Bi-tangential hybrid IMRT for sparing the shoulder in whole breast irradiation

Quantifying radiation dose delivered to individual shoulder muscles during breast radiotherapy

BACKGROUND AND PURPOSE

Radiotherapy is an effective treatment for managing breast cancer, but patients may experience shoulder morbidity after completing radiotherapy. There is a knowledge gap regarding how the inclusion of the regional lymphatics in radiation treatment regimens influence the radiation dose delivered to the underlying shoulder musculature.

MATERIAL AND METHODS

Five standardized radiation treatment regimens were developed from the computed tomography (CT) scans of 11 patients: tangent fields only (T), high tangent fields (HT), T+supraclavicular fossa and axillary apex with an anterior oblique beam (SCV), T+SCV+axillary nodes with an anterior oblique beam (SCV+AX), and T+SCV+AX with the nodal regions treated with a directly opposed beam configuration (DO). The muscle volumes for nine shoulder muscles anatomically located with the treatment regimens were segmented from the same CT scans. The effect of the nine muscles and five treatment regimens on the percentage of each muscle receiving at least 48Gy (V48Gy) was analyzed with two-way and one-way repeated measures ANOVAs.

RESULTS

A statistically significant interaction existed between the nine shoulder muscles and five treatment regimens (p<0.001) on the V48Gy dose. Subsequent one-way analyses found statistically significant main effects of treatment plan on the V48Gy dose for each muscle (p<0.001). The pectoralis major and minor had the greatest V48 doses across the five treatments regimens. The HT, SCV+AX and DO treatment regimens produced statistically significant increases in the V48 dose of the latissimus dorsi and teres major. The infraspinatus, subscapularis, supraspinatus, teres minor, and trapezius only observed statistically significant V48 doses when treated with a DO plan.

CONCLUSIONS

These findings highlight the muscles (pectoralis major, pectoralis minor, latissimus dorsi, and teres major) that may exhibit future morbidity after radiation, and indicate that nodal RT delivered with a DO beam arrangement delivers the highest muscle dose.

Comparison of breast simultaneous integrated boost (SIB) radiotherapy techniques

Purpose

To dosimetrically evaluate different breast SIB techniques with respect to target coverage and organs at risk (OARs) doses.

Methods

Four IMRT techniques were compared in 12 patients. Three techniques employ tangential whole breast irradiation with either two coplanar fields (T-2F), or four non-coplanar fields (T-NC), or one Volumetric Modulated Arc Therapy (T-VMAT) for the boost volume. The fourth technique is a fully-modulated VMAT technique (f-VMAT). Dosimetric parameters were compared for the boost and breast target volumes as well as OARs. Delivery efficiency was analysed based on number of monitor units (MUs) and estimated delivery time.

Results

T-VMAT and f-VMAT ranked highest with respect to integral assessment of boost and breast treatment quality measures. T-VMAT significantly outperformed f-VMAT with respect to ipsi-lateral lung and left-sided patients’ heart volumes ≥ 5 Gy (35 % ± 5 % vs. 52 % ± 6 % and 11 % ± 5 % vs. 22 % ± 6 %, respectively). f-VMAT significantly outperformed T-VMAT with respect to ipsi-lateral lung volume ≥ 20 Gy (13 % ± 2 % vs. 15 % ± 3 %) and heart volume ≥ 30 Gy in left breast cancer (0 % ± 0 % vs. 1 % ± 1 %). T-VMAT and f-VMAT needed 442 ± 58 and 1016 ± 152 MUs, respectively.

Conclusions

The hybrid T-VMAT is considered the technique of choice due to its balance of quality, efficiency and dose to OARs.

Axillary irradiation omitting axillary dissection in breast cancer: is there a role for shoulder-sparing proton therapy?

The recent EORTC 10981-22023 AMAROS trial showed that axillary radiotherapy and axillary lymph node dissection provide comparable local control and reduced lymphoedema in the irradiated group. However, no significant differences between the two groups in range of motion and quality of life were reported. It has been acknowledged that axillary irradiation could have induced some toxicity, particularly shoulder function impairment. In fact, conventional breast irradiation by tangential beams has to be modified to achieve full-dose coverage of the axillary nodes, including in the treatment field a larger portion of the shoulder structures. In this scenario, alternative irradiation techniques were discussed. Compared with modern photon techniques, axillary irradiation by proton therapy has the potential for sparing the shoulder without detrimental increase of the medium-to-low doses to the other normal tissues.