Lymph node biopsy for prostate cancer best planned with hybrid imaging

Sentinel lymph node (SLN) biopsies determining primary prostate cancer metastases require diversified imaging techniques due to the location of these lymph nodes buried within the pelvis and elsewhere. As many as 44 percent of SLNs are located outside the pelvic region. Hybrid near-infrared fluorescence and SPECT/CT or PET/MR may provide some advantages before and during surgery, according to a review in the March issue of The Journal of Nuclear Medicine.

The use of laparoscopic SLN biopsy to detect prostate cancer metastases in nearby lymph nodes has been validated by large-population studies with high sensitivity and a low rate of false negatives. In this review by a team of authors from Leiden University Medical Center in Leiden and The Netherlands Cancer Institute in Amsterdam, a range of hybrid molecular imaging techniques were presented for pre-procedure planning and image-guided biopsies of sentinel nodes in prostate cancer patients.

Radioguided biopsy is often combined with optical imaging techniques; however, conventional blue dyes may not be as effective for deep-lying SLNs. Near infrared (NIR) fluorescence guidance was found to provide optical imaging of lesions in real time, as long as they are less than 10mm deep. However, NIR fluorescence was combined with radiotracers and more conventional molecular imaging techniques using SPECT to provide thorough surgical mapping.

“We found that premixing of the clinically approved NIR dye indocyanine green and an albumin-based radiocolloid (99m Tc-nanocolloid) yields the noncovalent indocyanine green–99m Tc-nanocolloid complex,” the authors wrote. “This complex has migratory properties similar to the parental 99m Tc-nanocolloid. Other hybrid nanoparticles also have the potential to guide SLN biopsy.”

Combinations using SPECT and 18F-FDG were validated and Cerenkov luminescence PET imaging was presented as a possible optical technique.

Research has turned to tumor-specific hybrid imaging agents. For instance, 111-In and NIR dye CW800 was combined to pinpoint the over-expression of prostate-specific membrane antigens in preclinical studies.  

Pre-procedure tracer deposition was improved with the addition of MR imaging data to conventional ultrasound needle guidance.

SPECT/CT was found to be superior to conventional lymphoscintagraphy and can map effectively the distribution of radiotracers with the structural context provided by the CT component. PET/CT and PET/MR were presented as promising modalities for surgical mapping of lymph node biopsy.

“For example, LN mapping can be performed using radiocolloids suitable for PET imaging, via the direct identification of LN metastasis using targeted PET tracers or using ultrasmall superparamagnetic iron oxide particles or targeted dendrimers suitable for MR imaging,” noted the authors.

In the operating room, surgeons were advised to use dual-isotope imaging with 125-In to guide the laparoscopic gamma probe to SLNs. Robotic surgery was improved when using robotics technology featuring software that can upload and integrate 3D SPECT image data to create 3D motion controllers.

These techniques are still under investigation and require further study to translate from the research bench to general clinical use, but they represent steps forward for surgical teams aiming to improve staging of disease for prostate cancer patients, the researchers concluded.