Respiratory and Breath Hold Motion in Contemporary Breast Irradiation: Dosimetric Impact and Management Techniques
Abstract
Radiation therapy breast treatment plans are developed using a static computed tomography image that does not account for intrafraction motion during treatment. Motion during breast radiotherapy can result in suboptimal plan quality, decreased target coverage, and increased dose to organs at risk. This thesis examines two sources of respiratory motion during breast radiotherapy: (1) free-breathing motion, and (2) residual motion during deep inspiration breath hold. The effect of free-breathing motion was examined for external beam accelerated partial breast irradiation (APBI). Using existing volunteer respiratory motion data and patient APBI treatment plans, a population-based margin formula based on respiratory motion amplitude was derived.
Deep inspiration breath hold (DIBH) is used in breast radiotherapy to alter patient anatomy during treatment and subsequently reduce heart dose. We conducted a planning study demonstrating that DIBH provides the most cardiac dose sparing benefit for patients receiving locoregional irradiation including the internal mammary chain (IMC) nodes. DIBH is a difficult manoeuvre to achieve and maintain, and the associated uncertainties may be larger than conventional free-breathing treatments. The positional uncertainties of the breast and heart were characterized for a low-resource, manually-gated DIBH technique. We found that the manual technique had larger positional uncertainties than more resource-intensive gating methods; however, the dosimetric impact of these larger uncertainties was unknown. To determine the dosimetric impact of breath hold level variance on locoregional DIBH treatments, we conducted a study to collect patient residual DIBH motion data over a treatment course. These data were used in a motion escalation modelling study with the aim of determining the impact of increasing residual DIBH motion on target coverage, cardiac dose, and plan quality. We found that intrafractional residual breath hold motion has minimal effect on heart dose and target coverage for most patients; however, coverage can be degraded for even small DIBH uncertainties in the posterior direction. This can be mitigated by adapting processes to reduce shallow breath hold errors and/or accounting for known errors in planning. The results from the investigations presented in this thesis have led to change in clinical practice at our centre.
Description
Keywords
Biophysics--Medical, Oncology, Physics--Radiation
Citation
Conroy, L. (2017). Respiratory and Breath Hold Motion in Contemporary Breast Irradiation: Dosimetric Impact and Management Techniques (Doctoral thesis, University of Calgary, Calgary, Canada). Retrieved from https://prism.ucalgary.ca. doi:10.11575/PRISM/27648