A new operative gamma camera for Sentinel Lymph Node procedure

Transcription

1 A new operative gamma camera for Sentinel Lymph Node procedure A physicist device for physicians Samuel Salvador, Virgile Bekaert, Carole Mathelin and Jean-Louis Guyonnet 12/06/ samuel.salvador@ires.in2p3.fr 1

2 The Sentinel Lymph Node (SLN) procedure in case of breast cancer The day prior the surgery The day of the surgery 20 MBq in 4 periareolar injections of 99m Tc radiomarked colloidal solution 2 scintigraphic planar images in a Nuclear Medicine Department (anterior anterior and 45 oblique views) SLN detection efficency of ~80% What about per and postoperative scintigraphic images? 4 periareolar injections of a blue dye solution for colorimetric visualization method SLN (of few kbq) ) identification using a gamma probe [1] Two cases: SLN without metastasis (70 % of cases) Stop of the procedure SLN with metastases Complete axillary clearance [1] Mathelin C, Piqueras I, Guyonnet JL. Performances of a new prototype handheld scintillating probe for the search of sentinel lymph nodes in breast cancer. Eur J Surg Oncol 2006;32(1):24-8a. 2

3 The new prototype of operative gamma camera A mm² field of view (FOV) using a GSO:Ce crystal of 2 mm thick 4 MultiAnode PhotoMultiplier Tubes (64 channels each) Dedicated electronics Designed to enter in the operating room Why GSO crystal? 3

4 GSO:Ce GSO Gd 2 SiO 5 :Ce YAP YAlO 3 :Ce BrilLanCe 380 LaBr 3 :Ce BrilLanCe 350 LaCl 3 :Ce LSO Lu 2 SiO 5 :Ce PreLude 420 Lu 1.8 Y 0.2 SiO 5 :Ce ρ (g.cm -3 ) μ/ρ (cm².g -1 ) /μ (cm) Z eff n τ (ns) λ (nm) Light Yield (photons.mev -1 ) Hygroscopic no no yes yes no no ρ: density n: refractive index μ: linear attenuation coefficient at 140 kev τ: decay time constant μ/ρ: mass attenuation coefficient at 140 kev λ: Scintillation wavelength at maximum emission Z eff : effective Z number High Z eff, high attenuation coefficient for a smaller design (2 mm thick attenuate 70 % of 140 kev γ-ray) A fast decay time Non hygroscopic and non radioactive 4

5 The design Dedicated and fully developed electronics at IPHC in collaboration with the LAL/Orsay Large surface mm 3 Zr-GSO Ce 1.0%/mol (GSOZ:Ce) from Hitachi Chemical Corporation glued on 4 MAPMTs Hamamatsu H8500 Lead collimator Thickness = 10 mm Φ hole = 2 mm septa = 0.2 mm 5

6 Energy calibration Using a collimated point-like source of 57 Co positioned in front of each MAPMT channel Maximisation of the fitted photopeak position in ADC channel to 122 kev Energy window ( kev) ) for Compton and X-rays X resections Fit including 122 kev KeV 57 Co γ-rays Compton and materials fluorescence 47% energy 122 kev 6

7 Projection construction Anodes GSO crystal γ ray Optical photons spreading Events clusterisation with a mean number of fired pixels of 12 ± 5 <n> = 12 σ = 5 In blue with energy cut and a cut in minimum number of pixels per cluster of 3 Barycentric calculated cluster centers to deduce the interaction positions in the crystal 7

8 Projection construction 2D histogram (1 1 1 mm² binning) in real time with profiles Intrinsic spatial resolution of 3 mm and spatial resolution with the collimator of 6.1 mm (at d = 0) 2.19 ± 0.05 cps kbq -1 detection efficiency Profiles along X and Y axis with a gaussian fit applied in order to obtain the FWHMs Example of an image of two 57 Co phantoms (4.3 kbq and 9.8 kbq) located in front of the collimator acquired in 2 minutes with one quarter of the full design 8

9 Linearity 2500 source positions with a 2 mm pitch in the two axial directions to cover the whole crystal surface Projections of the 2500 source positions before and after linearity correction. The deviation to the linearity is equal to 5% in the whole FOV 9

10 Clinical study Design of a mechanical arm for the gamma camera to be used in the operative room Articulated arm Gamma camera Support for an acquisition PC 10

11 Internal Research Protocol on 25 patients at Hôpitaux Universitaires de Strasbourg Comparison with standard lymphoscintigraphy using a prototype of a mm² FOV: Injection site of 20 MBq One SLN radiomarked Two close SLN radiomarked Lymphoscintigraphic image made in 15 min. with a cm² FOV by the Nuclear Medicine Department Preoperative gamma camera projection made in 2 min. 11

12 The third dimension Correlation between the signal FWHM and the distance of the source to the collimator Example of X profiles with gaussian fits of a 57 Co source placed in front of the entrance face of the collimator at different distances The FWHM is linearly correlated to the source distance [2] [2] Mathelin C, Salvador S, Huss D, Guyonnet JL. Precise localization of sentinel lymph nodes and estimation of their depth using a prototype intraoperative mini gamma-camera in patients with breast cancer. J Nucl Med 2007;48(4):

13 SLN Depth After SLN visualization on the 2D image, evaluation of their depth using signal FWHM FWHM 2D image X and Y profiles with gaussian fit and flat background The SLN was visualized in the 2D image and using the profiles, its i depth was calculated at 56±11 mm and the surgery measured it at 55±5mm 13

14 SLN Depth Correlation between the measured depth dm and the expected depth dp of 12 SLN 14

15 The postoperative image After SLN resection, 2 minutes data acquisitions to evaluate the remaining SLN in the axillary area One SLN One SLN still in place No SLN remaining Preoperative projection in 2 min. data acquisition of a 9.6kBq SLN Peroperative projection in 2 min. data acquisition of a 0.5 kbq SLN Postoperative projection 15

16 The gamma camera A high detection efficiency of 2.2 cps kbq -1 with a good spatial resolution for our purpose (10 mm at 50 mm distance to the collimator) 2 minutes data acquisition time Online data processing by a dedicated software Postoperative images used as quality control documents 16

17 Outlooks New clinical trial on 100 patients (fall 2007) Comparison between: One mm 3 GSOZ:Ce crystal coupled to four Hamamatsu H8500 MAPMTs Four mm 3 GSOZ:Ce crystals coupled to four MAPMTs R & D: One mm 3 GSOZ:Ce crystal coupled to one Multi Channel Plate developed by Photonis with new dedicated electronics developed at IPHC 17

18 Acknowledgments This work is partly supported by: The Ligue Nationale contre le Cancer Institut National du Cancer 18