Purpose: TomoTherapy uses Megavoltage CT (MVCT) to verify patient position and alignment prior to treatment and it is usually good enough to verify the patient's position and anatomy prior to treatment. However, sometimes, a greater resolution and contrast in patient images obtained by the MVCT scan would be beneficial in verifying patient anatomy and set‐up. The effects of changing different machine parameters and consequently the signal to noise ratio (SNR) had on MVCT image quality and resolution were studied. Method and Materials: The machine parameters were changed in two ways and their effects on MVCT image quality were studied, first by imaging with different doses, and then with different beam energies. A cylindrical phantom with a resolution plug (different size holes) was scanned. The machine pulse amplitude control (PAC) value was varied in intervals to adjust delivered dose and the resulting images were analyzed. CTDI measurements were then made at each of the varying PAC values. A Catphan phantom was imaged to measure low contrast visibility, uniformity, and spatial resolution. Next, the injector current (INJI) was changed to modify the MVCT beam energy. The cylindrical phantom was scanned again and the Catphan phantom tests were repeated Results: Increasing the PAC value leads to an increase in dose. In observing the images that were taken, it can be see that the resolution and quality of the image improves as the PAC value is increased. Also the low contrast visibility and uniformity of the images improve. The images were not noticeably improved as much for changes to INJI as measured visually or by imaging tests. Conclusion: Slightly higher dose during a MVCT scan can improve the image quality and resolution for the TomoTherapy system. These observations will be used in future investigation of more complex imaging tasks to improve MVCT imaging.

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Purpose: Intensity Modulated Arc Therapy (IMAT) is gaining widespread attention from various radiation oncology vendors and several centers are implementing them clinically. The aim of this study is to compare Plan quality between Rapid Arc (Varian), Volumetric Modulated Arc Therapy (Elekta) and Smart Arc (Pinnacle) for the same dataset and plan objectives. Methods: 3 anonymized prostate cancer cases with the same DICOM RT structure set were used to compare between the 3 IMAT delivery schemes. The Rapid Arc plans were generated using Eclipse Treatment Planning System (TPS), the VMAT plans were generated using MONACO TPS, and the Smart Arc plans were generated using Pinnacle TPS. The Dose Volume Histograms (DVH) was exported for each plan and plotted together to compare the DVH between 3 different TPS for each patient. In each case the plan objectives were kept the same. Also, the RT dose files were compared from the 3 different delivery methods by importing them into a 3rd party software. Results: To achieve the same plan quality, the Rapid Arc plans were generated using 2 arcs. There was no substantial improvement in plan quality when 2 arcs were used in VMAT plans using MONACO, therefore plans were generated using only one 360 degree arc for both VMAT and Smart Arc plans. The VMAT plans have more dose heterogeneity across the target volume while organs at risk sparing varied depending on the case. The Smart Arc plans had the lowest total monitor units among the 3 delivery methods while the Rapid Arc plans had the largest because 2 arcs were needed to achieve same plan quality.Conclusion: All 3 IMAT methods produced acceptable plans for Prostate IMRT. The relative strengths of each system varied depending on the complexity of the case and there is a trade off between each delivery method.

Purpose: TomoTherapy uses Megavoltage CT (MVCT) to verify patient position and alignment prior to treatment and it is usually good enough to verify the patient's position and anatomy prior to treatment. However, a greater resolution and contrast in patient images obtained by the MVCT scan would be beneficial in verifying patient anatomy and set‐up. The effects that changing the MVCT dose and consequently the signal to noise ratio (SNR) had on MVCT image quality and resolution were studied. Method and Materials: A “cheese” phantom with a resolution plug (different size holes) was scanned. The machine pulse amplitude control (PAC) value was varied in intervals from 2.22 to 3.34 to adjust delivered dose and the resulting images were analyzed. The dose was measured with an A1SL ion chamber at the clinically used PAC value of 2.78 to be 2 cGy, 0.4 cGy at a Pac value of 2.22 and 3.8 cGy at a PAC value of 3.34. Results: Increasing the PAC value leads to an increase in both dose and energy. In observing the images that were taken, it can be see that the resolution and quality of the image improves as the PAC value is increased. When comparing the MVCT image taken at the normal PAC value of 2.78 and an increased PAC value of 3.34, the smaller diameter density plug holes can be seen more clearly, the contrast between the holes and the cheese phantom are more sharply defined, and the holes appear more concentric for the image taken at PAC 3.34. Conclusion: Slightly higher dose during an MVCT scan can improve the image quality and resolution for the TomoTherapy system. These observations will be used in future investigation of more complex imaging tasks to improve MVCT imaging. Conflict of Interest: Main author is an employee of TomoTherapy, Inc.