Ic profiler

The patient case selected as relevant to locoregional treatment in our clinic has a plan with six fields, as described in Table 1 and illustrated in Fig. 1. The Monte Carlo calculation of each of the four main fields, excluding MLC and wedges, is validated against measurements using a water box geometry and setting the gantry angles to zero. Furthermore, the combined dose distribution from the two main anterior fields (1 and 4) and the two posterior fields (2 and 5), respectively, is analyzed without MLC and wedges. The dose level for the fields, separate and combined anterior/posterior, is verified by ion chamber measurements, (0.125 cm3 PTW Semiflex chamber 31010; Freiburg, Germany), centrally in the field and in the tail region just outside the field at 3 cm depth in solid water. The shape of the separate field profiles is verified with the ion chamber profiler device IC Profiler (Sun Nuclear Corp., Melbourne, FL).
Monte Carlo calculations for the tangential posterior field 5 is also verified with wedge included using IC Profiler, as well as one ion chamber measurement centrally in the field. The special consideration of field 5 is motivated by its asymmetry and length in combination with the wedge.

TG‐51‐compliant reference dosimetry of the Halcyon™ 6 MV‐FFF beam was performed in a water tank (1D Scanner™, Sun Nuclear Corporation, Melbourne, FL) using a 0.6‐cc waterproof Farmer chamber (PTW 30013, Freiburg, Germany) and electrometer (Fluke F35040, Fluke Biomedical, Everett, WA) calibrated by the University of Wisconsin Accredited Dosimetry Calibration Laboratory. PDD measurements were performed with the Farmer chamber, as well as a 0.015‐cc PinPoint chamber (PTW 31014, Freiburg, Germany), with corrections for the effective point of measurement. Farmer chamber measurements of the PDD were performed with and without a 1‐mm lead foil suspended 30 cm from the water surface as outlined in the TG‐51 protocol.
In order to assess whether the Farmer chamber's dimensions were appropriate for calibration of the Halcyon's 6 MV‐FFF beam, profiles were measured using an IC Profiler (Sun Nuclear) ion chamber array. The array is made up of 251 ion chambers, each with a width of 2.9 mm, spaced 5 mm apart. Relative profiles were acquired in the crossline and inline directions at isocenter with 0.9 cm buildup, inherent in the IC Profiler.
Finally, an OSLD housed in an acrylic block provided by IROC Houston Quality Assurance Center was irradiated under specified conditions and returned for independent verification of our beam calibration.

Dose matrix post‐processing was performed by an in‐house built Matlab code, PDDs were calculated by averaging the neighboring four voxels at the same depth and then normalized to the maximum dose. Measured percentage depth ionizations (PDIs) in the water phantom were converted to PDDs by multiplying the stopping power ratio based on the methods reported in Supplement to the recommendation of Task Group 25.²¹ For PDDs comparison, parameters including percentage surface dose, depth of maximum dose (d_max), depth of the 80% dose (R₈₀), depth of 50% dose (R₅₀), and x‐ray contamination at 10 cm depth were also compared.
Simulated lateral profiles at 1 cm depth were calculated by averaging the voxels in two neighboring depths and normalized to the value at the central axis. It was further smoothed by a median filter to preserve the field edges. Profiles at the same depth are also measured using the mini ion chamber array detector IC Profiler (Sun Nuclear Corporation, Melbourne, FL, USA). Dose difference between simulation and measurement was calculated.