes sowie eines ersten und zweiten Toleranzbereiches aus den gespeicherten Ausbeuten;
7. g) Speicherung des Mittelwertes und der ersten und zweiten Toleranzbereiche aus Schritt f) als Bezugswerte für Ausbeuteprüfung mit dem aktuellen Datum.

The proposal according to the invention for testing a medical gamma probe comprises the following steps:

1. a) determination of the current date and implementation of a series of measurements from a predetermined number of individual radiation measurements over a predetermined time interval and storage of the associated radiation measurement values of the gamma probe per time interval;
2. b) calculation of the mean value and a first and second tolerance value from the stored radiation measurement values;
3. c) storing the mean value and the first and second tolerance values from step b) as reference values for background testing with the current date;
4. d) Determination of the current date and provision of a test source emitting gamma radiation, whereby the calibration date and the radiation activity of the test source on the calibration date are recorded and the difference between the current date and the calibration date of the test source is calculated and the radiation activity of the test source based on the calculated difference and the half-life of the test source is corrected;
5. e) Carrying out a series of measurements from a predetermined number of individual radiation measurements over a predetermined time interval, with the radiation measurements being carried out on the test source and the yield of the gamma probe per unit of time being calculated from the quotient of the radiation measurement values per time interval and the corrected radiation activity of the test source and storage the calculated yields of the gamma probe per unit time;
6. f) calculation of the mean value and a first and second tolerance range from the stored yields;
7. g) storing the mean value and the first and second tolerance ranges from step f) as reference values for yield checking with the current date.

The reference values determined as part of the preceding steps a) to g) for the background test and the yield test are determined and stored as part of an acceptance test to be carried out once when the gamma probe is put into operation. The first and second tolerance values and tolerance ranges calculated from the mean values obtained also serve as reference ranges in subsequent consistency or quality tests.

To carry out a constancy test, for example every working day, a first radiation measurement is carried out according to the invention over the predetermined time interval in the absence of the test source and the determined radiation measurement value of the gamma probe is compared with the reference values for the background test. Furthermore, the current date is determined and a second radiation measurement is carried out on the test source, whereby the difference between the current date and the calibration date of the test source is calculated and the radiation activity of the test source is corrected based on the calculated difference and the half-life of the test source. The yield of the gamma probe is calculated from the quotient of the determined radiation measurement value of the gamma probe and the corrected radiation activity of the test source and compared with the reference values for yield testing and if the determined radiation measurement value and/or the calculated yield of the gamma probe exceeds or falls below the reference values, a corresponding one is recorded alarm signal issued.

Within the scope of the method according to the invention, it is therefore possible, for example by actuating a corresponding hardware or software switch on a control and display device connected to the medical gamma probe, to carry out the acceptance test according to steps a) to g) automatically and automatically during initial commissioning and As part of the desired constancy tests, the further radiation measurements are also carried out automatically and automatically. The determined first tolerance values and ranges are preferably more closely based on the mean than the second tolerance values and ranges, so that the first tolerance values and ranges as standard values for the deviations determined as part of the constancy test and the second tolerance values and ranges limit ranges for no more represent acceptable measurement results. For example, the first tolerance value of the environmental measurement based on the calculated mean value can be set at plus 20% of the determined mean value and the second tolerance value at plus 50% of the determined mean value. Correspondingly, the first tolerance range for the yield check can be defined at ±10% of the determined mean value and the second tolerance range at ±15% of the determined mean value. According to the invention, a first intervention threshold is thus defined in the first tolerance value and/or first tolerance range, which prevents tolerance limits from being present as the first hard limit. Only when the second tolerance value or range is exceeded does the user have to shut down the gamma probe. As a result, the gamma probe is checked quickly and reliably to determine whether the measured radiation values determined by the gamma probe are within the specified reference values for the background test and for the yield test, with the decrease in the radiation activity of the test source being taken into account on a daily basis and corrected accordingly. The method according to the invention can therefore be carried out quickly, reliably and with high accuracy of the measured values determined.

