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Submitted by C├ęcile ETARD, IRSN
   Commenting on behalf of the organisation
Document Diagnostic Reference Levels in Medical Imaging
 

-  Page 10, Ligne 4: The use of phantom is disconnected from clinical practice. Dose measurement on phantom is comparable to a quality control of the device avoiding the evaluation of the clinical practice. If the use of phantom for DRL quantities' collection is not excluded, a caution should be mentioned in order to notify that phantom use is not equivalent to patient survey and doesn’t allow reaching entirely the goal of dose optimisation.


-  P11, L13: “at” should be suppressed


-  P11, L14/15: use the same wording as in the glossary for “DRL value”: the 75th percentile of the medians of DRL quantity distributions observed at multiple facilities”


-  P13: add units to all the quantities


-  P14, L16: “mGy.cm”


-  P15, L11: “J.kg-1


-  P16, L44: [including interventional radiology] should be added after “For medical exposures,…”


-  P21, L22: the European projet “PiDRL” should be mentioned


-  P22, L1: the huge lack of data for some types of practice (pediatrics) inducing inconsistency of DRL values or impossibility of DRL definition is also an important issue with the current DRL process


-  P22, L20: “the administered activity is, in some cases, weight-based”.


-  P24, L36 (§26): General agreement on image quality is not met among radiologists and physicists, for CT in particular, as it is mentioned in §125. This paragraph (26) should be either removed or modified considering the following points:



  • EC criteria were defined 20 years ago and have not been updated to current practice and technology.

  • Current trend is to develop objective image quality metrics that are correlated to the perceived image quality but not operator-dependant (cf. ICRU 87). A lot of research efforts is needed before these metrics come into clinical practice and could be used for combined dose/image quality assessments at a national level.

  • Clinical image quality is a relative notion, as it depends on the indication of the examination (e.g. a given CT of the abdomen can be scored as ‘non diagnostic’ for an evaluation of a kidney cancer or as ‘good quality’ for a kidney stone assessment). If DRL are not given per indication, it is most of the time illusory to establish a link with image quality.


-  P32, L21:The sentence of paragraph (78) could be used to define more precisely what cover the words ““healthcare providers”


-  P32, L30: very important for pediatrics but it is not necessary for adults if the sample is large enough


-  P33, L1: The words “regional”, “national”, “local” should be defined more precisely because they can be differently understood, depending on the administrative structures of the country. For example the word “region” can be interpreted as a smaller area than the nation. For example, France is divided in several administrative and cultural regions.


-  P33, L17: replace “examiantions” by examinations.


-  P33, L32: “indicate” should be replaced by “are correlated to”.


-  P33, L33: “administered activity applied” should be moved into the parenthesis of the line 31 with the others metrics.


-  P34, L28: “or is less than some specified percentile” suggests that a "minimum" dose is required. If the image quality is relevant the dose can be as low as possible. The limit should be defined by the image quality not by the dose. A proper quality control program should be in place to ensure image quality and the daily practice of radiologists should also alert on a decrease in image quality.


-  P35, Table2.1, 2nd line: “phantom measurement” for mammography seems to be contradictory with (54).


- P38, L9: “a local DRL will normally be lower than the national DRL”. Why? Is there any reference stating this point? In our experience, it is not a general rule. This is contradictory with the “case mix” mentioned further in the document (287).


- P39, L19: we do not agree with “smaller facilities may employ unusual practices that do not reflect those used widely across the country”. It is not so simple: Good or bad practices are not related to the size of the facilities. And ICRP cannot accept such a situation: guidance should be established nationally or regionally and used in every facility, small or large. This is very important regarding equity of care. Therefore the survey to establish DRL should involve a selection of representative facilities: private, public, small and large.


- P43, L18: the specification of the clinical task seems to be relevant for CT but not for very standardized examinations as X-Ray chest.


- P48, L6: “DRL” instead of “DR”?


- P51, L16 (§120): Somewhat contradictory with §119 (P51,L8). As DRLs are established by a survey of the clinical practices in a given country or region, it is not likely that they could be driven ever downward. If a modified imaging protocol does not provide the necessary diagnostic quality, it will not be accepted by the radiologists and will therefore not be accounted for in the next DRL survey.


- P51, L22 (§121): Acceptable functioning of the imaging equipment should be covered by the quality control program. Consider modifying the 1st sentence as “… surveyors should ensure that imaging equipment is functioning acceptably, by mean of a proper quality control program and a particular attention to the accuracy of the dosimetric quantity of interest”.


- P51, L36 (§123): Why focus on Chest radiography? This paragraph seems to be not appropriate. Furthermore it refers to an old ICRU report (1995) and imaging techniques have changed since 1995.


- P52, L11: remove “CT and other digital”


- P52, L12-14: Replace the whole sentence by “The factors involved relate to (1) low-contrast detectability and (2) spatial resolution of the displayed image”. Window level and width are not sufficient for determination of contrast. Spatial resolution is affected by other parameters than focal spot size and reconstruction kernel.


