Toward adaptive stereotactic robotic brachytherapy for prostate cancer: Demonstration of an adaptive workflow incorporating inverse planning and an MR stealth robot

Abstract

To translate any robot into a clinical environment, it is critical that the robot can seamlessly integrate with all the technology of a modern clinic. MRBot, an MR-stealth brachytherapy delivery device, was used in a closed-bore 3T MRI and a clinical brachytherapy cone beam CT suite. Targets included ceramic dummy seeds, MR-Spectroscopy-sensitive metabolite, and a prostate phantom. Acquired DICOM images were exported to planning software to register the robot coordinates in the imager's frame, contour and verify target locations, create dose plans, and export needle and seed positions to the robot. The coordination of each system element (imaging device, brachytherapy planning system, robot control, robot) was validated with a seed delivery accuracy of within 2 mm in both a phantom and soft tissue. An adaptive workflow was demonstrated by acquiring images after needle insertion and prior to seed deposition. This allows for adjustment if the needle is in the wrong position. Inverse planning (IPSA) was used to generate a seed placement plan and coordinates for ten needles and 29 seeds were transferred to the robot. After every two needles placed, an image was acquired. The placed seeds were identified and validated prior to placing the seeds in the next two needles. The ability to robotically deliver seeds to locations determined by IPSA and the ability of the system to incorporate novel needle patterns were demonstrated. Shown here is the ability to overcome this critical step. An adaptive brachytherapy workflow is demonstrated which integrates a clinical anatomy-based seed location optimization engine and a robotic brachytherapy device. Demonstration of this workflow is a key element of a successful translation to the clinic of the MRI stealth robotic delivery system, MRBot.

Key words::

• Robotic brachytherapy
• prostate cancer
• adaptive workflow
• seed location

Acknowledgements

This work was supported in part by the UCSF Department of Radiation Oncology and in part by Nucletron.

Declaration of interest: The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the paper.

Notes

¹This term is derived from the Greek word “brachios” meaning short: brachytherapy consists of placing radioactive sources – about the size of a grain of rice – close to or inside a tumor or diseased organ. This contrasts with external beam radiation therapy in which radiation often must pass through healthy organs and tissue to reach the tumor.

²To be clear, the term needle is used in two different manners. (1) The optimization engine generates a dosimetry plan that consists of seed positions. These seed positions are relegated to sets which fall along a straight line. These sets are colloquially called needles because each set was inserted using one needle. (2) The robot itself has one needle that is used for the insertion of all the seeds. Where confusion may arise, optimized needle is used to refer to case 1 and robot needle to refer to case 2.

³The knee coil was used for phantom studies to provide good signal-to-noise imaging data for the relatively small phantom employed in these studies. For patient studies, excellent signal-to-noise can be achieved over the prostate and pelvis using the body coil for excitation and a combination of endorectal and pelvic phased array coils for signal reception. This coil combination produces sufficient signal-to-noise for the acquisition of spectroscopic and other functional imaging data from the prostate, and can be used with MRBot.

⁴The TPS environment used is designed for high dose rate (HDR) brachytherapy. Because the boundaries of the abilities of the treatment planning systems are being pushed, the older PPI treatment system made by Nucletron does not support the alternative needle patterns that are employed using this robotic device. However, the functionality of the TPS software necessary for the PPI planning done in these experiments is a subset of those necessary for HDR planning. The image processing, contouring, and optimization functionalities all exist on either system.