This study was carried out in the NM unit of a referral hospital in West Java, Indonesia. The unit utilized two adjacent buildings in its service operations, with building one being old and the waste piping system blueprint was no longer available. Meanwhile, the second was a new six-story building that utilized the basement as the location for NM service. The study focus was on the management of radioiodine therapy patient's excreta in both places. In the NM installation of building one, liquid waste was not directed to the hospital's centralized WWTP, while in NM installation of building two, the waste was temporarily settled before entering the hospital's WWTP. I-131 Therapy is carried out in buildings one and two, adjusted for the availability of isolation beds in each building. In general, the workload of therapy places can be seen from the weekly patient data tabulation in each of the following buildings:

There are 14 isolation rooms in building one that are equipped with a variety of treatment options for patients in building two's liquid waste. The waste treatment in building one is terminated at the decay tank located in the parking lot, and it does not go on to the hospital's WWTP. Building two has four isolation rooms, each with its own advanced waste treatment system that connects to the hospital's WWTP, which ultimately empties into local rivers. Because of issues with water seepage on the walls of the NM room, the infiltration well serves the purpose of a well to manage the runoff of surface water that is caused by rain. This problem was caused by the NM room. In order to determine whether or not there is a leak in the decay tank located in building two, measurements of I-131 activity were taken in the infiltration well.

As depicted in figure 1, decay tank A receives waste from the isolation and post-injection rooms; decay tank B receives waste from the hot lab and four uptake rooms; and decay tank C may receive waste from patients who do not understand the recommendations for excretion procedures after and/or while waiting for patient discharge, causing radioiodine concentrations in the main sewage pit.

Figure 1. Water an air sampling point.

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Sampling was carried out on liquid and air waste around the NM unit. Furthermore, the number of sampling points was determined using a systematic method. The process was performed by considering the flow and storage of patients waste from points A to I and from points 1–6 for liquid and air samples, respectively, as shown in figure 1.

Liquid waste was collected using the WS750 Wastewater-Stormwater Sampler with a 1 l Marinelli beaker tube container based on the required capacity for contaminated sample analysis for radionuclide counters. Iodine-131 therapy with a dose above 1110 MBq requires 3 × 24 h until the patient can be discharged, resulting in two therapy terms per week. The weekly therapy schedule begins on Monday with a scheduled patient release on Wednesday. The second term begins on Wednesday afternoon with a scheduled patient release on Friday. At storage tanks A, B, and C, sampling was carried out in sequence every 12 h, starting at 12 h on the first day of therapy and ending at 48 h (day a term of therapy I-131). At locations D to I, sampling was performed only at 48 h to determine the settling or flow of waste containing I-131.

Air samples were taken using DFHV-1E High Volume Air Sampler (220–240 VAC) with a Charcoal filter and was counted on the high-purity germanium (HPGe) detector. The procedure of extraction efficiency determining CH3I-131 follows the American Standard for Testing and Materials (ASTM D 3803-79, 1979). Determination of CH3I-131 absorption efficiency of an activated charcoal filter is done at a temperature range of 30 °C–45 °C, the flow rate of 13 lpm to 26.3 lpm, and air humidity of 30%–90%. Sampling medium at locations marked 1–6, as shown in figure 1. These six points have the potential for the spread of I-131 in the air due to their proximity to the service unit and the temporary processing site of patient's liquid waste.

Equipment used for measuring radionuclides in wastewater was a gamma spectrometer counting system with an Ortec HPGe detector. The system consisted of an HPGe detector placed in a 10 cm thick shielding system. Furthermore, the pre-amplifier was attached to the detector body. The amplifier, HV bias supply, and multi-channel analyser were integrated into a single module called DespecPro. The gamma spectrometer system was operated with Maestro or Gamma Vision software, as schematically shown in figure 2. The device was calibrated with a standard mixed source consisting of radionuclides Co-60, Ba-133, Cs-134, Cs-137, Pb-210, and Am-241 that were traceable to the IAEA. Prepared samples were then placed in containers, such as vials or Marinelli beaker, labelled, and wrapped in plastic to prevent contamination. The radionuclide concentration in the sample was measured using a gamma spectrometer equipped with an HPGe detector calibrated using a standard source [17].

Figure 2. HPGe detector.

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Calibrating energy and efficiency used equations [18]:

Standard source decay,

With:

:activity during counting (Bq)

: initial activity (Bq)

: delay time (days)

T: half-life (days)

Energy calibration,

With:

Y: gamma energy (keV)

a and b: linear constant numbers

X: channel number

Efficiency calibration,

With:

γ : counting efficiency (%)

Ns : standard count

NBG: background count

ts : standard count time (seconds)

tBG: background count time (seconds)

At : standard source activity at the time of count (Bq)

pγ : gamma energy abundance (%)

To calculate the concentration of radionuclides contained in the sample (CSp), the following equation was used [19]:

With:

CSp: the concentration of radioactive substances in the sample (Bq/lt or Bq/kg)

Cavg: average concentration of radioactive substances in the sample (Bq/lt or Bq/kg)

uT : measurement uncertainty (Bq lt−1 or Bq kg−1)

With:

NSp: sample count rate (cps)

NBG: background count rate (cps)

γ : efficiency at gamma energy (%)

pγ: yield of gamma energy (%)

WSp: sample volume or weight (lt or kg)

With:

: sample count uncertainty (%)

: efficiency uncertainty at gamma energy (%)

: yield uncertainty (%)

: sample volume uncertainty (%)

k: 1

The minimum detectable concentration (MDC) for a gamma spectrometer system was influenced by counting efficiency, background count rate, and sample weight. To calculate the MDC with a 95% confidence level, the following equation [18] was used

With:

MDC: MDC (Bq/lt or Bq/kg)

NB : background count rate (cps)

tB : background count time (seconds)

γ : count efficiency (%)

pγ : gamma energy abundance (%)

Fk : self-absorption correction factor (when sample ρ is different from the standard ρ)

w: sample volume or weight (lt or kg)