Pre-treatment and in-vivo dosimetry of Helical Tomotherapy treatment plans using the dosimetry Check system

Dosimetry Check (DC) is the world's first commercially available software that provides patient-specific pre-treatment (PTD) and in-vivo transit (IVD) dose quality assurance of static and rotational intensity-modulated radiotherapy treatments. To investigate the feasibility of replacing pre-treatment verification with in vivo dosimetry for Helical Tomotherapy (HT), the commissioning and the application of the DC software was realised. Dose distributions were reconstructed from Mega Voltage Computed Tomography (MVCT) detectors, inside phantoms or patients for a total number of 6 treatment plans. Planned, reconstructed MVCT dose and measurements using ionisation chambers and a matrix detector inserted in cylindrical and octagonal phantoms, respectively, were compared at the isocenter and in two dimensions using the γ_2D and γ₁₀-index (3%/3 mm). The dose reconstruction PTD and IVD methods of DC software provided, compared to detector measurements and for three Quality Assurance (QA) plans, similar point dose deviations and γ_2D-index passing rates: (0.4 ± 0.1)% vs. (-1.4 ± 1.6)%, and (96.8 ± 0.9)% vs. (98.9 ± 0.6)%, respectively. In terms of γ₁₀-index passing rate, PTD and IVD modalities reached mean values of (99.3 ± 0.1)% and (97.2 ± 1.9)%, respectively. Also for the remaining three clinical plans, similar results were reached for IVD with γ₁₀-index passing rate reaching mean values of (95.9 ± 3.4)%. Therefore, either the PTD and the IVD verification modalities proved to be a very promising tool for the patient-specific QA of HT Plans.