MRI-guided single fraction ablative radiotherapy for early-stage breast cancer: a brachytherapy versus volumetric modulated arc therapy dosimetry study

doi:10.1016/j.radonc.2015.09.023

Radiotherapy and Oncology

Volume 117, Issue 3, December 2015, Pages 477-482

https://doi.org/10.1016/j.radonc.2015.09.023 Get rights and content

Abstract

Background and purpose

A radiosurgical treatment approach for early-stage breast cancer has the potential to minimize the patient’s treatment burden. The dosimetric feasibility for single fraction ablative radiotherapy was evaluated by comparing volumetric modulated arc therapy (VMAT) with an interstitial multicatheter brachytherapy (IMB) approach.

Methods and materials

The tumors of 20 patients with early-stage breast cancer were delineated on a preoperative contrast-enhanced planning CT-scan, co-registered with a contrast-enhanced magnetic resonance imaging (MRI), both in radiotherapy supine position. A dose of 15 Gy was prescribed to the planned target volume of the clinical target volume (PTV_CTV), and 20 Gy integrated boost to the PTV of the gross tumor volume (PTV_GTV). Treatment plans for IMB and VMAT were optimized for adequate target volume coverage and minimal organs at risk (OAR) dose.

Results

The median PTV_GTV/CTV receiving at least 95% of the prescribed dose was ⩾ 99% with both techniques. The median PTV_CTV unintentionally receiving 95% of the prescribed PTV_GTV dose was 65.4% and 4.3% with IMB and VMAT, respectively. OAR doses were comparable with both techniques.

Conclusion

MRI-guided single fraction radiotherapy with an integrated ablative boost to the GTV is dosimetrically feasible with both techniques. We perceive IMB less suitable for clinical implementation due to PTV_CTV overdosage. Future studies have to confirm the clinical feasibility of the single fraction ablative approach.

Section snippets

Patient characteristics

This study included patients from the pre-existing NTR3198 study, approved by our institutional review board [7]. Patients with tumors up to 30 mm, scheduled for breast-conserving surgery and whole breast irradiation were included. Baseline characteristics of the 20 patients are shown in Table 1. Patients underwent a contrast-enhanced (CE) CT and CE-MRI in supine RT treatment position on a wedge board at 10° of inclination, with arms in abduction above the head. Details on patient positioning

Results

The tumor and ipsilateral breast characteristics are presented in Table 1. Tumors were mainly laterally located in the left breast. The median tumor size was 13.5 mm, with a median distance of 10.0 mm and 9.0 mm to the skin and chest wall, respectively.

Due to the additional 3 mm PTV margin required with VMAT, IMB resulted in a lower median PTV_GTV (1.8 cc vs. 6.1 cc, p < 0.05) and PTV_CTV (74.8 cc vs. 100.9 cc, p < 0.05) (Table 2). The median PTV_GTV and PTV_CTV receiving at least 95% of the prescribed dose

Discussion

A comparative planning study on single fraction treatment was performed to evaluate the dosimetric feasibility of single dose MR-guided ablative radiotherapy for early-stage breast cancer. The VMAT and IMB treatment approach resulted in adequate target volume coverage for all cases. Due to the additional PTV margin required for VMAT, the PTV_CTV was significantly lower with IMB. However, the extent of high dose volumes in the PTV_CTV was considerably lower with VMAT compared to IMB. Appendix 1B

Conflict of interest

None.

Acknowledgements

This study was supported by a grant from the Pink Ribbon Association. We thank professor E. van Limbergen from the radiation-oncology department at the University Hospital Leuven in Belgium for his remarks on the brachytherapy treatment planning.

