P171] Quality control measurements for head and neck cancer patients with SHANE Phantom

Abstract

Purpose To investigate irradiation techniques for simultaneous integrated boost (SIB) treatment of nasopharyngeal cancer (NPC) case in terms of organs at risk (OAR) toxicity and patient specific quality control (QC). This study is a part of an end-to-end audit programme for dose delivery using intensity modulated radiation therapy (IMRT). Methods CIRS SHANE Phantom was used to create four different treatment plans for a NPC patient. SIB schedule prescribes 54 Gy, 60 Gy and 70 Gy in 30 fractions for elective nodes (both sides), involved nodes (right side) and primary nasopharynx respectively, using 1, 2 or 3 arcs RapidArc (RA) or 7 field Sliding Window (SW) techniques. Patient specific quality control measurements were performed using EPID. Varian Portal Dosimetry was used with local gamma analysis using 2%/2 mm and 3%/3 mm criteria with 10% threshold. Results All plans met the criteria of dose to OARs: D2% of the spinal cord and the brainstem on average were 35 Gy and 35.5 Gy; mean dose of the left parotid on average was 22.9 Gy. Patient specific QC was performed without any interruption. MUs for 1, 2, 3 arcs and 7 field SW were 602, 706, 696 and 2447, respectively. Gamma analysis on EPID images gave 96.2%, 96.2%, 96.7%, 82.6% and 98,8%, 98.9%, 99.3%, 92,1% passing rate on average for 2%/ 2 mm and 3%/ 3 mm criteria, respectively. Conclusions All treatment techniques are suitable for NPC irradiation with SIB in terms of OAR toxicity although RA with 2 or 3 arcs are more preferable in terms of number of MUs.