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  4. Dosimetric Accuracy of A Novel PRESAGE Radiochromic Sheet

Dosimetric Accuracy of A Novel PRESAGE Radiochromic Sheet

Y Wang1*, P Black2 , C Velten3 , J Adamovics4 , R Coakley5 , C Wuu6 , (1) Columbia University Medical Center, New York, New York (2) Columbia University Medical Center, New York, New York (3) Columbia University Medical Center, New York, New York (4) Rider University, Lawrenceville, NJ, (5) Rider University, Lawrenceville, NJ, (6) Columbia University Medical Center, New York, New York

Presentations

(Thursday, 8/2/2018) 10:00 AM - 12:00 PM

Room: Davidson Ballroom A

Purpose: A novel 2D radiochromic PRESAGE sheet with variable thickness has been developed to provide in-vivo dosimetry. It can be used for patient surface dosimetry or as a bolus with dosimetry capability. Its softness and flexibility to conform with the patient’s skin makes this product a valuable tool for future in-vivo dosimetry. In this study a comprehensive investigation into its dosimetric accuracy at different scanning times was performed.

Methods: A radiochromic sheet was irradiated with a 6 MV photon beam on a TrueBeam to six different doses for linearity measurement. For dose rate dependence, 5 Gy were delivered to the sheet using 100, 300, and 600 MU/min. Additionally, 5 Gy were delivered using an 18 MV photon beam to investigate the energy dependence. The sheet was scanned at five different time points after irradiation using a high resolution scanner to acquire information about the optical density (OD) development and fading of the dosimeter.

Results: The results show that this radiochromic sheet exhibits a stable linear response to dose and negligible dose rate (error < 1%) and energy dependence (error < 2.5%) if scanned within two hours after irradiation. The divergence of linear dose response with time is due to different rates of OD increase and fading at different doses. Moreover, the fading of OD in low dose region happens later than in high dose region. This effect leads to larger penumbra of the beam profiles if scanned after 2 hours. However, since the dosimeter is used for relative dose measurement, the normalization makes error smaller than 3%.

Conclusion: This study shows the dosimetric characteristics and temporal stability of a novel in-vivo dosimeter. If scanned within two hours of irradiation, the radiochromic sheet can provide accurate relative dose measurement, which makes it capable of evaluating relative dose shortly after treatment delivery.

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