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All MRI-linac plans met the coverage and predefined OAR constraints. The prone approach appeared to be more favorable with respect to the chest wall, and ipsilateral lung dose compared to the supine position. No dosimetric differences were observed for the ipsilateral breast. No treatment position was clearly more beneficial for the skin or heart, since dosimetry varied among parameters. Overall, the MRI-linac and clinical plans were comparable, with minor absolute dosimetric differences.
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Following breast-conserving surgery and post-operative 3D-conformal accelerated partial breast irradiation (APBI), suboptimal cosmetic results have been reported. Preoperative radiation delivery to the intact tumor enables better target visualization and treatment volume reduction. Single dose preoperative APBI has the potential to improve toxicity profiles, reduce treatment burden and enable in vivo exploration of breast cancer radiogenomics.
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Noninvasive or minimally invasive treatments are being developed as alternatives to surgery for patients with early-stage breast cancer. Patients’ preferences with regard to these new treatments have not been investigated.
To assess preferences of patients with breast cancer and of healthy women regarding these new techniques, compared with conventional surgical treatments.
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Seventy-one patients with breast cancer and 50 healthy volunteers participated. Overall, BCT was rated the highest in terms of VAS (0.80) and TTO (0.90) scores. After stratification, BCT ranked the highest in most subgroups, with the exception of healthy individuals, who had given the highest score to ablative boost (VAS, 0.80; TTO, 0.88). Mastectomy with immediate reconstruction was the least preferred in most subgroups.
This study showed no significant preference for minimally invasive treatment for breast cancer. Using hypothetical scenarios, breast cancer survivors attributed the highest scores to BCT, whereas healthy volunteers showed a slight preference for minimally invasive treatments.
Multicatheter interstitial brachytherapy versus intensity modulated external beam therapy for accelerated partial breast irradiation: A comparative treatment planning study with respect to dosimetry of organs at risk
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To dosimetrically compare multicatheter interstitial brachytherapy (MIBT) and intensity modulated radiotherapy (IMRT) for accelerated partial breast irradiation (APBI) with special focus on dose to normal tissues and organs at risk (OAR-s).
Thirty-four patients with early stage breast cancer treated with MIBT were selected for the study. For each patient an additional IMRT treatment plan was created using the same CT data and contours as used in MIBT plans. OAR-s included ipsilateral non-target and contralateral breast, lung of both sides, skin, ribs and heart for left sided lesions. The CTV was created from the outlined lumpectomy cavity with a total margin (surgical + radiation) of 20 mm in six main directions. The PTV in IMRT plans was generated from CTV with an addition of isotropic 5 mm margin. The prescribed dose was 30.1 Gy with 7 × 4.3 Gy fractionation for both techniques. From dose-volume histograms quality parameters including volumes receiving a given dose (e.g. V100, V90, V50) and doses to specified volumes (e.g. D_0.01 cm³, D_0.1 cm³, D_1 cm³) were calculated and compared.
Except for high dose, non-target breast received less dose with MIBT. V90 was 3.6% vs. 4.8% and V50 was 13.7% vs. 25.5% for MIBT and IMRT, respectively. Ipsilateral lung was spared better with MIBT. Mean lung dose was 5.1% vs. 7.1%, $D_{1 {cm}^{3}}$ was 39.0% vs. 54.3% and V5 was 32.9% vs. 41.7% in favour of MIBT. For left sided lesions the heart was generally irradiated by larger doses with MIBT. Mean heart dose was 4.5% vs. 2.0% and $D_{2 {cm}^{3}}$ was 18.3% vs. 19.7%, correspondingly. Volumetric maximal skin doses were similar, but regarding dose to 0.1 cm³ and 1 cm³ of most exposed volume MIBT provided significantly less doses (76.6% vs. 94.4% and 60.2% vs. 87.8%, respectively). Ribs received less dose with MIBT with values of 45.6% vs. 69.3% for $D_{1 {cm}^{3}}$ and 1.4% vs. 4.2 cm³ for V50. Dose to contralateral breast and lung was low with both techniques. No significant differences were observed in maximal doses, but dose to volumes of 0.1 cm³ and 1 cm³ were less with MIBT for both organs. $D_{1 {cm}^{3}}$ was 3.2% vs. 6.7% for breast and 3.7% vs. 5.6% for lung with MIBT and IMRT, respectively.
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Breast radiotherapyMRI-guided single fraction ablative radiotherapy for early-stage breast cancer: a brachytherapy versus volumetric modulated arc therapy dosimetry study

Abstract

Background and purpose

Methods and materials

Results

Conclusion

Section snippets

Patient characteristics

Results

Discussion

Conflict of interest

Acknowledgements

Lancet Oncol

Lancet Oncol

Int J Radiat Oncol Biol Phys

Int J Radiat Oncol Biol Phys

Radiother Oncol

Semin Radiat Oncol

Radiat Oncol

Radiat Oncol

Int J Radiat Oncol Biol Phys

Comput Methods Programs Biomed

Breast radiotherapy
MRI-guided single fraction ablative radiotherapy for early-stage breast cancer: a brachytherapy versus volumetric modulated arc therapy dosimetry study