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Comparison of Volumetric Modulated Arc Therapy (VMAT) and 3D Conformal Radiotherapy (3D-CRT) Treatment Planning for Left-Sided Post-Mastectomy Radiotherapy (PMRT) Including Regional Lymphatic Nodes (RLN) with Continuous Positive Airway Pressure (CPAP)

S Hossain1,2*, W Kil1, T Pham1, (1) VA Medical Center, Oklahoma City, OK, (2) Department of Radiological Sciences, University of Oklahoma Health Sciences Center


(Tuesday, 7/31/2018) 1:15 PM - 1:45 PM

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 180° partial -arcs (two clockwise and two counter-clockwise; gantry angle 310°-130°) to encompass PTVs with involved nodes with 30° or 330° collimator angles. The prescribed dose was 50 Gy in 25 fractions without boost dose.

Results: By using CPAP, patient’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 1.88±1.43Gy for 3D-CRT and 4.65±0.25Gy for VMAT plans. VMAT plans showed lower radiation dose to lung compared to 3D-CRT plans. The mean ipsilateral lung dose was 17.98±0.04Gy vs. 14.83±0.58Gy, and V20Gy was 35.64±0.63% vs. 26.50±3.09% for 3D-CRT and VMAT, respectively. The mean total lung dose was 8.84±0.56Gy for 3D-CRT vs. 8.69±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.


Radiation Therapy, Breast, Treatment Planning


TH- External beam- photons: treatment planning/virtual clinical studies

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