Quantification of Acute Skin Toxicities in Patients With Breast Cancer Undergoing Adjuvant Proton versus Photon Radiation Therapy: A Single Institutional Experience

Abstract

Purpose: Acute skin toxicity in the form of radiation dermatitis (RD) or skin hyperpigmentation (SH) is a common problem experienced by patients undergoing breast irradiation. Proton radiation has been thought to deliver higher doses to skin compared with photon radiation because of differences in the physical properties between photons and protons; however, limited literature exists directly comparing toxicity outcomes.

Methods and materials: The highest recorded grades of acute RD and SH were analyzed in 86 patients undergoing adjuvant radiation therapy to the breast with or without regional lymph nodes after lumpectomy (breast-conserving surgery) or mastectomy with either proton pencil-beam scanning (n = 39) or photon (n = 47) radiation therapy within a single institution to analyze differences in severity of acute skin reactions. For 34 of 47 photon and 33 of 39 proton patients, a "skin" contour was retroactively created in our treatment planning systems, and multiple dosimetric parameters were calculated to quantify objective radiation doses received by skin.

Results: On χ² analysis, the highest reported grade of RD was significantly higher in women undergoing proton radiation compared with photon radiation; grade ≥2 RD was present in 69.2% versus 29.8% of patients receiving proton and photon therapy, respectively (P = .002). Rates of grade 3 RD were 5.1% versus 4.3% for proton versus photon radiation, respectively (P = .848). Overall, there were no significant differences in rates of SH between modalities. There were no grade 4 to 5 toxicities in either cohort.

Conclusions: In a comparison with patients receiving photon radiation, a significantly higher rate of grade ≥2 RD was observed in patients undergoing proton radiation, with very low rates of grade 3 toxicity in both groups. Rates of SH did not differ significantly between modalities. Women should be counseled regarding the possibility of increased grade 2 toxicities, although this might present a dosimetric advantage for physicians when treating patients in the postmastectomy setting or when skin was involved on presentation.