It is estimated that 50% or more patients of high risk prostate cancer will relapse after definitive treatment (1
). There are substantial data suggesting many of these relapses may be due to microscopic metastasis in pelvic lymph nodes (2
). Recent surgical data indicated that the incidence of positive nodes is higher than once thought (2
Nomogram predictors (5
) help identify potential high risk of involved pelvic nodes. In order to confirm the microscopically involved nodes, lymphadenectomy combined with a pathologic analysis is necessary. Radical prostatectomy combined with an extended pelvic lymph node dissection (6
) is one of the standard treatments for localized prostate cancer. However, in some cases, this represents an overly aggressive and invasive approach.
External beam radiotherapy or brachytherapy is presented with the same challenges. However, there is no method to assess nodal involvements unless anatomical imaging shows enlarged (over 1 cm diameter) lymph nodes. There are recent studies that suggest therapeutic value to treating potentially involved nodes by radiation (1
). For example, the phase III trial by the Radiation Therapy Oncology Group (RTOG-9413) demonstrated that prophylactic pelvic lymph node irradiation improves progression-free survival for high-risk patients, suggesting that treatment of the primary tumor and local lymph nodes can be curative (7
Pelvic irradiation can increase the probability of treatment side effects. The exact volume of nodes to include in the radiation field is, therefore, critical, and has been much debated (8
). Currently, most whole-pelvic radiotherapy planning is based on assumptions about standardized anatomic lymphatic drainage patterns (9
). However, as shown in radioguided surgical lymph node dissection results, the patterns of each patient’s lymphatic drainage of the prostate are highly variable (9
Whole-pelvic irradiation of patient-specific lymphatic drainage with a highly conformal radiotherapy technique such as intensity-modulated radiotherapy (IMRT) could improve long-term tumor control outcomes (11
Tc-nanocolloids (colloidal particles smaller than 100 nm) can be used to achieve the goal of personalized whole-pelvic radiation planning (9
The most popular 99m
Tc-nanocolloid is a commercial product called 99m
Tc-Nanocoll (GE Healthcare, Chalfont St. Giles, UK) that is colloid of human serum albumin (13
). Extensive studies using this nanocolloid were performed to map sentinel lymph nodes of prostate (14
). However, this product has not received the US Food and Drug Administration (FDA) clearance yet. In the United States, 99m
Tc-sulfur colloid is used in breast lymphoscintigraphy as well as for other applications (17
). The 99m
Tc-sulfur colloid can be formed into nanocolloid by filtering using a 100-nm polycarbonate membrane filter, resulting in the particle size range similar to that of Nanocoll (13
). The important factor that contributes to the kinetic properties of a radiocolloid is the distribution of particle size, which is yet to be studied for filtered 99m
Tc-sulfur nanocolloid for prostate lymphoscintigraphy.
We report our experiences from a feasibility study of developing a practice procedure of prostate lymphoscintigraphy using filtered 99mTc-sulfur nanocolloid and single photon emission computed tomography combined with CT (SPECT/CT).