In-vivo skin dose measurement using gafchromic EBT3 film dosimetry in the radiation therapy of Head and Neck cancers: 2DRT versus IMRT

Background and Purpose: Head and neck cancers involve very high curative doses of about 70 Gy which is usually associated with acute toxicities most importantly of the skin as it receives the radiation first. Intensity-modulated radiotherapy (IMRT) has the potential to decrease the skin dose thereby reducing the side effects, as well as the unplanned treatment interruptions that could otherwise result in less outcome of treatment. The purpose of this study was to compare and evaluate the skin dose during head and neck radiation therapy between 2-dimensional radiotherapy (2 DRT) with cobalt 60 beam and Intensity Modulated Radiotherapy (IMRT) with high energy linear accelerator. Materials and methods: Nasopharynx carcinoma patients receiving adjuvant radiation therapy of 60 Gy were selected for the study. Study patients were divided into two groups Group I received 60 Gy by 2-dimensional radiotherapy (2 DRT) and Group II received 60 Gy by seven field Intensity Modulated Radiotherapy (7 F-IMRT). The surface dose was measured using multiple 2 cm² Gafchromic EBT^-3 films placed underneath the thermoplastic cast along the treatment isocenter as well as other sites within the irradiated field. The paired t-test was used to analyze the difference in the skin doses between the two techniques. Results: Sixty-three cases of head and neck irradiation from Group I and Group II both were analyzed for in-vivo skin dose for a prescribed dose of 2 Gy per fraction to the target using Gafchromic EBT3 films. The means were compared using a paired t-test. There was a significant difference in the dose to skin per fraction in 7 F-IMRT (Mean=1.62 Gy, SD= 0.23) compared to 2 D-RT (Mean = 2.21 Gy, SD = 0.33), at the conditions of paired t-test with 62 degrees of freedom-t (62) =-10.015, ρ= 0.00 (Table 1). The skin dose was more in 2 DRT by 26.7% than in 7 F- IMRT. Also, measured dose was compared to the treatment planning calculated dose and a difference of less than 1.6% was observed. Conclusion: Radiotherapy of Head and Neck Cancers is better managed with Intensity Modulated Radiotherapy not only in terms of the possible dose escalation but also in terms of better skin-sparing and thereby fewer skin toxicitie