The use of directional interstitial sources to improve dosimetry in breast brachytherapy.

The purposes of this study were to investigate the feasibility of improving dosimetry with temporary low-dose-rate (LDR) multicatheter breast implants using directional 125I (iodine) interstitial sources and to provide a comparison of a patient treatment plan to that achieved by conventional high-dose-rate (HDR) interstitial breast brachytherapy. A novel 125I source emitting radiation in a specified direction has been developed. The directional sources contain an internal radiation shield that greatly reduces the intensity of radiation in the shielded direction. The sources have a similar dose distribution to conventional nondirectional sources on the unshielded side. The treatment plan for a patient treated with HDR interstitial brachytherapy with 192Ir (iridium) was compared with a directional 125I treatment plan using the same data set. Several dosimetric parameters are compared including target volume coverage, volume receiving 50%, 100%, and 150% of the prescription dose (V50, V100, and V150, respectively), dose homogeneity index (DHI), and the skin surface areas receiving 30%, 50%, and 80% of the prescription dose (S30, S50, and S80, respectively). The HDR and LDR prescription doses were 34 Gy in ten fractions delivered over five days and 45 Gy in 108 h, respectively. Similar and excellent target volume coverage was achieved by both directional LDR and HDR plans (99.2% and 97.5%, respectively). For a 170 cm3 target volume, the dosimetric parameters were similar for LDR and HDR: DHI was 0.82 in both cases, V100 was 214.4 cm3 and 225.7 cm3, and V150 was 39.1 cm3 and 40.4 cm3, respectively. However, with directional LDR, significant reductions in skin dose were achieved: S30 was reduced from 100.6 to 62.5 cm2, S50 from 50.6 to 16.1 cm2, and S80 from 2 cm2 to zero. The reduction in V50 for the whole breast was more than 100 cm3 (386.1 cm3 for LDR versus 489.2 cm3 for HDR). In this case study, compared with HDR, directional interstitial LDR 125I sources allow similar dose coverage to the subcutaneous target volume while lowering the skin dose due to a more conformal dose distribution and quicker falloff beyond the target. The improved dose distribution provided by directional interstitial brachytherapy might enable partial breast treatment to tumors closer to the skin or chest wall or in relatively small breasts.

[1]  R G Dale,et al.  Dose-rate effects in targeted radiotherapy. , 1996, Physics in medicine and biology.

[2]  E. Rakovitch,et al.  A permanent breast seed implant as partial breast radiation therapy for early-stage patients: a comparison of palladium-103 and iodine-125 isotopes based on radiation safety considerations. , 2005, International journal of radiation oncology, biology, physics.

[3]  R. Dale,et al.  The assessment of RBE effects using the concept of biologically effective dose. , 1999, International journal of radiation oncology, biology, physics.

[4]  J. Williamson,et al.  Update of AAPM Task Group No. 43 Report: A revised AAPM protocol for brachytherapy dose calculations. , 2004 .

[5]  Rakesh R. Patel,et al.  Image-guided breast brachytherapy: an alternative to whole-breast radiotherapy. , 2006, The Lancet. Oncology.

[6]  L. Stitt,et al.  TLD skin dose measurements and acute and late effects after lumpectomy and high-dose-rate brachytherapy only for early breast cancer. , 2005, International journal of radiation oncology, biology, physics.

[7]  M Saiful Huq,et al.  Procedures for establishing and maintaining consistent air-kerma strength standards for low-energy, photon-emitting brachytherapy sources: recommendations of the Calibration Laboratory Accreditation Subcommittee of the American Association of Physicists in Medicine. , 2004, Medical physics.

[8]  F. Vicini,et al.  Long‐term cosmetic results and toxicity after accelerated partial‐breast irradiation , 2006, Cancer.

[9]  D. Wazer,et al.  Accelerated partial breast irradiation: an analysis of variables associated with late toxicity and long-term cosmetic outcome after high-dose-rate interstitial brachytherapy. , 2006, International journal of radiation oncology, biology, physics.

[10]  Rakesh R. Patel,et al.  TU‐EE‐A1‐05: The Use of Directional Interstitial Sources to Reduce Skin Dose in Breast Brachytherapy , 2006 .

[11]  L. Dewerd,et al.  Brachytherapy dosimetry of 125I and 103Pd sources using an updated cross section library for the MCNP Monte Carlo transport code. , 2003, Medical physics.

[12]  G. Gustafson,et al.  Low-dose-rate brachytherapy as the sole radiation modality in the management of patients with early-stage breast cancer treated with breast-conserving therapy: preliminary results of a pilot trial. , 1997, International journal of radiation oncology, biology, physics.

[13]  Harry Easton,et al.  First report of a permanent breast 103Pd seed implant as adjuvant radiation treatment for early-stage breast cancer. , 2006, International journal of radiation oncology, biology, physics.

[14]  Bert M. Coursey,et al.  New National Air-Kerma-Strength Standards for 125I and 103Pd Brachytherapy Seeds , 2003, Journal of research of the National Institute of Standards and Technology.

[15]  Rakesh Patel,et al.  3D CT-based high-dose-rate breast brachytherapy implants: treatment planning and quality assurance. , 2004, International journal of radiation oncology, biology, physics.

[16]  Søren M. Bentzen,et al.  135 : New Directional Brachytherapy Sources And Repair Half-Time Data Indicate Monotherapy for Intermediate Risk T2b and High Risk T2c Prostate Tumors , 2006 .

[17]  A. Meigooni,et al.  A Monte Carlo evaluation of the dosimetric characteristics of the Best Model 2301 125I brachytherapy source. , 2002, Applied radiation and isotopes : including data, instrumentation and methods for use in agriculture, industry and medicine.

[18]  Bruce R. Thomadsen,et al.  TU-D-T-617-03: Assessment of a Prostate Treatment Plan Using Directional Brachytherapy Sources , 2005 .

[19]  W. Butler,et al.  Erratum: Update of AAPM Task Group No. 43 Report: A revised AAPM protocol for brachytherapy dose calculations (Medical Physics (2004) 31 (633-674)) , 2004 .

[20]  S. Tong,et al.  Partial breast brachytherapy after lumpectomy: low-dose-rate and high-dose-rate experience. , 2003, International journal of radiation oncology, biology, physics.