Author: Laura I. Cervino, Linda X. Hong, Jessica Pagan, Angelica A. Perez-Andujar, Maria Thor 👨🔬
Affiliation: Department of Medical Physics, Memorial Sloan Kettering Cancer Center, Memorial Sloan Kettering Cancer Center, Memorial Sloan-Kettering Cancer Center 🌍
Purpose: Three-dimensional conformal radiotherapy (3DCRT) and Volumetric-Modulated Arc Therapy (VMAT) are used to treat locally advanced breast cancer. The 3DCRT treatment plans use the treatment fields, and the VMAT treatment plans segmented tumor volumes. We hypothesized that 3DCRT and VMAT lead to different normal tissue and treated volume doses, and that there is a patient characteristics-specific treatment technique selection bias among these patients.
Methods: Forty patients with locally advanced breast cancer (N=20 left-sided; 20 right-sided, each with 10 patients treated with 3DCRT/VMAT) were randomly selected from the database (N=500; consecutively treated in 2016-2023). The patients received 50 Gy over 25 fractions for breast with comprehensive nodal irradiation: 32 received various boost dose to the tumor bed. The composite isodose lines (IDLs) volumes irradiated to 55, 50, 25 and 5 Gy, and ten normal tissue dose-volume guidelines were compared between 3DCRT and VMAT. Further, age and body mass index (BMI) were compared between the two techniques. All normal tissues were auto-segmented using SIEMENS VIASyngo. All comparisons were supported by a Wilcoxon rank-sum test (significance: two-sided p-value<0.05).
Results: All dose metrics except 50Gy IDL were significantly different between 3DCRT and VMAT (p=4E-8-0.03). While VMAT spared ipsilateral normal tissues to higher doses (lung V20Gy, V50Gy, brachial plexus max dose), 3DCRT delivered 1.3-876 times lower normal tissue doses (in 9/14 metrics). Further, VMAT significantly reduced the 55Gy IDL volumes but increased the 25Gy and 5Gy IDL volumes. Patients treated with VMAT had higher BMI but were not older/younger than patients treated with 3DCRT (median: BMI=28 vs. 24 kg/m2; p=0.03; Age=55 vs. 45 years; p=0.08).
Conclusion: VMAT leads to less volume receiving higher doses, but larger volumes receiving lower doses compared to 3DCRT for locally advanced breast cancer. These dose patterns should be factored in together with patient characteristics when deciding upon RT treatment technique.