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First Beam Commissioning Report of a Novel Medical Linear Accelerator Designed for Biologically Guided Radiotherapy. International journal of radiation oncology, biology, physics Han, B., Kovalchuk, N., Capaldi, D. P., Simiele, E., White, J., Purwar, A., Yeung, T., Maganti, S., Mitra, A., Voronenko, Y., Oderinde, O. M., Shirvani, S. M., Kuduvalli, G., Vitzthum, L., Chang, D. T., Xing, L., Surucu, M. 2021; 111 (3S): e512

Abstract

PURPOSE/OBJECTIVE(S): A biologically guided radiotherapy (BgRT) system was developed and equipped with a novel O-ring gantry Linac, positron emission tomography (PET) and computed tomography technologies. This architectural design is to support real-time PET-guided treatment, termed biology-guided radiotherapy. To reduce latency between PET data acquisition and radiation delivery, the BgRT system incorporates a fast-transitioning binary multi-leaf collimator (MLC) leaves sandwiched between a split-jaw. This study reports the dosimetric commissioning of the first clinical BgRT machines at our institution, and compared with the reference data provided by the manufacturer.MATERIALS/METHODS: The dosimetric commissioning of the 6 MV flattening filter-free (FFF) photon beam was characterized using a 3D water phantom and diode detectors at a source to surface distance of 85 cm. In-air profiles of 40cm x 2cm field, 40cm x 1cm field, and various leaf combinations plus in water PDD data of 12 field sizes (1.25, 2.5, 5, 10, 20 and 40 cm MLC opened leaves with 1 and 2cm jaw settings) were acquired first for beam modeling. Additional longitudinal and transverse profile scans were performed for these 12 field sizes at the depth of 1.5, 5, 10, 15 and 20 cm to verify the beam model accuracy. The relative outputs factors were measured with the W2 1mmx1mm scintillator at the depth of 10cm for the field sizes from the smallest 0.6cm x 1cm to the maximum 40cm x 2cm.RESULTS: For the PDDs of reference field size of 10cm x 2cm measured at Stanford, the maximum doses (dmax) were 12.5mm within the manufacturer's reference range of 13 ± 0.75 mm. The percentage doses at 10cm depth (d10) at reference field size were 56.9% and 57.6% for Stanford and RefleXion measurements, respectively. The longitudinal field sizes for all tested fields were agreed within 0.5mm and the transverse off-axis ratio is within 1% in the beam core (80% of nominal field size). The output factors measured at our institute were ranging from 0.706 to 1.012 relative to the reference 10cm x 2cm field.CONCLUSION: This evaluation represents the first commissioning evaluation of the dosimetric characteristics of the BgRT system with architecture designed to accommodate both PET detector and LINAC subsystems. This data will serve as a clinical reference for the BgRT treatment planning system's beam model and can act as a standard for comparison and beam model improvement for units installed at future clinical sites.

View details for DOI 10.1016/j.ijrobp.2021.07.1404

View details for PubMedID 34701630