Dosimetric verification of stereotactic head treatmentsperformed with Helical Tomotherapy using alanine dosimetersand gafchromic films

Purpose The aim of this work is the dosimetric verification of stereotactic head treatments performed with Helical Tomotherapy [ [1] Soisson E.T. A technique for stereotactic radiosurgery treatment planning with helical tomotherapy. Med Dosim. 2011; 36: 46-56 Google Scholar ] using an anthropomorphic phantom, the Rando Head Alderson, combined with alanine [ [2] Marrale M. EPR/alanine dosimetry for two therapeutic proton beams. NIMB. 2016; 368: 96-102 Google Scholar ] dosimeters and EBT3 gafchromic films [ [3] Sorriaux J. Evaluation of Gafchromic EBT3 films characteristics in therapy photon, electron and proton beams. Phys Med. 2013; 29: 599-606 Abstract Full Text Full Text PDF PubMed Scopus (152) Google Scholar ]. Methods A CT scan of Rando Head Phantom was used to simulate five different clinical situations regarding “tumor” dimension, position and proximity relations with Organs at Risk (OAR). All five treatment plans were computed using 1 cm beam width, pitch values lower than 0.215 and modulation factor between 1.6 and 2.5. In all cases, the dose constraints required for OAR have been met. During treatment delivery, the alanine dosimeters were placed in the phantom housings to perform dose-specific measurements for either the PTV and OAR, and gafchromic films were inserted between contiguous slices of the phantom to achieve bidimensional dose distributions on the transverse plane. Results Dose distributions measured by gafchromic films were compared to those calculated using the 3% – 3 mm criterion for the gamma function using the Tomotherapy DQA module. Also the results of point measurements made with alanine agree with the dose values calculated by TPS within the experimental uncertainties. Conclusions The data show an excellent agreement between calculated and measured dose not only for PTV but also for the OAR, receiving significantly lower doses.