Implant breast reconstruction followed by radiotherapy: Can helical tomotherapy become a standard irradiation treatment?
Introduction
The use of primary reconstructive surgery after breast cancer surgery is becoming increasingly common.1, 2, 3, 4, 5 Although the clinical indications for adjuvant breast radiotherapy remain unchanged, the practicalities of delivering radiotherapy can be altered because of the reconstructive surgery.5 Over recent years, new techniques for radiotherapy imaging and 3D planning and delivery have been developed to obtain better dose distribution in breast cancer. Standard tangential fields with 3D conformal radiotherapy, using shaped radiation beams and nonuniform intensity beams for the field-in-field technique, have been routinely used for several years in the Department of Radiation Oncology of the Institut Curie.6
Despites these advances, radiotherapy after reconstructive implant surgery remains a challenging issue,7 especially in cases that require loco-regional irradiation. Some authors have shown that plans for radiation treatment after immediate breast reconstruction are compromised in more than half of patients (52%), with the largest compromises observed in those with left-sided tumors and/or with internal mammary nodes (IMN) irradiation.5, 7 The IMN irradiation remains a controversial issue because the line is very thin between the benefits and the side effects, as evidenced by the wide range of practice in this regard internationally. First, women with breast cancer who have positive axillary nodes are known to also have involvement of the IMN in about 30% of cases.8 Second, the IMNs are included in the target volumes in randomized trials that established the benefit of postmastectomy radiation therapy (PMRT).9 The Early Breast Cancer Trialists Collaborative Group is suggesting, however, that locoregional radiation therapy can produce deleterious long-term effects, especially to the lungs and/or heart for left-sided breast cancer. The European Organization for Research and Treatment of Cancer trial 22922/10925, whose results are expected by 2012, is evaluating the potential survival benefit of nodal irradiation—including the IMN—in women treated by mastectomy or breast-conserving surgery at high risk for locoregional recurrence. Until the results are in, we are performing at the Institut Curie the IMN irradiation for women with positive axillary nodes or with high risk of relapse. The use of intensity-modulated radiotherapy (IMRT) can readily overcome obvious difficulties in this particular setting. IMRT uses inverse planning and optimized nonuniform beam intensities with treatment plans generated from computer algorithms to ensure target-volume conformity and to avoid damaging the lungs and heart, as reported by Krueger for postmastectomy radiation therapy.10 It also eliminates the problem of overlapping fields because the target volumes are treated in continuity without a field junction.
Helical tomotherapy (HT) is a form of IMRT radiation that delivers a modulated fan beam using a 6-MV linear accelerator mounted on a ring gantry that rotates around the patient as the treatment table slowly advances through the gantry bore. It has been recently introduced for the treatment of breast cancer, after being used in various other tumor localizations.11, 12 Aeshenafi et al. reported on the dosimetric advantages of HT for postmastectomy chest-wall irradiation,13 but to date, its use in loco-regional therapy after a total mastectomy with an immediate implant-based reconstruction has not been evaluated. The purpose of this study was to evaluate the benefits and limitations of HT in these cases. A comparison between HT dosimetric outcomes and conventional linac-based plans, using a simplified field-in-field technique, was performed on 10 patients.
Section snippets
Patient selection
Ten breast cancer patients with implants, previously treated at the Institut Curie, were randomly selected for this comparative study. The patients were treated according to our institution's standard protocols, but imaging results were retrospectively used for the study. Each patient had 2 treatment plans: 1 plan used a conventional technique and the other used the helical tomotherapy (HT) treatment planning system (TPS).
Image acquisition
A computed tomography (CT) scan was performed to plan treatment using a
Results
Ten breast cancer patients (6 left-sided and 4 right-sided tumors) treated in the radiation oncology department of the Institut Curie between September 2008 and May 2010 were entered into our study. All patients but one underwent a skin-sparing total mastectomy and an axillary lymph node dissection with immediate breast reconstruction using unilateral retropectoral implants. The remaining patient had a previous bilateral breast augmentation and underwent conservative surgery with lymph node
General and technical issues
Our study presents a dosimetric comparison between an optimized 3D field-in-field technique associated with IMN electron-beam irradiation or HT to irradiate challenging loco-regional areas after a total mastectomy and immediate implant reconstruction. Comparison between the HT optimization parameters revealed that HT gave better target coverage and better dose homogeneity in a target volume that included both the tissue anterior to the breast implant and the lymph nodes. To our knowledge, this
Conclusion
This dosimetric study represents the first step toward successful optimization of comprehensive loco-regional radiation therapy after total mastectomy and implant-based reconstruction of the breast. However, planning of optimal radiation treatment for each patient must still be based on clinical judgment and on a discussion of the risks and benefits. An additional study on the HT technique needs to be performed to analyze the unknown clinical implications of some of the dosimetric differences
Acknowledgments
The authors thank Malika Amesis, Stéphanie Lamart, Ph.D., and Romain Viard for their substantial help with this study.
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