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Session: SBRT Planning and Outcomes [Return to Session]

Development of Automated Sphere Placement Script for Lattice SBRT Using the Eclipse Scripting Application Programming Interface (ESAPI)

W Tucker*, M Schmidt, T Mazur, J Hilliard, M Spraker, J Kavanaugh, Washington University School of Medicine in St. Louis, St. Louis, MO


WE-C1030-IePD-F3-4 (Wednesday, 7/13/2022) 10:30 AM - 11:00 AM [Eastern Time (GMT-4)]

Exhibit Hall | Forum 3

Purpose: Lattice stereotactic body radiation therapy (Lattice SBRT) is a form of spatially fractionated radiation therapy that produces characteristic high-dose peaks and low-dose valleys by manual placement of multiple high- and low-dose 1.5 cm diameter spheres in an alternating grid-like pattern. While the manual sphere placement follows set guidelines, it can be subjective and inefficient. This study investigated the utility of an automated Lattice SBRT sphere placement script, developed with Varian’s ESAPI, to improve efficiency while maintaining the quality of high dose spheres (HDS) within the GTV and the corresponding achieved dosimetric plan quality.

Methods: Sphere placement efficiency and quality of the script was compared to manual sphere placement completed by three clinical staff on 22 retrospective Lattice SBRT patients. Planning efficiency was quantified as the time for the script and clinical staff to place the HDS and low dose spheres. Sphere placement quality was assessed by comparing the number of HDS inside the tumor contour. Five Lattice SBRT plans were generated utilizing the automated sphere placement with OAR dose and PTV target coverage compared to the corresponding clinical plans. Significance was evaluated using a paired t-test.

Results: The script was significantly faster than manual sphere placement, with a mean time of 2.48±1.67 minutes, compared to 19.30±9.85 minutes (P=1.90E-08), 24.95±10.72 minutes (P=6.58E-10), and 29.85±12.91 minutes (P=5.11E-10) for the physicist, clinical dosimetrist, and research dosimetrist, respectively. The script placed a mean of 13.9 spheres (0 violations), compared to the physicist (15.6 spheres, 2.9 violations), clinical dosimetrist (13.6 spheres, 1.6 violations), and research dosimetrist (12.5 spheres, 1.7 violations). All plans generated using the script met or improved clinical dosimetric criteria compared to clinical plans.

Conclusion: This study shows the proposed script allows for efficient and consistent placement of HDS in the target volume and produces clinically viable Lattice SBRT plans.


Stereotactic Radiosurgery, Computer Software, Treatment Planning


TH- External Beam- Photons: Treatment planning using machine learning/Knowledge Based Planning/automation

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