Abstract
The purpose of this study was to compare the dosimetry of CG‐Darc with three‐dimensional conformal radiation therapy (3D CRT) and volumetric‐modulated arc therapy (RapidArc) in the treatment of breast cancer with APBI. CG‐Darc plans were generated using two tangential couch arcs combined with a simultaneous noncoplanar gantry arc. The dynamic couch arc was modeled by consecutive IMRT fields at 10° intervals. RapidArc plans used a single partial arc with an avoidance sector, preventing direct beam exit into the thorax. CG‐Darc and RapidArc plans were compared with 3D CRT in 20 patients previously treated with 3D CRT (group A), and in 15 additional patients who failed the dosimetric constraints of the Canadian trial and of NSABP B‐39/RTOG 0413 for APBI (group B). CG‐Darc resulted in superior target coverage compared to 3D CRT and RapidArc (V95%: 98.2% vs. 97.1% and 95.7%). For outer breast lesions, CG‐Darc and RapidArc significantly reduced the ipsilateral breast V50% by 8% in group A and 15% in group B (p<0.05) as compared with 3D CRT. For inner and centrally located lesions, CG‐Darc resulted in significant ipsilateral lung V10% reduction when compared to 3D CRT and RapidArc (10.7% vs. 12.6% and 20.7% for group A, and 15.1% vs. 25.2% and 27.3% for group B). Similar advantage was observed in the dosimetry of contralateral breast where the percent maximum dose for CG‐Darc, 3D CRT, and RapidArc were 3.9%, 6.3%, and 5.8% for group A and 4.3%, 9.2%, and 6.3% for group B, respectively (p<0.05). CG‐Darc achieved superior target coverage while decreasing normal tissue dose even in patients failing APBI dose constraints. Consequently, this technique has the potential of expanding the use of APBI to patients currently ineligible for such treatment. Modification of the RapidArc algorithm will be necessary to link couch and gantry rotation with variable dose rate and, therefore, enable the use of CG‐Darc in clinical practice.PACS number: 80
Highlights
162 Popescu et al.: Couch gantry arc in partial breast with partial breast radiotherapy fields are attractive alternative options
Based on the improved dosimetry achieved by volumetric-modulated arc therapy (VMAT) and continuous dynamic arc couch rotation (C-ARC) techniques, we developed an Accelerated partial breast irradiation (APBI) technique utilizing continuous couch and gantry dynamic arc therapy (CG-Darc)
Study patients were in two cohorts: Group A included 20 patients who were treated at our center with APBI under Randomized Trial of Accelerated Partial Breast Irradiation (RAPID) trial, and Group B consists of 15 patients who failed one or more dose constraints using 3D CRT and received whole breast radiation therapy (WBRT) because of trial ineligibility
Summary
162 Popescu et al.: Couch gantry arc in partial breast with partial breast radiotherapy fields are attractive alternative options These techniques shorten treatment duration from several weeks to one week, while reducing the high-dose radiation exposure of ipsilateral breast tissue and surrounding organs at risk (OARs) such as lung, heart, and contralateral breast. Initial efficacy results (locoregional control and toxicity) of RTOG 0319 using 3D CRT to deliver APBI(4) were comparable with other published studies with similar fallow-up. These preliminary data support continued accrual to APBI trials, and emphasize the need for further follow-up to fully evaluate long-term tumor control and late toxicity
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