Session Item

Recently, a system that more accurately reconstructs the dose by reflecting the variables related to the treatment period during treatment has been commercialized. The radiation dose reconstruction method includes a log file-based method and a method based on actual measurement. The log file-based extracts the log of the treatment device and provides the recalculated dose and dose distribution for each organ by reflecting the MLC location and the irradiated MU. In the case of the measurement base, not only the mechanical properties at the time but also the dose change can be reflected by actually measuring through the phantom. This study aims to provide guidelines when the user selects a dose reconstruction system or interprets the results according to the two systems.

For the dose reconstruction system, log file-based Mobius FX (Varian, USA) and measurement-based Delta4DVH-anatomy (ScandiDos, Sweden) were used (hereinafter referred to as MobiusFX and Anatomy). For patient data, 49 cases of left breast cancer patients were used. Analysis was performed based on 1 fraction, and organs used for analysis were Lungs, Rt lung, Lt lung, Heart, Esophagus, and Spinal cord. The average reconstructed dose for each system, the amount and rate of change from the standard TPS (Treatment Planning System) Eclipse 16.1 (Varian, USA) value were analyzed. Data sorting and paired t-test statistical analysis were performed using Python 3.9.7.

All data are more than 30 cases, therefore it was assumed normality. In Lt lung adjacent to the target, the reconstructed average dose is lower for MobiusFX and higher for Anatomy compared to TPS. Therefore, the average dose of the reconstructed Anatomy is 0.039Gy±0.011 higher than that of TPS, and 0.066Gy±0.091 higher than that of MobiusFX (p-value 0.000). When calculated as the total prescribed dose, there is a difference of about 1 Gy in Lt lung. On the other hand, in the case of Rt lung with relatively low dose, there is no statistically significant difference between the two methods. In the case of Heart, MobiusFX shows the same value as TPS, and Anatomy shows a reconstructed dose that is 0.044±0.008 Gy higher. (p-value 0.000) Both lungs show the same trend as heart. (p-value 0.000) Esophagus and Spinal cords with small volume do not show a statistically significant difference.

Anatomy showed a higher reconstructed dose than the reference value in most OARs, and Mobius showed relatively equal or less different reconstructed doses. It can be seen that the Anatomy reflects the dose change, which is maintained high within the range of 1% on average. Anatomy is inconvenient to measure but sensitively reflects dose reconstruction, and Mobius responds slightly insensitively in the 1Gy range, but may increase cost-effectiveness. These systems can be selected according to the institution's preferences.