We present treatment planning methods based on four-dimensional computed tomography (4D-CT) to incorporate tumour motion using (1) a static field and (2) a dynamic field. Static 4D fields are determined to include the target in all breathing phases, whereas dynamic 4D fields are determined to follow the shape of the tumour assessed from 4D-CT images with a dynamic weighting factor. The weighting factor selection depends on the reliability of patient breathing and limitations of the delivery system. The static 4D method is compared with our standard protocol for gross tumour volume (GTV) coverage, mean lung dose and V20. It was found that the GTV delineated on helical CT without incorporating breathing motion does not adequately represent the target compared to the GTV delineated from 4D-CT. Dosimetric analysis indicates that the static 4D-CT based technique results in a reduction of the mean lung dose compared with the standard protocol. Measurements on a moving phantom and simulations indicated that 4D radiotherapy (4D-RT) synchronized with respiration-induced motion further reduces mean lung dose and V20, and may allow safe application of dose escalation and CRT/IMRT. The motions of the chest cavity, tumour and thoracic structures of 24 lung cancer patients are also analysed.

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A first-time survey across 15 cancer centers in Ontario, Canada, on the current practice of patient-specific quality assurance (PSQA) for intensity modulated radiation therapy (IMRT) and volumetric modulated arc therapy (VMAT) delivery was conducted. The objectives were to assess the current state of PSQA practice, identify areas for potential improvement, and facilitate the continued improvement in standardization, consistency, efficacy, and efficiency of PSQA regionally. The survey asked 40 questions related to PSQA practice for IMRT/VMAT delivery. The questions addressed PSQA policy and procedure, delivery log evaluation, instrumentation, measurement setup and methodology, data analysis and interpretation, documentation, process, failure modes, and feedback. The focus of this survey was on PSQA activities related to routine IMRT/ VMAT treatments on conventional linacs, including stereotactic body radiation therapy but excluding stereotactic radiosurgery. The participating centers were instructed to submit answers that reflected the collective view or opinion of their department and represented the most typical process practiced. The results of the survey provided a snapshot of the current state of PSQA practice in Ontario and demonstrated considerable variations in the practice. A large majority (80%) of centers performed PSQA measurements on all VMAT plans. Most employed pseudo-3D array detectors with a true composite (TC) geometry. No standard approach was found for stopping or reducing frequency of measurements. The sole use of delivery log evaluation was not widely implemented, though most centers expressed interest in adopting this technology. All used the Gamma evaluation method for analyzing PSQA measurements; however, no universal approach was reported on how Gamma evaluation and pass determination criteria were determined. All or some PSQA results were reviewed regularly in twothirds of the centers. Planning related issues were considered the most frequent source for PSQA failures (40%), whereas the most frequent course of action for a failed PSQA was to review the result and decide whether to proceed to treatment.

We have developed a four-dimensional weighted radiotherapy (4DW-RT) technique. This method involves designing the motion of the linear accelerator beam to coincide with the tumour motion determined from 4D-CT imaging while including a weighting factor to account for irregular motion and limitations of the delivery system. Experiments were conducted with a moving phantom to assess limitations of the delivery system when applying this method. Although the multi-leaf collimator motion remains within the tolerance of the linear accelerator, the extent of motion was less than 1 mm larger than the designed one, and there was a net system latency of approximately 0.2 s. The dose distributions were measured and simulated using different weighting factors and motion scenarios. The breathing characteristics (period, extent of motion, drift and standard deviations) of 32 patients were evaluated using the Varian RPM system. Breathing variability was assessed by plotting the average breathing motion as a function of the breathing phase. Simulations were carried out to determine the optimal weighting factor based on typical patient breathing characteristics. These results establish that the 4DW-RT method demonstrates potential for dose escalation without increasing exposure to healthy tissue.

Purpose: Respiratory motion introduces uncertainties during CT and radiation therapy delivery. Reliable equipment and quality assurance (QA) techniques must be established to assess and overcome these uncertainties. Our goal was to validate the performance of a programmable motion phantom for QA and to demonstrate the dosimetric impact of breathing motion on treatment delivery. Method and Materials: The “Quasar” phantom (Modus Medical, London, ON) was assessed for suitability in QA procedures for radiation therapy involving respiratory motion. The phantom is equipped with a programmable unit, which introduces motion to cylindrical lung inserts. We tested the standard mode of motion and the “oscillation” mode, in which patient breathing profiles are imported and reproduced. Phantom motion reproducibility and accuracy were assessed using the Varian Real‐time Position Management (RPM) system and video for the extreme breathing periods (1 and 15seconds) and a patient representative breathing period of 4seconds. An in‐house designed cedar lung insert was built containing a target (4cm by 7cm). Film is placed in the insert to assess the dose distribution under phantom motion from static and dynamic delivery under phantom motion. The dynamic MLC treatment delivery was synchronized with target motion. Results: Using the RPM system, percent differences between the intended and actual periods for each were 0.57%, −1.70% and −0.22% respectively. When the amplitude was changed from 2cm to 1cm, the measured period did not change. Comparison of the breathing profiles in oscillation mode with profiles generated using the RPM system shows a close correspondence, with slight divergence at extreme direction or speed variation. Dose distribution for a phantom motion of 2cm peak‐to‐peak and period of 3.2sec along the moving direction indicates significant broadening of (80–20%) penumbra for static delivery (1.67cm) compared to dynamic delivery (0.80cm) Conclusion: The Quasar phantom is suitable for QA and dosimetric measurements of moving targets.