Brachytherapy is a technique commonly used in the treatment of prostate cancer that relies on the precise
placement of small radioactive seeds near the tumor location. The advantage of this technique over traditional
radiation therapies is that treatment can be continuous and uniform, resulting in fewer clinic visits and a shorter
treatment duration. Two important phases of this treatment are needle guidance for implantation, and post-placement
verification for dosimetry. Ultrasound is a common imaging modality used for these purposes, but it
can be difficult to distinguish the seeds from surrounding tissues, often requiring other imaging techniques such as
MRI or CT. Photoacoustic imaging may offer a viable alternative. Using a photoacoustic system based on an L7-
4 array transducer and a realtime ultrasound array system capable of parallel channel data acquisition streamed
to a multi-core computer via PCI-express, we have demonstrated imaging of these seeds at an ultrasound depth
of 16 mm and laser penetration depths ranging up to 50 mm in chicken tissue with multiple optical wavelengths.
Ultrasound and photoacoustic images are coregistered via an interlaced pulse sequence. Two laser pulses are used
to form a photoacoustic image, and at these depths, the brachytherapy seeds are detected with a signal-to-noise
ratio of over 26dB. To obtain this result, 1064nm light was used with a fluence of 100mJ/cm2, the ANSI limit
for human skin exposure at this wavelength. This study demonstrates the potential for photoacoustic imaging
as a candidate technology for brachytherapy seed placement guidance and verification.