Application of radiosurgery principles to a target in the breast: a dosimetric study.
OBJECTIVE
To investigate the technical and physical feasibility of using a radiosurgery-like technique to irradiate a small target within the breast with a single fraction.


METHODS
During diagnostic biopsy, a tantalum surgical clip is placed in the lesion identified at mammography. Transverse CT scans over the entire breast are obtained, as the patient lies prone on a special table that allows the breast to hang down. The clip is used as a reference point to define the isocenter of the radiation treatment.


RESULTS
The clip is visible on port films taken with a 4 MV beam, allowing the isocenter to be set to its planned location. No movement of the hanging breast is visually detected. The possible beam directions are enclosed by a 220 degrees horizontal x 180 degrees vertical angular interval. Dosimetry of two "radiosurgical" examples, (A) seven fixed horizontal beams and (B) six 45 degrees arcs and a 90 degrees sagittal arc using a 4 MV x-ray beam with a 32 mm diameter collimator, are discussed. Both field arrangements produce adequate tumor coverage: the minimum target dose is 83% of the dose maximum in the fixed beam arrangement and 86% in the multiarc setup. In arrangement A the lung and other tissues external to the breast receive dose only from scattered radiation. In arrangement B the maximum lung dose is less than 5% of the dose to isocenter.


CONCLUSIONS
From a dosimetric point of view both described techniques are feasible, and the radiosurgery-like treatment is executable.
Jozsef
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G
Department of Radiation Oncology, School of Medicine, University of Southern California, Los Angeles 90033, USA. jozsef@hsc.usc.edu
Luxton
G
G
Formenti
S C
SC
D055592:Biophysical Phenomena; D001703:Biophysics; D001943:Breast Neoplasms / Q000000981:diagnostic imaging / Q000601:surgery*; D005260:Female; D006801:Humans; D008327:Mammography; D011857:Radiographic Image Interpretation, Computer-Assisted; D016634:Radiosurgery / Q000295:instrumentation / Q000379:methods* / Q000706:statistics & numerical data; D013813:Therapy, Computer-Assisted / Q000295:instrumentation / Q000379:methods* / Q000706:statistics & numerical data; D014057:Tomography, X-Ray Computed