Encrypted login | home

Program Information

Dosimetric Impact of Spherical Applicator Size in IntrabeamTM IORT for Treating Unicentric Breast Cancer Lesions

H Zhang

Y Saleh , H Zhang*, Northwestern Memorial Hospital, Chicago, IL


SU-I-GPD-T-1 (Sunday, July 30, 2017) 3:00 PM - 6:00 PM Room: Exhibit Hall

Purpose: To characterize the dosimetric impact of using different sizes of spherical applicators of IntrabeamTM Intraoperative Radiation Therapy (IB-IORT) to treat unicentric breast cancer lesions.

Methods: The three-dimensional dosages of the 3.5, 4.0, 4.5, and 5.0 cm spherical applicators of the IB-IORT machine were established. Five different cancer cell infiltration depths of unicentric breast lesions were formulated by a linearly declining cancer cell density distribution with the depth. The equivalent uniform dose (EUD), which is the dosage of a homogeneous dose treatment for killing the same amount of cancer cells as IB-IORT in the same target volume, was then calculated using the modified linear quadratic model (MLQ). The radiobiological response of acutely responding and slow responding breast cancer cell lines in the TARGIT-A clinical trial of 20 Gy dose was estimated. The Therapeutic Ratio (TR), which was defined by a ratio between the survival fractions of normal tissue cells respectively in IB-IORT and in homogeneous dose treatments, was derived from each treatment scenario.

Results: The EUDs were independent of applicator size, cancer cell radiosensitivity and cancer cell population percentage at the applicator surface. However, the EUDs rapidly decrease with the cancer cell infiltrating depth for all sizes of applicators, EUD is 18.5 Gy for 1 mm depth, but only10 Gy for 10 mm depth. TRs were dependent on both the applicator size and cancer cell infiltrating depth.

Conclusion: The use of different sizes of applicators was found not to significantly affect the EUDs, but a smaller applicator produced a greater TR for the shallow lesions (depth < 3 mm). IB-IORT is advantageous over EB-IORT when treating unicentric breast cancer at shallow infiltration depths as EUDs remain at a high dosage, while a large TR means a large fraction of normal tissue would still be spared.

Contact Email: