Measurement of mean cardiac dose for various breast irradiation techniques and corresponding risk of major cardiovascular event

Abstract

After breast conserving surgery, early stage breast cancer patients are currently treated with a wide range of radiation techniques including whole breast irradiation (WBI), accelerated partial breast irradiation (APBI) using high-dose rate (HDR) brachytherapy, or 3D-conformal radiotherapy (3D-CRT). This study compares the mean heart's doses for a left breast irradiated with different breast techniques. An anthropomorphic Rando phantom was modified with gelatin-based breast of different sizes and tumors located medially or laterally. The breasts were treated with WBI, 3D-CRT, or HDR APBI. The heart's mean doses were measured with Gafchromic films and controlled with optically stimulated luminescent dosimeters. Following the model reported by Darby (1), major cardiac were estimated assuming a linear risk increase with the mean dose to the heart of 7.4% per gray. WBI lead to the highest mean heart dose (2.99 Gy) compared to 3D-CRT APBI (0.51 Gy), multicatheter (1.58 Gy), and balloon HDR (2.17 Gy) for a medially located tumor. This translated into long-term coronary event increases of 22, 3.8, 11.7, and 16% respectively. The sensitivity analysis showed that the tumor location had almost no effect on the mean heart dose for 3D-CRT APBI and a minimal impact for HDR APBI. In case of WBI large breast size and set-up errors lead to sharp increases of the mean heart dose. Its value reached 10.79 Gy for women with large breast and a set-up error of 1.5 cm. Such a high value could increase the risk of having long-term coronary events by 80%. Comparison among different irradiation techniques demonstrates that 3D-CRT APBI appears to be the safest one with less probability of having cardiovascular events in the future. A sensitivity analysis showed that WBI is the most challenging technique for patients with large breasts or when significant set-up errors are anticipated. In those cases, additional heart shielding techniques are required.

Keywords: brachytherapy; breast neoplasms; heart diseases; radiation dosage; radiotherapy.

Figure 1

(A) Materials used during the breast phantom manufacture. (1) Styrofoam slices cut to fit CT contours. (2) Thermoplastic 3D breast contour obtained from the Styrofoam mold. (3–5) Small, medium, and large size of gelatin-based breast phantoms. (B) Styrofoam slices cut to the patient profile using CT images. (C) Thermoplastic mold over the Rando phantom modified with the large breast to ensure good contact.

Figure 2

Fields arrangement and various breast treatments dosimetry. (A.1) Medium size WBI treatment dosimetry and (A.2) tangential fields 3D representation. (B.1) 3D-CRT APBI dosimetry and (B.2) five fields no coplanar 3D representation. (C) Multicatheter HDR APBI dosimetry.

Figure 3

Breast treatments. (A) Multicatheter HDR APBI. (B) Foley catheter used for balloon HDR APBI. (C) 3D-CRT APBI.

Figure 4

Optically stimulated luminescent dosimeters and Gafchromic film placement between Rando slices with a 5 mm bolus.

Figure 5

Correlation between OSLDs and Gafchromic films measurements.

Figure 6

DVHs for WBI of medium and large breasts. More heart is receiving a higher dose for large breasts. WBI, whole breast irradiation.

Figure 7

Cumulative DVHs for various adjuvant breast irradiation techniques for a medially located tumor and a medium breast. The 3D-CRT APBI appears to be the safest by far. WBI, whole breast irradiation; 3D-CRT APBI, beam 3D-conformal radio therapy accelerated partial breast irradiation; HDR, high-dose rate.

Figure 8

Cumulative DVHs for various tumor locations and APBI techniques. There is no impact of location for 3D-CRT as opposed to HDR techniques. 3D-CRT APBI, beam 3D-conformal radio therapy accelerated partial breast irradiation; HDR, high-dose rate.

Figure 9

Cumulative DVHs for the sensitivity analysis on set-up error and motion effect for a medium sze breast and a medially located seroma. There is little impact of those factors for HDR, but a dramatic effect for WBI. WBI, whole breast irradiation; HDR, high-dose rate.