According to one proposal of the invention, the determined radiation measurement values and calculated yields of the gamma probe, including the values from the acceptance test, are archived electronically with the associated current date, which can be done, for example, on a suitable memory chip, such as an SD card, to ensure complete, paperless documentation .

According to a further proposal of the invention, the calibration date and the radiation activity of the test source used on the calibration date are also read in from a suitable data carrier, for example an SD card.

According to one proposal of the invention, the predetermined time interval over which the radiation measurement value of the gamma probe is measured in the absence of the test source for carrying out the background test can be 10 to 200 seconds, preferably 30 to 100 seconds.

According to a further proposal of the invention, the measurement series for determining the mean values in step a) and/or e) as part of the background test and the yield test can each comprise 5 to 20, in particular 10 measurements.

The invention also relates to a gamma probe with a control and display device connected to the gamma probe and means that are suitable for carrying out the method steps explained above. The connection between the gamma probe and the control and display device can be either wired or wireless.

Furthermore, the invention also encompasses a computer program comprising instructions which cause the device, i. H. the gamma probe with associated control and display device that performs procedural steps.

Finally, a computer-readable medium on which the computer program explained above is stored is also the subject matter of the present invention.

• 1 ein Ablaufdiagramm zur Durchführung der Abnahmeprüfung für Untergrundmessung nach dem erfindungsgemäßen Verfahren;
• 2 ein Ablaufdiagramm zur Berechnung der Zerfallskorrektur des Prüfstrahlers nach dem erfindungsgemäßen Verfahren;
• 3 ein Ablaufdiagramm zur Durchführung der Abnahmeprüfung für Ausbeutemessung nach dem erfindungsgemäßen Verfahren;
• 4 ein Ablaufdiagramm zur Durchführung der Konstanzprüfung zur Untergrundmessung nach dem erfindungsgemäßen Verfahren;
• 5 ein Ablaufdiagramm zur Durchführung der Konstanzprüfung zur Ausbeutemessung nach dem erfindungsgemäßen Verfahren.

Further configurations and details of the method according to the invention are explained in more detail below using an exemplary embodiment and with reference to the accompanying drawings. Show it:

• 1 a flowchart for carrying out the acceptance test for underground measurement according to the method according to the invention;
• 2 a flow chart for calculating the decay correction of the test radiator according to the method according to the invention;
• 3 a flow chart for carrying out the acceptance test for yield measurement according to the method according to the invention;
• 4 a flowchart for carrying out the constancy test for background measurement according to the method according to the invention;
• 5 a flow chart for carrying out the constancy test for yield measurement according to the method according to the invention.

A medical gamma probe with a control and display device are connected to one another in a manner known per se by means of a signal line. The control and display device executes a computer program that causes it to carry out the following method steps.

In order to carry out an acceptance test, which is to be carried out and documented in particular once when the medical gamma probe is put into operation, a background measurement is first carried out to determine the background noise.

According to 1 the computer program read into the control and display device from a computer-readable medium first waits for a corresponding command from the user to initiate the background acceptance test.

When activated, the current date is first read from a system clock, for example, and a series of measurements from a predetermined number, in this case a total of 10 individual radiation measurements, is carried out over a predetermined time interval of 30 seconds. The arithmetic mean is calculated from the determined measured values and then a first tolerance value is determined as the reaction threshold and a second tolerance value as the tolerance limit.

The first tolerance value serving as a reaction threshold is set at plus 20% in relation to the determined mean value. The second tolerance value serving as a tolerance limit is set at plus 50% in relation to the determined mean value. These tolerance values are later applied to the constancy or quality check, which is to be carried out in particular every working day and which will be explained below. The values determined from the substrate acceptance test and the associated tolerance values saved in the control and display unit on a suitable storage medium, for example an SD card, together with the current date.

