[Intensity modulation in breast radiotherapy: development of an innovative field-in-field technique at Institut Gustave-Roussy]

Purpose: To assess the potential dosimetric gain of presegmentation modulated radiotherapy (OAPS, DosiSoft™) of breast, compared to routine 3D conformal radiotherapy.

Patients and methods: Twenty patients treated with conservative surgery for breast cancer (9 right and 11 left sided) with various breast volume (median 537 cm(3); range [100-1049 cm(3)]) have been selected. For each patient, we have delineated a breast volume and a compensation volume (target volumes), as well as organs at risk (lungs and heart). Two treatment plans have been generated: one using the routine 3D conformal technique and the other with the presegmentation algorithm of DosiSoft™ (OAPS). The dose distribution were analyzed using the conformity index for target volumes, mean dose and V30 Gy for the heart, and mean dose, V20 Gy and V30 Gy for lungs.

Results: Over the 20 patients, the conformity index increased from 0.897 with routine technique to 0.978 with OAPS (P<0,0001). For heart and lung, OAPS decreased irradiation (mean cardiac dose 1,3 vs 1,6 Gy [P<0,0001] and pulmonary V20 Gy 6,6 vs 7,1 [P<0,0001]).

Conclusion: OAPS (DosiSoft™) is an original method of segmentation of breast. It is automatic, fast and easy, and is able to increase the conformity index, while sparing organ at risk.