1. Skin dose, effective dose and related risk in TAVI procedures –
Is the cancer risk acceptable for younger patients?
A Karambatsakidou1, A Omar1, B Chehrazi1, A Rück2 and J Scherp Nilsson1 
1Department of Medical Physics, Karolinska University Hospital, Stockholm, Sweden
2Department of Cardiology, Karolinska University Hospital, Stockholm, Sweden
Introduction
Methods & Materials
Structural heart interventions, such as transcatheter aortic valve implantation (TAVI), are included in the group of interventional radiology which already are defined as high dose procedures (European Directive 97/43/Euratom). Currently, these examinations are performed in elderly and high risk patients who are not suitable for cardiac surgery but the constantly growing population may entail, in the near future, to structural heart interventions in younger and lower surgery risk patients according to the specialist discussions in European Society of Cardiology congress Interventional cardiology procedures are dose demanding and besides deterministic radiation effects also stochastic radiation effects are of concern to younger patients.
The objective of this work was to report typical conversion factors for maximum entrance skin dose (CFS) and conversion factors for effective dose (CFE) for patients undergoing TAVI, and further to assess the total risk of exposure-induced cancer death (REIDtot) for prospectively younger patients subjecting the same procedures. Additionally, the organ at risk for TAVI has been evaluated.
X-ray equipment:
Monoplane Philips AlluraClarity X-ray unit (Philips, Best, the Netherlands) equipped with a flat detector and an integrated dose area-product (DAP) meter (Diamentor; PTW-Freiburg, Germany).
Patient cohort:
Doses and risks were estimated for 22 patients (11 female, 11 male) ranging from 70 to 93 years of age (female) and 69 to 92 years of age (male).
Maximum entrance skin dose (MESD) was estimated by clinical measurement using Gafchromic film, for a subgroup of 15 patients.
Patient dosimetry:
Estimated MESD using the self-developing XR-RV3 Gafchromic film (International Specialty Products), calibrated in place against an R100B detector on a Barracuda electrometer (RTI Electronics AB, Mölndal, Sweden) for 70 kVp (half value layer 5.6 mm Al) and 80 kVp (half value layer 6.4 mm Al). Conversion factors for maximum entrance skin dose were established, for the entire examination, with the relation:
CFS =MESD/DAP
Doses and risks were estimated with the software PCXMC v.2.0 by using the dose related data, withdrawn from the system, as input parameters for each projection angle. The following relations were established:
CFE=E/DAP
REIDtot/DAP divided in age and gender
REIDorgan/REIDtot divided in age and gender
Conclusions
The CFS for TAVI is comparable with the CFS for percutaneous coronar intervention (PCI)
The CFE for TAVI is approximately 30% higher compared to PCI
Results from this study show an increased risk for developing cancer with a factor of 1.5 (male) and 2 (female) for patients undergoing TAVI in their 40s and 50s compared to the elderly patient population (69-93 years of age).
The main organ at risk is the lung
Recommends limiting the TAVI procedures on elderly and only on younger patients with high surgical risks.
Results & Discussion
(a)
(b)
(a)
(b)
(c)
Figure 2(a-c) illustrates the percentage share of the patients being within the different risk levels. The terminology applied for the different risk levels are defined by UK Department of Health (except for “close to moderate risk”, own supplement).
Examinations of the current patient population (a) (69-93 years of age) are within the low risk level interval (low risk level: %) and for younger patients (40- (c) and 50 years (b) of age), three of 22 are within the moderate risk level (moderate risk level: %) and one is very close to the moderate risk level ( %). However, the result of the present study shows that 15-20% of the younger patients (40- and 50 years of age) are within, or very close to, the moderate risk level.
Figure 1 (a, b) shows the distribution of the CFSs (a) and the CFEs (b) with the endpoints of the box plot indicating, to some extent, the complexity of the procedures and the differences in examination techniques between the operators. The mean value of CFS and CFE was estimated to be 9.7±1.5 mSv/Gycm2 and 0.24±0.02 mSv/Gycm2, respectively. There was good linear correlation between MESD and DAP (r=0.97) and between E and DAP (r=0.99).
Figure 3 presents the relationship REIDtot/DAP divided in gender and age, which is highest to the youngest, female patients. Additionally, the difference in REIDtot/DAP between the genders is obvious in younger patients and decreases with higher ages.
The linear correlation (r) between REIDtot and DAP was between 0.98 and 1.00 for all age groups and gender.
Figure 4 shows the relation REIDorgan/REIDtot, where the different colors indicate different cancer sites. The organs contributing most to the REIDtot are the lungs with about 70 % (female) and 50 % (male), followed by leukemia with % (female) and % (male).
Presenting author: Tel: +46(8)
OXMI 2015, Fourth Malmö Conference on Medical Imaging, May 2015, Gothenburg, Sweden