Radiation exposure to surgical staff during hyperthermic isolated limb perfusion with ^99mTechnetium labeled red blood cells

Abstract

Purpose: Hyperthermic isolated limb perfusion (HILP) is an effective method in the treatment of recurrent melanomas and soft tissue sarcomas. To avoid systemic toxicity, leakage from the limb perfusate into the systemic circulation is real-time monitored by administration of a radioactive agent to the limb circuit. This has made HILP safe for the patient. However, the radiation exposure to the surgical staff has never been measured and could be a limiting factor for the use of HILP. The purpose of the present study was to measure and evaluate the radiation exposure to the surgical staff performing HILP with ^99mTechnetium labeled red blood cells.

Materials and methods: Thirteen patients had HILP performed in 11 lower limbs and two upper limbs at our inpatient clinic between October 2006 and February 2007. The surgeon and nurse had thermoluminescence dosimetry (TLD) chips attached to the finger pulp and to the ring area of the left fourth finger, as well as an electronic dosimeter attached to the anterior lining of the trousers. The anesthesiologist and perfusion technologist also carried electronic dosimeters.

Results: The surgeon had the highest radioactive exposure with an average dose per procedure to the finger pulp of 16.2 µSv, to the ring area of 8.5 µSv, and to the abdominal wall of 4.2 ± 0.6 µSv.

Conclusions: HILP with ^99mtechnetium-labeled red blood cells does not constitute a safety risk to the operating team with respect to radioactive exposure. Routine dose monitoring of the staff or special precautions for fertile women are not necessary.

• Hyperthermic isolated limb perfusion
• dosimetry
• radiation
• melanoma
• sarcoma

Introduction

Hyperthermic isolated limb perfusion (HILP) is an effective method in the treatment of recurrent melanomas and soft tissue sarcomas [1], [2]. First described by Creech et al. in the late 1950s, the affected limb is isolated from the systemic circulation by a tourniquet and chemotherapeutic agents are administered by an extracorporeal bypass circuit via a cannulated artery and vein [3]. To avoid systemic toxicity, leakage from the limb perfusate into the systemic circulation is real-time monitored by administration of a radioactive agent to the limb circuit, a method used since the early 1960s [4]. When a scintillation probe is positioned over the heart, an unacceptable leak from the limb circuit into the systemic circuit can be registered by a rise in the radioactive count. The technique has been refined and changed over the years, and different approaches with radioactive tracers varying from ^125/131I-albumin [5], [6], ^99mTechnetium-albumin [7], [8], or ^99mTechnetium-labeled red blood cells [9] to combinations of these [10] have been described.

Continuous leakage monitoring has made HILP safe for the patient. However, the radiation exposure to the surgical staff has never been measured and could be a limiting factor for the use of HILP.

The purpose of the present study was to measure and evaluate the radiation exposure to the surgical staff performing HILP with ^99mTechnetium labeled red blood cells.

Materials and methods

Thirteen patients had HILP performed in 11 lower limbs and two upper limbs at our inpatient clinic between October 2006 and February 2007. Eight patients were treated for melanoma and five patients for soft tissue sarcoma. The chemotherapeutic agent used was melphalan with or without tumor necrosis factor alpha (TNFα). At every procedure, 100 MBq ^99mTechnetium labeled red blood cells were administered to the limb circulation and 10 MBq to the systemic circulation (Figure 1). A fixed scintillation detector measured the radioactivity over the cardiac zone. The complete procedures lasted on average 5.7 hours (4.7–7.3) with the actual limb perfusions lasting from 60 to 90 minutes. In one case, perfusion was interrupted prematurely because of leakage to the systemic circuit.

Figure 1. Principle of hyperthermic isolated limb perfusion. (1) reservoir; (2) pump; (3) oxygenator and heater; (4) Discharge; (5) Ringer's lactate; (6) tourniquet; (7) scintillation probe.

The surgeon and nurse had thermoluminescence dosimetry (TLD) chips (MTS-type, Rados, Turko, Finland) attached to the finger pulp and to the ring area of the left fourth finger, as well as an electronic dosimeter (RAD-60S, Rados, Turko, Finland) attached to the anterior lining of the trousers (Figure 2). The anesthesiologist and perfusion technologist also carried electronic dosimeters. The TLD chips were supplied by the Danish National Institute of Radiation Hygiene (SIS, Herlev, Denmark). Each set of chips was used for three to seven procedures. Between operations, chips were stored together with three TLD chips used for measurement of background radiation in a box shielded from any other radiation exposure. After four to six weeks, chips were sent to SIS for determination of radiation exposure, corrected for background radiation. In all, three sets of TLD chips were used.

Figure 2. Placing of thermoluminescence and electronic dosimeters.

The radiation doses determined by TLD chips have an error of 8% and a lower detection limit of 0.01 mSv. The electronic dosimeters were calibrated with a ¹³⁷Cs source, 662 keV at 2 mSv/h and had an error of 5%.

Data were analyzed using the SPSS statistical analysis program version 13.0 (SPSS Inc., Chicago). When comparing radiation values measured by electronic dosimeters, unpaired t-tests were used. Values are presented as mean ± SEM with range in parenthesis.

