2897 - Prospective Evaluation of Acute Cutaneous Toxicity during Proton vs. Photon Radiotherapy for Patients with Head and Neck Cancer and Varied Baseline Skin Pigmentation
Presenter(s)
R. J. Thomas1, A. K. Yoder1, Y. Yi2, A. F. M. Salem1, K. N. Nordlund1, A. J. Bishop1, R. Lin3, A. Lee1, C. D. Fuller1, A. Farooqi1, B. A. Guadagnolo1, and D. Mitra1; 1Department of Radiation Oncology, The University of Texas MD Anderson Cancer Center, Houston, TX, 2The University of Texas MD Anderson Cancer Center, Houston, TX, 3Department of Radiation Oncology, University of Texas MD Anderson Cancer Center, Houston, TX
Purpose/Objective(s): Acute radiation dermatitis (RD) is a common toxicity of head and neck (HN) radiotherapy (RT). Recent studies have reported worse dermatitis with proton RT compared to photon RT. We sought to evaluate how Fitzpatrick phototype (FZ), a classification of skin pigmentation and UV sensitivity, influences the evolution of cutaneous injury across RT modality.
Materials/Methods: Between 2022-2044, patients undergoing definitive HN RT were enrolled on a prospective study to evaluate biophysical properties of skin during fractionated RT (<3 Gy/fraction). RD (as graded by 3 blinded radiation oncologists) and quantitative erythema and melanin measured using a handheld spectrophotometer were assessed weekly. Peak change and the trajectory of change over time were compared between RT modality (photon vs. proton) and skin phototype (lighter pigmentation [FZ 1-3] vs. darker pigmentation [FZ 4-6]). The effect of RT modality and FZ were evaluated using a linear mixed-effects model including week, treatment, FZ group, and their interaction terms.
Results: Fifty-eight patients were assessed (22 proton, 36 photon). Baseline characteristics (including age, sex, proportion of FZ 1-3 vs. 4-6, melanin, erythema and volumetric skin dose parameters) did not differ between RT modalities. Peak RD also did not differ between proton or photon RT (proton 2.2 vs. photon 2.3, p=0.71). However, patients with FZ 4-6 had worse peak RD than FZ 1-3 patients (FZ 4-6 2.4 vs. FZ 1-3 2.2, p=0.04). The trajectory of RD change in the overall population and FZ cohorts was not impacted by RT modality (p=0.28). Similarly, the trajectory of erythema change did not significantly differ between proton and photon cohorts (p=0.79). The peak change in erythema was more pronounced in FZ 1-3 patients (median change 291) vs. FZ 4-6 patients (median change 62, p<0.001). However, the trajectory of melanin change significantly differed between proton and photon RT (p<0.001). When broken down by FZ cohort, this difference was found to be driven by the trajectory of FZ 4-6 patients, where more confluent desquamation at week 5-6 led to loss of measured melanin (p=0.002).
Conclusion: In this prospective cohort of patients receiving HN RT, changes in RD and quantitative erythema did not differ between RT modalities. Patients with higher FZ experienced worse RD regardless of RT modality. These findings suggest that skin phototype is associated with acute HN skin toxicity that supersedes RT modality.