Real-time radio-transparent dosimeter for X-ray imaging system

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Abstract

Possible consequences of using X-ray devices as imaging support during surgical practices may be the development of skin diseases due to the combination of high local dose and long exposition time. Our group developed an original dosimeter which meets the following requirements:

  • transparency to X-ray to avoid image degradation,

  • measurement and localization in real-time of the dose absorbed by the skin on the whole exposed surface.

The main purpose of this dosimeter is to allow the practitioner to change the beam orientation during the intervention in order to reduce the local dose and then avoid, in the extreme cases, the development of tumors. The dosimeter is composed of a lattice of scintillator fibers connected to a 64 channels photomultiplier tube. The detector combined with an appropriate electronics provides in real time an accurate measurement of the dose on the whole exposed surface. A linear relation between the photon count rate and the dose is demonstrated. Our dosimeter provides also in real time a map of the dose which leads to a very efficient monitoring of the dose during all the exposition time.

Introduction

The use of X-ray radioscopy devices allows the physician to simplify the surgery in some cases. During the intervention, the surgeon introduces small instruments in the patient body using a catheter and performs the therapeutic work with the aid of a real-time movie produced by an X-ray detector. The movie is made up of images obtained with short X-ray pulses of few milliseconds. The image rate, usually equal to 25 images/s, is high enough to ensure a visual comfort. The voltage and the current of the X-ray tube are automatically calculated by the device based on the intervention type and the patient corpulence in order to optimize the image contrast. The main disadvantage of this procedure is the high dose delivered by the X-ray tube to the patient during the intervention time. Skin diseases leading to tumors can be the consequences of an extreme exposition of the patient to X-ray (few Grays). In order to reduce the dose absorbed by the patient, the use of a dosimeter is needed during the surgical intervention. However, there are no available commercial devices matching to the constraints of the surgery which are real time information, radio-transparency and large sensitive surface. The dosimeter presented in this paper allows the physician to measure in real time the dose absorbed by the patient skin on the whole surface potentially exposed. In the case where the dose reaches a dangerous defined threshold, the surgeon can change the angular view of the radioscopy device in order to distribute the global dose on a larger surface. A file is created providing the dose history of the patient and allowing the physician to follow the eventual consequences. This file can also provide elements in the case of lawsuit between the patient and his surgeon. This paper presents the development of the dosimeter and the first results obtained.

Section snippets

Material and methods

The sensitive part of the dosimeter is based on a 31×31cm2 thin detector placed between the patient and the X-ray tube at the skin level. The detector is transparent to the X-ray and introduced no artifact in the radioscopy image. The surface is large enough to cover the body part potentially exposed to the X-ray. A typical skin surface exposed is about 10×10cm2. The dose measured by the dosimeter is similar to the dose absorbed by the skin which is the most relevant in this context. A

Results and discussion

The dosimeter has been tested with a radioscopy device where it was possible to set manually the X-ray tube parameters. Fig. 4 shows a very good linearity between the counting rate and the beam intensity. The measurement has been done by only changing the X-ray tube current keeping the voltage at 70kV. The expected behavior is observed when the X-ray tube voltage is changed keeping the current at 2mA (Fig. 5). A comparative measurement has been done with an ionization chamber reference

Conclusions

The realization of an original dosimeter for radioscopy application has been presented. An accurate measurement of the dose absorbed by the patient skin is performed in real time during the surgical interventions without any perturbation. The map of the dose is given by the software allowing the physician to monitor the exposition of the patient to the X-ray during the surgery. A study with a large number of patients is scheduled to evaluate the benefit of this dosimeter during the surgery. A

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