Accelerated IMRT of the Breast in Prone Position Is Feasible, Well Tolerated After Breast Conservation

DENVER-Accelerated intensity-modulated radiation therapy (IMRT) of the breast in the prone position is feasible and has only modest acute toxicity in patients who have undergone breast-conserving surgery for breast cancer, according to a report presented at the 47th Annual Meeting of the American Society for Therapeutic Radiology and Oncology (abstract 1062).

Silvia C. Formenti, MD, chair of radiation oncology, NYU School of Medicine, and her colleagues enrolled 90 women with stage I or II breast cancer in the study (NYU 03-30). All underwent breast-conserving surgery with negative margins and either sentinel lymph node biopsy or axillary lymph node dissection. The study includes collection of blood specimens for TGF-β polymorphism assessment. A secondary endpoint consists of correlating the polymorphism with long-term cosmetic outcome after at least 3 years of follow-up.

After surgery, the patients underwent CT simulation while in the prone position to be used for treatment; this position often has the benefit over the supine position of sparing normal tissues, including the lung and heart, Dr. Formenti told ONI in an interview. The investigators contoured the postoperative tumor bed (clinical target volume, CTV), ipsilateral breast volume, heart, and lungs.

Accelerated IMRT was delivered over a 3-week period. Radiation was given to a dose of 40.5 Gy in 15 fractions to the ipsilateral breast volume. In addition, a further 0.5 Gy concomitant boost was given to the postoperative tumor volume (PTV, defined as the CTV plus a 1-cm margin) for a total dose of 48 Gy. The 90 patients in the study had a median age of 57 years; 86% were white. The left breast was the treated breast in 57% of patients. The median tumor diameter was 14 mm (range, 1 to 40 mm), and 74% of patients had stage I disease.

The most common acute toxicity was dermatitis, which occurred with grade 1 severity in 42% of patients, grade 2 in 10%, and grade 3 in 2%. This toxicity occurred in the week after completion of radiation therapy. Other acute toxicities were all grade 1-fatigue in 17% of patients, breast edema in 8%, and breast pain in 4%. Ongoing follow-up will include assessment of late toxicities, including cosmetic outcomes, and their possible association with TGF-β genotype. At a median follow-up of 14 months, one patient has experienced a nodal recurrence.

"Accelerated IMRT in the prone position is feasible and well tolerated," Dr. Formenti said of the findings. "This is particularly relevant because, in most patients, it is superior to a supine setup in enabling optimal sparing of heart and lung tissue when the breast is treated. Longer follow-up is required to assess local control and late toxicity, likely to determine the cosmetic result."

The investigators also plan future research on optimal positioning during breast radiation therapy, Dr. Formenti noted. "We are now exploring whether there are ways to establish in advance (without planning the patient both prone and supine) in which position the individual patient is best treated," she explained.