Comparison of organ doses for patients undergoing balloon brachytherapy of the breast with HDR {sup 192}Ir or electronic sources using Monte Carlo simulations in a heterogeneous human phantom

Journal Article · Mon Feb 15 00:00:00 EST 2010 · Medical Physics

DOI:https://doi.org/10.1118/1.3292292· OSTI ID:22096626

Mille, Matthew M.; Xu, X. George; Rivard, Mark J. ^[1]

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1. Nuclear Engineering and Engineering Physics Program, Rensselaer Polytechnic Institute, Troy, New York 12180 (United States)

Purpose: Accelerated partial breast irradiation via interstitial balloon brachytherapy is a fast and effective treatment method for certain early stage breast cancers. The radiation can be delivered using a conventional high-dose rate (HDR) {sup 192}Ir gamma-emitting source or a novel electronic brachytherapy (eBx) source which uses lower energy x rays that do not penetrate as far within the patient. A previous study [A. Dickler, M. C. Kirk, N. Seif, K. Griem, K. Dowlatshahi, D. Francescatti, and R. A. Abrams, ''A dosimetric comparison of MammoSite high-dose-rate brachytherapy and Xoft Axxent electronic brachytherapy,'' Brachytherapy 6, 164-168 (2007)] showed that the target dose is similar for HDR {sup 192}Ir and eBx. This study compares these sources based on the dose received by healthy organs and tissues away from the treatment site. Methods: A virtual patient with left breast cancer was represented by a whole-body, tissue-heterogeneous female voxel phantom. Monte Carlo methods were used to calculate the dose to healthy organs in a virtual patient undergoing balloon brachytherapy of the left breast with HDR {sup 192}Ir or eBx sources. The dose-volume histograms for a few organs which received large doses were also calculated. Additional simulations were performed with all tissues in the phantom defined as water to study the effect of tissue inhomogeneities. Results: For both HDR {sup 192}Ir and eBx, the largest mean organ doses were received by the ribs, thymus gland, left lung, heart, and sternum which were close to the brachytherapy source in the left breast. eBx yielded mean healthy organ doses that were more than a factor of {approx}1.4 smaller than for HDR {sup 192}Ir for all organs considered, except for the three closest ribs. Excluding these ribs, the average and median dose-reduction factors were {approx}28 and {approx}11, respectively. The volume distribution of doses in nearby soft tissue organs that were outside the PTV were also improved with eBx. However, the maximum dose to the closest rib with the eBx source was 5.4 times greater than that of the HDR {sup 192}Ir source. The ratio of tissue-to-water maximum rib dose for the eBx source was {approx}5. Conclusions: The results of this study indicate that eBx may offer lower toxicity to most healthy tissues, except nearby bone. TG-43 methods have a tendency to underestimate dose to bone, especially the ribs. Clinical studies evaluating the negative health effects caused by irradiating healthy organs are needed so that physicians can better understand when HDR {sup 192}Ir or eBx might best benefit a patient.

• OSTI ID: 22096626
• Journal Information: Medical Physics, Vol. 37, Issue 2; Other Information: (c) 2010 American Association of Physicists in Medicine; Country of input: International Atomic Energy Agency (IAEA); ISSN 0094-2405
• Country of Publication: United States
• Language: English

Related Subjects

62 RADIOLOGY AND NUCLEAR MEDICINE
71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
BALLOONS
BIOMEDICAL RADIOGRAPHY
BRACHYTHERAPY
COMPUTERIZED SIMULATION
DOSE RATES
EFFICIENCY
FEMALES
HEART
IRIDIUM 192
IRRADIATION
LUNGS
MAMMARY GLANDS
MONTE CARLO METHOD
NEOPLASMS
PATIENTS
PHANTOMS
RADIATION DOSES
SKELETON
THYMUS