2115 - Predicting False Intrafraction Motion during Frameless Stereotactic Radiosurgery Using Quantification of Skin Tone and Glossiness

02:30pm - 04:00pm PT

Hall F

Screen: 19

POSTER

Presenter(s)

Nicholas Johnson, BS - University of Alabama at Birmingham, Birmingham, AL

N. R. Johnson¹, J. B. Fiveash², D. N. Stanley³, R. Sullivan¹, C. D. Willey⁴, and R. A. Popple²; ¹University of Alabama at Birmingham, Birmingham, AL, ²University of Alabama at Birmingham Department of Radiation Oncology, Birmingham, AL, ³Department of Radiation Oncology, University of Alabama at Birmingham, Birmingham, AL, ⁴University of Alabama Birmingham, Birmingham, AL

Purpose/Objective(s):

Surface imaging is one method to manage intrafraction motion during frameless radiosurgery, but a subset of patients shows false intrafraction movement during treatment. Prior studies have most frequently observed false deviations at non-zero couch angles when one or more surface imaging cameras were blocked, and in patients self-identified as Black. In the current study, we hypothesize that commercial dermatologic tools that quantitatively measure skin tone (Fitzpatrick scale) and skin glossiness will better identify patients at higher risk of false positive intrafraction motion.

Materials/Methods:

Dermatological instruments were applied to the forehead to quantify skin tone (Fitzpatrick scale) and glossiness. After initial CBCT localization, intrafraction motion was monitored with the surface imaging system using a region of interest from the open-face device. Surface imaging logs at non-zero couch angles were compared to quantified measurements of skin glossiness and tone.

Results:

Seventy-six patients underwent radiosurgery with skin measurements taken. 16/76 (21%) had the darkest skin tone (Fitzpatrick 6). At non-zero couch angles Fitzpatrick 6 patients had higher deviations even if a camera was not blocked (1.0 vs 0.8 mm, p=0.01). When a camera was blocked at non-zero angles, larger deviations were noted in the patients with the darkest skin tone (1.3 vs 0.8 mm, p<0.01). Skin glossiness did not predict a shift when the either a camera was blocked or not.

Conclusion:

For patients undergoing frameless radiosurgery with real-time surface imaging to monitor intrafraction positioning, Fitzpatrick skin tone 6 predicts false positive deviations in patient positioning including deviations over our institutional threshold (1mm) to continue treatment. These false positive deviations have the potential to increase the frequency of unnecessary intrafraction CBCT and lengthen the procedure. Manufacturers of surface imaging tools should assess accuracy in patients with a variety of skin tones.