- P54, L17: repetition “image quality and image-quality”.


- P58, L10: Skull x-ray is no more justified in France, therefore DRL for this examination has been suppressed in 2011.


- P59, L10: “Whether or not the x-ray beam passes through the patient couch” influences the Ka,e and the relation between PKA and Ka,e. As the purpose of DRLs is not to evaluate individual doses, it seems not to be an issue. Furthermore it only concerns C-arms and interventional radiology installations where x-ray tube can be placed under the patient couch.


- P59, L20: “measured on clinical images” is confusing. It might be replaced by ”measured on the patient during the acquisition of the image” or equivalent.


- P59, L25: Available softwares allow the calculation of Ka,e without output measurement. IRSN offers a calculation tool (free)on his website (MICADO: http://nrd.irsn.fr/micado).


- P60, L2: what is the DDI? It should be precisely defined if relevant (in the glossary).DDI “should also be recorded”? What for? Collection of this index might be difficult and time consuming. How is it used in terms of dose optimisation?


- P62, L22-39: these paragraphs refer to QA considerations which do not fit in a publication on DRLs. They are too much detailed and should be removed. If such details are given for mammography, you should also precise QA for radiography, CT, etc.


- P67, L32: “patients”


- P67, L39: it also depends on the place of artery catheterization: femoral or radial artery?


- P80, L1: Although it is theoretically a good approach, the establishment of different DRLs according to the clinical purpose as recommended at (94) and according to the type of detector will make the data collection very difficult. Huge amount of data would be necessary to offset the data subdivision and might be impossible to collect.


-  P82, L1: CTDIvol might be inappropriate with SSCT or sequential acquisition with MSCT.


- P83, L1: anatomical limits (for ex: diaphragmatic domes to pubic symphisis) or position coordinates? In this second case requesting for the scan length might be more consistent.


- P83, L9: What does "calibration" refers to? Accuracy tests? A mentioned P52 (see above) it should be referred to a proper quality control program. Moreover, the phantom characteristics (i.e. 16 or 32cm diameter) should be specified in the DRL value, especially for pediatrics), and checked during the data collection in order to avoid any confusion between some DRLs defined with one phantom and collected data from the other one.


-  P83, L24: Is it a suggestion or a first step for the introduction of DRLs in the field of control imaging in radiotherapy? If yes, dedicated CT for radiotherapy should also be taken into account.


-  P83, L36: “mGy.cm²”.


-  P84, L26: Previously, only the radiopharmaceutical was considered in order to define a DRL. The use of such detectors (CZT) modifies the amount of administered activity to patients for an examined region (e.g. heart). DRLs should consider the technology of the camera in addition to the radiopharmaceutical.


- P86, L1: Iterative reconstruction is recent for CT but not really for NM. Software advances in image reconstruction in general (including attenuation correction, noise regularization, resolution recovery) would fit better with the idea of this sentence. Iterative reconstruction concerns (or will concern in the near future) the CT in hybrid imaging (PET/CT or SPECT/CT).


- P86, L4: “Excepted for specific devices as CZT cameras” should be added after “For most planar nuclear medicine procedures…”.


- P86, L15: Theoretically the definition of DRLs in terms of MBq/kg allows avoiding the selection of patient weight range.


- P87, L10: other radiopharmaceuticals for PET imaging should be considered: F-DOPA, F-Na…


- P87, L26: The two sentences of this paragraph are not consistent.


- P87, L31: It should be mentioned that this maximum value of administered activity refers to overweighed patients.


- P93, L36: and what about the number of patients per weight band if weight is known? On a practical point of view it is very difficult to get data for 30 patients per age group in a “reasonable” period.


- P105, L13: replace “shoulld” by “should”.


- P108, L33: AEC could also be used with films.


- P109, L3: AEC can also be used in analogic mammography.


- P110, L34: “associated to a protocol adaptation” should be added after ”applied”. If the protocol is not modified, iterative reconstruction technique will not by itself reduce the amount of radiation.


- P119, L18: this summarized recommendation doesn't seem to be consistent with what as been proposed for mammography in the text body (survey with 50 patient data – see p41 L19). No mention of the breast thickness appears above in the report

- P119, L26: CTDIvol might be inappropriate with SSCT or sequential acquisition with MSCT. How will the introduction of SSDE be taken into account in the definition of DRLs?


- P119, L37: Although many countries use standard activity for adult patients, this practice is contradictory with the objective of dose optimisation.


- P123, L21: the word “facility” should be defined (in the glossary). Is it an x-ray unit (a camera) or a department?


- P123, L19 : what interval is recommended for the collection of DRL quantities in the facility? According to §284 : “A representative selection of examinations for each x-ray unit should be surveyed at intervals of about three years, and whenever substantial changes in technology or software have been introduced.” It should be clarified here.