- Email: [email protected]
Radioguided occult lesion localization: better delineation of the injection site with a high-resolution collimator
ARTICLE IN PRESS
Nuclear Instruments and Methods in Physics Research A 527 (2004) 216–219
Radioguided occult lesion localization: better delineation of the injection site with a high-resolution collimator B. Geisslera, D. De Freitasa, F. Cachina, D. Mestasa, G. Lebouedecb, J. Maublanta,* a
Division of Nuclear Medicine, Jean Perrin Cancer Center, 63011 Clermont-Ferrand, France b Division of Surgical Oncology, Jean Perrin Cancer Center, Clermont-Ferrand, France
Abstract Aim: Radioguided Occult Lesion Localization (ROLL) is a method for guiding the excision of occult breast lesions. A radiotracer is injected preoperatively in the tumor. The surgeon can locate the lesion with a gamma probe. It has been recommended that the tissue is resected where the activity falls rapidly. But this cut-off level can fluctuate depending on the user. The aim of this study was to compare the accuracy of two different types of collimation. Materials and methods: To simulate the detection of a radioactive ‘‘lesion’’, 0.2 ml of a solution of 99mTc labeled colloids (4 MBq) were deposited at 3 cm depth in a chunk of cow muscle. Detection was performed with a gamma probe (GammaSup, Clerad, F) equipped either with a regular or with an additional high-resolution collimator. The response curve was drawn moving laterally the probe on the chunk of cow by 5 mm steps. Edges of resection were determined with different cut-off levels (from 5 to 50% of maximum counts by 5% steps). Results: Without additional collimator, the mean distance between injection point and resection edge was 18 mm, standard deviation 7.8 mm with a range between 11 and 18 mm. With additional collimator, the mean distance decreased to 10 mm ( 44%), standard deviation 4.2 mm ( 46%) with a range between 6 and 10 mm. Conclusion: The results demonstrate that the additional collimator provides more precise and reproductive delineation of the injection site. It should be optimal for the ROLL technique. r 2004 Elsevier B.V. All rights reserved. PACS: 87.50.Gi; 87.59.Qx; 87.62.+n Keywords: Surgery; Gamma probe; Radioisotope
0. Introduction Radioguided Occult Lesion Localization (ROLL) is a new method that has been developed by De Cicco et al. [1] to localize and guide the *Corresponding author. Tel.: +33-473-27-81-55; fax: +33473-27-80-78. E-mail address: [email protected] (J. Maublant).
excision of non-palpable breast lesions. A solution of 99mTc labeled nanocolloids is preoperatively injected into the suspected area to be excised under mammography or echography control. The radioactive area is then preoperatively localized using a hand-held gamma probe allowing us to have an acoustic signal and a count rate proportional to the detected activity. In front of the injection point, the signal is maximal and decreases rapidly
0168-9002/$ - see front matter r 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.nima.2004.03.123
ARTICLE IN PRESS B. Geissler et al. / Nuclear Instruments and Methods in Physics Research A 527 (2004) 216–219
when the surgeon moves the probe laterally. For the few teams who have experimented this technique [1–3], the outer limits of the tissue to be excised are roughly defined where a rapid fall of the activity is observed when the probe is moved away from the center of the lesion. A certain threshold level can be selected. For example, the 10% level have been chosen by Barros et al. [2]. Thus, the precision of the excision depends on the operator, the radioactive colloids injection protocol and the material of detection. A new additional high-resolution collimator has been developed by Clerad (Clermont–Ferrand, France) in order to improve the spatial resolution of the GammaSuP probe [4]. The aim of this study was to assess, with different thresholds, which benefit in terms of precision and reproducibility, this collimator could present comparatively to the regular collimation. Measurements were performed in experimental conditions using an animal soft tissue sample.
1. Materials and methods 1.1. Materials The gamma probe GammaSuP was constituted with a 7-mm CsI(Tl) crystal coupled with a photomultiplier tube (Fig. 1). The crystal transforms each interacting gamma ray into light. These light photons are transformed into electric pulses through the photomultiplier tube. The amplitude of the electric pulse is proportional to the energy of
Fig. 1. Functional diagram of the gamma probe.
