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a lead equivalent value of min. 1.0 mm. The new DIN EN 61331-3, issue May 2002 [11] stipulates for »gonadal protection aprons« an attenuation equivalent of min. 0.55 mm Pb according to standard sizes (for children and adults). In addition, this new standard also recommends »light testicle protection« with min. 0.5 mm Pb and »heavy testicle protection« and »ovary protection« each with an attenuation equivalent of min. 1.0 mm Pb. It goes without saying that existing patient protection devices according to the old DIN 6813 can still be used. The specialist doctor decides about using the existing radiation protection accessories from case to case.

Annex III of the Expert Guidelines [5] lists the necessary patient protection devices for X-ray diagnosis machines depending on the various areas of application. For surgical and orthopaedic applications, the devices are as follows:

4 gonadal protection aprons in several sizes, 4 testicle capsule (enclosing) in several sizes, 4 ovary shields, 4 patient protection aprons, 4 lead rubber covers in several sizes.

Together with these necessary patient protection devices as per DIN 6813 [10], the recommendations for use of the accessories in the (old) standard must also be heeded. The radiation protection accessories as per DIN 6813 must have at least the lead equivalents shown in O Table 4.2.

The effectiveness of the shields decreases out of all proportion in the face of higher energy radiation, i.e. generated with higher tube voltage. But the radiation protection accessories are still ideally effective for the tube voltage range of about 70 kV required in surgery. So consistent use of the radiation protection accessories constitutes a very effective radiation protection measure.

Radiation protection of the patient should also be mentioned by the responsible surgeon in his personal information session with the patient. This is part of his duty to inform as required in the professional code of conduct of the state Medical Councils in order to obtain the patient's consent for the intended medical procedures.

4.1.2.8 Records

According to § 28 of the X-ray Ordinance, suitable records are to be produced about using X-rays on persons, which must also contain

4 information about earlier medical use of ionising radiation, insofar as this is significant for the intended application and 4 in the case of female persons of an age capable of bearing children, information about whether they are pregnant or not.

In the case of X-ray examinations, X-ray cards are to be kept available and offered to the patient (§ 28 Para. 2 of the X-ray Ordinance).

The records in the X-ray card should help to avoid unnecessary X-ray pictures or examinations in individual cases. But the patient is not obliged to keep such an X-ray card on him.

Together with the information obtained by asking the patient about past X-rays, records must also be kept of every use of X-rays. These records must contain all information required to reconstitute the radiation exposure in each individual case, even months and years after the radiation application. Since the amended X-ray Ordinance came into effect in 2002, all newly commissioned X-ray radiography equipment including surgical image intensi-fiers must be equipped with devices for registering the exposed radiation, for example a dose surface product measuring device or a device which calculates and displays the exposed radiation from the operating parameters. Correct recording of the dose surface product (DFP) is therefore particularly important - also including the unit of measurement, for example in »|iG*m2« or »cGy*cm2«. The dose surface product can be used to reliably ascertain the effective dose for a patient for a defined application. All surgical image intensifiers already in use must be retrofitted with a device to register the radiation exposed during operation within an interim period. Furthermore, since 2003 standard DIN 6868 Part 7 [12] has been available to all users, which allows for reliable estimation of the radiation exposure for the patient on the basis of the application parameters for the patient.

The records of X-ray examinations, i.e. also about radiation applications with surgical image intensifiers, must be kept for 10 years. The records must be organised in such a way that they indicate 4 the point in time, 4 the type of application,

4 the parts of the body being examined, 4 information about justifying the use and 4 the obtained findings.

The records about the point in time of the application, the parts of the body being examined and the details of the doctor performing the examination are to be entered in the X-ray card if submitted by a patient.

4.1.2.9 Quality assurance according to the X-ray Ordinance

According to § 16 of the X-ray Ordinance, the rules for quality assurance also apply to surgical image intensifiers, as described in detail in the above mentioned guidelines for quality assurance [6]. This includes in particular the acceptance test and possibly also partial acceptance tests in accordance with the X-ray Ordinance by the manufacturer or supplier of the X-ray machine, regular constancy tests to be carried out by the owner, and advice from the Medical Department of the corresponding federal state. The overall concept of quality assurance and radiation protection for X-ray diagnostic equipment is shown in O Fig. 4.9 in a simplified manner in relation to the operating time of an X-ray diagnosis machine.

