Decreasing Skin Toxicity in Whole Breast Irradiation with Helical Tomotherapy IMRT

Abstract

To decrease skin toxicity resulting from whole breast irradiation with Helical Tomotherapy IMRT. Patients treated with the Helical Tomotherapy IMRT planning yielded an average mean skin dose and maximum skin dose of about 85% and 102% of the prescribed dose respectively resulting in brisk erythema. Target volumes and dose parameters were in accordance to the NSABP B51 protocol guidelines using a breast PTV cropped 5mm from the skin surface. A unique treatment planning technique was designed to decrease the skin toxicity while delivering the desired dose to the breast PTV. We started by determining a tolerable skin dose while not compromising breast PTV coverage. This was determined by evaluating the skin dose of patients treated via conventional tangent fields using similar dose prescription. The conventional tangent fields yielded an average mean skin dose and maximum skin dose of about 70% and 100% of the prescribed dose respectively. These patients had G1 skin toxicity. The next step was to design a helical tomotherapy IMRT treatment planning technique that would deliver a comparable tolerable mean skin dose to the conventional tangent fields. This technique was implemented by utilizing a 3mm skin rind limiting the dose to a maximum point ≤ 95% and a mean of 70%-75% of the prescribed dose. Treatment plans were generated using the 3mm skin rind as an OAR and a Breast PTV at 6mm, 7mm and 8mm from the skin surface to mimic the coverage seen in the conventional tangential fields. The findings for the 3 groups were as followed: 6mm: The Breast PTV coverage was good with above 90% and 97.7% of the volume receiving 100% and 95% of the prescribed dose respectively. Only 1.5% or 17.32cc of the volume received 105% of the prescribed dose. The skin rind received a mean dose of 69.4% and a maximum dose of 90.1%. 7mm: The Breast PTV coverage was at 88.4% and 96.2% of the volume receiving 100% and 95% of the prescribed dose respectively. Only 1.6% or 19.88cc of the volume received 105% of the prescribed dose. The skin rind received a mean dose of 67.5% and a maximum dose of 86.6%. 8mm: The Breast PTV coverage was good with above 79.9% and 90% of the volume receiving 100% and 95% of the prescribed dose respectively. Only 2.2% or 26.16cc of the volume received 105% of the prescribed dose. The skin rind received a mean dose of 64.3% and a maximum dose of 79.6%. 5/7patients treated prior to this technique experienced G2 toxicity while none of the 13 patients treated with technique developed greater than G1 toxicity. With a Breast PTV cropped 6mm from skin surface a mean dose of 75% and a maximum dose of 95% was achieved in these 13 patients CONCLUSION: Adding the skin rind as an OAR allowed a reduction in skin dose without compromising coverage of the breast PTV with a breast PTV cropped 6mm from the skin surface.