BREAST DOSE SURVEYS IN THE NHSBSP: SOFTWARE AND
Contents
1. Figure 1 The following sections discuss the use of each page of the form in turn The first page of the form contains descriptive data for the mammography system The second page of the form is used to enter the radiation characteristics of the X ray set Information on each clinical exposure is entered on the third page of the form Subsequent pages display the calculated doses and summary data for the current survey Sample data for a few dose surveys are included to illustrate how the software works Once the user is familiar with the package this demonstration data should be deleted NHSBSP July 2004 4 Breast dose surveys in the NHSBSP software and instruction manual V2 0 Microsoft Access SURVHEAD HE File Edit View Insert Format Records Tools Window Help laix ACEA EEE X ray set details x ray set data Exposure data Calculated MGD Graph of data Summary of analysis Survey Number LJ Centre Worthing Date of first exam 22 11 2001 Date of last exam 21 02 2002 Make of X ray set Model of X ray set Local ID of X ray set None Room 2 Type of installation Mode of kV selection Standard kV selection 0 24x30 cassettes available Block mAs Block density Physics Centre Guildford Physicist Bemhard Warr Film and processing details Processor make Processor type Processor ID Fuji FPM2800 1 Developer Fuji Hunt Fixer Proc2. e g the sample data provided it is necessary to delete all the records from the three main tables SURVHEAD DOSEDATA and X ray set characteristics with the appropriate survey number The records from the DOSEDATA and X ray set characteristics tables should be deleted before those in the SURVHEAD table Any deleted survey numbers may then be reused for new surveys 6 3 Incorporating survey data from previous version It is likely that most users of the software have survey data in a previous version of the software that they wish to transfer into this new version The appropriate way to do this is to select and copy all the records from each of the following three tables in turn The records should then be paste appended to the corresponding tables in the new version of the software Delete the demonstration data included with the software as described above e SURVHEAD e X ray set characteristics e DOSEDATA This will leave a few new fields added at the end of the new tables blank e g PMMA thickness mA These can be completed later if required 7 REFERENCES 1 Law J et al Commissioning and routine testing of mammographic X ray systems York Institute of Physics and Engineering in Medicine IPEM Report No 59 2 1994 2 Recommended standards for the routine performance testing of diagnostic X ray imaging systems York Institute of Physics and Engineering in Medicine 1997 IPEM Report No 77 3 Guidelines on patient dose to p
3. have 40mm entered and new surveys 45mm No calculations depend on this field 3 2 Diagnostic reference level The lonising Radiation Medical Exposure Regulations 2000 require employers to establish DRLs for radiodiagnostic examinations DRLs are defined in the regulations as dose levels for typical medical x ray examinations for groups of standard sized patients or standard phantoms and for broadly defined types of equipment The employer is required to establish DRLs and to ensure that procedures are in place for using them on the understanding that they are not expected to be exceeded for standard procedures when good and normal practice is being followed The employer is moreover obliged to undertake appropriate reviews whenever DRLs are consistently exceeded and to ensure that corrective action is taken when the excessive exposures cannot be clinically justified The Institute of Physics and Engineering in Medicine IPEM along with the National Radiological Protection Board NRPB the College of Radiographers CoR the Royal College of Radiologists RCR and the British Institute of Radiology BIR have established a Working Party to provide guidance on the implementation of DRLs for diagnostic x ray examinations The Working Party have proposed a dose audit measure for mammography which is the average MGD for medio lateral oblique mammograms for breasts with a compressed thickness of 55 5mm A minimum of 10 women should be included in the do
4. main films for each type of view number of films for each target filter KV combination Note that a main film has a view code of LOB ROB LCC or RCC View codes of LOB2 RCC3 etc are not classed as main films The average doses for oblique views of breasts with a compressed breast thickness of 50 to 60mm are shown for comparison with the DRL The user may perform more detailed analysis by copying the data to a spreadsheet NHSBSP July 2004 10 Breast dose surveys in the NHSBSP software and instruction manual V2 0 Microsoft Access SURVHEAD E le x E File Edit View Insert Format Records Tools Window Help le x x auant Les oe SU YR Mx Ims X ray set details X ray set data Exposure data Calculated MGD Graph of data Summary of analysis pd 11 Anode Filter kV films mE pw a px Mo Mo 2 we Co Ee ee Mo Mo a 5 vo we a0 7 Count of films view main films Extra films cc 144 OB 130 doses per main film min max mean view No of films MaD MeD MeD mG mG mm cc 144 1 08 5 24 3 05 50 mean Thickness o T Tu 7 3m Average MGD for 50 60mm thick breasts View No af average 2 average films MGD sem thickness o 3 35x oar nooo rsa ble Record I4 4 b yx of 332 jean Num Form view ipRstort Baz Sf eyo ppm So EMO SMA Cheeks 19 00 Figure 6 Form displaying summary data m
