Samuel Salvador

Precise localization of sentinel lymph nodes and estimation of their depth using a prototype intraoperative mini gamma-camera in patients with breast cancer.

The aim of this study was to evaluate the ability of a prototype intraoperative mini γ-camera, the CarolIReS, with a 50 × 50 mm field of view, to precisely localize sentinel lymph nodes (SLNs) and to determine their depth in a series of patients with infiltrative breast cancer requiring SLN excision. Methods: With the use of phantoms, the broadness of the signal of an acquired projection was shown to linearly depend on its distance from the collimator. A preclinical ex vivo study of 25 excised SLNs demonstrated that SLN size did not influence depth estimation. The minimum activity threshold for successful use of the proposed method was determined. After a preoperative radioisotope injection and lymphoscintigraphy, the SLN was localized in a series of 11 patients using both the mini γ-camera and a γ-probe. During surgery, a ruler was used to measure the depth of all SLNs before their excision. Results: Using the measured linear dependence of image broadness, we found that the expected SLN anatomic depth was compatible with its measured depth during surgery. Conclusion: This study showed that the mini γ-camera efficiently estimated the location of SLNs in 3 dimensions.

Design of a High Performances Small Animal PET System With Axial Oriented Crystals and DOI Capability

In most positron emission tomography (PET) systems dedicated to small animal imaging, the geometry of the detector module is based on a block structure where the crystal elements are coupled to a reduced number of photomultiplier tubes (PMT). In this configuration, the spatial resolution and the detection efficiency depend on the crystal dimensions and thus there is a correlation between these two figures of merit. In this paper, we present a method already used by Ter-Pogossian et al in the 1970s allowing the spatial resolution and the detection efficiency to be independent of each other. The crystals are oriented in the axial direction readout on both sides by individual photodetector channels. The spatial resolution in the transverse plane is driven by the crystal section and the spatial resolution in the axial direction is proportional to the contrast of the light collected on both sides of the crystal. The detection efficiency depends on the number of radial crystal layers and the geometry of the system. With the perfect knowledge of the interaction depth, the inner diameter of the PET system can be reduced to a minimum value leading to an increase in detection efficiency. We investigate two particular geometries dedicated to mouse and whole purpose studies and based on the same detection module. Each module consists on a matrix of 32 times24 LYSO:Ce crystals of 1.5 mm times 1.5 mm times 25 mm each read at both ends by a Photonis Corp multichannel plate photodetector. The surface treatment is optimized to reach a volumetric spatial resolution of 1 mm3. The detection efficiency of each system is evaluated using Monte Carlo simulation. The mouse and whole purpose systems are based on 4 and 6 modules with an inner diameter of 61.2 mm and 103.2 mm where the axial extent is 25 mm leading to a detection efficiency of 18% and 13%, respectively. This geometrical configuration leads to a detection efficiency close to the system solid angle with a volumetric spatial resolution of 1 mm3 .

Optimization of sentinel lymph node biopsy in breast cancer using an operative gamma camera

BackgroundSentinel lymph node (SLN) procedure is now a widely accepted method of LN staging in selected invasive breast cancers (unifocal, size ≤ 2 cm, clinically N0, without previous treatment). Complete axillary clearance is no longer needed if the SLN is negative. However, the oncological safety of this procedure remains to be addressed in randomized clinical trials. One main pitfall is the failure to visualize SLN, resulting in incorrect tumor staging, leading to suboptimal treatment or axillary recurrence. Operative gamma cameras have therefore been developed to optimize the SLN visualization and the quality control of surgery.Case presentationA 44-year-old female patient with a 14-mm infiltrative ductal carcinoma underwent the SLN procedure. An operative gamma camera was used during and after the surgery. The conventional lymphoscintigraphy showed only one SLN, which was also detected by the operative gamma camera, then removed and measured (9.6 kBq). It was analyzed by frozen sections, showing no cancer cells. During this analysis, the exploration of the axillary area with the operative gamma camera enabled the identification of a second SLN with low activity (0.5 kBq) that conventional lymphoscintigraphy, surgical probe and blue staining had failed to visualize. Histological examination revealed a macrometastasis. Axillary clearance was then performed, followed by a postoperative image proving that no SLN remained. Therefore, the use of the operative gamma camera prevented an under-estimation of staging which would have resulted in a suboptimal treatment for this patient.ConclusionThis case report illustrates that an efficient operative gamma camera may be able to decrease the risk of false negative rate of the SLN procedure, and could be an additional tool to control the quality of the surgery.Trial RegistrationClinicalTrials.gov Identifier: NCT00357487