Advice from the Medical Department (7 § 17a of the X-ray Ordinance) suggesting measures to reduce radiation exposure of patients and optimise image quality is based on the new guidelines »Medical and Dental Departments« dated 5 November 2003 [13] and consists essentially in evaluation and assessment of 4 the documents required for acceptance tests or partial acceptance tests, for radiation protection inspection by an officially appointed expert and the regular constancy tests by the owner, together with the 4 required patient X-ray pictures (direct or indirect X-ray pictures either from the X-ray image intensifier output or from another downstream imaging system).

Fig. 4.9. Regulations for quality assurance in X-ray diagnosis

The records of constancy tests for X-ray imaging equipment also include X-ray film pictures of a special technical test body. These test body pictures are compared with the reference pictures taken during the acceptance test by the manufacturer or supplier. Such objective picture documents must be produced during constancy tests of radiography equipment with image intensifier TV chains, i.e. also with surgical image intensifiers, if these units are used to produce X-ray pictures e.g. for documentation purposes. The constancy tests of these units also assesses the monitor picture of the test body by the owner or doctor in visual terms in reference to certain parameters for »physical picture quality«. This assessment cannot be based without doubt on the comparison monitor picture assessed during the acceptance test by the manufacturer or supplier. In order to ascertain gradual changes in the monitor picture over time, the Medical Department rightly insists that the owner's records about the constancy tests on these radiography machines are confirmed on an annual basis by the manufacturer, e.g. as part of regular maintenance, or by an officially appointed expert.

The new X-ray Ordinance and its implementing regulations also contain stricter rules and standards for the requirements made of the reproduction systems for X-ray examinations, i.e. at the end of each complete imaging system, also with regard to the increasing digitisation of X-ray diagnosis and its integration in medical IT systems in hospitals and general medical practices.

The quality assurance guidelines therefore also state technical requirements for film viewing equipment (film viewers) for image documentation systems (e.g. hardcopy cameras, hardcopy printers) and for image reproduction units. Insofar as this equipment is also used as part of surgical image intensifiers, it has to fulfil the corresponding requirements. Quality tests (acceptance test and constancy test) are to be performed in particular for image reproduction systems for C-arm units. Section 8 of the quality assurance guideline describes the requirements for image reproduction systems from a medical point of view and defines the terms evaluation and viewing. Evaluation refers to the diagnostic image quality as defined in the X-ray Ordinance. By contrast, viewing (only) refers to the image features and contents of images which have already been evaluated as part of doctor information, demonstration and control. According to the quality assurance guideline, image reproduction units (monitors, VDUs, displays) and film viewers must be marked by the radiation protection manager according to their purpose for evaluation or viewing.

Image reproduction units which were already commissioned when the new quality assurance guideline came into effect (old units) are to be tested along the lines of the acceptance test according to DIN V 6868-57 [8]. This additional acceptance test of old units is to be completed by 31 December 2005 at the latest with verification sent to the supervisory authorities. Following the acceptance test,

Cut through a standing anode X-ray tube

1 Cathode

2 Filament (electron source)

3 (Thermal) focal spot

4 Tungsten diaphragm

5 Vacuum chamber

6 Hard glass piston

7 Anode (copper shaft)

8 Primary ray diaphragm

9 Effective ray cone (shaded)

X-ray quantum Electron

Cut through a standing anode X-ray tube

1 Cathode

2 Filament (electron source)

3 (Thermal) focal spot

4 Tungsten diaphragm

5 Vacuum chamber

6 Hard glass piston

7 Anode (copper shaft)

8 Primary ray diaphragm

9 Effective ray cone (shaded)

X-ray quantum Electron

D Fig. 4.10. Diagram to show the generation of X-rays constancy tests are to be carried out for these units on a daily, quarterly or 6-monthly basis, depending on the characteristics of the image reproduction unit.

Quality tests are also prescribed for film viewers and image documentation systems.

4.1.3 Generating X-rays

Since the almost coincidental discovery of X-rays in 1895 by Wilhelm Conrad Röntgen in his physical laboratory at the University of Würzburg, X-rays have been used for many medical and technical purposes. The key role in their discovery was played by the so-called luminescence effect. The light emitted by a barium platinum cyanide screen, which was accidentally hit by X-rays during experiments with cathode ray tubes, prompted Röntgen to pursue these phenomena and to examine the newly discovered rays and how to generate them in greater depth.

X-rays are produced among other things by the interaction of accelerated electrons, i.e. negative charge carriers, with a metallic anode (positive pole), e.g. a heat-resistant tungsten anode. This interaction of the electrons with the atomic shell of the tungsten atoms produces the so-called X-ray Bremsstrahlung (or braking radiation), which plays the major role in X-ray diagnosis. This interaction process is triggered in a high vacuum glass vessel, the so-called X-ray tube. High electric voltage applied between the cathode and anode accelerates the electrons emitted by

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