Prospective Trial of Individual Optimal Positioning (Prone Versus Supine) for Whole Breast Radiotherapy: Results of the First 168 Patients
Presenter: Silvia C. Formenti, MD
Presenter's Affiliation: New York University Medical Center
Type of Session: Scientific
- External beam radiation therapy as part of breast conservation therapy for early stage breast cancer has traditionally used tangential fields to treat the whole breast of patients in the supine position. Newer reports have indicated that certain patients treated in the prone position might benefit from less dose inhomogeneity, less toxicity to the lungs, heart and ribs, and increased breast separation to minimize dose to the contralateral breast.
- Prone whole breast radiotherapy has previously been shown to be deliverable with hypo-fractionation and a concomitant boost IMRT regimen (Formenti SC, et al. J Clin Oncol. 2007;25(16):2236-42).
- This trial aimed to demonstrate that prone positioning would allow for decreased radiation dose to the heart and lungs in most patients, but trial investigators hypothesized that some patients would have increased cardiac and pulmonary normal tissue sparing in the supine position.
- NYU 05-181 protocol, which was designed to obtain both prone and supine CT images, conduct CT planning, and select optimal individual positioning for each patient, was used in this study in an attempt to identify specific anatomic characteristics that would make patients more likely to benefit from supine versus prone position.
- Patients with Stage 0 to 2 breast cancer after segmental mastectomy with negative margins were enrolled in this prospective trial.
- Breast tissue borders were delineated with radio-opaque markers while patients were in the supine position.
- Patients underwent supine CT simulation with 2.5 mm slice thickness images. They were then CT simulated in the prone position with a dedicated breast mattress, allowing for the index breast to fall freely through an opening.
- Contouring and treatment planning were conducted for both supine and prone images. The whole index breast was used for the treatment volume and was determined according to conventional supine breast simulation.
- The decision to treat patients in the supine versus prone position was based on the plan that investigators determined optimal based on treatment volume, maximum heart sparing, and maximum lung sparing.-Patients received 40 to 50 Gy to the whole breast in 15 fractions over three weeks with a concomitant boost to the tumor bed.
- 224 patients have accrued to the study. Median age was 57 years and 81% of patients were Caucasian. Among study participants, 117 had left-sided malignancies and 107 had right-sided disease.
- Optimal setup was determined to be in the prone position in 91.1% of cases and the supine position in 8.9% of cases (p<0.001). Patients with right-sided disease were more likely to achieve optimal setup in the prone position when compared to those with left-sided malignancies (96.2% versus 86.3%).
- Most patients in this study achieved optimal treatment planning in the prone position.
- Optimal set in the supine position was seen in only 8.9% of cases but was more common among patients with left-sided malignancies due to cardiac toxicity, as prone positioning was associated with a displacement of the heart towards the anterior chest wall.
- The investigators plan to accrue 400 patients to this trial, with 200 patients each with left- and right-sided breast cancers. From this population, they hope to determine which anatomic characteristics would make patients more likely to benefit from supine versus prone positioning.
Over the past few years, interest has increased in treating patients with early stage breast cancer in the prone position. Although long-term data regarding local failure rates and overall survival are lacking, early reports have shown that many patients are able to achieve superior dose homogeneity in the prone position. This is especially true for patients with large, pendulous breasts. Additionally, when compared with traditional supine treatments, prone position may also reduce radiation dose to the underlying and adjacent normal tissues, including the heart, lungs, ribs, and contralateral breast. However, some investigators have reported worse cosmetic outcomes and increased rates of radiodermatitis and chronic fibrosis following prone treatment. It is also important to note that not all patients with breast cancer are candidates for prone treatment. While no randomized trials exist, many experts would agree that prone positioning should only be used in patients with Stage 0 to II early breast cancer with negative resection margins following lumpectomy. Additionally, some radiation oncologists would treat in the prone position only in patients with a negative sentinel lymph node biopsy or axillary dissection.
Partially funded by an unrestricted educational grant from Bristol-Myers Squibb.