Staff dose and good prac/ces in CT guided IR procedures. Jonas Andersson Medical Physicist, Ph.D.

Transcription

1 Staff dose and good prac/ces in CT guided IR procedures Jonas Andersson Medical Physicist, Ph.D.

2 Contents Good prac/ces for staff dose management Staff dose reported in the literature Staff dose measurements at the University Hospital of Umeå Feasibility and uncertainty

3 CT guided IR procedures

4 CT guided IR procedures

5 Good prac/ces for staff dose management

6 Good prac/ces for staff dose management

7 Good prac/ces for staff dose management

8 Good prac/ces for staff dose management GE Healthcare Half Scan X-ray exposure will be blocked up to 130 in order to limit the x-ray irradiation on radiologist, meanwhile maintain the acceptable image quality. Half Scan First view of half scan Last view of half scan

9 Staff dose reported in the literature Joemai et al. (2009) AJR Occupa/onal (and pa/ent) dose from MDCT fluoroscopy (n = 107) Measurements with diode (n = 547) of staff dose outside lead apron Interven/onal radiologists Assis/ng radiologists Radiologic technologists Most common interven/on biopsy and drainage (n = 62) Thermocoagula/on (n = 18), radiofrequency abla/on (n = 12), other (n =15)

10 What is a CT guided biopsy? A couple of scan projec/on radiographs A spiral scan for procedure planning Comparison with previous diagnos/c material (CT, PET, MR) Computer aid for needle entrance and target /ssue Several axial scans for biopsy needle guidance Staff in room Different choices of follow up (conven/onal or CT) The most common CT guided IR procedure Amongst biopsies, thorax is the most common

11 What is a CT guided biopsy?

12 What is a CT guided biopsy?

13 Staff dose reported in the literature Joemai et al. (2009) AJR

14 Staff dose reported in the literature Joemai et al. (2009) AJR

15 Staff dose reported in the literature Joemai et al. (2009) AJR Staff dose measurement results, median (maximum) Interven/onal radiologists 14 usv (1 636 usv) Assistant radiologists 5 usv (1 884 usv) Radiologic technologists 1 usv (133 usv) For calcula/on of staff effec/ve dose (behind lead apron) Conversion factor 0.2 usv/usv, i.e. 20 % transmission Interven/onal radiologist dose outside lead apron, per DLP 0.03 usv / mgycm

16 Staff dose measurements in Umeå Follow up of staff present in room during contrast injec/on Technique parameters 100 kvp, 20 mas, 5 mm Dosimeters placed on the chest, outside lead apron Angiography (aorta, pulmonary, caro/d) and mul/phase exams Measurement period to Measurement equipment RaySafe i2 Total recorded dose 0.3 msv Number of examinations 81 Failed measurements 14 Median dose per exam 0.5 usv Mean dose per exam 3.9 usv

17 Follow up of staff dose from bolus tracking (Feb-Mar 2017) Aorta angio DLP 3392 mgycm Measured staff dose [usv] Pancreas 2-phase DLP 2962 mgycm Date

18 Staff dose measurements normalized to examina=on DLP Staff dose per DLP [usv / mgycm] 1,80 1,60 1,40 1,20 1,00 0,80 0,60 0,40 Aorta angio 0.05 usv/dlp Pancreas 2-phase 0.03 usv/dlp Statistics, n = 66 [usv / mgycm] Mean 0.17 usv Median 0.12 usv Minimum usv Maximum 1.53 usv Std.dev usv Rel.var. 145 % 0,20 0, Date

19 Staff dose measurements normalized to examina=on DLP (Body) Staff dose per DLP [usv / mgycm] 1,80 1,60 1,40 1,20 1,00 0,80 0,60 Statistics, n = 54 [usv / mgycm] Mean 0.20 usv Median 0.14 usv Minimum usv Maximum 1.53 usv Std.dev usv Rel.var. 128 % 0,40 0,20 0, Date

20 Staff dose measurements normalized to examina=on DLP (Head) Staff dose per DLP [usv / mgycm] 0,12 0,10 0,08 0,06 0,04 Statistics, n = 12 [usv / mgycm] Mean 0.02 usv Median 0.01 usv Minimum usv Maximum 0.11 usv Std.dev usv Rel.var. 156 % 0,02 0, Date

21 Comparison with theory, sources of uncertainty Measurements of staff dose per DLP (Body and Head) Body 0.2 usv per DLP (rela/ve variance 128 %) Head 0.02 usv per DLP (rela/ve variance 156 %) From manufacturer scajer survey and technique parameters Body 0.08 ugy per DLP (100 kvp, 5 mm beam, 32 cm body phantom) Head 0.04 ugy per DLP (100 kvp, 5 mm beam, 20 cm head phantom) Sources of uncertainty Diodes (intrinsic) Pa/ent size and posi/on Staff posi/on during exposure

22 CT guided biopsies in Västerbojen

23 CT guided biopsies in Västerbojen Mean 10 biopsies per month (n = 308, Mar-2015 Sep-2017) Mean DLP 263 mgycm (88 % rela/ve variance, mgycm) Conversion to staff dose, outside lead apron (Joemai et al., 2009) Mean 8 usv ( usv) Sources of variance (DLP) Pa/ent size and posi/on Complica/on of biopsy Comparison with conven/onal fluoroscopy (CBCT) Uncertainty! (JCGM 100:2008 GUM )