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Simultaneous integrated bilateral breast and nodal irradiation with volumetric arc therapy: case report and literature review

Abstract

Aim

For simultaneous bilateral breast cancer (SBBC) treatment, conventional radiotherapy (RT) has a number of critical shortcomings. Thus, the usefulness of volumetric arc therapy (VMAT) for SBBC is undeniable.

Case report

A 34-year-old woman with SBBC received neoadjuvant chemotherapy followed by breast-conserving surgery and bilateral lymph node dissection. Given the conservative surgery and the nodal involvement after neoadjuvant chemotherapy, bilateral adjuvant RT to the breasts and regional nodes with doses of 50 Gy in 25 fractions and a simultaneous integrated boost (SIB) of 60 Gy to the surgical bed was proposed. Monoisocentric VMAT using 2 pairs of arcs was performed with adequate target dose coverage and low doses to the organs at risk. The results of this case were compared with those of previous studies in terms of RT technique and irradiated volumes.

Conclusions

VMAT is feasible and safe in the treatment of SBBC with SIB and nodal irradiation.

Tumori 2016; 102(Suppl. 2): e32 - e34

Article Type: CASE REPORT

DOI:10.5301/tj.5000568

Authors

Alba Fiorentino, Umberto Tebano, Ruggero Ruggieri, Francesco Ricchetti, Filippo Alongi

Article History

Disclosures

Financial support: None.
Conflict of interest: None of the authors has any conflict of interest related to this study to disclose.

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Introduction

Breast cancer is the most common cancer in women. Synchronous bilateral breast cancer (SBBC), defined as 2 or more malignant tumors occurring simultaneously in both breasts, is an uncommon condition, accounting for approximately 1%-3.5% of all breast tumors (1).

The treatment options for SBBC are similar to those for unilateral breast cancer, and include neoadjuvant or adjuvant chemotherapy, radical or breast-conserving surgery (BCS), and radiotherapy (RT). Moreover, neoadjuvant chemotherapy (N-CHT) has become the standard of care for patients with locally advanced breast cancer and is being increasingly prescribed to women with large operable disease (1). BCS should be considered for patients without an increased risk of complications; postoperative RT has decreased the local recurrence rate, providing a 4%-5% survival gain (1-2-3).

Conventional RT (CRT) consists of whole-breast irradiation (WBI), generally delivered with 2 tangential fields for a total dose of 45-50 Gy, 1.8-2 Gy per fraction. Boost irradiation with a total tumor bed dose of 60-66 Gy is usually prescribed (1).

RT has also been performed to reduce the risk of nodal recurrence and should be given to all node-positive patients after N-CHT, as well as patients with locally advanced cancer, patients with inflammatory breast carcinoma, and patients with more than 3 positive lymph nodes (1, 2).

In SBBC, significantly larger normal tissue volumes are treated compared to unilateral breast treatment. Hence, highly conformal RT is critical to achieve the required target dose coverage while ensuring adequate normal tissue sparing to keep the risk of acute and late toxicity at acceptable levels (4, 5). The new RT approaches, including intensity-modulated RT (IMRT) and volumetric arc therapy (VMAT), represent a suitable option that provides high-precision delivery, avoiding organs at risk (OARs) (4-5-6).

We here report on a SBBC patient who received bilateral concomitant adjuvant whole-breast and regional node RT.

Clinical case

In June 2015, a 34-year-old woman underwent bilateral mammography and ultrasonography which revealed SBBC consisting of a unifocal lesion of 23 mm in the right breast, a lesion of 13 mm in the left breast, and suspicion of bilateral axillary lymph node metastases. A core biopsy of both breast nodules showed infiltrating ductal carcinoma, G3 (right breast tumor: ER 90%, PgR 90%, Ki67 20%, HER2 negative; left breast tumor: ER 90%, PgR 90%, Ki67 15%, HER2 negative). In July 2015 bilateral sentinel lymph node biopsy revealed infiltrating ductal carcinoma metastases.

From July 2015 to January 2016, the patient received N-CHT consisting of 4 cycles of epirubicin and cyclophosphamide and subsequently 12 weekly cycles of paclitaxel, followed by triptorelin and daily aromatase inhibitors.

In March 2016, bilateral BCS and concomitant bilateral axillary lymph node dissection were performed. Histological examination revealed on the right side a 20-mm invasive ductal carcinoma (G3, ER 100%, PgR 5%, Ki67 8%) and a nodal metastasis (1/24), and on the left side a 10-mm invasive ductal carcinoma (G3, ER 90%, PgR 60%, Ki67 15%) and a nodal metastasis (1/10).

In April 2016, the patient was referred to our department to discuss the RT approach. Considering the conservative surgery performed, the biological nature of the disease and the nodal involvement after N-CHT, bilateral adjuvant RT to the breasts and regional nodes was proposed (1). The patient gave her informed consent. The treatment was delivered without interruption and without any acute side effects, except for G1 acute skin toxicity according to CTCAE v. 4.