Following the acceptance test for background measurement, the acceptance test for yield measurement is carried out according to 3 carried out.

For this purpose, a test source emitting gamma radiation is first provided, with the isotope used, the calibration date and the radiation activity of the test source on the calibration date being read from a suitable storage medium, e.g. an SD card in the control and display device, and the difference between the current date and calculated from the calibration date of the test source and the radiation activity of the test source is corrected based on the calculated difference and the half-life of the test source. This process is in 2 shown.

wobei N(t) die tagesaktuelle Strahlungsaktivität, No die Strahlungsaktivität bei Herstellung des Prüfstrahlers, T_1/2 die Halbwertszeit des verwendeten Isotops und t die Differenz in Tagen zwischen dem Kalibrierdatum und dem aktuellen Datum bezeichnen.The calculation of the radiation activity is based on the following formula: $$N\left(t\right)=N_0\cdot e^{-\frac{\text{ln}\left(2\right)}{T_{1/2}}t}$$

where N(t) is the daily radiation activity, No is the radiation activity when the test source was manufactured, T _1/2 is the half-life of the isotope used and t is the difference in days between the calibration date and the current date.

For example, based on this formula, the control and display device determines a daily activity of the test source of 144.39 kBq on September 30, 2020 for the nuclide Co-57 used as a test source with an original radiation activity of 803 kBq on the calibration date April 1, 2018.

Then according to 3 using the gamma probe, a series of measurements from a predetermined number, for example 10 individual measurements, is carried out on the test source and the yield of the gamma probe per unit of time is determined from the quotient of the radiation measurement values per time interval and the corrected radiation activity of the test source. The determined yields of the series of measurements are saved and then an arithmetic mean is calculated from these measured values. The first and second tolerance ranges are then defined as a reaction threshold and as a tolerance limit for the calculated mean value.

The first tolerance range, which serves as a reaction threshold, is set at ±10% based on the determined mean value. The second tolerance value serving as a tolerance limit is set at ±15% in relation to the determined mean value. These tolerance ranges are later applied to the constancy or quality check to be carried out in particular every working day, which will be explained below. The values determined from the yield acceptance test and the associated tolerance ranges are stored in the control unit together with the current date on a suitable storage medium, such as an SD card, and are also stored in the EEPROM of the control and display unit.

After the acceptance test has been carried out once when the gamma probe is put into operation and the values for the background measurement and the yield measurement have been saved, the required constancy test for the background and yield measurement can then be carried out regularly, in particular every working day.

For this purpose, the control and display device offers a corresponding selection button via hardware or software and, when pressed accordingly, starts the constancy test for the background measurement according to 4 .

• Zum einen kann der gemessene Wert unterhalb der festgelegten Reaktionsschwelle liegen, worauf hin das Steuer- und Anzeigegerät den ermittelten Messwert beispielsweise grün anzeigt, was die bestandene Prüfung signalisiert.

A first radiation measurement is performed for the predetermined time interval according to the acceptance test, with no test source present, and the determined radiation measurement value of the gamma probe is compared with the reference values for the background test from the acceptance test. The result can be divided into three different cases:

• On the one hand, the measured value can be below the specified reaction threshold, whereupon the control and display device displays the determined measured value in green, for example, which signals that the test has been passed.

On the other hand, the measured value can also be above the defined reaction threshold, but still below the tolerance limit. In this case, the control and display device shows the determined measured value in yellow, for example, which signals to the operator that the measurement must be repeated and, if necessary, that a radiation protection specialist must also be informed.

Finally, the measured value can also exceed the tolerance limit. In this case, the control and display device shows the determined measured value in red, for example, which signals to the operator that the gamma probe may no longer be used until the cause has been clarified. If necessary, the further function of the gamma probe can also be blocked in the software until it is unlocked again by the manufacturer.