5. 6 LCC 27 LOB 27 LOB 31 LOB2 27 ROB 28 ROB2 27 5 5 Calculated MGD Mo Mo Mo Mo Mo Mo Rh Mo Rh Rh Mo Mo Rh Rh Rh Rh Rh Rh Rh Rh ss mm 49 42 72 78 61 60 80 72 80 80 mAs 130 101 262 318 125 126 142 168 161 162 large cassette used Auto man auto auto auto auto auto auto auto auto auto auto Automatic mode CNT CNT CNT CNT STD STD STD STD STD STD AEC density set o oO oo O O O GOOG Age Comment The fourth page of the form displays the calculated mean glandular dose for each exposure as shown in Figure 4 This is the field labelled dose The field old dose has been deleted in this version If this field is blank some of the information necessary to calculate the dose is missing Microsoft Access SURVHEAD ADAM E3 Ele Edit View Insert Format Records Tools Window Help el xl B amp gl amp sans MGD calculation subform Survey Nu Patient Number Mew Thicknes KV Anode teri m s dose _ OOOO OO OOO OO OOO O O aua 319875 319875 329049 329049 329049 329049 330553 330553 337779 337779 340880 340880 340886 340886 340888 340888 340888 340888 Record a 4 Il 2b ot rx of 332 OCOLURI v Ao B ia Xray set details X ray set data Exposure data Calculated MGD Graph of data Summary of analysis Form view wAstart ae 0 Bkz fv s arn o Figure 4 Form
6. AINTAINING THE DATABASE init hte te tede tet teuer etd 11 6 lt BACKING UIP Cal aloe nenea ea tela dtiteipataotutetiadideyeteu nuits 1l 6 2 Deleting dose SUrv8ys oe ti tte ito ates out ate bte e eee inae 12 6 3 Incorporating survey data from previous Version 12 Ta REFERENCES nord iine m teer i ee di tse LP ota 12 APPENDIX 1 NHSBSP PATIENT DOSE DATA RECORDING FORM seen 13 APPENDIX 2 METHOD OF DOSE CALCULATION ener 15 APPENDIX 3 TABLES AND FIELDS USED TO CALCULATE DOSE 16 APPENDIX 4 MODIFICATION OF DOSE CALCULATION TO ADJUST FOR AGE 17 NHSBSP July 2004 1 Breast dose surveys in the NHSBSP software and instruction manual V2 0 1 INTRODUCTION Measuring the mean glandular dose to the standard breast has for many years been the main means of assessing the doses from mammographic systems Although this is a valuable and simple approach to dose measurement it provides limited information on the doses received by individual women As a result the periodic measurement of doses for samples of women undergoing mammographic examinations is recommended 2 This manual describes the use of Version 2 0 of a software programme that calculates and stores the results of such dose surveys The latest version of the previously distributed software was known as Version 16 i e the 16 variation of Version 1 It is intended that the use of this software will help to standardise do
7. BREAST DOSE SURVEYS IN THE NHSBSP SOFTWARE AND INSTRUCTION MANUAL Version 2 0 Report 04 July 2004 K C Young National Co ordinating Centre for the Physics of Mammography Guildford Breast dose surveys in the NHSBSP software and instruction manual V2 0 CONTENTS Tt INTRODUCTION i torte RP Pee pre PO E COO D Ee OR penis 2 BOSIMETRY PROTOGOL USED tri tite ecd t e Een eee 3 NEW FEATURES IN THIS VERSION 31 Naw standard breasts ice ini ee e ee oi etel otn deg 3 2 Diagnostic reference level eene eene ener enne 3 2 Gorrecting ION AGC uitae tt reed utet ed od eres er rto ed doa erede rade 3 4 Calculation of exposure times ssssssssssssseseseeeeee eee eren ente ee 3 5 Record of compression force eee nee eene 3 0 Change to s factors e eot eae Gea ailes rete acdsee aes uaa 4 SURVEY METHODOLOGY a 1 5 mette Blt dte de de ba SR denos teres 5 USING THE SOFTWARE TO CALCULATE DOSES IN A BREAST DOSE SURVEY Mos 5 2 Mammography system details sse eee Did sXeray set datas eet i er rv RS en teen entis Genero d e rae 5 4 ExpoSure data nte e etasete bene et tae etshertisu n edet tit Toa Calculated MGD nicht e repa a io ede n bouem aon esi nas 5 6 Graph OF data o oe te erectae net ere apetito 10 DEL Summary oFanalysls itte icto E ete e tao prse Ie aee tbe Pee ebore tu s 10 5 8 Printed t pott iie o erede te recte tetti deceret fe li 6 M
8. P software and instruction manual Microsoft Access MGD calculation Select Query 1 D x EE Bie Edt view Insert Query Tools window Help 181 xj e G 2R7 tees Sle 9 x n e v E en 3 large cassette used auto man Automatic mode Age group HYL thickness C factor HYL Thickness View code Anode Dose data plus HVL Dose data plus HVL Dose data plus HVL Dose data plus HVL Dose dt Patient Number Dose data plus HVL Field Survey Number Table Dose data plus HYL Criteria or NM Ready J j tg start aao e amp vavo RY Mcrosof Cycontrac BE Mcrosof Sipatent Q microsof amp Micros SoH 14 21 Figure 9 Query used to calculate dose NHSBSP July 2004 18
