Master of Science (MS)
Physics and Astronomy
Purpose: The present work investigates the impact of intrafraction motion of the chest wall due to respiration on Post Mastectomy Radiotherapy (PMRT) with TomoTherapy. The hypothesis of this work is that the impact of intrafraction motion on TomoTherapy PMRT will be insignificant as (1) the largest intrafraction movement of the chest wall (CW) in the medial-lateral, anterior-posterior, and superior-inferior dimensions will not exceed 1 cm and (2) that 95% of in-vivo CW point doses on the patient surface will be within 5% of calculated dose and all doses within 10% of calculated dose. Methods: 4DCT scans were acquired and intrafraction motion of the CW near mastectomy scar was analyzed for 5 PMRT TomoTherapy patients. In-vivo patient CW dose measurements, acquired for clinical purpose using TLD were analyzed. Measured dose was compared to the TomoTherapy calculated dose. Daily MVCT images were collected and the correlation between the amount of air cavity between CW skin and the bolus and the dose difference between TLD measured and calculated dose was studied for each patient. Surface dose measurement using a CW anthropomorphic phantom was performed to add confidence to the patients’ data. Results: The maximum anterior posterior (ant-pos) CW movement of our five patients did not exceed 0.15 cm. 28% of the TLD measured doses differed from the calculated dose by more than 5%, and 2% of all data differed from the calculated dose by more than 10%. Slight positive correlation between air cavity between bolus and the CW surface and measured dose difference was observed for both patients’ and phantom data. Conclusions: The result of this work indicates that the impact of intrafraction motion on TomoTherapy PMRT will be insignificant. Discrepancies between TLD measured CW point dose and calculated dose, but overall, the average dose differences were within 5%. Air cavities created between the bolus and the CW may impact on cause underdosing of the CW surface.
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Ito, Shima, "Impact of intrafraction motion on post-mastectomy TomoTherapy of the chest wall" (2009). LSU Master's Theses. 144.