E. Bogaert

Patient-Specific Dose and Radiation Risk Estimation in Pediatric Cardiac Catheterization

Background—Because of the higher radiosensitivity of infants and children compared with adults, there is a need to evaluate the doses delivered to pediatric patients who undergo interventional cardiac procedures. However, knowledge of the effective dose in pediatric interventional cardiology is very limited. Methods and Results—For an accurate risk estimation, a patient-specific Monte Carlo simulation of the effective dose was set up in 60 patients with congenital heart disease who underwent diagnostic (n=28) or therapeutic (n=32) cardiac catheterization procedures. The dose-saving effect of using extra copper filtration in the x-ray beam was also investigated. For diagnostic cardiac catheterizations, a median effective dose of 4.6 mSv was found. Therapeutic procedures resulted in a higher median effective dose of 6.0 mSv because of the prolonged use of fluoroscopy. The overall effect of inserting extra copper filtration into the x-ray beam was a total effective dose reduction of 18% with no detrimental effect on image quality. An excellent correlation between the dose-area product and effective patient dose was found (r=0.95). Hence, dose-area product is suitable for online estimation of the effective dose with good accuracy. With all procedures included, the resulting median lifetime risk for stochastic effects was 0.08%. Conclusions—Because of the high radiation exposure, it is important to monitor patient dose by dose-area product instrumentation and to use additional beam filtration to keep the effective dose as low as possible in view of the sensitivity of the pediatric patients.

A large-scale multicentre study of patient skin doses in interventional cardiology: dose–area product action levels and dose reference levels

For 318 patients in 8 different Belgian hospitals, the entire skin-dose distribution was mapped using a grid of 70 thermoluminescence dosimeters per patient, allowing an accurate determination of the maximum skin dose (MSD). Dose-area product (DAP) values, exposure parameters and geometry, together with procedure, patient and cardiologist characteristics, were also registered. Procedures were divided into two groups: diagnostic procedures (coronary angiography) and therapeutic procedures (dilatation, stent, combined procedures (e.g. coronary angiography + dilatation + stent)). The mean value of the MSD was 0.310 Gy for diagnostic and 0.699 Gy for therapeutic procedures. The most critical projection for receiving the MSD is the LAO90 (left anterior oblique) geometry. In 3% of cases, the MSD exceeded the 2 Gy dose threshold for deterministic effects. Action levels in terms of DAP values as the basis for a strategy for follow-up of patients for deterministic radiation skin effects were derived from measured MSD and cumulative DAP values. Two DAP action levels are proposed. A first DAP action level of 125 Gy cm(2) corresponding to the dose threshold of 2 Gy would imply an optional radiopathological follow-up depending on the cardiologists decision. A second DAP action level of 250 Gy cm(2) corresponding to the 3 Gy skin dose would imply a systematic follow-up. Dose reference levels - 71.3 Gy cm(2) for diagnostic and 106.0 Gy cm(2) for therapeutic procedures - were derived from the 75 percentile of the DAP distributions. As a conclusion, we propose that total DAP is registered in patients record file, as it can serve to improve the follow-up of patients for radiation-induced skin injuries.

Interventional cardiovascular procedures in Belgium: effective dose and conversion factors

Effective dose (E), representing the risk of late radiation-induced effects, can be estimated by the use of conversion factors (CF), converting direct measurable quantities such as dose-area-product into E. Eight Belgian hospitals participated in the study with a total number of 318 procedures. E-values, calculated with PCXMC, were compared for the different hospitals for diagnostic and therapeutic procedures separately. E-values varied significantly depending on the hospital where the procedure was performed (P < 0.001), on filtration insertion (P < 0.001), on whether a centre is a training centre or not, the dose conscious action of the cardiologists and the complexity of the procedure (P < 0.001). Hospital-specific CF were calculated. An average CF of 0.185 mSv Gycm(-2) was obtained with a satisfactory correlation (r = 0.966, P < 0.001). The differences in CF between hospitals were due to, a large extent, the availability of additional filtration in cinegraphy mode (P < 0.001) and not to the differences in irradiation geometries in the clinical protocol of the interventional procedures.