9. assette was used leave blank Enter man if the beam quality was selected manually and auto if it was selected automatically or on the recommendation of the X ray set e g Siemens 3000 Where a mammography system has different automatic modes please enter the one used here e g Contrast with an IGE DMR AEC density setting such as 0 or 1 This field is available for the radiographer to enter any comments or explain any unusual aspects of the exposure This is a Yes No field with the default value No If this field is changed to Yes this record of exposure data will not be used in the display and calculation of summary data This could be done if the user suspects that the underlying data e g mAs or breast thickness is faulty This may be apparent from an inspection of the graph of dose versus thickness Where this occurs it is usually best to eliminate all the dose data for this patient i e set Yes for each record NHSBSP July 2004 8 Breast dose surveys in the NHSBSP software and instruction manual V2 0 Note This field is not shown on the data entry form and can only be changed by altering the appropriate records in the table DOSEDATA Table 1 Example of a set of exposure data Survey Patient Number Number AA10615 AA10615 AA1292 AA1292 AA14120 AA14120 AA14608 AA14608 AA14608 AA14608 c c 2c c c c 2c 2 View kV Anode Filter Thickne code LCC 25 RCC 25 LCC 26 RCC 2
10. d but doses are reduced by about 1 where a Mo Rh target filter combination is used Although these changes are rather smaller than the errors in the overall methodology users may notice small differences in the calculated doses when entering old data in to this new software version 4 SURVEY METHODOLOGY A breast dose survey involves the measurement of the mean glandular doses for a series of breast examinations e g for 50 to 100 women on a single mammographic system For each exposure the X ray factors are recorded including target material filter material tube voltage and mAs The radiographer determines the compressed breast thickness by reading the display on the X ray set The accuracy of the displayed thickness should be verified before starting the survey This can simply be done by compressing a rigid material e g Perspex of known thickness to a typical force of 100N If significant errors 22mm are encountered correction factors should be applied or the unit re calibrated From a knowledge of the output of the X ray set for the kV and target and filter material used the mAs value may be used to estimate the entrance air kerma at the surface of the breast K and hence the mean glandular dose 5 USING THE SOFTWARE TO CALCULATE DOSES IN A BREAST DOSE SURVEY 5 1 Introduction The software provided comprises a Microsoft Access Database which uses a multi page form for the entry and display of data for each survey as shown in
11. displaying calculated doses a Num s ng S6 E amp CbacHA 15 5 NHSBSP July 2004 Breast dose surveys in the NHSBSP software and instruction manual V2 0 5 6 Graph of data The fifth page displays a graph of the dose versus breast thickness for all the exposures in the current survey as shown in Figure 5 Note that it may be necessary to press the Refresh Graph button to update this graph This graph may show some outliers caused by errors in the exposure data A typical example is where the thickness is incorrectly recorded e g it is entered as 10 mm when it was really 100 mm Any such outliers should be checked for the accuracy of the underlying data Microsoft Access SURVHEAD le x EE File Edit View Insert Format Records Tools Window Help 1 x a Bl amp 7 X Gs f s 5 amp els Z1 E Y A B m O9 Xray set details X ray set data Exposure data Calculated MGD Graph of data Summary of analysis Graph of doses against breast thickness 9 4 b us Record Record 4 4 gt rt rs of 332 Form View Num Weser Ae 20 Maz Sn fm ea mem So 5 RISO HOBA 1s Figure 5 Form displaying graph of doses against thickness 5 7 Summary of analysis This page of the form Figure 6 shows an analysis of the dose data in the current survey including number of oblique and CC films average doses for
