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ESTRO 2020

Session Item

Physics track: Dose measurement and dose calculation
9319
Poster
Physics
00:00 - 00:00
Commissioning of Tomotherapy treatment planning in RayStation
Kai Schubert, Germany
PO-1411

Abstract

Commissioning of Tomotherapy treatment planning in RayStation
Authors: Jürgen Debus.(University Hospital Heidelberg, Department of Radiotherapy and Radiation Oncology, Heidelberg, Germany), Sinem Erdem.(University Hospital Heidelberg, Department of Radiotherapy and Radiation Oncology, Heidelberg, Germany), Dieter Oetzel.(University Hospital Heidelberg, Department of Radiotherapy and Radiation Oncology, Heidelberg, Germany), Kai Schubert.(University Hospital Heidelberg, Department of Radiotherapy and Radiation Oncology, Heidelberg, Germany), Clemens Weinmann.(University Hospital Heidelberg, Department of Radiotherapy and Radiation Oncology, Heidelberg, Germany), Xenia Wester.(University Hospital Heidelberg, Department of Radiotherapy and Radiation Oncology, Heidelberg, Germany)
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Purpose or Objective

Before using RayStation (RS) as an independent treatment planning option for Tomotherapy (Tomo) units, a unique beam modelling and commissioning process has to be performed. All Tomo systems are calibrated according to a gold standard, which contains the basic beam information, while an individual calibration of the MLC characteristic and the output is added at the end of installation. The Tomo machine has a specific treatment couch, which needs to be considered during dose calculation. Since the calculation of open beams configurations is not possible, special attention has to be paid to individual plan verifications. Here measurements with a two dimensional array and calculations with an independent Monte Carlo algorithm were used.

Material and Methods

After the beam model was imported from Precision 2.0.0.1 (Accuray) into RS 8B (RaySearch) the ‘gold standard beams’ were recalculated in the RayPhysics module. As a next step the ‘Tomo couch’ needed to be modelled. Here 3 TomoDirect plans for the Tomo ‘Cheesephantom’ with gantry angels of 0°, 180° (complete couch) and 130° (only thru the upper pallet) were calculated in Precision and imported into RS. While Precision is importing the Tomo couch into the planning CT, RS is importing a structure set with an upper and a lower pallet. The densities of the pallets were adjusted, till all 3 treatment plans showed the same dose deviation from the Precision calculation.

The Tomo calibration plans were imported from Precision into RS and recalculated.  The differences in dose were used to tune the dose normalization and the jaw output factors of the beam model. Finally new calibration plans were generated in RS and measured in the Cheesephantom.

For the first 22 patients plan QA was performed with the Octavius detector 729 and a local gamma analysis was performed with a 3%/3mm criteria and a threshold of 10% of the dose. Additionally an independent Monte Carlo dose calculation was executed on the patient CT using SciMoCa (ScientificRT). Here a local gamma criteria of 3%/1mm with a threshold of 50% was used for the whole patient and for the target volume.

Results

Profiles and depth dose curves in the RayPhysics module were in good agreement.

A density of 0.65g/cm³ for the upper pallet and of 1.1 g/cm³ for the lower pallet of the TomoCouch was determined. The deviation in the calculation between RS and Precision was 1% for the 3 TomoDirect plans.

For the Precision calibration plans deviations of 0.9%, 0.75% and 1.35% were yield for the field lengths of 1cm, 2.5cm and 5cm. The measurements of the RS calibration plans after the adjustment of the beam model were in good agreement with the calculations (-0.17% and 0.71% deviation).

Plan QA passed for all patients with a mean passrate of 98.9% for the measurements and 96.9% for the MC calculations in the whole patient, respectively 99.3% for the target. Results are shown in the graph.

Conclusion

The commissioning of RS for Tomo treatment planning showed no major deviations, including plan QA.