Hypofractionated whole‐breast radiotherapy using a three‐dimensional conformal technique: Toxicity comparison in different breast sizes
Authors: Kim Jae , Forouzannia Afshin , Saini Amitpal , Hwang Catherine 
Published: November 2018

Objectives

Patients with larger breast sizes have been considered to be contraindicated for hypofractionated radiation therapy. In the present retrospective study, we analyzed the dosimetric and clinical toxicity outcomes of patients with different breast sizes and treatment positions. We conclude that three‐dimensional conformal radiotherapy (3D‐CRT) hypofractionated radiation therapy can be therapeutically applied regardless of the breast size and treatment position. The aim of this study is to report a comparison of the dosimetry and toxicity of 3D‐CRT on patients with different breast volumes who received whole‐breast hypofractionated radiation therapy.

Methods

From November 2014 to May 2017, 106 patients with stage 0–IIA breast cancers were treated at Florida Hospital Altamonte Radiation Oncology. The patients were divided into two groups, group 1: large breast (chest wall separation >25 cm or planning target volume [PTV] >1500 cm3; n = 30); and group 2: small breast (chest wall separation <25 cm and PTV <1500 cm; n = 76). Patients were treated in the prone or supine position. Patients underwent hypofractionated 3D‐CRT to the whole breast (42.56 Gy in 16 fractions) followed by a boost dose (10 Gy in 5 fractions). A comparison of dosimetric and clinical toxicity outcomes during acute and subacute follow up among the two groups were analyzed and reported.

Results

The mean PTV V95 (percentage of volume receiving ≥95% of prescribed dose) was 99.07%, and the mean V105 (percentage of volume receiving ≥105% of prescribed dose) was 30.77%, whereas the mean V107 (percentage of volume receiving ≥107% of prescribed dose) was 6.25%. The maximum cardiac dose was comparable between the two groups, and did not correlate with the breast size or volume (P = 0.41). The maximum cardiac point dose in group 1 was 26 Gy, and that of Group 2 was 22 Gy. The maximum skin dose was 45.5 Gy for both groups, and did not increase with increased breast size (P = 0.92). The maximum dose to the ipsilateral lung did not increase with breast size (P = 0.08), but the mean dose to the ipsilateral lung did increase with the breast size (P < 0.0001). When comparing supine and prone treatment positions, PTV of the breast in the supine position was significantly larger compared with the prone position (P < 0.0042). Likewise, the mean ipsilateral lung dose was substantially increased in the supine position compared with the prone position (P < 0.0001). Radiation Therapy Oncology Group grade 0, 1, and 2 skin toxicities during therapy were noted in 2%, 56%, and 36% of patients, respectively. Large breasted patients had higher grade 1 skin toxicity compared with small breasted patients (60% vs 55%), but without statistical significance (P > 0.05). Likewise, the small breasted group had higher acute grade 2 skin toxicity compared with the large breasted group (30% vs 38%), but without statistical significance (P > 0.07).

Conclusions

For early‐stage breast cancer (0–IIA), adequate PTV coverage and toxicities to the heart, lung, and skin were achieved with 3D‐CRT hypofractionated radiation therapy, regardless of breast size and treatment position. Contrary to previously reported data based on intensity‐modulated radiation therapy, the supine position did not have an increased dose to the heart in our 3D‐CRT treatments. Overall, these results show that 3D‐CRT hypofractionated radiation therapy can be therapeutically applied regardless of the breast size and treatment position.