Accelerated partial-breast irradiation using 3D Conformal External Beam Radiotherapy for patients with early-stage breast cancer: Preliminary results of an ongoing Phase I trial

Abstract

To investigate the feasibility and side effects of using 3D Conformal External Beam Radiotherapy (3D-CRT) to give accelerated partial breast irradiation (APBI)following tumor excision in patients with early-stage breast cancer. From August 2003 to February 2004, 24 patients have been enrolled on a Phase I, IRB approved study (with an accrual goal of 100 patients). Data analysis was performed on the first 22 patients who have completed therapy. Eligibility criteria include: infiltrating ductal carcinoma (or special subtype) of 2 cm or less; negative sentinel node or axillary dissection; margin width 2 mm or greater; no lymphovascular invasion; and no extensive intraductal component. The gross target volume (GTV) consisted of the lumpectomy cavity. The planning target volume (PTV) consisted of the GTV plus a 15–20 mm margin which included 5mm for breathing motion and treatment setup uncertainties. This figure was estimated based on pilot study measurements, but is being measured formally in a companion study. The prescribed dose (PD) was 32 Gy in 8 fractions b.i.d. separated by 6 hours; dose inhomogeneity across the PTV was to be less than 10%. The treatment was delivered in 4 consecutive days for 21 patients and within a week in one patient. Patients were treated in the supine position with 3 beams (17 patients) or 4 beams (5 patients) using a Varian 2100C machine. Mixed photons-electron fields were used in 21 patients and photons only in 1 patient. Cosmesis and skin reaction were assessed by the patient and the treating physician at the start of treatment, after 3–4 weeks and after 6–8 weeks, and then every 6 months. Follow-up ranged from 1–6 months All patients consented to the study. The average tumor size was 0.86 cm (SD, 0.5 cm), and the median was 0.9 cm. Fourteen patients had left and 8 right-sided breast cancers. Two patients received adjuvant chemotherapy and 10 started hormonal therapy after APBI. The mean and median GTV was 42.9 cc and 34.0 cc, respectively (range, 6–196 cc). The mean and median PTV was 178.1 cc and 151 cc, respectively (range, 78–568 cc). The median percentage of the whole breast designated as PTV was 23% (range 11%-41%). The mean doses received by 20% (V20), 10% (V10) and 5% (V5) of the ipsilateral lung volume were 2.3 Gy, 4.5 Gy and 6.7 Gy, respectively. The mean V20, V10 and V5 doses of the heart in patients with left breast tumors were 1.5 Gy, 2.2 Gy and 3.2 Gy, respectively. The mean and median doses received by 50% of the non-target breast tissue (whole breast minus PTV) were 6.7 Gy and 4.0 Gy, respectively. No skin changes greater than Grade 1 erythema were noted during or at the end of treatment. At the initial follow-up visit, 9/22 patients (41%) experienced mild erythema, 2/22 (9%) had moderate erythema, and none had moist desquamation. Cosmetic results were rated by the patient and treating physician as good or excellent in all cases. This initial report of an ongoing phase I trial using 3D-CRT APBI shows that such treatment is technically feasible with minimal acute toxicity. Doses to the lung and heart are significantly reduced compared with whole breast irradiation. Compared with interstitial approaches to APBI, 3 DCRT delivers more dose to non-target breast tissue, but the long-term biological consequences of this additional exposure is unknown. Completion of the trial and additional follow-up are needed to assess the long-term effects of this approach on normal-tissue sequelae and treatment efficacy