Lymphoscintigraphy and Radiation – Occupational Exposure During Sentinel Node Assay

Ionizing radiation has many practical applications, but it is also, as it is well known, dangerous to human health. The purpose of this study was to estimate the dose and exposure for medical staff involved in sentinel node assay and to determine how safe this assay really is. The theoretical method was used for calculation. Three groups of medical staff were selected: nuclear medicine specialist, nuclear medicine technologist and a surgeon. The results obtained show that the most exposed staff member is nuclear medicine specialist and that dose received by the surgeon is smaller then the dose limit.


Introduction
Th e human body is permanently or temporarily exposed to various kinds of radiation, one of them being ionizing radiation.Th e ionizing radiation is a product of nucleus decay, acceleration of charged particles in electrical or variable magnetic fi elds and target collision ().Because of their complex structure, living organisms are very sensitive to the infl uence radiation.It aff ects the living functions of cell and thus it aff ects tissues, organs and organisms themselves.Accordingly, two types of radiation infl uence can be distinguished: direct infl uence on atoms incorporated in the molecules of living tissue and indirect infl uence on atoms of the surrounding media, mostly water.Th e consequence of this infl uence is the change in the cell function.Ionization of living matter depends not only on the absorbed dose but on relative biological eff ect (RBE) as well.Relative biological eff ect can be produced by various types of ionizing radiation.Th e energy deposited by radiation causes serious eff ects in the matter and it changes its properties.A portion of the absorbed energy by mass unit of the exposed material is known as absorbed dose and it is expressed as SI unit Gray (Gy) ().Equal doses of alpha, beta and gamma radiation will not produce the same eff ects in an organism.Th erefore, the term equivalent dose is introduced.It is expressed in Sieverts (Sv).Th e equivalent dose is equal to the product of the absorbed dose and radiation quality factor wR. Th e radiation quality factor is one of the factors of modifi cation used to describe biological eff ectiveness of radiation ().Th e effective dose is the sum of products of equivalent dose and risk factor that corresponds to a specifi c tissue or organ.It is used to estimate the risk of radiation for the whole body, regardless of which parts of the body were exposed to radiation.
. w Ti corresponds to the risks of the stochastic eff ects infl uencing the tissue i.According to the total stochastic eff ects on equally exposed body, risk factors values for various tissues and organs are given in the Table  ().Application of ionizing radiation in medicine means adhering to the basic radiation protection principles: justifi cation, optimization and dose limits for staff and public.Th e main aim of this study was to determine the dose rates and exposure in personnel directly involved in lymphoscintigraphy and biopsy of sentinel node.Lymphoscintigraphy is nuclear medicine assay used in early stages of malignant diseases and in therapy planning and predictions.Th e assay is performed in breast cancer and melanoma.Radionuclide used in this assay is m Tc. m Tc is gamma emitter with  keV and half time of , hours.Nano-colloid albumin labeled with  MBq of m Tc is used as tracer.

Subjects and Method
Main requirements for sentinel node scintigaphy are: -Radiopharmeceutical preparation.m Tc pertechnetate is produced from  Mo/  Tc generator.Th e vial, containing albumin colloid particles, is placed in a led container and by aseptic method  - MBq of m Tc Sodium pertechnetate in - ml is added.-Allowed activity for sentinel node scintigraphy is  MBq in the volume of , ml.-Radiopharmaceutical is applied by intratumor or peritumor injection at breast carcinoma or melanoma location, intracutaneous injections in diff erent places: near the tumor or along the scar.-A nuclear medicine specialist performs the application.
-Gamma camera is an instrument for the detection and monitoring of lymph nodes drainage.Siemens dual head gamma camera with LEHR collimators was used.
-After the application of radiopharmaceutical, dynamic acquisition is made in the duration of  min,  x  fr/min.-Following the dynamic acquisition, two static acquisitions are made:  minutes anterior and posterior images.-Identifi cation and localization of the sentinel node is done by Co- pen-marker, and after marking with pen marker a gamma probe is used.Th e probe is used for identifi cation of the most sensitive node and verification of the node location.-Marking of the node on the skin is made by the skin marker ().After the detection and marking of the sentinel node, the patient is sent to surgery, and the process of biopsy begins.

Methods
Th e theoretical model (D R =nΓ/d  ) was used for calculation of dose rate and exposure during sentinel node assay.This model tried to introduce the work conditions of the staff involved in the process of lymphoscintigraphy and biopsy of sentinel node.Th e dose rate and exposure to hands and body at  meter distance are calculated for staff in contact with the source material and the patient in different stages of the assay.Th e model was made for diff erent groups of staff : -Nuclear medicine specialist during the application of radiopharmaceutical; -Nuclear medicine technologist, who assists the specialist and operates gamma camera; -Surgeon, during biopsy of sentinel node (,  and  hours after administration).
It was necessary to make a correction for the factor of decay e -λt , where λ is decay constant and t is time interval from the moment of administration of radiopharmaceutical to the time of measurements.

Results and Discussion
-Nuclear medicine specialist, holding syringe with  MBq of m Tc between fi ngers (d=, cm) in  minutes period of radiopharmaceutical application, will receive , mSv.In that period, at  meter distance from the source, dose to the body will be , μSv.-Nuclear medicine technologist in a period of  minutes at  meter distance will receive dose of , μSv.-For surgeon during one hour that is needed for this assay, depending on the period after the administration results were as follows: - hours after the administration of radiopharmaceuticals , MBq of administrated activity remains.In this case, surgeon will receive a dose of , μSv to hands and , μSv to the body.- hours after the administration, activity of m Tc will be , MBq and dose to hands will be  μSv and to body , μSv.- hours after the administration the dose will be negligible (, MBq).In this case the hands will receive a dose of , μSv and , μSv to the body.
An assumption is made that all the other staff present in the surgery theatre is at more than one meter distance from the patient, so the received dose is negligible.

Conclusion
After calculating the dose rate and exposure of medical staff during lymphoscintigraphy and biopsy of sentinel node our results showed that the most exposed professional was the nuclear medicine specialist.Th e nuclear medicine technologist was the second most exposed member of the staff .Surgeons and other medical personnel who work in the team, receive doses that are negligible and  times bellow the dose limit.Th ese results are in accordance with those found in studies (), () and ().Th e dose rate and exposure during the assay are minimal and there should be no fear of radiation and its consequences after this assay.