ALARA in mammography screening. Hilde Bosmans et al.

Transcription

1 ALARA in mammography screening Hilde Bosmans et al.

2 ALARA in the mammography Overview 1. Screening 2. The balance: 1. Image quality 2. Radiation dose 3. In practice

3 Screening

4 leeftijd

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6 Mammography Screening RX examination of the breast to find breast cancers in an early stage performed on the population proven decrease in breast cancer mortality if properly performed

7 Required Quality Parameters at INITIAL screening Performance parameter Acceptable Desirable Participation rate 70% > 75% Additional imaging - at the time of screening < 5% < 1% Recall rate < 7% < 5% Cytology/biopsy procedures with an inadequate result (% ) < 25% < 15% Total cancer detection rate (per 1000 women screened)*** - invasive cancer detection rate - in-situ cancer detection rate 3xIR* >3xIR* Invasive cancers 10 mm diameter (% of inv. cancers detected) NG* 25% Benign open biopsy rate (per 1000 women screened) < 5 < 4 Benign to malignant biopsy ratio < 1 to 1 <0.5 to 1 * IR = expected incidence rate in the absence of screening

8 Required Quality Parameters at SUBSEQUENT screening Performance parameter Acceptable Desirable Participation rate 70% > 75% Additional imaging - at the time of screening < 3% < 1% Recall rate < 5% < 3% Cytology/biopsy procedures with an inadequate result (% ) < 25% < 15% Total cancer detection rate (per 1000 women screened)*** - invasive cancer detection rate - in-situ cancer detection rate 1,5xIR** NG* Invasive cancers, 10 mm diameter (% of inv. cancers detected) NG* 25% Benign open biopsy rate (per 1000 women screened) < 3,5 < 2 Benign to malignant biopsy ratio < 1 to 1 < 0,2 to 1 * NG = none given ** IR = expected incidence rate in the absence of screening *** The cancer detection rate per five-year age category is further specified in table IV.4.

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10 Vlaamse resultaten Aantal verwijzingen verder onderzoek (%) Proportie gekende FU Detectiegraad (/1000 gescreende vrouwen %invasieve kankers 10mm % invasieve kankers /totaal Ca 5,0% 77,4% 5,4 24,3% 83,1% initial acceptable <7% 3xIR 20% 90% desirable <5% >3xIR 25% 80-90% subsequent-regular acceptable <5% 1,5xIR 25% 90% desirable <3% >1,5xIR 30% 80-90% %DCIS IR=incidentieratio 16,9% M. Van Goethem, G. Villeirs. De Vlaamse gezondheidsconferentie. Dec 2005.

11 Eerste resultaten, periode per leeftijdsgroep leeftijdsgroep Detectiegraad (/1000 gescreende vrouwen) 4,3 4,7 6,0 Detectiepercentage invasieve kankers 78,6 83,8 85,6 Detectiepercentage invasieve kankers <= 10 mm 22, ,1 Detectiepercentage DCIS 21,4 16,2 14,4 M. Van Goethem, G. Villeirs. De Vlaamse Gezondheidsconferentie ,6 83,9 27,0 16,1

12 Quality Assurance in screening X-ray system, detector, processing, viewing Screening organisation / initiative Radiographer Reading, 2nd reading, 3rd reading Follow-up, feedback, Treatment

13 The balance Image quality Performance of the system Daily situation of the system Dose (mean glandular dose)

14 Image quality (film-screen) Spatial resolution Contrast resolution

15 Image quality (digital mammography) Contrast detail analysis

16 Radiation dose Usually Mean glandular dose (and not effective dose) Calculated from Tube output, beam energy, mas Thickness of the breast Glandularity of the breast

17 Image quality evaluation in practice

18 10,00 1,00 A typical result, compared to limits diameter 0,01 The required thickness of gold in order to see a disc with given diameter contrast (% 0,1 1 0,10 0,01 acceptable limits ach mean 10 De diameter die een goudstip minstens moet hebben om zichtbaar te zijn

19 Image quality in practice Manual reading is subjective This test object does not test image processing The methodology to read is a topic of much debate Reading will be computerized, but need link computer reading human reading

20 Limitations of this image quality test It tests only X-ray tube, detector and dose It does not test image processing, the viewing station of the radiologist, the visual perception of the radiologist

21 The surprising use of monitors

22 Daily situation of the system Evaluate from homogeneous images Is a necessity, even for digital imaging Can be automated, supervision can be centralized

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24 Dosimetry in practice 3 yearly investigation = Legal obligation a/f 1=Mo/Mo a/f 2=Mo/Rh a/f 3=W/Rh kvp setting effective kvp HWL intreedosis HWL intreedosis HWL intreedosis

25 3 yearly dosimetry in practice

26 Half yearly check on PMMA

27 K. Smans et al., Rad Prot Dos 2003 Patient Dose vs Phantom Dose 2,5 2 1,5 1 0,5 y = 0,6614x + 0,3384 R 2 = 0,8111 Phantom Dose (mgy) 0 0 0,5 1 1,5 2 2,5 3 Patient Dose (mgy) Figure 1: Correlation between patient dose and phantom dose Group 1 Group 2

28 PMMA seems to work, after calibration The two different DRLs were calculated (figure 2): The 95 percentile of the mean AGDs (of the thickness range from 48mm to 58mm) is 2.46 mgy The 95 percentile of AGD values calculated from the 45mm PMMA blocks is 2.08 mgy. Histogram: Patient Dose Histogram: Phantom Dose ,81-1,00 1,01-1,20 1,21-1,40 1,41-1,60 1,61-1,80 1,81-2,00 Dose (mgy) 2,01-2,20 2,21-2,40 2,41-2,60 2,61-2,80 0 0,61-0,80 0,81-1,00 1,01-1,20 1,21-1,40 1,41-1,60 Dose (mgy) 1,61-1,80 1,81-2,00 2,01-2,20 2,21-2,40 The same two centres exceed the DRL. Number of centers Number of centers

29 The future of dosimetry in mammography has started

30 Automated dose control

31 Dosimetry today in (digital) (mammography) Is a necessity, as doses can go up without direct evidence in the radiological image as new technologies do not always reduce patient dose Is possible, if automated Is a major stimulus towards more general dosimetry actions We propose to run on-line dose monitoring of all mammograms in the screening centers

32 Future Digital imaging -> automated approaches Link computer reading and human reading Check quality & dose continuously