Acute Radiation Dermatitis In Head And Neck Patients Treated With Vmat Versus Imrt

VMAT has notable advantages in treatment delivery efficiency, however it may spread low doses to larger volumes compared with IMRT. We had qualitatively observed a trend towards increased skin toxicity for head and neck squamous cell carcinoma (HNSCC) treated with VMAT vs. IMRT. We present a quantitative clinical analysis of skin toxicity in HNSCC patients (pts) treated with VMAT vs. IMRT. In addition, we present the results of surface dose measurements on a phantom with VMAT and IMRT plans. Skin toxicity data of consecutive 102 HNSCC pts treated with IMRT and 88 pts irradiated with VMAT between 2013 and 2014 were reviewed. An assessment of the skin toxicity during treatment was conducted by the treating physician using the Common Terminology Criteria for Adverse Events (CTCAE v4.0). Skin toxicity was defined as ≥2. The Cochran-Armitage trend test was used to evaluate the relationship between treatment type, chemotherapy and skin toxicity. To evaluate any potential surface dose measurement differences between VMAT and IMRT, a model HN patient case was planned on an anthropomorphic phantom for both IMRT and VMAT to achieve clinically similar dose distributions. Surface dose was measured using OSLDs in 4 locations on the phantom neck surface. Each plan was delivered 8 times between which the phantom position was reproduced. After correcting for average dose differences, a two sample t-test was performed to determine the difference in mean surface dose between IMRT and VMAT. Pts treated with IMRT or VMAT were: 49 and 47 pts oropharyngeal, 34 and 20 oral cavity, 2 and 4 nasopharyngeal, 3 and 5 hypopharyngeal, 9 and 7 laryngeal and 5 and 5 unknown primary cancers, respectively. The majority of pts had stage III/IV disease (91% and 93% respectively), and the rest had stage I/II. 66 (65%) pts in the IMRT group and 62 (70%) pts in VMAT arm were treated definitively, the rest received adjuvant radiation. The median target dose for definitive radiation was 70 Gy in each group whereas median dose for adjuvant treatment was 60 Gy in IMRT irradiated pts as opposed to 66 Gy in VMAT. 70 (69%) pts in the IMRT group had chemoradiation compared with 72 (88%) pts in the VMAT group. In pts treated with RT alone, VMAT radiation delivery was marginally associated with higher skin toxicity compared with IMRT (p= 0.06). This trend disappears with addition of chemotherapy to radiation, which by itself was a strong predicting factor for acute dermatitis (p< .0001). In our phantom study, mean fractional surface dose for VMAT (1.33 Gy) was measured to be 6% higher (p