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Effect of Small Field Dosimetry On Stereotactic Radiosurgery Treatment Plans

O Senkesen1*, (1) Acibadem Mehmet Ali Aydinlar University, Istanbul, 34, TR


PO-BPC-Virtual-10 (Saturday, 4/17/2021)   [Eastern Time (GMT-4)]

Purpose: To compare the treatment plans made by using two different planning systems in which 2x2 cm² and 0.5x0.5 cm² data were entered as the smallest field sizes.

Methods: Ten brain metastasis patients with an average PTV volume of 0.17 cm³ were included in the study. The plans of all patients were created by using dynamic conformal arc, 6FFF photon energy, which was shaped by MLC by keeping the 2x2 jaw size constant in the Eclipse treatment planning system (TPS). Dynamic conformal arc treatment plans were created using the same table, collimator and gantry angles and energy in the Iplan TPS. Planning goal was to cover 98 % of the PTV with 98% of the prescribed dose. Acuros (version 13.6) algorithm was used in the Eclipse TPS. Pencil beam (PB) and Monte Carlo (MC) algorithms were used in the Brainlab-iPlan TPS(version 4.4.5). In treatment plans, tissue volume receiving the prescribed dose (V100), PTV receiving the prescribed dose (PTV V100), Conformity Index (CI), Gradient Index (GI), volume of the tissue receiving the prescribed dose (V50), PTVmax, PTVmin, PTVmean dose values, treatment time (MU), brain tissue volume receiving 10Gy (BV10Gy) were compared. The differences were evaluated by comparing Eclipse Acuros with Iplan PB, Acuros (Acu), and MC and PB-MC algorithms.

Results: When Acuros and PB and Acu-MC algorithms were compared, no significant differences were found between tissue V100, PTV V100, and CI values. Significant differences were found between V50, GI, PTVmax, PTVmean MU, and BV10Gy doses. p values of the comparisons are presented in Table 1.

Conclusion: Dose distributions varied significantly for field sizes smaller than 2x2cm² created by MLCs. In addition to the appropriate dose calculation algorithms of small volume targets, the use of beam data by small field dosimetry contributes significantly to obtaining more precise and accurate dose calculation results.


Radiosurgery, DMLC, Treatment Planning


TH- External Beam- Photons: Small field computational dosimetry

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