12. e look up tables depending on the HVL age group and anode and filter material used Linear interpolation was used to generate additional values for these tables The entrance air kerma K is calculated from the output per mAs corrected for paddle transmission and the inverse square law The equation 2 is used in the database to calculate the mean glandular dose per exposure where square brackets denote a field name dose s factor c factor g factor transmission mAs output 1000 distance thickness mm 2 NHSBSP July 2004 45 Breast dose surveys in the NHSBSP software and instruction manual APPENDIX 3 TABLES AND FIELDS USED TO CALCULATE DOSE The tables and fields used to calculate the dose are shown in Figure 7 The straight lines between tables represent linked fields and the bold arrows indicate the fields used in the calculation The queries that are used in the calculation are discussed in Appendix 4 survey number Region code Centre Date of First Exam Date of Last Exam X Ray Make Model Sub model Local id Installation kV mode Processor model Processor id Developer Fixer Proc time Dev Temp Cassette type Film make Film type Film subtype Screen make Screen type Screen resolution Block mAs Block density 24x30 cassettes MGD auto manual MGD AEC setting MGD kv target filter MGD mAs MGD HVL MGD MGD density Physics centre Physicist tel no Routine age trial MGD kV
13. ear 5 8 Printed report Pressing the button Print summary data form prints a one page summary of the data in the current survey The printer used is the default printer set on the host computer In addition to the data in section 3 7 this printout shows the average doses for one and two view examinations The doses for an examination are calculated by summing the doses for all the films used in an examination and dividing by 2 6 MAINTAINING THE DATABASE The user has free access to all aspect of the database design This will allow the user to trouble shoot any problems However care should be taken not to corrupt features that are essential to the correct working of the database The original version of the database software used is Microsoft Access 1997 Version 2 0 is also available in later versions of Access Earlier versions of Access will not be able to run the database In the event of difficulties contact the author for help and software upgrades 6 1 Backing up data As with any other software package it is important to regularly back up your data This can be achieved by making a backup copy of the database using the command Tools Database Utilities Compact Database to both compress the database and save a copy using a different name NHSBSP July 2004 11 Breast dose surveys in the NHSBSP software and instruction manual V2 0 6 2 Deleting dose surveys When deleting a survey from the database
14. ert Query Tools Window Help ajx O G SaY Leesl olm t mzla eaan code Centre Date of First Exam Date of Last Exam X Ray Make Model Sub model Local id Installation kv mode Processor model Processor id Developer Fixer Proc time Dev Temp Thickness mm m s large cassette used auto man Automatic mode xi Field ox time mAs m lage group Ilf age 50 Age trial Routine screening Table Sort Show iv iv Criteria or T Nj x per GA OD amp jvaoo R Microsof contrac BE Microsof patient y Microsof E Micros tie Hy 14 23 Figure 8 Dose data plus HVL query Ready gO start Query MGD calculation The second query is shown in figure 9 This query uses the data in Dose data plus HVL to calculate the dose which is now corrected for the age of the patient by using the appropriate c factor c factors Age Group This field is now related to the field Dose data plus HVL Age group instead of the field Dose data plus HVL Routine age trial This means that an appropriate c factor will automatically selected based on the age of the patient If no age information is provided the woman is assumed to be in the usual screening age NHSBSP July 2004 17 Breast dose surveys in the NHSBS
15. fferent compressed breast thicknesses in the age ranges 50 to 64 and 40 to 49 The factor s makes a correction for the use of an X ray spectrum other than Mo Mo 3 NEW FEATURES IN THIS VERSION 3 1 New standard breast The Quality Assurance Standards for the NHSBSP were revised on 1 April 2004 In these the dose standard is based on the new standard breast model introduced in IPEM Report 89 The data published in Dance et al 2000 for the equivalence between Perspex and typical compressed breasts has been used to establish a new standard breast simulated with a 45mm thick Perspex phantom instead of the 40mm thick phantom used previously The new standard breast model can be expected to result in doses that are approximately 2596 greater than those found with the old model if the same beam quality 28 kV Mo Mo is used However the exposures should be at the clinical settings The minimum standard for the mean glandular dose for the new standard breast at clinical settings is less than or equal to 2 5 mGy film It is expected that all new dose surveys be recorded using the dose to the standard breast using 45mm Perspex However some old surveys may have been collected using a 40mm thick NHSBSP July 2004 2 Breast dose surveys in the NHSBSP software and instruction manual V2 0 phantom To accommodate this the software has a new field to record the PMMA thickness used to measure the standard breast Old surveys should