If the constancy test for the background measurement has delivered acceptable values, the constancy test for the yield measurement of the gamma probe can then be initiated. The process is in the 5 shown.

• Zum einen kann der gemessene Wert unterhalb der festgelegten Reaktionsschwelle liegen, worauf hin das Steuer- und Anzeigegerät den ermittelten Messwert beispielsweise grün anzeigt, was die bestandene Prüfung signalisiert.

Accordingly, the current date is first determined by the control and display unit and a second radiation measurement is carried out on the test source, with the decay correction of the test source first or subsequently according to 2 carried out again on a daily basis. The yield of the gamma probe is then calculated from the quotient of the determined radiation measurement value of the gamma probe and the corrected radiation activity of the test source and compared with the reference values for the yield test. The result can be divided into three different cases:

• On the one hand, the measured value can be below the specified reaction threshold, whereupon the control and display device displays the determined measured value in green, for example, which signals that the test has been passed.

On the other hand, the measured value can also be above the defined reaction threshold, but still below the tolerance limit. In this case, the control and display device shows the determined measured value in yellow, for example, which signals to the operator that the measurement must be repeated and, if necessary, that a radiation protection specialist must also be informed.

Finally, the measured value can also exceed the tolerance limit. In this case, the control and display device shows the determined measured value in red, for example, which signals to the operator that the gamma probe may no longer be used until the cause has been clarified. If necessary, the further function of the gamma probe can also be blocked in the software until it is unlocked again by the manufacturer.

In any case, the yield measurement includes the correction of the decay of the test source and the measured values of the daily background and yield measurement are documented and stored on the SD card in the control and display device of the gamma probe together with the current date and saved or archived .

Example:

The functionality of the procedure explained above and the sequence of the corresponding procedural steps are shown on the basis of a chronologically documented process: Date: 09/30/2020 - Commissioning of the gamma probe Step 1: The test source data are transferred to the control and display unit via the SD card: Nuclide: Co-57 Activity: 803 kBq Calibration date: 04/01/2018 Step 2: The device internally calculates the corrected activity of the check source with a value of 144.39 kBq for the date of commissioning. Step 3: Starting the background acceptance measurement: 10 readings are recorded and the mean value is calculated. All values and the calculated limits are shown on the display of the control and display unit: Background = 49counts/30s Background = 52counts/30s Background = 54counts/30s Background = 42counts/30s Background = 43counts/30s Background = 44counts/30s Background = 29counts/30s Background = 31 counts/30s Background = 46counts/30s Background = 48counts/30s Mean-background decrease : 43counts/30s Background Response Threshold : 51counts/30s Background Tolerance Limit : 64counts/30s Step 4: Start the yield acceptance measurement with the help of the test source: 10 measured values are recorded and the mean value is calculated. All values and the calculated limits are shown on the display: Yield = 39.19cps/kBq Yield = 39.59cps/kBq Yield = 39.31cps/kBq Yield = 39.55cps/kBq Yield = 39.52cps/kBq Yield = 39.50cps/kBq Yield = 39.39cps/kBq Yield = 39.34cps/kBq Yield = 39.50cps/kBq Yield = 39.33cps/kBq Mean yield decrease in cps/kBq 39.42 Yield response thresholds in cps/kBq: 35.48< yield <43.36 Yield tolerance limit in cps/kBq: 33.51< yield <45.34 Step 5: All values and limits are stored in the device and on the SD card and used for daily quality control.

