Study On Radiation Exposure To Patients And Operators During Cardiovascular Intervention

In recent years, digital subtraction angiography (DSA) is widely used in medical diagnostic procedures and interventional treatment all over the world. In cardiovascular intervention DSA is extensively applied, and occupational exposure of the medical staff is among the highest. Coronary angiography (CA) is the gold standard for diagnosis of cardiovascular disease, percutaneous transluminal coronary angioplasty (PTCA) is the basic method of treating cardiac artery stenosis while percutaneous intracoronary arterial stenting (PICAS) is often used after PTCA, serving as the primary treatment method for coronary heart disease.Interventional treatment benefits the patients but may cause potentially high radiation dose of both the patients and staff at the same time. A lot of research work has proved that cardiovascular intervention may result in high patient dose that deserves attention. Long time of fluoroscopy and digital cine make the cumulative dose of the patient's skin exceed the threshold of deterministic effect, as a result many cases of skin injury have been reported. Meanwhile all the interventional procedures are performed in such a manner that the medical staff has to stand near the patient. The patient is physically regarded as a secondary radiation source that emits scattered X rays. Therefore the medical staff is exposed to a considerable amount of scattered radiation. The main reason for significantly high occupational doses is the long fluoroscopy time which may exceed 1 or 2 hours. In China cardiovascular intervention are performed not only by radiologists but also by physicians, meanwhile auxiliary staff members are also exposed in the scattered radiation. Lacking in consciousness of radiation protection make many operators pay little attention to personal protection.It is reported in EU Scientific Seminar 2003 that C-arm systems with under table X ray tube are mandatory for interventional procedures. The dose of the operator's eyes, head and neck are greatly reduced when angiography systems with over-couch X ray tube are substituted by angiography systems with under table X ray tube. As personal protection becomes more notable, clinical investigations have been made extensively to monitor patients' dose and occupational dose. Our research includes clinical investigation and phantom study.Research work was carried out in a certain Third Class Grade A hospital. In clinical investigation, related parameters of radiation exposure to the patient and staff in 26 cardiovascular interventions including CA, PTCA and PICAS were collected and analyzed. Fluoroscopy time, dose-area product (DAP), Entrance skin dose (ESD) and peak skin dose (PSD) of the patients, and surface dose of the main organs (such as eyes, thyroid, left lung, chest, abdomen, liver, testis and hands) of the operators were metered.In phantom study, an anthropomorphic phantom was used to substitute the patient and it was placed at the center of the angiography table. Then it was irradiated by pulsed fluoroscopy in posterior-anterior (PA) direction in clinical conditions. Many thermoluminescent dosimeters (TLDs) were put in the cavity of the simulated organs or tissues in the phantom before fluoroscopy. Those TLDs would collect the dose of the tissues or organs. In this way relationship between effective dose and ESD of the patient, and relationship between effective dose of the patient and DAP could be found out. Thus radiation protection of the patient would be recommended. Meanwhile k(?) distribution of the scattered X rays in the working place was measured by TLDs, as a result relationship between the dose of the operator (including effective dose, surface dose or organ dose of thyroid, left lung, eyes, left hand and right hand) and ka of the working place could be found. Except from lead drape and lead curtain, table height and size of irradiation field were taken into consideration to explore the influence on the ka distribution in the working place, because they could be changed by the operator easily.In cardiovascular intervention patient's dose is very high, thus reasonable measures should be taken to reduce patient's dose on the premise that diagnostic and therapeutic procedures are not influenced. By comparison, more attention should be payed to patients'close and operators' occupational dose in CA+PTCA or PICAS procedures. Results show that The range of fluoroscopy time is 0.80～42.4 min, range of DAP, ESD, PSD of the patients is 1.54～161 Gy·cm2,3.85～402 mGy,19.8～2128 mGy, respectively. For CA and PTCA or PICAS procedures all the results are significantly different. In general average effective dose of the operator per operation is 2.99μSv (under protection),45.6μSv (without protection) and 6.99μSv(with Boetticher's method). Average equivalent dose of the eye, left hand and right hand is 112μSv,213μSv,82.6μSv, respectively.According to the data obtained from experimental study, a computer programme is developed to evaluate the effective dose and dose of unprotected organs such as eyes and hands. The parameters of the prime operator's position, different ka distribution, and proportion of the interested positions of the operator's height can all be set by the users. But the programme takes only PA direction into consideration, thus the results are the conservative estimation of the truth-value. Effective dose of the operator is estimated by Hp(10) (under and over the lead apron), and personal dose equivalent underneath the lead apron in the chest region and personal dose equivalent over the lead collar (recommended by von Boetticher). The programme can estimate effective dose of the operator and equivalent dose of the eyes and hands in different protection conditions. Results of the estimation are smaller than the data collected from clinical intervention, the reason is that frames of cine, oblique angulation increasing the exposure of X rays, the extent of using the protective devices may greatly affect occupational exposure.If the entrance point of the X rays at the phantom back is taken as the reference point, when the operation table was set at 90 cm high, ka rate of positions above 80 cm high in the working place was almost in inverse square relationship with the distance to the reference point. In the working place ka rate increases as field of view (FOV) gets bigger and the height of operation table gets higher. The correlation between ESD, PSD of the patients and E of the operators is not that good. Radiation exposure of the operator could only be roughly estimated by ESD of the patient. In order to decrease the radiation risk to the lowest level, reducing fluoroscopy time, femoral artery access to the patients, small FOV and short table height are recommended during interventional procedures and more advanced equipments should be applied and radiation protection should be fully managed.