Purpose: We present a novel three-dimensional conformal radiation therapy (3D-CRT) technique to treat the lumpectomy cavity, plus a 1.5-cm margin, in patients with early-stage breast cancer and study its clinical feasibility.
Methods and materials: A 3D-CRT technique for partial-breast irradiation was developed using archived CT scans from 7 patients who underwent an active breathing control study. The clinical feasibility of this technique was then assessed in 9 patients who were prospectively enrolled on an Investigational Review Board-approved protocol of partial-breast irradiation. The prescribed dose was 34 Gy in 5 patients and 38.5 Gy in 4 patients, delivered in 10 fractions twice daily over 5 consecutive days. The impact of both breathing motion and patient setup uncertainty on clinical target volume (CTV) coverage was studied, and an appropriate CTV-to-PTV (planning target volume) margin was calculated.
Results: By adding a CTV-to-PTV "breathing-only" margin of 5 mm, 98%-100% of the CTV remained covered by the 95% isodose surface at the extremes of normal inhalation and normal exhalation. The "total" CTV-to-PTV margin employed to accommodate organ motion and setup error (10 mm) was found to be sufficient to accommodate the observed uncertainty in the delivery precision. Patient tolerance was excellent, and acute toxicity was minimal. No skin changes were noted during treatment, and at the initial 4-8-week follow-up visit, only mild localized hyperpigmentation and/or erythema was observed. No instances of symptomatic radiation pneumonitis have occurred.
Conclusions: Accelerated partial-breast irradiation using 3D-CRT is technically feasible, and acute toxicity to date has been minimal. A CTV-to-PTV margin of 10 mm seems to provide coverage for most patients. However, more patients and additional studies will be needed to validate the accuracy of this margin, and longer follow-up will be needed to assess acute and chronic toxicity, tumor control, and cosmetic results.