Increasingly in Nuclear Medicine, aseptic processes for the manufacture of drugs are being used. Aseptic control during manufacturing can be achieved through a combination of many factors (classified environments, use of controlled raw materials, perfect workflow organisation, well trained operators) and obviously a validated procedure of the cleaning and sterilisation of the environments and tools that are involved in the production process. It is therefore essential to ensure the decontamination of both environments and tools where the drug is manufactured and/or manipulated to ensure the sterility of the final product that will then be in contact with the person during radiotherapy or diagnostics.
The phases for the decontamination of the shielded isolators are four: dehumidification, injection 1, injection 2, and aeration.
DEHUMIDIFICATION: The purpose dehumidification is to create the initial conditions required for decontamination within the isolator. Usually during this phase the relative humidity of the isolator is lowered to load the chamber with the vaporised peroxide without having problems of condensation.
INJECTION 1: The second phase aims to reach the maximum concentration of the peroxide (expressed in ppm, parts per million) in the shortest possible time. The liquid peroxide is vaporised and introduced into the chamber as a gas in the air through ventilation. The peroxide that is now in the gas phase can start attacking cell membranes, DNA, and other microbial agents. In this phase, the condensation of peroxide gas on any surface should be avoided: in this way the surfaces are safeguarded against possible deterioration.
INJECTION 2: This phase serves to keep the peroxide concentration stable for the period that is necessary to reach the desired value of decontamination (usually SAL=10-6, SAL=Sterility Assurance Level). Given that sterility is an absolute concept, one can talk about the probability of sterility: to reach a SAL=10-6 means guaranteeing after decontamination the probability that only one micro-organism in a million is alive.
AERATION: The fourth phase is used to reach a concentration of peroxide which allows ensuring the safety of the personnel before opening the room and which does not alter the quality of the product or of the test that must be executed in the room. An aeration of the isolator usually follows this phase in order to speed up the time in which it reaches the threshold limit.
What alternative methods to VPHP exist for the decontamination of the shielded isolators in Nuclear Medicine, and what are the safety issues (for the operator, for the patient, for the environment…) linked to decontamination?
There are several methods for decontamination: by mechanical means (for example, flushing); chemical (use of specific liquid or gaseous agents), physical (through x-rays or through heat).
The most widely used are chemical decontamination procedures (an action of the chemical agent on the object to be sterilised) and they are usually applied by means of liquid or gas. The application through dry gas/vapour solves the problem of homogeneous distribution on all surfaces with respect to the ‘wet’ method. Since chemical agents are involved, they are intrinsically related to various dangers such as toxicity, flammability, irritation, dangers for the environment, etc. These agents must ensure the broadest spectrum of action, i.e., have a killing effect on multiple micro-organisms.
Hydrogen peroxide in the VPHP vapour phase seems to perfectly match all the requirements as an ‘ideal decontaminant agent’ because:
Given its excellent antimicrobial activity and its non-toxic residues, the VPHP is supplanting its predecessors such as formaldehyde and ethylene oxide (toxic, carcinogenic…) for the sterilisation of thermolabile materials, which therefore cannot withstand a sterilisation by means of heat.
The Comecer VPHP generator is designed and sized exactly for the environments of Comecer cells. It can be either integrated directly in the cell at the time of purchase or subsequently integrated to Comecer cells that are VPHP-ready after pre-sale analysis.