Evaluation of patient effective dose from sentinel lymph node lymphoscintigraphy in breast cancer: A phantom study with SPECT/CT and ICRP-103 recommendations

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Abstract

Objective

To evaluate the effective dose delivered to patients undergoing sentinel lymph node (SLN) lymphoscintigraphy by taking into account both the transmission dose using the CT component of a SPECT/CT system and the 99mTc internal emission dose.

Materials and methods

An adult female humanoid phantom and a set of thermoluminescent dosimeters were used in dose measurement from the CT transmission irradiation. The choice of measurement organs in the humanoid was guided by the recommendations described in the International Commission on Radiological Protection report number 103 (ICRP-103). The effective doses due to 99mTc internal emission source were re-calculated from measurement data reported in our previous study on the same subject with the use of tissue weighting factors of ICRP-103.

Results

CT transmission dose is the main contribution to the patient total effective dose for both 1-day and 2-day lymphoscintigraphy protocols and for different surgical procedures. Patients undergoing SLN lymphoscintigraphy receive about the same amount of total effective dose of about 3 mSv for both 1-day and 2-day protocol, regardless of whether the tissues containing radioactivity would be excised at surgery or not.

Conclusion

Although the total effective dose from using SPECT/CT is equivalent to the annual natural background radiation of about 3 mSv, nuclear medicine physicians should be aware of the increase in effective dose for SLN lymphoscintigraphy using hybrid imaging technique of SPECT/CT when compared to conventional planar 57Co flood source for transmission scan. Results from the current study provide update information in radiation exposure to patients undergoing SLN lymphoscintigraphy with the use of SPECT/CT.

Introduction

The technique of sentinel lymph node (SLN) biopsy in the clinical management of breast cancer has become a standard practice [1], [2], [3], [4]. In our previous study [1], organ absorbed radiation doses were measured both for internal emission dose due to injected 99mTc and for transmission dose due to the use of a 57Co flood source. Using the concept of cumulated activity, effective dose (ED) were calculated for patients undergoing different lymphoscintigraphy protocols (1-day and 2-day protocol) and surgical procedures (whether the radiation containing tissues are excised or not).

It has been an increasing trend to use hybrid imaging system SPECT/CT, SPECT imaging system in combination with a low dose CT scanner, for direct correlation of anatomic information and functional information resulting in better localization and definition of SLN scintigraphic findings [4]. From dosimetry point of view, patient receives radiation dose from 99mTc as internal emission source and from CT as transmission irradiating source, the latter of which has not yet been studied for SLN lymphoscintigraphy.

Furthermore with the recent introduction of ICRP-103 recommendations [5] to replace those of ICRP-60 [6], tissue weighting factor of breast is different between ICRP-103 (being 0.12) and ICRP-60 (being 0.05) recommendations, indicating that the equivalent dose for breast would be 2.4 times higher for the same radiation exposure. It is the aim of the present study to evaluate the patient ED in SLN lymphoscintigraphy according to ICRP-103 recommendations together with the application of SPECT/CT system.

In the present study, direct measurements were made for patient ED due to CT transmission radiation using a reference female humanoid phantom and a set of thermoluminescent dosemeters (TLD). Organ absorbed radiation doses, due to internal emission radiation, were re-calculated using measurement data from our previous study with the tissue weighting factors of ICRP-103. Patient total ED, summation of ED due to CT transmission and internal emission radiation, would then be calculated for different lymphoscintigraphy protocols and for different surgical procedures.

Section snippets

CT transmission dose

A SPECT/CT system (Hawkeye 4, GE Healthcare, Milwaukee, WI, USA) and an Alderson-Rando standard adult female phantom (The Phantom Laboratory, New York, USA) were used in the CT transmission dose measurements. The dose delivered to the phantom was measured with lithium fluoride TLD chips (type TLD-100H, The Harshaw Chemical Company, Solon, OH, USA) with dimensions of 3.2 mm × 3.2 mm × 0.6 mm placed into the phantom. The batch of TLDs was calibrated using a 120 kVp X-ray beam from a superficial X-ray

CT transmission dose

Table 2 tabulates the values of organ absorbed doses measured with CT irradiation using the SPECT/CT system and the CT scanning protocol in our institution. The patient ED due to CT irradiation was measured as 2.397 mSv, which was at the low range of adult ED for various CT procedures (approximately 2–20 mSv) [9]. The mean value of organ absorbed dose averaged over the two breasts from CT irradiation was measured as 2.769 mGy. Its equivalent dose, after multiplying the tissue weighting factor for

Discussion

There is a need to evaluate the effective dose delivered to patients undergoing SLN lymphoscintigraphy with the application of SPECT/CT and ICRP-103 recommendations. Firstly, tissue weighting factor of breast is different between ICRP-103 (being 0.12) and ICRP-60 (being 0.05) recommendations, indicating that the equivalent dose for this radiation sensitive organ would be 2.4 times higher according to ICRP-103 than to ICRP-60 recommendation for the same radiation exposure. Secondly, the CT

Conflict of interest

All the authors of the manuscript entitled ‘Evaluation of patient effective dose from sentinel lymph node lymphoscintigraphy in breast cancer: a phantom study with SPECT/CT and ICRP-103 recommendation’ declare that there is no conflict of interest with regard to equipment, contrast, drug and other materials described in the study.

Acknowledgements

The authors greatly appreciate the assistance from Mr. Samuel Leung, medical physicist of Pamela Youde Nethersole Eastern Hospital of Hong Kong, for the TLD calibration using a superficial X-ray machine.

References (9)

  • M. Law et al.

    Patient effective dose from sentinel lymph node lymphoscintigraphy in breast cancer: a study using a female humanoid phantom and thermoluminescent dosimeters

    Br J Radiol

    (2003)
  • J.P. Coffey et al.

    Breast sentinel node imaging with low dose SPECT/CT

    Nucl Med Commun

    (2010)
  • A.K. Buck et al.

    SPECT/CT

    J Nucl Med

    (2008)
  • E. Hindie et al.

    The sentinel node procedures in breast cancer: nuclear medicine as the starting point

    J Nucl Med

    (2010)
There are more references available in the full text version of this article.

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