SU‐E‐T‐188: An Effective Quality Assurance Method for TomoTherapy Craniospinal Irradiation Patients with A 3D Semiconductor Phantom

Purpose: This study aims to develop an effective and efficient approach to perform delivery quality assurance (DQA) to any large length spine in Tomo craniospinal irradiation (CSI) with a 3D semiconductor phantom. Methods: It is challenging to use conventional method to perform DQA to an entire large length of spine because the Tomo machine limits the maximum longitudinal distance between red and green laser (=18 cm). In order to overcome this limit, three DQA plans for each CSI patient were generated for covering the entire treatment site, in which we intentionally overlapped the red and green laser in DQA calculation, then we measured the distance (d) between the centers of the phantom and lasers. When using SunNucelar QA software to compute the plannar dose, we set the center of the cylindrical surface by applying d to the IEC Z coordinate. In phantom setup, we first align the center of phantom with green laser then manually shift the phantom superiorly or inferiorly d. With this new approach, we measured five CSI patients using a commercial 3D semiconductor phantom, the ArcCHECK (SunNuclear). The measured and computed dose is compared with gamma analysis and (3%, 3 mm) agreement criteria. Results: For all CSI patients and sections measured, the acquired dose distribution covered the complete treatment length and matched the computed data very well. All the DQA passed the gamma criteria with an average passing rate of 99.1%. The total delivery time of DQA using the new method was 66.7% of the time using the conventional method. Conclusion: The measured DQA results from the five CSI patients demonstrate that this new method overcomes the distance limitation of 18 cm between the red and green laser in the conventional DQA method. The DQA delivery becomes more efficient with 33.3% reduction of beam‐on time.