The patient was immobilized in the supine position on a Posiboard™ frame (Civco Inc.) for the planning computed tomography without intravenous contrast medium (3-mm-thick slices). The clinical target volume (CTV) including the glandular breast parenchyma and the supraclavicular and infraclavicular nodes was outlined on both sides. The pectoral fascia and 5 mm of tissue beneath the skin was excluded. A 5-mm expansion in the transverse plane and 8 mm in the cranial-caudal direction was used to obtain the 2 lateral planning target volumes (PTVBN). A CTVboost including the tumor bed was defined for both sides. The 2 lateral PTVboosts were generated using a 5-mm isotropic expansion from the lateral CTVboost. The pectoral fascia muscles were excluded from the target and a 5-mm margin from the skin was considered for the bilateral PTVBN to avoid potential hot spots from inverse planning. A total dose of 50 Gy in 25 fractions was prescribed to both PTVBNs with a simultaneous integrated boost (SIB) of 60 Gy on the PTVboost.

RapidArc™ (Varian Inc.) VMAT monoisocentric treatment using 2 pairs of 220° arcs with 6-MV photon beams from a TrueBeam™ (Varian Inc.) linac was optimized on a 2-mm dose grid. The use of pairs (clockwise and counterclockwise) of coplanar 220° arcs with the same gantry variability, 200°-60° and 300°-160°, was chosen to give the optimizer the necessary freedom of modulation. The isocenter was positioned below the sternum. To compensate for intrafraction respiratory motion, a 1-cm virtual bolus was added interiorly to the body and the final plan was reoptimized to extend the apertures of the leaves out of the body.

For planning approval, PTVBN D95% ≥47.5 Gy, PTVboost D95% ≥57 Gy, a near-maximum dose (D2%) ≤64.1 Gy to the PTVboost and a minimum dose to 95% of both PTVs not lower than 95% of their respective prescribed doses were required. The OAR constraints for planning approval were: V20<10% and Dmean<10 Gy to the total lungs; Dmean<5 Gy to the heart, D0.1cc<30 Gy to the spinal cord planning risk volume; D1cc<30 Gy to the esophagus.

The monoisocentric plan is depicted in Figure 1. In Table I, the values of the conceived dose-volume metrics for the PTVs and OARs are reported.

Values for PTVs and OARs of the conceived dose-volume metrics

PTV OAR
PTV = planning target volume; OAR = organ at risk.
PTV50 opt Heart
D2% 57.1 Gy V25 0.0%
D95% 48.5 Gy Dmean 5.0 Gy
VPTV47.5 98.0% D1cc 18.8 Gy
PTV60 Esophagus
D2% 63.3 Gy V35 3.4%
D95% 60.0 Gy Dmean 9.3 Gy
VPTV57 100.0% D1cc 29.3 Gy
Lungs
V20 9.7%
V5 64.7%
Dmean 9.1 Gy
Liver
Dmean 3.8 Gy
Spinal cord
D0.1cc 24.4 Gy
Larynx
Dmean 13.4 Gy

Color wash for target dose coverage, with 20-Gy (yellow line) and 10-Gy (orange line) isodose lines for OAR sparing.

Discussion

Adjuvant WBI after lumpectomy is a keystone in breast cancer treatment. Despite the improved technology and techniques, CRT still remains the standard of care. Although reduction of acute skin toxicity has been obtained with IMRT, the routine use of IMRT/VMAT in breast irradiation is not currently recommended given the lack of a clinical advantage in terms of local recurrence and survival (1, 4-5-6).

For the treatment of SBBC, CRT presents a number of critical shortcomings including multiple field junctions, heterogeneous dose distribution, and a significantly higher irradiation volume of OARs. Thus, the usefulness of VMAT or IMRT is undeniable in unfavorable situations, including bilateral breast irradiation (1, 4-5-6-7-8-9-10).

Few previous studies have reported on the feasibility of IMRT in SBBC irradiation and only one provided data about bilateral breast and nodal irradiation with helical tomotherapy (HT) in 4 patients (7-8-9-10). To our knowledge, the present case report is the first in which SBBC plus SIB and regional nodes were treated using VMAT, and the results were compared with those of previous studies in terms of RT technique and irradiated volumes.

Seppälä et al (8) analyzed VMAT in 2 patients with SBBC, but without SIB and regional node irradiation. Despite the reduced irradiated volumes, there were higher OAR doses compared with the present case: Dmean and V20 for the lungs of 10.1 Gy and 17%; Dmean and V25 for the heart of 6.6 Gy and 4.2%, respectively.

When HT with SIB to the bilateral tumor beds without regional node irradiation is considered, the reported dose sparing to the OARs is similar to the results presented here (7, 9, 10). Wadasadawala et al (9) reported a low dose to OARs in 10 SBBC patients treated with HT (WBI plus SIB): to the lungs, a Dmean of 7.4 Gy versus 9.1 Gy in the present report, and V20 of 8.7% versus 9.7%; to the heart, a Dmean of 4.7 Gy versus 5 Gy and V25 of 3.5% versus 0%, respectively. By contrast, Kaidar-Person et al (10) reported the results of 9 patients treated with HT (WBI plus regional node RT including internal mammary nodes). Considering that the irradiated volumes were larger than in the present case, the authors reported increased OAR dose involvement: lungs V20 of 29%; heart Dmean and V25of 20 Gy and 32% (10).

In conclusion, VMAT is feasible and safe in the treatment of SBBC with SIB and nodal irradiation. However, based on a single case analysis it is not possible to ascertain whether the present favorable dosimetric results are due to the different technique adopted or to differences in the irradiated volumes.

Disclosures

Financial support: None.
Conflict of interest: None of the authors has any conflict of interest related to this study to disclose.
References
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Authors

Affiliations

  • Department of Radiation Oncology, Sacro Cuore Don Calabria Hospital, Negrar (Verona) - Italy

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