An operative gamma camera for sentinel lymph node procedure in case of breast cancer

Large field of view gamma cameras are widely used to perform lymphoscintigraphy in the sentinel lymph nodes (SLN) procedure in case of breast cancer. However, they are not specified for this application and their sizes do not enable their use in the operative room to control the excision of the all SLN. We present the results obtained with a prototype of a new mini gamma camera developed especially for the operative lymphoscintigraphy of the axillary area in case of breast cancer. This prototype is composed of 10 mm thick parallel lead collimator, a 2 mm thick GSO:Ce inorganic scintillating crystal from Hitachi and a Hamamatsu H8500 flat panel multianode (64 channels) photomultiplier tube (MAPMT) equipped with a dedicated electronics. Its actual field of view is 50 × 50mm2. The gamma interaction position in the GSO scintillating plate is obtained by calculating the center of gravity of the fired MAPMT channels. The measurements performed with this prototype demonstrate the usefulness of this mini gamma camera for the pre, per and post-operative identification of SLNs and how its complementary role with an intraoperative handheld gamma probe enables to improve the efficiency of this practice. A 100 × 100mm2 field of view camera designated to cover the entire axillary area is under investigation

Evaluation of a 1024 Anodes Micro-Channel Plate PMT for Preclinical PET Imaging

A new generation of flat panel photomultiplier tube (PMT) based on micro-channel plates (MCP) offers characteristics suitable for PET imaging. We are developing a preclinical PET system composed of four detection modules arranged around the animal. Each module consists in 768 LYSO:Ce crystals read at both ends by MCP PMT. The particular geometry combined with an inner diameter of 61.2 mm lead to a high detection efficiency with a volumetric spatial resolution of 1 μl. The purpose of this work is to characterize the 1024 anodes of the MCP-PMT (Planacon XP85023/A1, Photonis Corp.) used in our preclinical PET system. The Planacon has very compact size (58 × 58 × 13.7 mm3) with an active area of 53 × 53 mm2. The anode array consists in a 32 × 32 matrix in which each individual anode is 1.4 × 1.4 mm2 with a pitch of 1.6 mm. Due to the lack of backside connectors and in order to individually readout the anode current, a dedicated connection board has been developed. The dark current, the gain and the timing resolution of one anode are measured as well as the cross talk, the gain uniformity and the intrinsic spatial resolution on the entire active field of view. With a timing resolution below 100 ps, an intrinsic spatial resolution of 400 μm, a low dark current and a high gain, the Planacon XP85023/A1 offers a promising photodetector for PET imaging.

Optimization of crystal length and coating to improve the Depth Of Interaction spatial resolution in PET imaging

Recent researches in PET instrumentation tend to improve the reconstructed spatial resolution using the gamma ray Depth Of Interaction (DOI) information. This method, already introduced by Moses et al., requires reading both ends of a scintillating crystal to be efficient. The recorded charges obtained by the two photodetector such as Photomultiplier Tubes (PMT) or Avalanche PhotoDiodes (APD) are dependent on the depth gamma ray interaction. Braem et al. recently used the contrast calculated as the ratio between the difference of the recorded charges and their sum to improve the DOI spatial resolution. In this work, we investigate the optimization of the crystal length and coating to improve the depth of interaction spatial resolution in PET applications. For a 1.5 × 1.5 mm2 LYSO:Ce crystal section read at both ends by PMT, we find that a length of 25 mm and a coating made with PMMA and 30% of TiO2 are appropriate to reach a DOI spatial resolution of 1 mm.

Study of 4 inorganic scintillating crystals for an operative gamma probe in radioguided surgery

In case of lymphatic cancers, the sentinel lymph node technique is performed using a gamma probe for intraoperative radioguided surgery. The inorganic scintillating crystal gamma probe developed at IPHC was equipped with 4 fast decay time inorganic scintillators: YAP, LYSO, LaCl3 and LaBr3. Energy resolutions are compared experimentally with single photon radioisotopes for small crystal cylinders (4 mm diameter, 12 mm length). The 6.1% measured energy resolution at 511 keV demonstrates the great advantage to use the high photon yield LaBr3 crystal for detection of γ-ray coming from positron annihilation using β+ radiomarked molecules.