16. must lay out the data as on this form using a spreadsheet Survey Nu Patient Number View code kv Anode Filter Thickness mAs large cassette used auto man 8319875 9 319875 9 329049 9 329049 9 329049 9 329049 9 330553 9 330553 9 337779 9 337779 9 340880 9 340880 9 340886 9 340886 9 340888 rPPrPprrrrrrrprrrrp Form View Num Record a 4 2 gt ot rx of 332 wAstert Ae DOR Maz anam amp e pre Sol SC BESLSLO DEUS OBRA i5 Figure 3 Form for entering exposure data Survey Number Each exposure in the series must be identified with the same survey number provided in sections above Patient Number Each patient must be identified by a code which is unique to this survey This can be any combination of letters and numbers View code Each exposure requires a view code that is unique to that patient The codes for main films are as follows LCC for left cranio caudal RCC for right cranio caudal LOB for left mediolateral oblique NHSBSP July 2004 7 Breast dose surveys in the NHSBSP software and instruction manual V2 0 kV Anode Filter Thickness mAs Age ROB for right mediolateral oblique Where additional films have to be taken for the same views e g if the breast was too big to fit on the first film the following codes should be used LCC2 for a second film of the left cranio caudal view LCC3 for a second film of
17. on the physical characteristics of the X ray set being surveyed are entered on the second page of the form as shown in Figure 2 In order for the software to calculate entrance air kerma one needs to supply the following parameters for each kV target filter combination used clinically on the X ray set being tested Survey Number This number must be the same as that entered above kV Set kV and therefore an integer Anode The anode material must be identified by the appropriate code Mo or Rh or W NHSBSP July 2004 5 Breast dose surveys in the NHSBSP software and instruction manual V2 0 Filter Output HVL Distance Transmission mA The filter material must be identified by the appropriate code Mo or Rh Output in uGy per mAs at 1 metre from the focus of the X ray tube on the usual measurement axis i e one that passes through a point 4 cm from the chest wall edge It is assumed here that this is measured at a distance of about 50cm and then recalculated to a distance of 1 metre It is further assumed that attenuation by a compression paddle is not included If you wish to use an output measurement through a compression plate this can be done if the transmission factor is set to 1 0 This is the half value layer in mm of Aluminium measured as described in IPSM59 2 and should include attenuation by the compression plate It should be quoted to two significant figures This is the distance from
18. racteristics of X ray set Figure 2 is based on a suitable dataset for an IGE DMR It is not necessary to directly measure all of these parameters as interpolation can easily be applied It may be convenient to assemble this NHSBSP July 2004 6 Breast dose surveys in the NHSBSP software and instruction manual V2 0 data in a spreadsheet before paste appending it to the appropriate table in the database i e X ray set characteristics 5 4 Exposure data A record of the exposure factors for each mammogram is required Appendix 1 shows a paper form that can be used by radiographers to collect this data An example of such a dataset is shown in Table 2 The form on the database for entering this data is shown in Figure 3 The types of data requested and how they should be entered into the database are discussed below It is important that the data entered are in the right format Where numerical values are requested do not enter the unit e g type in 28 rather than 28 kV R vicrosott Access SURVHEAD Beles IE File Edit view Insert Format Records Tools Window Help a x B l amp Ba amp 5 VP ALL S Y UA neo Lm is ray set details ray setdata Exposure data Calculated MGD Graph of data Summary of analysis Data on each exposure in this survey can be entered manually or more conveniently may be pasted into this form using the Paste Append command First you
19. romote the optimisation of protection for diagnostic medical exposures NRPB Report Volume 10 No 1 1999 4 Dance DR Skinner CL Young KC Beckett JR and Kotre CJ Additional factors for the estimation of mean glandular breast dose using the UK mammography dosimetry protocol Phys Med Biol 45 3225 3240 2000 5 Young KC Burch A Radiation doses received in the UK breast screening programme in 1997 and 1998 British Journal of Radiology 73 278 287 2000 NHSBSP July 2004 12 APPENDIX 1 NHSBSP PATIENT DOSE DATA RECORDING FORM X ray Unit Date Screening Centre Sequential View code Patient LOB Number ROB LCC RC Compressed Breast Thickness mm Large Mode of kV Automatic AEC cassette selection mode e g density used auto man CONT with set Yes No DMR Breast dose surveys in the NHSBSP software and instruction manual APPENDIX 2 METHOD OF DOSE CALCULATION The mean glandular dose is calculated for each exposure by means of look up tables in the database as illustrated in Appendix 3 Note that the interconnections between tables have been somewhat simplified to illustrate the underlying method The arrows indicate where a field is used in the dose calculation The links between tables used in the dose calculation query are shown as connecting lines between tables The formula applied is that shown in equation 1 The g factor s factor and c factor are taken from thre
