Intensity Modulated Radiation Therapy (IMRT) Decreases Acute Skin Toxicity for Women Receiving Radiation for Breast Cancer

Abstract

To determine the clinically observed incidence and severity of acute skin toxicity with breast intensity modulated radiation therapy (IMRT), and compare the results with a matched cohort of patients treated by conventional radiation therapy. Our hypothesis is that measures to decrease dose inhomogeneity within the breast and skin with IMRT will improve acute skin toxicity. The study population consists of 73 women with early stage breast cancer treated with breast-conserving surgery and IMRT. The IMRT technique involves an iteration method for optimization to generate the IMRT plan, Monte Carlo dose calculation, and a step-and-shoot technique using multileaf collimation for beam delivery. Other aspects of the technique including the clinical definition of the clinical target volume by the physician, patient positioning, tangential beam orientation, dose and field sizes were unchanged compared conventional tangential radiation. These patients were matched one-to-one to a control group of 60 women treated with conventional photon radiation by using their bra size and chest wall separation. The study end point was acute skin toxicity. There were no observed differences in the acute toxicity based upon common terminology criteria for adverse events (CTC) for acute radiation dermatitis. There was no desquamation in 42% of IMRT patients, dry desquamation in 37% and moist desquamation in 21%. The degree of desquamation was greater for conventional patients compared with IMRT patients -52% grade 0, 10% grade 1, and 38% grade 2 (P = 0.001). Subgroup analysis showed desquamation was significantly lower with IMRT for small (P = 0.038) and large breast sizes (P = 0.037), but not medium sizes (P = 0.454). For large breast sizes, the incidence of moist desquamation grade 2 was 48% with IMRT compared with 79% in controls. Significant predictors of moist desquamation on stepwise logistic regression were use of IMRT (P = 0.0011) and breast size (P < 0.0001). IMRT is associated with a decrease in severity of acute desquamation compared with a matched control group treated with conventional radiation therapy. As with conventional radiation, breast size remains the most important prognostic factor for acute skin toxicity. The CTC grading system for acute radiation dermatitis is not sensitive when applied to modern breast cancer treatment because of its dependence of subjective rating of erythema and inability to gauge variations in desquamation. Further study of patient symptoms, quality of life, and cosmesis is needed to evaluate the benefit of IMRT for breast cancer.