Stereotactic Radiosurgery to the Nucleus Accumbens: A Dosimetric Feasibility Study

Addiction remains a critical issue in the United States, and options for individuals suffering from treatment-refractory addiction are limited. The nucleus accumbens (NAc) is a region of interest for both invasive and non-invasive interventions aimed at treating addiction. Stereotactic radiosurgery (SRS) is an established modality for managing benign conditions. This study seeks to establish the technical feasibility of targeting the NAc with linear accelerator-based SRS.

A single de-identified image set from a patient previously treated with linac-based SRS for a benign condition was used. Computed tomography images of the patient's head, simulated in a stereotactic mask with corresponding high-resolution T1-weighted MRI brain and associated diffusion tensor imaging (DTI) data, were utilized for planning and localization. Three targets, named Ant, Mid, and Post, were placed on each side of the brain. Three separate plans were generated, targeting the bilateral NAc with one, two, and three shots to each side, with a maximal point dose of 140Gy, 120Gy, and 120Gy, respectively. The maximum dose to critical organs and volume of normal brain dose value V10Gy, V20Gy, and V60Gy were recorded.

For a two-shot plan, the maximum point dose to bilateral anterior targets was set to be 140Gy. The maximum dose to the optic chiasm, optical nerves, and brainstem was 5.4Gy, 3.6Gy, and 3.5Gy, respectively, with brain V20Gy of 1.0cc and V10Gy of 3.8cc. For a four-shot plan, bilateral Ant and Mid targets were targets with a maximum dose set to 120Gy. The resulting maximum dose to optic chiasm, optical nerves, and brainstem was 9.0Gy, 5.2Gy, and 5.4Gy, respectively, with brain V20Gy of 1.9cc and V10Gy of 8.4cc. Similar plans were created for a six-shot plan, with a maximum point dose of 120Gy. However, the maximum dose to the optical chiasm, optical nerve, and brainstem were 17.1Gy, 5.2Gy, and 5.4Gy, andthe brain V20Gy and V10Gy were 4.4cc and 22.3cc, respectively.

We demonstrated the technical feasibility of targeting the NAc with SRS for the management of treatment-refractory addiction using a single sample patient. Two- and four-shot models appear to be most feasible to achieve the highest point-dose while respecting critical structure constraints. The attempt to add a six-shot drove the optical chiasm dose over our institutional constraint of 10 Gy in a single fraction due to the proximity to the chiasm. Demonstrating the efficacy and safety of radiosurgery to the NAc for addiction will require further carefully defined pre-clinical and clinical studies.