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. 2025 Mar 29;10(6):101775.
doi: 10.1016/j.adro.2025.101775. eCollection 2025 Jun.

In Silico Assessment of the Radiation Dose Range for Definitive Stereotactic Body Radiation Therapy of Primary Breast Cancer

I Frank Ciernik  1   2 , Shubeen Singh  1 , Akash K Singh  2 , Philipp Goldschmidt  2 , Wilfried Budach  3 , Dirk Vordermark  4 , Jérôme Krayenbuehl  5
Affiliations

In Silico Assessment of the Radiation Dose Range for Definitive Stereotactic Body Radiation Therapy of Primary Breast Cancer

I Frank Ciernik et al. Adv Radiat Oncol. .

Abstract

Purpose: The maximal dose for partial breast irradiation (PBI) with stereotactic body radiation therapy for definitive local therapy of nonmetastatic breast cancer has not been established. Here we evaluate the maximal achievable coverage of the planning target volume suitable for PBI without violating organs-at-risk constraints.

Methods and materials: Planning computed tomography scans of 22 patients with pulmonary or cardiac risk factors and left-sided disease in prone and supine position (sp) were obtained. Plans for PBI in 5 fractions were generated according to the Guidelines of the American Society for Radiation Oncology. Maximum tolerated dose (MTD) was defined when the dose reached any constraint of a neighboring organ based on recommendations of the American Association for Physics in Medicine.

Results: Mean MTD was 45.9 ± 3.9 Gy (range, 38.8-53.9) in sp and 46.1 ±3.2 Gy (range, 37.3-53.9) in prone position (pp), respectively. The MTD was ≥44.3 Gy in sp and ≥44.8 Gy in pp in 95% of patients. Fat tissue was the dose limiting structure in 11 of 22 patients in sp and 15 of 22 in pp. Dmax to the fat tissue reached 40.0 Gy (±3.3 Gy) in sp and pp. Skin was the dose limiting structure in 7 of 22 patients in sp and in 6 of 22 in pp. Dmax to the skin was 30.5 Gy (±7.4 Gy) in sp and 31.0 Gy (±7.0 Gy) in pp (P = .8). Ribs were dose limiting in 4 of 22 patients in sp and in 1 of 22 in pp. Dmax to the ribs was 31.4 Gy (±9.5 Gy) in sp and 21.4 Gy (±11.0 Gy) in pp (P < .01). Dmax to the intraventricular artery was 3.4 Gy (±3.1 Gy) in sp and 7.5 Gy (±5.7 Gy) in pp (P < .01).

Conclusions: For definitive stereotactic body radiation therapy for early-stage breast cancer, we propose a dose escalation starting with 45 Gy in 5 fractions to be tested in a clinical trial. Prone position is advised for tumors close to the thoracic cage.

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Conflict of interest statement

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Figures

Figure 1
Figure 1
Beam geometry for stereotactic body radiation therapy. Two partial arcs used clockwise and counterclockwise complemented by 2 conformal fields with wedges. (A) Supine position. (B) Prone position.
Figure 2
Figure 2
Target volume coverage as a function of maximum tolerated dose (MTD). (A) Summary of dose-volume histograms (DVHs) in supine position. (B) Box plot of MTD to planning target volume (PTV) in supine position. (C) Summary of DVHs in prone position. (D) Box plot of MTD to PTV in prone position.
Figure 3
Figure 3
Normal dose distribution of maximum tolerated doses in supine and prone position.
Figure 4
Figure 4
Doses to organs-at-risk. (A) Mean dose-volume histogram (DVH) of fat in supine position. (B) Mean DVH of fat in prone position. (C) Mean DVH of bone in supine position. (D) Mean DVH of bone in prone position. (E) Mean DVH of skin in supine position. (F) Mean DVH of skin in prone position.
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