20. se measurements and simplify procedures for national reviews of radiation doses in the NHS Breast Screening Programme The software incorporates the changes in the UK dosimetry protocol outlined by Dance et al 4 2 DOSIMETRY PROTOCOL USED The UK and European protocols for mammographic dosimetry use conversion factors that relate incident air kerma to the mean glandular dose MGD within the breast The conversion factors published in IPSM 59 2 were obtained by computer simulation of a model breast with composition 5096 adipose and 5096 glandular tissues by weight 5096 glandularity Dance et al have published additional conversion factors which allow the extension of the protocols to breasts of varying glandularity and for a wider range of mammographic x ray spectra The data have also been extended to breasts of compressed thickness 11 cm To facilitate the calculation of MGD in patient surveys typical breast glandularities are tabulated for women in the age ranges 40 49 and 50 64 and for breasts in the thickness range 2 11 cm The software provided with this publication facilitates the implementation of a breast dose survey using these procedures using equation 1 D Kgcs 1 where the factor g is unchanged from that given in IPSM 59 2 and corresponds to a glandularity of 50 The factor c corrects for any difference in breast composition from 50 glandularity c factors have been calculated by Dance et al 4 for typical breast compositions at di
21. se sample The proposed National DRL for this dose audit measure is 3 5 mGy In this version of the software the average MGD for all oblique mammograms main films only with a compressed thickness of 50 to 60 mm is calculated for each dose survey For this calculation the number of films the statistical error in the mean and the average thickness are also shown The statistical error is shown as 2 standard errors in the mean 2 s e m For a few surveys the number of OB mammograms in this thickness range may be less than 20 i e equivalent to less than 10 women and would therefore be insufficient for accurately assessing compliance with the DRL 3 3 Correcting for age The software has composition correction factors c factors for younger women age 40 to 49 and women in the usual screening age aged 50 to 64 In the previous version older and younger women were entered as separate surveys even if exposed on the same X ray set The whole survey was then identified as either routine screening i e over 49 or age trial i e age 40 to 49 In this new version of the software the appropriate factor is determined by the age information entered with the exposure data If no age information is provided as is usually the case the software assumes all the women are aged 50 or over If an age is entered for an exposure record the appropriate factor will be used Note however that it is no longer sufficient to just enter age trial in the field ro
22. set MGD target MGD filter 24x30 bucky Processor make Cassette make standard kV Dose data Survey Number Patient Number View code AEC density set Age Comment Error Age group X ray set charactersistics Survey Number Output mAs Y large cassette used Distance auto man Automatic mode C factors Age group HVL thickness C factor g values HVL Thickness spectral factors Spectral factor Figure 7 Tables and fields used to calculate dose NHSBSP July 2004 16 Breast dose surveys in the NHSBSP software and instruction manual APPENDIX 4 MODIFICATION OF DOSE CALCULATION TO ADJUST FOR AGE This appendix explains the use of two queries used to calculate doses corrected for the patient s age Query Dose data plus HVL The first query is shown in figure 8 It adds an extra field called Age group Age Group This new field is calculated using an If statement If the patient is under 50 years old the age group is set to Age trial If the patient is over 50 years old or the patient age is left blank the age group is set to Routine Screening Microsoft Access Dose data plus HVL Select Query ej x H File Edit View Ins
