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Session: Novel Technology and Applications [Return to Session]

Viability of the Virtual Cone Technique Using a Fixed Small Multi-Leaf Collimator Field for Small Target Radiosurgery

T Neupane1, C Shang, MB2*, T Leventouri1, W Muhammad1, (1) Florida Atlantic University, Boca Raton, FL, (2) S. Florida Proton Therapy Institute, Delray Beach, FL


MO-G-202-4 (Monday, 7/11/2022) 2:45 PM - 3:45 PM [Eastern Time (GMT-4)]

Room 202

Purpose: Quantifying dosimetric uncertainties is challenging when using virtual cone technique with small,variable MLC fields. We evaluate the efficacy of the fixed field virtual cone approach for small target radiosurgery.

Methods: We employed a fixed virtual cone (fVC) method for small target radiosurgery such as trigeminal neuralgia. It was characterized by 0.5cm x 0.5cm HDMLC field defined at 100cm SAD, while jaws were positioned at 1.5cm x 1.5cm. A spherical dose distribution was generated by using the 10MV FFF beam in concert with 10–14 non-coplanar arcs during treatment planning. The dosimetric accuracy of this technique was validated using the SRS MapCHECK and EBT3 film measurements. Retrospectively, 10 treatment plans for trigeminal neuralgia consisting of various arc fields, collimator angles were analyzed using 6MV and 10MV FFF beams, including a field-by-field study (n=130 fields). Additionally, dosimetric uncertainties in the field defining fVC, caused by a minute (±0.5–1.0mm) leaf shift, were examined from the TPS, SRS diode measurements, and Monte Carlo (MC) simulations.

Results: The fVC technique for small target radiosurgery was validated (≤3% difference) using the SRS MapCHECK and EBT3 film measurements. The equivalent diameter of the 50% isodose distribution is comparable to 5mm physical cone. Pretreatment QA study showed average dose differences between SRS MapCHECK measurements and TPS as 4.0% and 2.5% for the 6MV and 10MV FFF beams respectively. In addition, dosimetric uncertainties in the field defining fVC, including diminutive leaf shifts was found ≤2% and ≤4% for diode measurements and TPS respectively. Furthermore, early results of MC study for these fields have shown similar (trend) dosimetric variation as measured.

Conclusion: The robustness of the fVC technique for small target radiosurgery is evaluated from measurements and calculations. This method can be a credible alternative to the physical cone that can be applied in routine radio-surgical treatment of trigeminal neuralgia.


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