Session Item

Radiation therapy (RT) for high-risk breast cancer includes the treatment of the breast or the chest wall (CW) and III and IV axillary lymph nodes levels (III-IV) and, in some cases, of the internal mammary nodes (IMN). However, treating such large and complex target volumes using conventional conformal RT or multi-field IMRT is not straightforward and may lead to suboptimal solutions.

In our Institution, we treat patients with large and complex targets and unfavourable anatomies using Helical TomoTherapy (HT) when clinical goals are not achieved with standard techniques. With HT we obtain good plan quality, although delivery times are long and planning workload is time-consuming.

In this study, a fully automatic VMAT technique (AP-VMAT) was developed to obtain plans at least of the same quality as clinical HT plans.

Twenty-five consecutive patients who received postoperative RT (50Gy in 25 fractions) using HT were replanned with AP-VMAT. The patient set was heterogeneous in target selection and included: 9 left and 5 right CW plus III-IV nodes, 2 left and 7 right CW and III-IV plus IMN irradiation, 1 left and 1 right breast and III-IV with simultaneous integrated boost (SIB 57Gy in 25 fractions).

AP-VMAT plans were obtained with a novel system for fully automated multi-criterial generation of deliverable VMAT plans implemented in Monaco TPS (M-AP) and based on lexicographic multi-criterial optimization using wish-lists, not yet commercially available [1]. To reproduce the same quality of clinical plans, the objectives required for AP-VMAT technique were selected starting from HT plans statistics. A comparison of selected dosimetric parameters between HT and AP-VMAT was performed. A paired two-sided Wilcoxon’s signed-rank tests (significance level 0.05) was used for assessing statistical significance.

In figure 1 the mean doses for the organs at risk (OARs) for the two techniques are presented, together with the differences. Small gains can be observed for AP-VMAT compared to HT in all OARs except for the heart. In figure 2 the population mean DVHs for the two techniques are presented. Concerning PTVs, there are no statistically significant differences in V95% for PTV CW and PTV III-IV while an increase in coverage for PTV IMN is observed (p<0.05) in AP-VMAT plans compared to HT. Only slight modifications in the wish-list were necessary to incorporate for the differences in targets and doses. Planning times were reduced from the 6 hours on average for HT to 2 minutes for M-AP (excluding calculation time of about 1 hour, which does not require any user involvement).

A new fully automated technique was developed for breast/CW and nodal irradiation. Dosimetric plan parameters show that the AP-VMAT were similar or higher in quality than the clinical HT plans. M-AP was shown to be able to fully automate the planning process, importantly reducing planning workload. 

References:

1)       R.Bijman et al., Radioter and Oncol, 2021