Does digital flat detector technology tip the scale towards better image quality or reduced patient dose in interventional cardiology

As dynamic flat-panel detectors (FD) are introduced in interventional cardiology (IC), the relation between patient dose and image quality (IQ) needs to be reconsidered for this type of image receptor. On one hand this study investigates IQ of a FD system by means of a threshold contrast-detail analysis and compares it to an image intensifier (II) system on a similar X-ray setup. On the other hand patient dose for coronary angiography (CA) procedures on both systems is compared by Dose-Area Product (DAP)-registration of a patient population. The comparative IQ study was performed for a range of entrance dose rates (EDR) covering the fluoroscopy and cinegraphy working mode. In addition the IQ investigation was extended to a similar study under automatic brightness control (ABC). As well the systematic study of IQ as a function of EDR as the study performed under ABC point to a better IQ for FD in cinegraphy mode and no difference between both systems in fluoroscopy mode. The patient population study resulted in mean DAP values of 31Gycm(2) (II system) and 33Gycm(2) (FD system) (p=0.68) for CA procedures. As well total DAP as contributions of fluoroscopy and cinegraphy on both systems are not significantly different. To conclude, we could state that profit was taken from the intrinsic better performance of the FD for cinegraphy mode in producing higher quality images in this mode but without any effect on patient dose for CA procedures.

Early biomarkers related to secondary primary cancer risk in radiotherapy treated prostate cancer patients: IMRT versus IMAT

PURPOSE To investigate whether rotational techniques (Volumetric Modulated Arc Therapy - VMAT) are associated with a higher risk for secondary primary malignancies compared to step-and-shoot Intensity Modulated Radiation Therapy (ss-IMRT). To this end, radiation therapy (RT) induced DNA double-strand-breaks and the resulting chromosomal damage were assessed in peripheral blood T-lymphocytes of prostate cancer (PCa) patients applying γH2AX foci and G0 micronucleus (MN) assays. METHODS AND MATERIALS The study comprised 33PCa patients. A blood sample was taken before start of therapy and after the 1st and 3rd RT fraction to determine respectively the RT-induced γH2AX foci and MN. The equivalent total body dose (D(ETB)) was calculated based on treatment planning data. RESULTS A linear dose response was obtained for γH2AX foci yields versus D(ETB) while MN showed a linear-quadratic dose response. Patients treated with large volume (LV) VMAT show a significantly higher level of induced γH2AX foci and MN compared to IMRT and small volume (SV) VMAT (p<0.01). Assuming a linear-quadratic relationship, a satisfactory correlation was found between both endpoints (R(2) 0.86). CONCLUSIONS Biomarker responses were governed by dose and irradiated volume of normal tissues. No significant differences between IMRT and rotational therapy inherent to the technique itself were observed.

EP-1535: Electron Skin Irradiation: refinement of an abutting field technique

Purpose or Objective: The Calypso 4D Localization System consists in an electromagnetic detection of implanted Beacon transponders in order to continuously track their moves. The use of this system requires a specific couch top and the introduction in the treatment beam of an electromagnetic array. The purpose of this study is to quantify the dosimetric impact of the new material introduction in photon beams.

OC-0468: Validation of Mask Based Registration in CBCT pretreatment imaging of locally advanced cervix ca

Purpose or Objective: Radiotherapy treatment for cervical cancers typically involves external beam irradiation to the whole pelvis followed by an intra-uterine brachytherapy boost to the primary tumour site. The purpose of the current study was 1) to assess dose reduction to OARs using a VMAT treatment technique compared to a conformal four field brick and 2) whether VMAT using sequential or simultaneous integrated boost can provide coverage to the tumour and OARs similar to brachytherapy.

PO-0901: Investigation of a fast CBCT protocol for supine accelerated whole breast Irradiation

ESTRO 35 2016 ______________________________________________________________________________________________________ result in any significant under-dosing of the target, the observed differences showed that the rectum broke our institutional DVCs during treatment. This is important data required to evaluate the robustness of institutional procedures for the planning and delivery of patients’ treatments.