23. the focus to the table top in mm Measured fraction of air kerma transmitted through the compression plate This field is optional and has been added to version 2 0 to allow the calculation of exposure times It should be completed for each kV target filter combination used for which exposure times are to be calculated It may also be left blank and has no effect on the dose calculations The mA can be determined from manufacturer s literature or exposure time measurements Microsoft Access SURVHEAD ENS s xl EE File Edit View Insert Format Records Tools Window Help amp x B Rl amp S T shes 5 VP ALL Ya V A 0 m is Xray set details ray set data Exposure data Calculated MGD Graph of data Summary of analysis You need to enter a row of data for each combination of kV anode and filter used Output in microGray per mAs at 1 metre from focus Distance from focus to table top in mm Transmission measured fraction of air kerma transmitted through compression plate mA Enter the mA only of you want to calculate exposure times oO DOO DODO DDO DOO OO O O a N Survey No kV Anode Filter HVL Output Distance transmission 226 Mo Mo 036 27 8 540 Mo Mo Rh Record 4 2 gt gt t rx of 332 A number specific to that X Ray Set f NUM iiffstart menor Mz Sam Fw SE RS LOSM AC Becba ess Figure 2 Form for entering physical cha
24. the left cranio caudal view and so on for the other views The software is designed for the two views used in screening i e mediolateral oblique and cranio caudal If some different views are used e g a lateral further codes may be used as follows LLAT for a left lateral view RLAT for a right lateral view Note however that the summary datasheet will only consider the standard views Enter the set kV used This should be an integer between 25 and 35 Note that the use of a non integer number will cause the dose calculation to fail The anode material must be identified by the appropriate code Mo or Rh or W The filter material must be identified by the appropriate code Mo or Rh The compressed breast thickness should be entered as an integer number of mm Note that the use of a non integer number will cause the dose calculation to fail Although most modern mammographic X ray sets will display compressed breast thickness it is important to check the accuracy The post exposure mAs Enter the age of the woman in years This information is optional However if it is entered it will determine the c factor used in the dose calculation The following fields are not used in the dose calculation but are requested since they can provide useful feedback on examination practice large cassette auto man Automatic mode AEC density set Comment Error If a large cassette 24x30cm was used enter Yes If a standard c
25. time s Fuji Hunt Dev Temp deg C Cassette make Cassette type Film make Film type Screen make Screen type MGD to standard bre Auto manual kV Auto AEC setting kV set target 31 5 Fuji IAD Fuji AD M Fuji AD M fine standard PMMA thickness MGD mAs HVL MGD filter film density Record I4 2 b DL bof 332 Form View Astart LI TV FTT NM T de39 J HBz cn Sw H mm So fw LO SM sss oaks 1742 Figure 1 Multi page form used for entering and reviewing dose survey data 5 2 Mammography system details It is important to record all the characteristics of the mammography system used However the only field that is essential and used in the dose calculation is the field survey number Survey Number The survey number is used to identify all the various sets of data from one survey and takes the form of an integer which can be incremented each time a survey is added to the database It is simplest if these are numbered sequentially from 1 upwards Routine age trial In the previous version of the software this field was used to determine which c factors should be used for a whole survey However in this version the c factors for younger women are selected whenever the age field is less than 50 The field is retained to provide background information only and for compatibility with earlier versions 5 3 X ray set data Information
26. utine age trial as this no longer has any effect on the dose calculation Further details on how this change was introduced are shown in Appendix 4 3 4 Calculation of exposure times The software can now calculate exposure times as well as dose for each exposure To do this an appropriate mA must be entered in the X ray set data The exposure time is then calculated as the mAs divided by the mA Note On some systems the mA may vary during the exposure in which case the calculated time based on a fixed mA will not be correct e g Siemens Mammomat 3000 can be set to use a lower mA at the start of the exposure to reduce grid lines on short exposures Also if the mAs is selected manually some systems e g Lorad mark IV may use a different mA for small mAs values NHSBSP July 2004 3 Breast dose surveys in the NHSBSP software and instruction manual V2 0 3 5 Record of compression force The compression force may be included in a new field along with the exposure data This has no effect on the dose calculation but does provide a more complete record of radiographic procedures 3 6 Change to s factors Some earlier versions of the software used s factors that were slightly different from those published by Dance et al In this version the factors are identical to those in the published paper Overall the effect of this change is very small There is no change to doses where a Mo Mo target filter combination is use
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