Abstract: Objective To experimentally measure the radiation dose of non-target tissues of patients in superficial X-ray therapy(SFXT),and to understand the dose received by tissues outside the target and organs under typical SFXT conditions,so as to provide experimental basis and guidance for evaluation of radiation hazard risk and protection of non-target tissues of patients. Method A SRT-100 superficial X-ray therapy system was used as the radiation source,and the surface doses corresponding to interested points of an ATOM 702 anthropomorphic phantom were measured.Fifteen measurement points were set on the surface of the phantom at locations corresponding to the eye lens,thyroid,breast,chest,abdomen and gonads,and each point was equipped with a thermoluminescent detector(TLD).A field size of Φ=10 cm was determined to simulate chest treatment conditions at 100 kV and 8 mA,with a cumulative dose of 32 Gy.The TLD Cube thermoluminescent dosimeter reader was used to measure the doses.The Mann-Whitney U test was used to determine the non-target radiation dose on the left and right sides of the simulated torso body surface,with P<0.05 considered statistically significant. Results Under unshielded conditions,the doses received by the left and right thyroid were 404.26 and 527.74 mGy,respectively.The doses received by the left and right breast were 512.62 and 446.74 mGy,respectively. The dose at the chest midline was 494.71 mGy. The doses received by the left and right eye lens were 22.09 and 27.44 mGy,respectively,and the doses received by the left and right gonads were 1.86 and 1.45 mGy,respectively.With the central axis of the irradiation field as the symmetry axis,the dose ranges at 27 points on the left and right sides of the torso surface were 0.31-512.62 mGy and 0.32-527.74 mGy,with average doses of 161.86 and 120.01 mGy,respectively.When the phantom surface was shielded with 0.35 mm Pb,the doses at the corresponding locations were reduced by over 90%. Conclusion The dose received by non-target tissues during superficial X-ray therapy is closely related to the distance from the irradiation field and the shielding conditions.It is essential to standardize the operational procedures for superficial X-ray therapy and non-target tissue protection to minimize the radiation risk to non-target organs of patients.

Key words: Superficial X-ray therapy, Non-target tissue, Radiation dose, Radiation protection