Since the publication of AAPM Task Group (TG) 148 on quality assurance (QA) for helical tomotherapy, there have been many new developments on the tomotherapy platform involving treatment delivery, on-board imaging options, motion management, and treatment planning systems (TPSs). In response to a need for guidance on quality control (QC) and QA for these technologies, the AAPM Therapy Physics Committee commissioned TG 306 to review these changes and make recommendations related to these technology updates. The specific objectives of this TG were (1) to update, as needed, recommendations on tolerance limits, frequencies and QC/QA testing methodology in TG 148, (2) address the commissioning and necessary QA checks,as a supplement to Medical Physics Practice Guidelines (MPPG) with respect to tomotherapy TPS and (3) to provide risk-based recommendations on the new technology

Dynamic jaw delivery on the TomoTherapy H‐series platform, entitled TomoEDGE™, is an effective tool to decrease the patient dose along the superior and inferior edges of the treatment target. The aperture of the TomoTherapy jaws, that is, field width (FW), defines the longitudinal dose profile. A consistent FW dose profile is an important quantity for accurate and reproducible dose delivery in TomoTherapy. To date, no evaluation has been made of the accuracy and precision of the dose profiles produced by dynamic jaws. This study aims to provide a long‐term evaluation of the dynamic jaw FW dose profiles obtained on TomoTherapy utilizing the TomoTherapy Quality Assurance procedure (TQA). A total of 840 dose profiles were measured during 84 TQA procedures, performed over a 2‐yr period. The full width at half maximum (FWHM) and constancy of the FW dose profile measurements were analyzed and compared with the tolerances proposed by AAPM Task Group 148 (TG‐148) and those used by the manufacturer. The FWHM evaluation showed that the FWs > 2.0 cm respect the TG‐148 tolerance of 1%, while the asymmetric FWs ≤ 2.0 cm were outside the limit in 17.3% of measurements. Constancy results evaluated along the full profiles showed that 95.2% of measurements were within 3% of the baseline for symmetric FWs and 94.8% of measurements were within 4% of the baseline for asymmetric FWs. In conclusion, the analysis confirms the accuracy and precision of TomoEDGE™ technology in jaw positioning. This study has identified the potential to establish an appropriate QA tolerance for the asymmetric FWs used in dynamic jaw movement. Finally, the clinical significance of the observed discrepancies should be studied further to understand the dosimetric effect on patient treatments.

Purpose: To demonstrate that μm‐scale signal extraction from Gafchromic EBT2 and EBT3 films can be used for accurate film calibration and point measurement. Methods: Absolute dose measurements were made using Gafchromic EBT2 and EBT3 films. The films were cut to rough squares of approx. 1–2mm. A film calibration was performed using solid water slabs with an Exradin A1SL ion chamber (IC), and irradiating 6 doses ranging from 15cGy to 400cGy. Each dose level was measured with a 5‐film sample and the sample mean was used as a single point. A ROI sample of 200x200 pixels (∼400×400μm2) was used in signal extraction for all measurements. The dosimetry method was verified with a set of 10 absolute dose measurements using an open‐field irradiation on a flat phantom. The film results were compared to IC measurements and TPS calculation. Results: The EBT2 verification set measured a mean absolute dose of 193.4cGy (σ=1.4cGy) while the IC measured an absolute dose of 190.7cGy. The EBT3 verification set measured a mean absolute dose of 192.1cGy (σ=0.7cGy) while the IC measured an absolute dose of 191.8cGy. The TPS calculated a dose of 191.7cGy. Uncertainty in film measurement increases from 1.4cGy to 2.7cGy for EBT2 and from 0.7cGy to 1.5cGy for EBT3 if a single film is used instead of a 5‐film sample. Conclusion: Submillimeter dose measurement with EBT2 and EBT3 films is shown to be very accurate. The difference in absolute dose observed in EBT2 measurements with respect to the IC readings could be due to a variation in scanner response from the time of film calibration. EBT3 shows much better precision than EBT2 with an uncertainty of 0.7cGy compared to 1.4cGy. Signal extraction from such a small spatial area allows for accurate measurement in small‐fields, steep dose gradients, and non‐flattened beams.

Purpose: To determine the effective depth of measurement for Gafchromic EBT2 and EBT3 filmsMethods: Absolute dose point measurements were made with EBT2 and EBT3 film on the surface of flat phantom and at various depths. The films were cut to an approx. 1–2 mm square size and placed on the beam central axis. Measurements with an Exradin A1SL ion chamber were performed for each irradiation. A dose of 1 Gy was delivered to Dmax=1.5 cm. A previously validated Monte Carlo (MC) model was used for simulation and comparison to measurements. The MC simulation data was collected at 0.1 mm steps along the beam central axis. Film measurements were converted to dose using a post‐irradiation signal consisting of the red and blue color channels from an Epson Expression 10000XL scanner. Film analysis was performed using ImageJ software and MATLAB. Measurements were converted to PDD and then compared to MC data to determine an effective depth of film measurement. Results: EBT2 measurements showed a systematic upstream shift of 0.10 mm with respect to the MC data while EBT3 showed the shift to be slightly less at 0.07 mm. The error in film measurement was estimated to be 0.04 mm (2σ). All measurements were within one STD of the MC error of 0.33 mm. Conclusion: The PDD measurements of EBT2 and EBT3 were consistent amongst themselves and agreement with MC was excellent. The observed shift in the results and the measurement error are smaller than the error in MC data, a possible indication that the nominal depth of measurement can be considered as the effective depth of measurement. A study with more accurate geometry for comparison is needed to determine a conclusive depth of measurement.

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