Purpose: In radiation treatment delivery, scattering and secondary particles exist far from the treatment target region, contributing unaccounted doses to the patient. This study aims to quantify the peripheral dose in the RefleXionᵀᴹ X1 radiotherapy machine.
Methods: Measurements were carried out with an Exradin-A14SL microchamber inside a solid-water phantom in the RefleXion X1 machine under the conditions of a flattening filter-free 6MV photon beam. Peripheral dose was measured at 5 points (2, 4, 6, 8, and 10 cm) from the edge of the fields in the IEC-X direction at 85 cm SSD for 10,000 MU. The fraction of dose was calculated using the CAX measurement as a reference. In addition, the dose was measured at 1.5, 5, and 10 cm depths in the solid-water phantom for beam segments defined with a 2 cm fixed jaw opening in the IEC-Y direction and 2.5, 5, 7.5, and 10 cm multi-leaf collimator (MLC) opening in the IEC-X direction.
Results: Peripheral dose for the RefleXion X1 machine was 0.39%, 0.55%, 0.69%, and 0.79% of the CAX dose, respectively, for the corresponding 2.5, 5, 7.5, and 10 cm MLC openings at a 1.5 cm depth in the phantom at a 2 cm extended distance from the field edge. The peripheral dose increased with depth from 75 cGy at 1.5 cm to 146.24 cGy at 10 cm depth for 10 cm MLC x 2 cm jaw field size. Also, radiation dose decreased with larger extended distances from the field edge: At 10 cm off-axis from the field edge, the ion chamber measurement was 0.11%±0.02%, 0.17%±0.07%, 0.20%±0.06%, and 0.23%±0.08% of the CAX measurement for the corresponding 2.5, 5, 7.5 and 10 cm MLC openings, respectively.
Conclusion: This study demonstrates that the RefleXion X1 machine's peripheral dose is low, even in scenarios where the scattering effect is pronounced.
Funding Support, Disclosures, and Conflict of Interest: Research supported by RefleXion Medical
Peripheral Dose, Radiation Dosimetry, Scatter
TH- External Beam- Photons: out of field dosimetry/risk analysis