The purpose of this study is to develop a practice procedure for lymphatic drainage mapping with the intent of providing a new tool that could potentially be used for radiation treatment planning. High-risk prostate cancer patients who are scheduled to be treated with intensity-modulated radiotherapy (IMRT) may be eligible to enroll in this study. 99mTc-sulfur nanocolloid, a radiopharmaceutical ("tracer") will be injected by a urologist using transrectal ultrasound guidance (TRUS)at the UCSF Urology Clinic. Participants will then undergo SPECT/CT imaging at the UCSF Nuclear Medicine Clinic. This study will evaluate the feasibility of transporting patients to the Nuclear Medicine Clinic for imaging within 1-3 hours after administration of 99mTc-sulfur nanocolloid.

The entire study procedure involves 1) preparation of 99mTc-sulfur nanocolloid, 2) administration of 99mTc-sulfur nanocolloid with transrectal ultrasound guidance, 3) transfer of the patient to the Nuclear Medicine clinic for SPECT/CT (Infinia Hawkeye, GE Healthcare) imaging, and 4) tomographically capturing distributions of 99mTc-sulfur nanocolloid uptake in the patient's lymphatic drainage sites within a practical image acquisition time (1-3 h postinjection) considering the patient transit time between injection and imaging.

Administration of 99mTc-sulfur nanocolloid will be performed at the UCSF Urology clinic. The injection will be performed following the clinically accepted method that has been described by European investigators. 99mTc-sulfur nanocolloid imaging utilizes trace amounts of radioactivity. 100-200 MBq (2.7-5.4 mCi) of 99mTc-sulfur nanocolloid will be administered into two lobes of the prostate gland under transrectal ultrasound guidance with three fractions each into peripheral and central zone of the prostatic apex, mid portion, and base. 1% Lidocaine may be administered for local anesthesia per routine clinical protocol as deemed appropriate by the performing urologist.

The procedure will be considered feasible if the practice procedure (from injection to completion of imaging) is successfully implemented within 3 hours of injection (including patient transport time). Imaging will be considered successful if radiotracer is qualitatively detected within the prostate and local lymphatic system.

Inclusion Criteria:

• Male

• Age ≥ 18 years

• Diagnosis of definitive high-risk prostate cancer

• Clinically eligible and scheduled for definitive IMRT treatment with pelvic lymph nodal radiation (not a study procedure)

• At least one of the following risk factors:

  1. Pathologically confirmed pelvic nodal involvement;
  2. Enlarged pelvic lymph nodes (greater than 1 cm in the short axis) visible on CT or MRI images, or
  3. Greater than 15% risk of lymph node involvement calculated using the equation: Risk of positive nodes (%) = (2/3) prostate specific antigen (PSA) + [(Gleason score - 6)] × 10]. This formula is used to estimate the pathologic stage of prostate cancer with preoperative prostate specific antigen (PSA) and Gleason score, and adopted by many radiation oncology clinics, including our own radiation oncology physicians.

• Ability to give written informed consent and willingness to comply with the requirements of the protocol

Exclusion Criteria:

• Any condition that compromises compliance with the objectives and procedures of this protocol, as judged by the principal investigator

One week. One-week adverse event assessment was about the SPECT/CT imaging procedure as well as the radiotracer injection.

The adverse event assessment was performed by verbal communication with the participants.