Session Item

Deep inspiration breath-hold (DIBH) is an established technique to reduce cardiac doses in radiotherapy of left-sided breast cancer (LSBC). Here, first results using a laser beam based distance sensor - the Anzai AZ-733VI Respiratory Gating system - are presented.

Twelve patients with LSBC were included in this retrospective study. All patients received adjuvant whole breast DIBH radiotherapy with 15 x 2.67 Gy. Planning CTs were performed in free breathing (fb) and DIBH. For both scans 3D conformal radiotherapy treatment plans with opposing tangential fields and additional segments were calculated. For each patient the laser sensor was positioned anterior to the xyphoid and the vertical chest movement was measured during the planning CT and every treatment. The distances were plotted as respiration curves in the gating system. Patients were instructed for DIBH during setup (portal imaging or cone beam CT) and irradiation. Treatment beam was triggered by the gating system when the DIBH amplitude reached the predefined gating window. Data of the respiratory curves were extracted from the gating software and analyzed using an in-house developed Python script. Means and standard deviations were calculated for every breath-hold. For evaluation of intrafraction stability, the maximum difference between the mean DIBH amplitudes of every fraction was calculated. Regarding interfraction variability, we evaluated the maximum difference of mean DIBH amplitudes per patient. Comparison of mean DVH parameters was done by using Mann-Whitney-U test, with p-values < 0.05 regarded as significant.

Median patient age was 51.3 years. Tumor stage was pTis in 1, pT1 in 10, pT2 in 1 and pN0 in 12 patients. In total 177 fractions and 647 mean DIBH amplitudes during setup and beam delivery were evaluable. The mean width of the gating window was 4.4 ± 0.7 mm. The mean vertical chest movement between fb and DIBH in planning CT was 14.7 ± 1.9 mm (measured on CT-scans). The mean DIBH amplitude of the respiration curves was 15.2 ± 2.4 mm during setup and treatment, respectively. Before treatment, patient setup corrections were performed in 39 % of fractions. After instruction for DIBH, the amplitude reached the gating window in 85.1 % and was held in 88.2 % of breath-holds during treatment. Intrafraction stability testing showed a mean value over all fractions of 1.0 ±0.6 mm. For interfraction variability the maximum difference in DIBH amplitudes across all patients was 3.3 ± 1.2 mm in average. Cardiac doses were significantly reduced with DIBH: Dmean heart 1.2 Gy vs. 2.2 Gy, Dmax heart 16.7 Gy vs. 36.9 Gy, Dmean LAD 3.1 Gy vs. 9.0 Gy, D2% LAD 6.9 Gy vs. 25.4 Gy; (p<0.01, for all comparisons).

DIBH radiotherapy for LSBC using a laser distance sensor based gating system could significantly reduce heart doses. The interfraction variability was not negligible in our cohort. However, with a high intrafraction stability and a setup procedure a safe treatment was possible.