# Feasibility of a Reusable Radiochromic Dosimeter
## 4 Discussion
### Reusability and Dose Sensitivity upon Reirradiation  
Subsequent re-irradiations of Formulations 1 and 3 (in duplicate) show that the OD cleared more rapidly than their respective initial irradiations, consistent with previously reported PRESAGE reusability studies [9]. The clearing times for Formulation 1 dropped to around seven days, while the clearing time for Formulation 3 dropped to less than 50 h.  
Figure 7 and Table 2 show that the calibration curve slope decreases upon reirradiation of Formulation 1, displaying a decrease in sensitivity after each subsequent irradiation. For example, the second and third irradiations showed significant drops in sensitivity (24% and 40%, respectively) from the initial irradiation. Still, the subsequent irradiations showed much more minor changes from the previous irradiation. In other words, the dose sensitivity decreases upon reirradiation, while the linearity is maintained with mean absolute percentage errors (MAPE) (Table 3) ranging from 1.2% to 4.5%. Similarly, the linearity of Formulation 3 (Figures 8 and 9, and Table 4) is maintained but differs significantly from Formulation 1 in that the dose sensitivity is much more consistent upon reirradiation. Figure 10 shows that the average sensitivity for both Group 1 and Group 2 agreed with a population standard deviation of 3.3% and 2.3%, respectively. Indicating that the sensitivity remains consistent upon reirradiation of Formulation 3 while also retaining linearity of response with MAPE values (Table 5) ranging from 1.8% to 4.7%. Both Formulations 1 and 3 have linear dose-response over the same dose range. However, Formulation 1 drops significantly after the first irradiation, while Formulation 3 retains response sensitivity upon reirradiation, with no systematic decrease in sensitivity observed. With varying results on the behavior of the sensor response upon subsequent irradiations for Formulation 1, it will not be possible to perform absolute dosimetry measurements with this formulation without requiring a new sensitivity measurement to be performed each time. Since Formulation 1 does, however, retain linearity with each subsequent irradiation, it is possible to perform accurate relative dosimetry measurements with dosimeters manufactured using this formulation. Formulation 3 is the most reusable since it retains linearity and sensitivity of response upon reirradiation. Therefore, it may be possible to manufacture reusable 3D dosimeters for absolute dosimetry with this formulation, certainly for relative dosimetry measurements. Both Formulations 1 and 3 show a decrease in clearing time upon reirradiation, with cuvettes in the present work stored at room temperature. PRESAGE samples stored in colder environments, such as refrigerated (4 \({}^{\circ}\)C) or freezing (\(-\)18 \({}^{\circ}\)C), exhibit greater stability in their temporal response and thus can be measured at later elapsed times post-irradiation while preserving their signal and maintaining a high degree of linearity [12]. Another factor influencing decay time is the dosimeter size, where scaling up from a small dosimeter cuvette to a larger 1 kg dosimeter has seen decay rates decrease by 3\(\times\)[9]. J.R.N. : Contribution Statement: The author made a substantial contribution to experimental design, drafting the article, data collection, analysis and interpretation, and final approval of the submitted article. M.R. : Contribution Statement: The author substantially contributed to data collection, analysis, experimental design, and article editing. J.A.H. : Contribution Statement: The author participated in data collection, dosimetric calculations, experimental design, editing the article, and final approval of the version to be submitted. G.S. : Contribution Statement: The author contributed to the article's data collection and analysis and editing. C.I. : Contribution Statement: The author contributed to data collection and analysis and editing the article. P.A.R.