Transcript CAK Skin dose in interventional CM

Cumulative dose and skin damage
Colin Martin and David Sutton
Skin effects
Histologic view of the skin
EPIDERMIS
DERMIS
From “Atlas de Histologia...”. J. Boya
Basal stratum cells, highly
mitotic, more susceptible
to radiation damage
 Transient erythema: May occur 1 to
24 hours after irradiation > 3 Gy
 Erythema: Occurs after 2-3 weeks
for doses of 3-10 Gy
 Alopecia(loss or absence of hair): 2-3
weeks, >3 Gy is reversible; 20 Gy
is irreversible.
 Dry or moist desquamation: after 35 weeks for doses 8-15 Gy.
Back Scattered Radiation
The skin receives a higher dose as some
radiation is scattered back from underlying
tissues.
Entrance surface dose is 30% higher than the
incident air kerma.
X-rays
Tissue
Backscatter
ICRP Report 85 (2001): Avoidance of Radiation
Injuries from Interventional Procedures
ICRP recommend:
 Warn patient of risk, if
maximum skin dose exceeds 3 Gy
 Identify patients who have
repeated interventions where the
dose exceeds 1 Gy and warn them
of risk
Use of a single projection
concentrates dose and increases skin damage
Complex procedures may
lead to high skin doses.
Multiple coronary
angiography and
angioplasty procedures
performed.
Evidence of injury 6-8
weeks after procedures.
Skin injury 18 months after
procedures
Images reproduced with permission from Wagner LK and Archer BR.
Minimizing Risks from Fluoroscopic Radiation, R. M. Partnership,
Houston, TX 2004, and T Shope from ICRP Publication 85 (2000).,
Distribution of Interventional
skin exposure
Different shape and size of the fields, films show changes in
collimation and beam angle during the procedure.
Lesions from overlapping fields
Examinations generally
use beams from different
directions.
There are risks of high
doses from overlapping
fields
Lesion required grafting
Erythema from Cardiology
procedures
Skin erythema after fluoroscopy
Cumulative build-up of dose from steeply
angled beams through large patient
Images reproduced with permission from Wagner LK and Archer BR.
Minimizing Risks from Fluoroscopic Radiation, R. M. Partnership,
Houston, TX 2004, and T Shope from ICRP Publication 85 (2000).,
Cumulative Dose
Interventional Reference Point
(IEC,60601-2-43, 2000)
15 cm in front of iso-centre
15 cm
15 cm
IRP
Isocenter
IRP
Isocenter
Cumulative dose does not take account of movement of X-ray tube
Method for MESAK evaluation:
radiochromic large area detector
Example: Radiochromic films type Gafchromic XR R 14”x17”
• usefull dose range: 0.1-10 Gy
• minimal photon energy dependence (60 - 120 keV)
• acquisition with a flatbed scanner:b/w image, 12-16 bit/pixel
or, measure of OD measurement with a reflection densitometer
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Relationship between Peak Skin
Dose and Cumulative dose
Neuroradiology
Interventional Cardiology
4.5
2.5
4.0
2.0
Peak skin dose (Gy)
Peak skin dose (Gy)
3.5
3.0
2.5
2.0
1.5
1.0
1.5
1.0
0.5
0.5
0.0
0.0
0
1
2
3
4
5
Cumulative entrance surface dose (Gy)
6
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
1.8
Cumulative entrance surface dose (Gy)
Reasonable link between peak skin dose and cumulative dose
Proposed follow-up for of skin injury
in other Interventional Radiology
Set “trigger values” for cumulative skin dose
that roughly equates to peak skin dose of 3 Gy
2-3 Gy Neuroradiology
3-5 Gy Cardiology
Identify where procedures are repeated on the
same patient giving a skin dose in this range.
Introduce a follow-up protocol for patients who
could have received high skin doses
Cumulative dose distribution for
Angiography and Stent procedures
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Percentage of cases
10
8
Single stent
Multiple stents
6
4
2
0
0- 0.1- 0.2- 0.3- 0.4- 0.5- 0.6- 0.7- 0.8- 0.9- 1.0- 1.2- 1.4- 1.6- 1.8- 2.0- 2.2- 2.4- 2.6- 2.8- 3.0- 3.2- 3.4- 3.6- 3.8- 4.0- 5.00.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 2.6 2.8 3.0 3.2 3.4 3.6 3.8 4.0 5.0 6.0
30
20
Coronary Angiography
Cardiac Ablations
15
10
A few percent of
procedures have
cumulative doses
above 5 Gy
5
0
00
0. . 1
10
0. . 2
20
0. . 3
30
0. . 4
40
0. . 5
50
0. . 6
60
0. . 7
70
0. . 8
80
0. . 9
91
1. . 0
01
1. . 2
21
1. . 4
41
1. . 6
61
1. . 8
82
2. . 0
02
2. . 2
22
2. . 4
42
2. . 6
62
2. . 8
83
3. . 0
03
3. . 2
23
3. . 4
43
3. . 6
63
3. . 8
84
4. . 0
05
5. . 0
06
6. . 0
07
7. . 0
08.
0
Percentage of cases
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Cumulative dose (Gy)
Cumulative Dose (Gy)
Doses to the skin depend on area
irradiated and focus to skin distance
Patients follow up Clinics
 The cumulative dose should be recorded in
the patient’s notes, so that it can be
referred to during follow-up clinic visits.
 The clinicians conducting the follow-up
should be aware if the patient’s dose has
exceeded the threshold
 Clinicians should be able to recognise
radiation skin effects
Patient dosimetry in IR
1. Dosimetry for quality assurance
 Air kerma area product (KAP, PKA)
2. Dosimetry for stochastic risk evaluation
 dose equivalent to selected organs
 effective dose
3. Dosimetry to prevent deterministic effects of
radiation (maximum skin dose assessment)
 Maximum skin dose (MSD or Dskin,max)
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