The study was performed in accordance with the Helsinki II declaration. Approval of the study by the Danish Ethical Committee was not required.

Results

The surgeon had the highest radioactive exposure with an average dose per procedure to the finger pulp of 16.2 µSv, to the ring area of 8.5 µSv, and to the abdominal wall of 4.2 ± 0.6 µSv (p < 0.001 vs. nurse, anesthesiologist, and perfusion technologist; Table I). For the nurse, the doses were 5.4 µSv, 3.1 µSv, and 0.9 ± 0.2 µSv, respectively. For the anesthesiologist and perfusion technologist, the doses to the abdominal wall were 0.9 ± 0.3 µSv and 1.3 ± 0.3 µSv, respectively. This corresponds to dose rates for the surgeon to the finger pulp of 2.9 ± 0.4 µSv/h, to the ring area of 1.4 ± 0.3 µSv/h, and to the abdominal wall of 0.77 ± 0.12 µSv/h (p < 0.001 vs. nurse, anesthesiologist, and perfusion technologist; Table I). For the nurse, the dose rates were 0.9 ± 0.1 µSv/h, 0.5 ± 0.1 µSv/h, and 0.16 ± 0.03 µSv/h, respectively. For the anesthesiologist and perfusion technologist, the dose rates to the abdominal wall were 0.16 ± 0.06 µSv/h and 0.23 ± 0.05 µSv/h, respectively.

Table I.  Mean radiation doses and dose rates for surgical staff performing hyperthermic isolated limb perfusion.

	Radiation dose per procedure (μSv)			Radiation dose rate (μSv/h)
	Finger pulp	Finger ring	Abdominal wall	Finger pulp	Finger ring	Abdominal wall
Surgeon	16.20	8.50	4.2 ± 0.6	2.9 ± 0.4	1.4 ± 0.3	0.77±0.12
Nurse	5.40	3.10	0.9 ± 0.2^a	0.9 ± 0.1^a	0.5 ± 0.1^a	0.16 ± 0.03^a
Anesthesiologist			0.9 ± 0.3^a			0.16 ± 0.06^a
Perfusion technologist			1.3 ± 0.3^a			0.23 ± 0.05^a

^aP < 0.001 vs. surgeon.

Discussion

The efficacy and safety of HILP is beneficial for many patients with melanoma or soft tissue sarcoma. However, radioactive exposure to the surgical staff could be a limiting factor for the use of HILP, especially since HILP is not performed at departments of nuclear medicine but by surgical staffs who may not be familiar with radioactivity and radiation safety.

The International Commission on Radiological Protection (ICRP, Stockholm, Sweden) has recommended upper limits for radiation exposure to radiation workers. The limit for the whole body is 20 mSv per year, averaged over five years, or a maximum of 50 mSv in any single year [11], and the limit for the fingers is 500 mSv per year [11]. For a fetus, the limit is 1 mSv through the whole pregnancy.

Thus, the most exposed member of the surgical team, the surgeon, received less than 0.025% of the maximally allowed annual radiation dose to the body per procedure performed. Additionally, if a pregnant surgeon performed HILP every week day for nine months (total dose: 0.8 ± 0.1 mSv), her fetus would still receive less than the maximal limit.

In comparison, annual radiation doses for international flight crew members have been measured to be up to 3.8 mSv because of exposure to cosmic radiation [12]. Hence, if the surgeon performed HILP 12 hours every day for 365 days, she would receive roughly the same radiation dose as an airline pilot (3.4 ± 0.5 mSv) which would be only about one sixth of the maximally allowed dose of 20 mSv.

The finger pulp of the surgeon received 16.2 µSv per procedure and the ring area approximately half of this. The difference must be due to the longer distance from the radioactive source to the ring area than to the pulpa and the pulpa is definitely the most exposed part of the body, especially when the surgeon manipulates the vessels with the tip of her fingers at the end of the ILP procedure or in case of leakage. Still, according to the ICRP recommendations, the dose to the pulpa is only 0.003% of the maximally allowed dose to an extremity.

From the data obtained in this study, it is not possible to draw conclusions regarding safety when operating with other radioactive tracers than technetium. But if beta-emission is disregarded and it is given that one twentieth dose (0.5 MBq + 5 MBq) of ¹³¹I is administered and that the absorbed dose speed for ¹³¹I is about three times higher than for technetium, the expected absorbed dose for the operating team would only be about one seventh of what was observed in this study. However, beta particle emission is considerably higher for ¹³¹I than for technetium and the relative contribution from beta particles to the absorbed dose in this case is unknown and therefore the calculation is speculative. Furthermore, the half-life for technetium is only about six hours, while it for ¹³¹I is around eight days. This raises the question about radiation exposure to nursing staff taking care of patients in the days after the procedure.

So even though our data indicate that HILP is safe for the surgical team also when using ¹³¹I, only a dosimetry study in an actual HILP setting with ¹³¹I could definitely clarify this.

Conclusions

In conclusion, HILP with ^99mtechnetium-labeled red blood cells does not constitute a safety risk to the operating team with respect to radioactive exposure. Routine dose monitoring of the staff or special precautions for fertile women are not necessary.

Declaration of interest: The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the paper.