Application of retrospective data analysis to clinical protocol design: can the potential benefits of breath-hold techniques for breast radiotherapy be assessed without testing on patients?

The advantages, in terms of heart dose sparing, resulting from using a breath-hold technique when treating supine left breast radiotherapy patients are widely accepted, and increasing numbers of radiotherapy departments are implementing breath-hold techniques. However, due to differences in patient setup and treatment planning protocols between radiotherapy departments, it is important to assess the benefits of using a breath-hold technique within each department, before or during implementation. This study investigated the use of retrospective analysis of past patient treatment plans, as a means to identify the potential for breath-hold techniques to benefit patients. In-house "Treatment and Dose Assessor" code was used to complete a bulk retrospective evaluation of dose-volume metrics for 708 supine and 13 prone breast and chest wall radiotherapy treatments, that were planned using the same clinical protocols, which did not utilise a breath hold technique. For supine patients, results showed statistically significant differences between heart doses from left and right breast treatment plans, in the absence of significant differences between lung doses from left and right breast treatment plans, confirming the potential benefit of using a breath-hold technique for supine left breast radiotherapy patients. Fewer than 1% of the right breast treatment plans showed heart doses high enough to suggest a possible benefit from using a breath-hold technique. Approximately 50% of the prone left breast treatment plans included very low heart doses without intervention, and may therefore have shown no noticeable dosimetric benefit from the use of a breath hold. This study demonstrated the extent of information that can be obtained using retrospective data analysis, before or instead of obtaining multiple CT images of patients and completing a process of dual planning and prospective dose evaluation.