Room: Exhibit Hall | Forum 4
Purpose: To compare treatment plan quality of VMAT and 3D-CRT radiotherapy plans of left-sided post-mastectomy cancer patients with internal-mammary(IM), supraclavicular(S/C), and axillary(AX) nodes using continuous-positive-airway-pressure(CPAP) for patients who were not eligible for deep-inspiration-breath-hold(DIBH).
Methods: Two left-sided post-mastectomy cancer patients were selected for this preliminary study. Single-isocenter VMAT and 3D-CRT plans were generated with CPAP image sets. A single physician contoured all the PTVs (chest-wall (CW), IM, S/C and AX nodes) and reviewed treatment plans following RTOG 1304 guidelines. The 4-field 3D-CRT photon only plan consisted of two Field-in-Field tangential fields covering PTV-CW and IMN, and anterior-posterior fields covering other PTV-RLN. VMAT plan was optimized using four 180Â° partial -arcs (two clockwise and two counter-clockwise; gantry angle 310Â°-130Â°) to encompass PTVs with involved nodes with 30Â° or 330Â° collimator angles. The prescribed dose was 50 Gy in 25 fractions without boost dose.
Results: By using CPAP, patientâ€™s thorax was inflated, there was an increase in the ipsilateral lung volume by 30% or more, and the heart was displaced from the chest-wall. Both CPAP VMAT and 3D-CRT plans showed comparable PTV coverages and clinically acceptable per RTOG. The mean heart doses were below 5Gy in both plans. Heart doses were lower in 3D-CRT plans compared to VMAT plans, however. The average mean heart dose was 1.88Â±1.43Gy for 3D-CRT and 4.65Â±0.25Gy for VMAT plans. VMAT plans showed lower radiation dose to lung compared to 3D-CRT plans. The mean ipsilateral lung dose was 17.98Â±0.04Gy vs. 14.83Â±0.58Gy, and V20Gy was 35.64Â±0.63% vs. 26.50Â±3.09% for 3D-CRT and VMAT, respectively. The mean total lung dose was 8.84Â±0.56Gy for 3D-CRT vs. 8.69Â±0.49Gy for VMAT plans.
Conclusion: Depending on the clinical priority of sparing heart or lung, either single isocenter VMAT or 3D-CRT plans with CPAP could be an alternative technique to treat post-mastectomy cancer patients with regional nodes.