Reproducibility and stability of spirometer-guided deep inspiration breath-hold in left-breast treatments using an optical surface monitoring system.

The aim of this study was to evaluate the reproducibility and stability of left breast positioning during spirometer-guided deep-inspiration breath-hold (DIBH) radiotherapy using an optical surface imaging system (AlignRT). The AlignRT optical tracking system was used to monitor five left-sided breast cancer patients treated using the Active Breathing Coordinator spirometer with DIBH technique. Treatment plans were created using an automated hybrid-VMAT technique on DIBH CTs. A prescribed dose of 60 Gy to the tumor bed and 50 Gy to the breast in 25 fractions was planned. During each treatment session, the antero-posterior (VRT), superior-inferior (LNG), and lateral (LAT) motion of patients was continuously recorded by AlignRT. The intra-breath-hold stability and the intra- and inter-fraction reproducibility were analyzed for all breath-holds and treatment fractions. The dosimetric impact of the residual motion during DIBH was evaluated from the isocenter shifts amplitudes obtained from the 50%, 90%, and 100% cumulative distribution functions of intra-fractional reproducibility. The positional variations of 590 breath-holds as measured by AlignRT were evaluated. The mean intra-breath-hold stability during DIBH was 1.0 ± 0.4 mm, 2.1 ± 1.9 mm, and 0.7 ± 0.5 mm in the VRT, LNG, and LAT directions, with a maximal value of 8.8 mm in LNG direction. Similarly, the mean intra-breath-hold reproducibility was 1.4 ± 0.8 mm, 1.7 ± 1.0 mm, and 0.8 ± 0.5 mm in the VRT, LNG, and LAT directions, with a maximal value of 4.1 mm in LNG direction. Inter-fractional reproducibility showed better reliability, with difference in breathing levels in all fractions of 0.3 mm on average. Based on tolerance limits corresponding to the 90% cumulative distribution level, gating window widths of 1 mm, 2 mm, and 5 mm in the LAT, VRT, and LNG directions were considered an appropriate choice. In conclusion, despite the use of a dedicated spirometer at constant tidal volume, a non-negligible variability of the breast surface position has been reported during breath-holds. The real-time monitoring of breast surface using surface-guided optical technology is strongly recommended.

Automated hybrid volumetric modulated arc therapy (HVMAT) for whole-breast irradiation with simultaneous integrated boost to lumpectomy area : A treatment planning study.

PURPOSE: To develop an automated treatment planning approach for whole breast irradiation with simultaneous integrated boost using an automated hybrid VMAT class solution (HVMAT). MATERIALS AND METHODS: Twenty-five consecutive patients with left breast cancer received 50 Gy (2 Gy/fraction) to the whole breast and an additional simultaneous 10 Gy (2.4 Gy/fraction) to the tumor cavity. Ipsilateral lung, heart, and contralateral breast were contoured as main organs-at-risk. HVMAT plans were inversely optimized by combining two open fields with a VMAT semi-arc beam. Open fields were setup to include the whole breast with a 2 cm flash region and to carry 80% of beams weight. HVMAT plans were compared with three tangential techniques: conventional wedged-field tangential plans (SWF), field-in-field forward planned tangential plans (FiF), and hybrid-IMRT plans (HMRT). Dosimetric differences among the plans were evaluated using Kruskal-Wallis one-way analysis of variance. Dose accuracy was validated using the PTW Octavius-4D phantom together with the 1500 2D-array. RESULTS: No significant differences were found among the four techniques for both targets coverage. HVMAT plans showed consistently better PTVs dose contrast, conformity, and homogeneity (p < 0.001 for all metrics) and statistically significant reduction of high-dose breast irradiation. V55 and V60 decreased by 30.4, 26.1, and 20.8% (p < 0.05) and 12.3, 9.9, and 6.0% (p < 0.05) for SWF, FIF, and HMRT, respectively. Pretreatment dose verification reported a gamma pass-rate greater than the acceptance threshold of 95% for all HVMAT plans. In addition, HVMAT reduced the time for full planning optimization to about 20 min. CONCLUSIONS: HVMAT plans resulted in superior target dose conformity and homogeneity compared to other tangential techniques. Due to fast planning time HVMAT can be applied for all patients, minimizing the impact on human or departmental resources.