Portal de Periódicos da CAPES

The importance of dose volume histogram evaluation in partial breast brachytherapy: a study of dosimetric parameters

2003; Elsevier BV; Volume: 57; Issue: 2 Linguagem: Inglês

10.1016/s0360-3016(03)01265-3

1879-355X

D.W. Arthur, David E. Wazer, Da Som Koo, Neenad M. Shah, L.P. Berle, Laurie W. Cuttino, Michael J. Yunes, Mark J. Rivard, Dorin Todor, S Tong, Todd Tenenholz, Thomas A. DiPetrillo,

Advanced Radiotherapy Techniques

Purpose/Objective: To evaluate dosimetric parameters used in the evaluation of breast brachytherapy implants and their relationship to normal tissue outcome. Materials/Methods: From 1995 – 2002, a combined group of 75 patients with early stage breast cancer were treated with Accelerated Partial Breast Irradiation at Virginia Commonwealth, Tufts and Brown Universities. Patients eligible included those with T1/T2, N0, N1 (≤3 nodes positive without extracapsular extension) and negative surgical margin. Following breast conserving surgery, all patients were treated with high dose rate (Ir192) brachytherapy delivering 34 Gy, 3.4 Gy bid over 5 – 7 days, to the target. The target was defined as the lumpectomy cavity plus a 2-cm margin. Methods of target delineation and catheter placement were uniform in all treatment locations. Comprehensive 3-dimensional evaluation with dose volume histogram analysis of each implant was completed and dosimetric parameters were evaluated to determine which parameters reliably determine the quality of the implant as measured by resulting skin and breast tissue toxicity. Results: Median follow-up was 42 months (range 7 – 86). Median patient age was 63 years. Tumor size ranged from .3 – 4 cm with a median of 1.2 cm. Six had positive nodes. No acute toxicity related to the treatment was reported although one patient developed an abscess nine months following treatment. At the time of last follow-up, there has been one (1.3%) in-breast failure and two (2.7%) developed subsequent distant metastasis. The global cosmetic outcome was reported to be good to excellent in 90.3%. RTOG grade 1 and 2 skin toxicity was reported in 18.1% and 4.2%, respectively. There was no documented grade 3/4 skin toxicity. The majority, 69.5%, had grade 0/1 subcutaneous toxicity, with 18.1% experiencing grade 2/3 and 12.5% experiencing grade 4 (fat necrosis). Resolution of fat necrosis signs and symptoms resolved in all patients with conservative care. Increased number of dwell positions (p=.04) and a decreased Dose Homogeneity Index of <.84 (p=.05) related to suboptimal cosmetic outcome. The volume of breast tissue treated to 6.8 Gy (200% of prescribed dose) was associated with the development of fat necrosis (p=.04). Dose homogeneity, as represented by the ratio of breast tissue volumes treated to 100% (3.4 Gy per fraction) and 150% (5.1 Gy per fraction) of the prescribed dose (1-V150/V100), directly correlated with the degree of skin (p=.04) and subcutaneous toxicity (p=.02). Conclusions: At this follow-up interval, in-breast failure rates and grade 3/4 toxicity remain low. The number of dwell positions and volume of tissue treated to 150% and 200% of the prescribed dose predict for late toxicity. Based on this experience, the risk of late skin and subcutaneous toxicity will be reduced or avoided if the volume of breast tissue treated to 5.1 Gy per fraction is limited to less than 50cc, the volume of breast tissue treated to 6.8 Gy per fraction is limited to less than 20cc and the volume ratio (1-V150/V100) is >.75.