Dose optimization of breast balloon brachytherapy using a stepping 192Ir HDR source.
There is a considerable underdosage (11%-13%) of PTV due to anisotropy of a stationary source in breast balloon brachytherapy. We improved the PTV coverage by varying multiple dwell positions and weights. We assumed that the diameter of spherical balloons varied from 4.0 cm to 5.0 cm, that the PTV was a 1-cm thick spherical shell over the balloon (reduced by the small portion occupied by the catheter path), and that the number of dwell positions varied from 2 to 13 with 0.25-cm steps, oriented symmetrically with respect to the balloon center. By assuming that the perfect PTV coverage can be achieved by spherical dose distributions from an isotropic source, we developed an optimization program to minimize two objective functions defined as: (1) the number of PTV-voxels having more than 10% difference between optimized doses and spherical doses, and (2) the difference between optimized doses and spherical doses per PTV-voxel. The optimal PTV coverage occurred when applying 8-11 dwell positions with weights determined by the optimization scheme. Since the optimization yields ellipsoidal isodose distributions along the catheter, there is relative skin sparing for cases with source movement approximately tangent to the skin. We also verified the optimization in CT-based treatment planning systems. Our volumetric dose optimization for PTV coverage showed close agreement to linear or multiple-points optimization results from the literature. The optimization scheme provides a simple and practical solution applicable to the clinic.
Choi
Chang Hyun
CH
Radiation Oncology, Seoul National University College of Medicine, Seoul, Korea.
Ye
Sung-Joon
SJ
Radiation Oncology, Seoul National University College of Medicine, Seoul, Korea.
Parsai
E Ishmael
EI
Department of Radiation Oncology, Medical University of Ohio, Toledo, Ohio, U.S.A.
Shen
Sui
S
Department of Radiation Oncology, University of Alabama College of Medicine, Birmingham, Alabama, U.S.A.
Meredith
Ruby
R
Department of Radiation Oncology, University of Alabama College of Medicine, Birmingham, Alabama, U.S.A.
Brezovich
Ivan A
IA
Department of Radiation Oncology, University of Alabama College of Medicine, Birmingham, Alabama, U.S.A.
Ove
Roger
R
Department of Radiation Oncology, Brody School of Medicine, East Carolina University, Greenville, North Carolina, U.S.A.
D001918:Brachytherapy / Q000295:instrumentation* / Q000379:methods; D001943:Breast Neoplasms / Q000532:radiotherapy*; D002404:Catheterization; D005260:Female; D006801:Humans; D007496:Iridium Radioisotopes / Q000008:administration & dosage* / Q000627:therapeutic use; D011879:Radiotherapy Dosage
D007496:Iridium Radioisotopes