217
the incident gamma ray. A system of discrimination allows to select the electric pulses resulting from the gamma rays where energy is included in a predefined energy window. The frequency of appearance of the pulses in the set energy window codes for the count rate and modulates the frequency of the generated sound. The count rate is displayed in counts per second. The gamma probe has been used either with a regular or with an additional high-resolution collimator. This collimator is made of several holes, a design that dramatically increases the spatial resolution of the probe when compared with a classical single-hole collimator. The multihole collimator is a 8-mm thick solid gold plate bored of 7 holes of 2-mm diameter. The single-hole collimator is a 1.5-mm thick solid gold plate with only one central 6-mm diameter hole. The sample used for the measurements was a chunk of cow muscle to simulate in vivo conditions with similar density and scattering effect than human soft tissues. The size of the sample was 15-cm length, 11-cm width and 4-cm thickness. 1.2. Measurements A 0.2 ml solution of 99mTc labeled colloids (Eg=140 keV) was deposited at 3 cm depth in the center of the sample. The amount of injected activity was 3 kBq. The energy window acquisition was set to 80–180 keV. The probe was moved laterally on the surface of the sample by 5 mm steps. Measurements were realized following a straight line from –3 cm to +10 cm relatively to the point of injection. For each position, the response of the probe was measured in counts per second (cps). Count rates were integrated for 10 s to reduce uncertainties mainly related to the measurement chain. With each collimator, at each position, the absolute sensitivity of the probe in cps per kilobecquerel (cps/kBq) was calculated. Thanks to these measurements, the lateral sensitivity curves in percent of maximum were drawn (Fig. 2). The distance between the point of injection and the theoretical edge was measured with these curves considering different threshold values from 5% to 50% of maximum counts by 5% steps. Thus, the values of edge obtained with
ARTICLE IN PRESS 218
B. Geissler et al. / Nuclear Instruments and Methods in Physics Research A 527 (2004) 216–219
Fig. 3. Response curves of the probe. Fig. 2. Scheme of the experimental.
each threshold allowed us to compare the two collimators in terms of standard deviation and range, assuming that the threshold level chosen by any surgeon should be included in the range 5–50%.
2. Results Fig. 3 shows the relative responses of the probe equipped with or without the additional collimator. The response of the probe was expressed in percent of the maximum response obtained at the vertical of the point of injection. Table 1 shows the values of distance between the point of injection and the theoretical edges measured with the probe response curves. The values are presented for each threshold level from 5% to 50% with an increment of 5%. Average values between the maximum and the minimum threshold level were calculated for each collimation as well as standard deviation and range. With the additional high-resolution collimator, the mean distance between the point of injection and the resection edge was decreased by 44%, the standard deviation of 46%, with a range between 6 and 10 mm instead of 11 and 18 mm. The loss of sensitivity of the multi-hole collimator was not a problem in these conditions because of the large amount of activity utilized in these experiments. It can be noticed that it will be the same in vivo since the activity contained in the detected area is directly injected and can therefore be monitored to be always at the proper level.
Table 1 Distance (in mm) between injected point and theoretical edge for different threshold levels (in %) %
Without additional collimator
With additional collimator
50 45 40 35 30 25 20 15 10 5
11 12 13 14 16 17 19 23 27 36
6 7 7 8 8 9 10 11 14 20
Mean Standard deviation Amplitude
18.8 7.8 25
10.0 4.2 14
3. Discussion and conclusion This experience on a biological sample does not preclude of the most appropriate threshold level to be used in ROLL, but it demonstrates that an additional high-resolution collimator mounted on a regular gamma probe can provide the operator with a more precise and reproductive delineation of the injected site. It should be useful not only by facilitating the surgeon procedure but also by minimizing the size of the excised tumor. In fact, this equipment has already been tested in a preliminary series of 30 patients at our institution.
ARTICLE IN PRESS B. Geissler et al. / Nuclear Instruments and Methods in Physics Research A 527 (2004) 216–219
Our surgeons rapidly switched to the probe equipped with the high-resolution collimator because they judged the determination of edges of resection to be more precise, and the overall surgical procedure to be more reproductible and easier than with the regular collimation. This example of experimental testing is a good demonstration that preoperative gamma-guided detection can benefit from preclinical laboratory experiments that allow the physicist to determine the optimal equipment and setting in accordance with the clinical conditions.
219
References [1] A. Barros, M.A. Cardoso, P.Y. Sheng, P.A. Costa, C. Pelizon, Eur. J. Nucl. Med. Mol. Imaging 29 (2002) 1561. [2] C. De Cicco, M. Pizzamiglio, G. Trifiro, A. Luini, M. Ferrari, G. Prisco, V. Galimberti, E. Cassano, G. Viale, M. Intra, P. Veronesi, G. Paganelli, Q. J. Nucl. Med. 46 (2002) 145. [3] L. Feggi, E. Basaglia, S. Corcione, P. Querzoli, G. Soliani, S. Ascanelli, N. Prandini, L. Bergossi, P. Carcoforo, Eur. J. Nucl. Med. 28 (2001) 1589. [4] D. De Freitas, P. Brette, P. Espinasse, J. Maublant, Eur. J. Nucl. Med. 29 (2002) S79.
Nuclear Instruments and Methods in Physics Research A 527 (2004) 216–219
Radioguided occult lesion localization: better delineation of the injection site with a high-resolution collimator B. Geisslera, D. De Freitasa, F. Cachina, D. Mestasa, G. Lebouedecb, J. Maublanta,* a
Division of Nuclear Medicine, Jean Perrin Cancer Center, 63011 Clermont-Ferrand, France b Division of Surgical Oncology, Jean Perrin Cancer Center, Clermont-Ferrand, France
Abstract Aim: Radioguided Occult Lesion Localization (ROLL) is a method for guiding the excision of occult breast lesions. A radiotracer is injected preoperatively in the tumor. The surgeon can locate the lesion with a gamma probe. It has been recommended that the tissue is resected where the activity falls rapidly. But this cut-off level can fluctuate depending on the user. The aim of this study was to compare the accuracy of two different types of collimation. Materials and methods: To simulate the detection of a radioactive ‘‘lesion’’, 0.2 ml of a solution of 99mTc labeled colloids (4 MBq) were deposited at 3 cm depth in a chunk of cow muscle. Detection was performed with a gamma probe (GammaSup, Clerad, F) equipped either with a regular or with an additional high-resolution collimator. The response curve was drawn moving laterally the probe on the chunk of cow by 5 mm steps. Edges of resection were determined with different cut-off levels (from 5 to 50% of maximum counts by 5% steps). Results: Without additional collimator, the mean distance between injection point and resection edge was 18 mm, standard deviation 7.8 mm with a range between 11 and 18 mm. With additional collimator, the mean distance decreased to 10 mm ( 44%), standard deviation 4.2 mm ( 46%) with a range between 6 and 10 mm. Conclusion: The results demonstrate that the additional collimator provides more precise and reproductive delineation of the injection site. It should be optimal for the ROLL technique. r 2004 Elsevier B.V. All rights reserved. PACS: 87.50.Gi; 87.59.Qx; 87.62.+n Keywords: Surgery; Gamma probe; Radioisotope
0. Introduction Radioguided Occult Lesion Localization (ROLL) is a new method that has been developed by De Cicco et al. [1] to localize and guide the *Corresponding author. Tel.: +33-473-27-81-55; fax: +33473-27-80-78. E-mail address: [email protected] (J. Maublant).
excision of non-palpable breast lesions. A solution of 99mTc labeled nanocolloids is preoperatively injected into the suspected area to be excised under mammography or echography control. The radioactive area is then preoperatively localized using a hand-held gamma probe allowing us to have an acoustic signal and a count rate proportional to the detected activity. In front of the injection point, the signal is maximal and decreases rapidly
0168-9002/$ - see front matter r 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.nima.2004.03.123
ARTICLE IN PRESS B. Geissler et al. / Nuclear Instruments and Methods in Physics Research A 527 (2004) 216–219
when the surgeon moves the probe laterally. For the few teams who have experimented this technique [1–3], the outer limits of the tissue to be excised are roughly defined where a rapid fall of the activity is observed when the probe is moved away from the center of the lesion. A certain threshold level can be selected. For example, the 10% level have been chosen by Barros et al. [2]. Thus, the precision of the excision depends on the operator, the radioactive colloids injection protocol and the material of detection. A new additional high-resolution collimator has been developed by Clerad (Clermont–Ferrand, France) in order to improve the spatial resolution of the GammaSuP probe [4]. The aim of this study was to assess, with different thresholds, which benefit in terms of precision and reproducibility, this collimator could present comparatively to the regular collimation. Measurements were performed in experimental conditions using an animal soft tissue sample.
1. Materials and methods 1.1. Materials The gamma probe GammaSuP was constituted with a 7-mm CsI(Tl) crystal coupled with a photomultiplier tube (Fig. 1). The crystal transforms each interacting gamma ray into light. These light photons are transformed into electric pulses through the photomultiplier tube. The amplitude of the electric pulse is proportional to the energy of
Fig. 1. Functional diagram of the gamma probe.
