Dosimetric Evaluation of Tangential Arc and Jaw Tracking Techniques in Volumetric Modulated Arc Therapy for Synchronous Bilateral Breast Cancer

Jiyong Zhang,1,* Zewei Chen,1,* Danli Hong2 1Department of Radiation Oncology, Cancer Hospital of Shantou University Medical College, Shantou, Guangdong, 515000, People’s Republic of China; 2Department of Endocrinology, The First Affiliated Hospital of Shantou University Medical College, Shantou, Guangdong, 515000, People’s Republic of China*These authors contributed equally to this workCorrespondence: Jiyong Zhang, Email [email protected]: This study presents a dosimetric comparison of volumetric modulated arc therapy (VMAT) treatment plans that employ static jaw, tangential arc, and jaw tracking techniques for patients with synchronous bilateral breast cancer (SBBC).Methods: VMAT plans employing static jaw (S-VMAT), tangential arc (T-VMAT), and jaw tracking (J-VMAT) techniques were generated for twelve SBBC patients, receiving a prescribed dose of 50 Gy in 25 fractions. All treatment plans had their dosimetric and delivery parameters meticulously recorded and analyzed for comparison. Dosimetric verification was conducted using gamma analysis with 3%/3 mm criteria, based on ArcCHECK phantom measurements.Results: PTV coverage was comparable among all three techniques, with no statistically significant differences in dose indices, CI, or HI (p > 0.05). In contrast, T-VMAT and J-VMAT showed significant advantages in OARs protection compared to S-VMAT. T-VMAT achieved the lowest lung and heart doses, with the heart Dmean reduced from 11.25 Gy (S-VMAT) to 7.44 Gy, and the heart V5Gy from 86.98% to 36.03%. J-VMAT also demonstrated substantial improvements, reducing heart Dmean to 9.21 Gy and V5Gy to 76.89%. Both techniques also showed lower doses to the liver, esophagus, trachea, and spinal cord compared to S-VMAT. In terms of efficiency, T-VMAT required significantly fewer MUs and achieved a markedly shorter delivery time, with a reduction of over one-third compared to S-VMAT and nearly half compared to J-VMAT. QA pass rates were above 99% for all plans, with no significant differences observed.Conclusion: T-VMAT and J-VMAT offer superior OAR sparing and efficient treatment delivery compared to S-VMAT. T-VMAT is particularly advantageous in reducing dose and treatment time, while J-VMAT provides a balanced approach between dosimetric quality and delivery accuracy. Both techniques represent promising strategies for optimizing VMAT planning in SBBC.Keywords: synchronous bilateral breast cancer, volumetric modulated arc therapy, jaw tracking, static jaw, organs at risk