The following steps are then carried out for the daily constancy test and the corresponding measured values are determined and saved: Date: 11/19/2020 with corrected check source activity 127.06kBq Step 1: Starting the background measurement - result: background = 13 c/30s → below reaction thresholds (green) Step 2: Start yield measurement - result: yield = 40.51 cps/kBq → below reaction thresholds (green) Step 3: Save to SD card Date: 11/23/2020 with corrected check source activity 125.76kBq Step 1: Starting the background measurement - result: background = 26 c/30s → below reaction thresholds (green) Step 2: Start yield measurement - result: yield = 37.28 cps/kBq → below reaction thresholds (green) Step 3: Save to SD card Date: 11/27/2020 with corrected check source activity 124.48kBq Step 1: Starting the background measurement - result: background = 26 c/30s → below reaction thresholds (green) Step 2: Start yield measurement - result: yield = 39.42 cps/kBq → Below reaction rates (green) Step 3: Save to SD card Date: December 2nd, 2020 with corrected check source activity 122.90kBq Step 1: Starting the background measurement - result: background = 18 c/30s → below reaction thresholds (green) Step 2: Start yield measurement - result: yield = 39.63 cps/kBq → below reaction thresholds (green) Step 3: Save to SD card

The method explained above enables the automated and time-saving testing of a medical gamma probe and contributes significantly to increasing the productivity of the user. Transmission errors are reduced and comprehensible and reliable results are generated through continuous decay correction of the test source used. Continuous electronic storage eliminates the need for paper records, which is particularly beneficial in the operating room.

It goes without saying that the method steps mentioned in the patent claims do not necessarily have to be processed in the order laid down there, but can also be processed in a different order or in parallel at the same time.

Claims (8)

Method for testing a medical gamma probe, comprising the following steps: a) determining the current date and carrying out a series of measurements from a predetermined number of individual radiation measurements over a predetermined time interval and storing the associated radiation measurement values of the gamma probe per time interval; b) calculation of the mean value and a first and second tolerance value from the stored radiation measurement values; c) storing the mean value and the first and second tolerance values from step b) as reference values for background testing with the current date; d) Provision of a test source emitting gamma radiation, whereby the calibration date and the radiation activity of the test source on the calibration date are recorded and the difference between the current date and the calibration date of the test source is calculated and the radiation activity of the test source is corrected based on the calculated difference and the half-life of the test source becomes; e) Determination of the current date and implementation of a series of measurements from a predetermined number of individual radiation measurements over a predetermined time interval, with the radiation measurements being carried out at the test source and a calculation of the yield of the gamma probe per unit of time from the quotient of the radiation measurement values per time interval and the corrected radiation activity of the test source is carried out and storage of the calculated yields of the gamma probe per unit of time; f) calculation of the mean value and a first and second tolerance range from the stored yields; g) storing the mean value and the first and second tolerance ranges from step f) as reference values for yield checking with the current date; In order to carry out a constancy test, a first radiation measurement is carried out over the predetermined time interval in the absence of the test source and the determined radiation measurement value of the gamma probe is compared with the reference values for the background test and the current date is determined and a second radiation measurement is carried out on the test source, the difference between the current date and the calibration date of the test source is calculated and the radiation activity of the test source is corrected based on the calculated difference and the half-life of the test source and the yield of the gamma probe is calculated from the quotient of the determined radiation measurement value of the gamma probe and the corrected radiation activity of the test source and with the reference values for yield testing is compared and an alarm signal is emitted if the determined radiation measurement value and/or the calculated yield of the gamma probe exceeds or falls below the reference values is issued. procedure after claim 1 , characterized in that the determined radiation measurement values and calculated yields of the gamma probe are archived with the associated current date. procedure after claim 1 or 2 , characterized in that the calibration date and the radiation activity of the test radiator on the calibration date are read from a data carrier. Procedure according to one of Claims 1 until 3 , characterized in that the predetermined time interval is 10 to 200 s, preferably 30 to 100 s. Procedure according to one of Claims 1 until 4 , characterized in that the series of measurements in step a) and/or e) comprises 5 to 20, in particular 10, measurements. Gamma probe with a control and display device connected to the gamma probe and means suitable for carrying out the method steps according to one of the preceding claims. Computer program comprising instructions that cause the device of the claim 6 the method steps according to one of Claims 1 until 5 executes Computer-readable medium on which the computer program claim 7 is saved.

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