###### Abstract  
Research conducted to-date, makes use of the IBA-Lynx scintillating screen and radiochromic film to analyze the proton field uniformity for dose-area product (DAP) determination. In this paper, the machine log file based reconstruction is proposed to calculate the field uniformity to simplify the measurement. In order to calculate the field uniformity, the dose distribution is reconstructed based on the machine log file with matRad (an open source software for analytical dose calculation in MATLAB). After acquisition of the dose distribution, the field flatness and symmetry are calculated automatically for different proton energies. A comprehensive comparison of DAP determined with Bragg peak chamber (BPC) and Markus chamber (MC) is presented. The actual delivered dose is reconstructed with the log file to analyze the lateral dose distribution of the scanned field. DAP of different energies are calculated ranging from 70.6 MeV to 235 MeV. The percentage difference is calculated, illustrating the DAP discrepancy between the MC and BPC to the mean value. The percentage difference ranges from \(-0.19\%\) to \(1.26\%\). The variation between DAP measured with the BPC and MC peaks at \(-2.5\%\). The log file based reconstruction to calculate field uniformity can be an alternative for DAP determination. The direct method using a large-area Bragg peak chamber is investigated. The two methods to determine DAP and calibrate beam monitor illustrate consistent results.  
dose-area product; reference dosimetry; proton beam; beam monitor calibration +
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into account; if not, approximately 3% error of DAP will be triggered [4; 6]. [PERSON] et al. [7] cross-calibrated the BPC with a Farmer type chamber in the center of a Spread-out Bragg Peak (SOBP). DAP was determined at the plateau region of mono-energetic proton pencil beam with both methods [4; 8].  
The delivered particles per MU can be calculated combining ionization chamber measurements and the Monte Carlo simulation. A 10 \(\times\) 10 cm\({}^{2}\) uniform field with the spot spacing 2.5 mm and given number of protons were simulated in TOPAS, sharing the same properties as the experiment [9]. [PERSON] [3] performed the calibration of the beam monitor at a shallow depth with a uniform field for carbon beam. The number of protons per MU was calculated with a uniform field for proton beam [9; 10; 11; 12]. Beam monitor calibration in terms of the number of protons with a single spot and uniform scanned field was analyzed [8; 13; 14]. The beam monitor was calibrated with an ionization chamber and a Faraday cup [9; 15].  
If the lateral dose distribution is not uniform, an additional corrective factor should be added to DAP determination. In addition, the scanned field uniformity can contribute to the uncertainty of DAP determination. A 0.5% uncertainty budget is found by [PERSON] [8] corresponding to the uniformity of the beam profile. Thus, it is necessary to analyze the scanned field uniformity. In previous research, lateral dose distribution was measured with the IBA-Lynx scintillating screen or radiochromic film to check the field uniformity [4; 8]. In this paper, it is proposed to utilize the log file based reconstruction to calculate the lateral dose uniformity for DAP determination. Furthermore, Beam monitor calibration is significant in the dosimetric commissioning of the proton beam therapy facility. The beam monitor performance is tested in periodic quality assurance (QA) because it is directly related to the dose delivery accuracy. During the commissioning stage of China's first domestically-made proton therapy facility named the Shanghai Advanced Proton Therapy facility (SAPT), the BPC and MC are employed to derive DAP and calibrate the beam monitor in terms of the number of protons per MU.