217
the incident gamma ray. A system of discrimination allows to select the electric pulses resulting from the gamma rays where energy is included in a predefined energy window. The frequency of appearance of the pulses in the set energy window codes for the count rate and modulates the frequency of the generated sound. The count rate is displayed in counts per second. The gamma probe has been used either with a regular or with an additional high-resolution collimator. This collimator is made of several holes, a design that dramatically increases the spatial resolution of the probe when compared with a classical single-hole collimator. The multihole collimator is a 8-mm thick solid gold plate bored of 7 holes of 2-mm diameter. The single-hole collimator is a 1.5-mm thick solid gold plate with only one central 6-mm diameter hole. The sample used for the measurements was a chunk of cow muscle to simulate in vivo conditions with similar density and scattering effect than human soft tissues. The size of the sample was 15-cm length, 11-cm width and 4-cm thickness. 1.2. Measurements A 0.2 ml solution of 99mTc labeled colloids (Eg=140 keV) was deposited at 3 cm depth in the center of the sample. The amount of injected activity was 3 kBq. The energy window acquisition was set to 80–180 keV. The probe was moved laterally on the surface of the sample by 5 mm steps. Measurements were realized following a straight line from –3 cm to +10 cm relatively to the point of injection. For each position, the response of the probe was measured in counts per second (cps). Count rates were integrated for 10 s to reduce uncertainties mainly related to the measurement chain. With each collimator, at each position, the absolute sensitivity of the probe in cps per kilobecquerel (cps/kBq) was calculated. Thanks to these measurements, the lateral sensitivity curves in percent of maximum were drawn (Fig. 2). The distance between the point of injection and the theoretical edge was measured with these curves considering different threshold values from 5% to 50% of maximum counts by 5% steps. Thus, the values of edge obtained with
ARTICLE IN PRESS 218
B. Geissler et al. / Nuclear Instruments and Methods in Physics Research A 527 (2004) 216–219
Fig. 3. Response curves of the probe. Fig. 2. Scheme of the experimental.
each threshold allowed us to compare the two collimators in terms of standard deviation and range, assuming that the threshold level chosen by any surgeon should be included in the range 5–50%.
2. Results Fig. 3 shows the relative responses of the probe equipped with or without the additional collimator. The response of the probe was expressed in percent of the maximum response obtained at the vertical of the point of injection. Table 1 shows the values of distance between the point of injection and the theoretical edges measured with the probe response curves. The values are presented for each threshold level from 5% to 50% with an increment of 5%. Average values between the maximum and the minimum threshold level were calculated for each collimation as well as standard deviation and range. With the additional high-resolution collimator, the mean distance between the point of injection and the resection edge was decreased by 44%, the standard deviation of 46%, with a range between 6 and 10 mm instead of 11 and 18 mm. The loss of sensitivity of the multi-hole collimator was not a problem in these conditions because of the large amount of activity utilized in these experiments. It can be noticed that it will be the same in vivo since the activity contained in the detected area is directly injected and can therefore be monitored to be always at the proper level.
Table 1 Distance (in mm) between injected point and theoretical edge for different threshold levels (in %) %
Without additional collimator
With additional collimator
50 45 40 35 30 25 20 15 10 5
11 12 13 14 16 17 19 23 27 36
6 7 7 8 8 9 10 11 14 20
Mean Standard deviation Amplitude
18.8 7.8 25
10.0 4.2 14
3. Discussion and conclusion This experience on a biological sample does not preclude of the most appropriate threshold level to be used in ROLL, but it demonstrates that an additional high-resolution collimator mounted on a regular gamma probe can provide the operator with a more precise and reproductive delineation of the injected site. It should be useful not only by facilitating the surgeon procedure but also by minimizing the size of the excised tumor. In fact, this equipment has already been tested in a preliminary series of 30 patients at our institution.
ARTICLE IN PRESS B. Geissler et al. / Nuclear Instruments and Methods in Physics Research A 527 (2004) 216–219
Our surgeons rapidly switched to the probe equipped with the high-resolution collimator because they judged the determination of edges of resection to be more precise, and the overall surgical procedure to be more reproductible and easier than with the regular collimation. This example of experimental testing is a good demonstration that preoperative gamma-guided detection can benefit from preclinical laboratory experiments that allow the physicist to determine the optimal equipment and setting in accordance with the clinical conditions.
219
References [1] A. Barros, M.A. Cardoso, P.Y. Sheng, P.A. Costa, C. Pelizon, Eur. J. Nucl. Med. Mol. Imaging 29 (2002) 1561. [2] C. De Cicco, M. Pizzamiglio, G. Trifiro, A. Luini, M. Ferrari, G. Prisco, V. Galimberti, E. Cassano, G. Viale, M. Intra, P. Veronesi, G. Paganelli, Q. J. Nucl. Med. 46 (2002) 145. [3] L. Feggi, E. Basaglia, S. Corcione, P. Querzoli, G. Soliani, S. Ascanelli, N. Prandini, L. Bergossi, P. Carcoforo, Eur. J. Nucl. Med. 28 (2001) 1589. [4] D. De Freitas, P. Brette, P. Espinasse, J. Maublant, Eur. J. Nucl. Med. 29 (2002) S79.