Radioactive Waste in Hospital

The management of radioactive waste involves two stages: collection and disposal. The radioactive waste should be identified and segregated within the area of work. Foot operated waste collection bins with disposable polythene lining should be used for collecting solid radioactive waste and polythene carboys for liquid waste.

Collecting radioactive waste in glassware should be avoided. Each package is monitored and labeled for the activity level before deciding upon the mode of disposal. Some hospitals that have incinerators and permission to dispose of combustible radioactive waste through incineration may also segregate combustible radioactive waste from non-combustible waste.

When two different isotopes of different half-lives like Tc-99m and I-131 are used, separate waste collection bags and bins should be used for each. Each bag or bin must bear a label with name of the isotope, level of activity and date of monitoring. 

Radioactive waste disposal

The collected radioactive waste is disposed as per the following:

• Dilute and Disperse
• Delay and Decay
• Concentrate & Contain (Rarely used)
• Incineration (Rarely used) 

Dilute and Disperse:

Low activity solid article may be disposed off as ordinary hospital waste provided the activity of the article does not exceed 1.35 microcuries (50 KBq) or the overall package concentration does not exceed 135 microcuries / m3 (5MBq / m3). Such articles include vials, syringes, cotton swabs, tissue papers etc. Similarly, liquid radioactive waste with activity less than microcurie level can be disposed off into the sanitary sewerage system with adequate flushing with water following the disposal. However, the maximum limit of total discharge of liquid radioactive material into sanitary sewerage system should not exceed the prescribed limits Table 

Delay and Decay:

Medium activity radioactive waste and those with half-lives of less than a month may be stored. The storage room should be properly ventilated with an exhaust system conducted through a duct line to a roof top exit. The storage space should have lead shielding of appropriate thickness (10 HVL) to prevent radiation leakage. The radioactive waste should be stored for a minimum period of about 10 half lives when after decay only 0.1% of the initial activity remains. The waste is then monitored for the residual activity and if the dose limit is low it is disposed off as low activity solid or liquid waste. Most of the low and medium level radioactive hospital waste is of short half-life permitting this type of waste disposal.

Concentrate and Contain:

This technique of radioactive waste disposal is sometimes used for radioactive materials with very high activity levels and for those with long half-lives (longer than a month). Their disposal by delay and decay method is impractical because of longer storage period, particularly if space availability is limited. Radioactive waste is collected in suitably designed and labeled containers and then buried in exclusive burial sites approved by the competent authority. In day-to-day work of a hospital, we do not come across radioactive waste of this nature and as such, this method of radioactive waste disposal is rarely used. 

Incineration :

Insoluble liquid waste such as that from the liquid scintillation systems may be disposed off by incineration. Inceneration reduces the bulk of waste and the activity is concentrated in a smaller volume of ash for further disposal. Since incinerators used for radioactive waste disposal release part of the radioactivity into the atmosphere they should operate under controlled conditions and in segregated places. Ashes collected have to be disposed off as solid radioactive waste separately. Environmental concerns and public pressure severely restrict the methods of ground burial and incineration as regular options of radioactive waste disposal. For these reasons, incineration and burial are rarely recommended. 

Special situation for radioactive waste Management in a Hospital

Disposal of sealed sources

Hospitals use sealed sources for a variety of applications, including teletherapy, brachytherapy, blood irradiation, calibration etc. Most of these sources are relatively small with activities ranging from a few up to a few hundred MBq, except the teletherapy and blood irradiation source, which may have high activities. Once the source becomes weak for further applications it has to be removed and replaced. Hospitals ordering and using such equipments must enter into a contract for safe removal and replacement of the sealed radioactive source with the suppliers. While ordering such equipment and the source, the Radiation Safety Officer of the hospital should 

Disposal of gaseous waste

Volatile radioactive sources like Iodine-131 and Iodine-125 release radioactive vapors, generating airborne radioactive waste. The containers of such radioactive substances should be opened under fume hoods connected through duct lines to highest roof top exit. Before the vapors are diluted and dispersed into the atmosphere, they should pass through charcoal and particulate air filters. Hospitals using radioactive gases should have efficient laminar airflow system. Other gaseous radioactive waste generating isotopes used are Xenon-133, Carbon-14, Hydrogen-3, Nitrogen-13, Technetium-99m aerosols.

Disposal of excreta and urine of patients administered high doses of radioisotopes:

Patients administered high therapeutic doses of radioisotopes (e.g., Iodine-131 in thyroid cancer) are admitted in isolation wards until their radiation emission levels are within the minimum safe limits (3 mRoentgens per / Hour at 1 meter distance). The excreta and urine of patients admitted in a high dose isolation ward (e.g. Iodine -131) after getting flushed passes the PVC pipes through the shortest route possible into customized storage tanks, called delay tanks for storage before dispersal into the sewerage system (Fig ). The delay tank should be located in an area where there is minimal movement of public.

The tank should be leak proof, corrosion free and should have smooth surface from inside. The capacity of the tank depends on the number of patients admitted each day. A facility admitting two patients would require two delay tanks of 6000 liters each. This capacity is based on the presumption that on an average each patient uses about 100 liters of water per day. At that rate, each patient will use 3000 liters per month and two patients will use 6000 liters. At the end of one month as the tank will be full, it is closed and the gate valve of the second tank is opened.

The full tank is kept closed for the period of one month that the second tank takes to fill. As such, each tank holds the radioactive waste for 2 months that is sufficient for the decay of Iodine-131 to low levels (Delay & Decay). However before releasing the effluent of the tank into the public sewerage system a sample is collected to check the activity, this should not be more than 1.2 microcuries per liter. No hospital is permitted to release into public sewerage system an aggregate 37 G Bq (1 Curie) of liquid radioactive waste in one year.

Record Keeping:

Proper records in the form of logbook must be maintained. Details of diagnostic and therapeutic radioisotopes procured and administered should be recorded. The records must also include the details of radioactive waste generated with the activity levels and the levels at the time of their disposal. The activity levels in the effluent of delay tank must be recorded prior to disposal into public sewerage system. The total activity disposed off annually in the sewerage system should be recorded. The names of persons authorized for administration and disposal of radioisotopes must be recorded

EXAMPLES OF RECORDS THAT MAY BE GENERATED UP TO AND INCLUDING CLOSURE

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Exposures From Patient

Contamination

Administered activity: 1000 MBq I-131

Generally larger than the derived limits for contamination given by ICRP (publ57)

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I-131 LIQUID DISCHARGES in University Hospital in Udine (Italy)

? ~100 pts/year

? ~ 5.55 GBq/pt

? Annuallimitof discharge: 70 MBq(~ 0.01 % of administeredactivity)

? Limit for dischargeintopublic sewage: 1 Bq/l

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Monitoring of Staff Internal Contamination

I-131 Special Monitoring

I-131 Routine Monitoring

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