Long-Term Outcomes of IMRT for Breast Cancer: A Single-Institution Cohort Analysis

McDonald. IJROBP 2008;762:1031

Purpose

To evaluate long-term outcomes of adjuvant breast intensity-modulated radiation therapy (IMRT), with a comparison cohort receiving conventional radiation (cRT) during the same period.

Breast-conservation therapy is the preferred management strategy for appropriately selected patients with ductal carcinoma in situ (DCIS)  and early-stage invasive breast cancer (IBC). Multiple randomized controlled trials established the importance of adjuvant breast radiotherapy (RT) after conservative surgery for DCIS or IBC

Conventional breast RT is delivered to the whole ipsilateral breast through two tangential fields with the use of megavoltage photons, usually with wedges to improve dose homogeneity. Conventional breast RT results in a moderate degree of acute skin toxicity in approximately one third to one half of patients. This usually is limited to brisk erythema or patchy moist desquamation of the breast, whereas more severe acute toxicity is exceedingly uncommon. Late toxicity may include telangiectasias, fat necrosis, lymphedema, and skin fibrosis, but moderate or worse grade late toxicity is uncommon. Increased frequency of both acute and late skin effects is associated with increased breast dose inhomogeneity and resultant “hot spots”. With conventional breast RT, a significant portion of the breast tissue may receive 110% of the prescription dose, with potential hot spots of up to 120%

Intensity-modulated RT (IMRT) was explored as a technique to improve breast dose homogeneity by decreasing hot spots and dose to normal tissues. IMRT is a treatment technique driven by computer-optimized planning that allows modulation of beam intensity within treatment fields to obtain highly conformal dose delivery. Breast IMRT is an area of active research, and in recent years, several publications showed feasibility, dosimetric superiority to conventional plans, and decreased acute side effects with breast IMRT compared with conventional RT (cRT), with the potential for decreased late complications . However, published long-term clinical outcomes for patients treated with breast IMRT have been sparse.

At The Emory Clinic, Atlanta, GA, we began using IMRT in adjuvant breast RT in 1999, using a forward planned treatment with two tangential fields with a combination of dynamic multileaf collimators (DMLCs) and enhanced dynamic wedges (EDWs). In 2003, we changed to a multibeam inverse planned IMRT technique using a simultaneous integrated boost to the resection cavity. We report clinical outcomes of patients treated with our initial IMRT technique used from 1999–2003 and a comparison cohort of patients treated during the same period using cRT with EDWs.
Methods and Materials

Retrospective review identified patients with Stages 0–III breast cancer who underwent irradiation after conservative surgery from January 1999 to December 2003. Computed tomography simulation was used to design standard tangential breast fields with enhanced dynamic wedges for cRT and both enhanced dynamic wedges and dynamic multileaf collimators for IMRT. Patients received 1.8–2-Gy fractions to 44–50.4 Gy to the whole breast, followed by an electron boost of 10–20 Gy.

Results

A total of 245 breasts were treated in 240 patients: 121 with IMRT and 124 with cRT. Median breast dose was 50 Gy, and median total dose was 60 Gy in both groups. Patient characteristics were well balanced between groups. Median follow-ups were 6.3 years for patients treated with IMRT and 7.5 years  for those treated with cRT. Treatment with IMRT decreased acute skin toxicity of Radiation Therapy Oncology Group Grade 2 or 3 compared with cRT (39% vs. 52%). For patients with Stages I–III, 7-year Kaplan-Meier freedom from ipsilateral breast tumor recurrence (IBTR) rates were 95% for IMRT and 90% for cRT. For patients with Stage 0 (ductal carcinoma in situ, n = 46), 7-year freedom from IBTR rates were 92% for IMRT and 81% for cRT. Comparing IMRT with cRT, there were no statistically significant differences in overall survival, disease-specific survival, or freedom from IBTR, contralateral breast tumor recurrence, distant metastasis, late toxicity, or second malignancies.

Conclusions

Patients treated with breast IMRT had decreased acute skin toxicity, and long-term follow-up shows excellent local control similar to a contemporaneous cohort treated with cRT.