149. Skin dose in radiotherapy: Results of in vivo measurements with Gafchromic EBT3 films. (December 2018)

• Record Type: Journal Article
• Authors: Giuliano, A.; Ravaglia, V.
• Is Part Of: Physica medica. Volume 56(2018)Supplement 2
• Page Start: 156
• Page End: 157
• Publication Date: 2018-12
• Subjects: Medical physics -- Periodicals; Biophysics -- Periodicals; Biophysics -- Periodicals; Imagerie médicale -- Périodiques; Radiothérapie -- Périodiques; Rayons X -- Sécurité -- Mesures -- Périodiques; Physique -- Périodiques; Médecine -- Périodiques; 610.153
• DOI: 10.1016/j.ejmp.2018.04.160
• Languages: English
• ISSNs: 1120-1797

Abstract

Abstract : Purpose: An accurate estimation of surface dose is becoming important in radiotherapy to avoid complications to skin[1] . However, the Treatment Planning Systems (TPS) do not accurately model skin dose. The aim of this study was to assess surface dose in vivo using EBT3 Gafchromic films. Methods: The measurements were performed applying films (2 × 2 cm 2 ) directly on patient skin or inside the thermoplastic mask. Targets included head and neck (H&N), brain and sarcoma in Tomotherapy; breasts at Linac and skin tumors in Plesio-Röntgen therapy. For each patient measurements were repeated for three fractions locating films in 1–3 reproducible points and compared with TPS-calculated doses. Films were read with a flatbed scanner and analyzed using red channel calibration. In vivo dose evaluations were compared with measurements performed on Cheese phantom both with and without thermoplastic mask. Results: A total of 117 film measurements were performed on 21 patients. The absolute value of the mean difference between measured and TPS-calculated doses was (11.3 ± 6.5) % (17.7% for Linac plans, 11.6% in Tomotherapy and 4.6% in Plesio-Röntgen therapy). At Linac and in Plesio-Röntgen there was not a clear trend of overestimation of the TPS compared to measurements. Instead in Tomotherapy the TPS underestimated measurements (−9.1 %) for H&N and brain treatments (with thermoplastic mask) and overestimated for sarcoma (9.2%). This trend was confirmed by assessments on Cheese phantom in Tomotherapy, where TPS overestimated without mask (28.6% vs −0.7% with mask). An improvement of the agreement between measurements and estimations in Pinnacle and Tomotherapy was shown with mask (28.6% to −0.7% in Tomotherapy and −20.7% to −16.3% at Linac). Conclusions: EBT3 films are suitable for skin measurements in radiotherapy and represent a useful detector for quality assurance, since TPS does not give accurate dose values in the first millimeters of skin.