Session Item

This study present a comprehensive Plan Quality [1] assessment of ultrahypofractionation of adjuvant radiation therapy (RT) following primary surgery in women affected by early breast cancer (EBC) [2], using Volumetric Arc Radiation Therapy (VMAT) and Deep Inspiration Breath Hold (DIBH). To evaluate the treatment plan quality we calculated Dose metrics, Robustness, Plan Complexity metrics and Delivery Time.

A total of 50 consecutive patients were selected to be treated with VMAT DIBH technique. All of them were able to comply with the requirement for DIBH, monitored by Varian Respiratory Gating System. ESTRO guidelines for the clinical target volume (CTV) delineation and FAST-FORWARD protocol for CTV to planning target volume (PTV) margin definition were followed. Total prescribed dose was 26 Gy in five fractions. Before plan approval, for each patient a comparison with tangential static field IMRT (SF) was carried out to assess feasibility and safety of VMAT plan. VMAT arc arrangement consist in two Arcs (6MV - FFF, maximum dose rate: 1400 MU/minute) completely blocked, apart the first and last 30° of rotation, collimators are rotated of ± 10–20°, and the dose distribution was computed with AcurosXB v.13.7. Relevant dose metrics for heart, left anterior descending (LAD) coronary artery, lungs, contra-lateral breast and PTV were analyzed. Plan complexity metrics for VMAT plans were extracted to track reference values for further and future comparison. [3] Robustness of plans were assessed using the built-in tool in Varian Eclipse Treatment Planning System, by estimating perturbed doses induced by patient setup offset in the range of 4 mm. The plan quality metrics of the different delivery strategies were compared through two‐tailed paired Student’s t‐test, with a significance level of 0.05, once their normality was ensured.

PTV coverage comparison between SF and VMAT plans showed significant increases for coverage (P<0.05) in VMAT technique; no statistically significant differences were observed regarding target homogeneity index, contra-lateral breast and lung DVHs. For organs at risks (OAR), statistically significant differences (P<0.05)  were  observed in terms of better ipsi-lateral lung V10% with SF, and of heart V20% and LAD maximum and mean dose with VMAT. Robustness analysis showed that the perturbed doses were less variable for VMAT than SF plans (P<0.05) in terms of target coverage, maximum and mean dose to OARs. Total number of MU was lower for VMAT for each patient, and mean delivery time (equal to breath old period for each patient) was lower for VMAT than SF plans: 62.5 ± 8.2 seconds vs 78.5  ± 9.8 seconds.

This study showed that VMAT DIBH treatments are safe in the framework of 1-week hypofractionated treatments for left EBC, without compromising patient compliance in terms of session duration.

[1] doi.org/10.1016/j.radonc.2020.09.038 0167-8140
[2] doi.org/10.1016/ S0140-6736(20)30932-6
[3] doi.org /10.1002/acm2.12908