Dosimetric evaluation of conventional radiotherapy, 3-D conformal radiotherapy and direct machine parameter optimisation intensity-modulated radiotherapy for breast cancer after conservative surgery.

Background: The use of conservative surgery combined with whole-breast irradiation (WBI) has been established as a valid alternative to mastectomy for the management of early-stage breast cancer. The aim of this study was to compare dosimetric parameters of the planning target volume(PTV) and organs at risk (OARs) between conventional radiation therapy (CR), 3-D conformal radiation therapy (3DCRT), and direct machine parameter optimisation intensity-modulated radiation therapy (DMPO-IMRT) after breast-conserving surgery.

Methods: Computed tomography (CT) scans from 20 patients (13 left-sided and 7 right-sided) previously treated with T1N0 or ductal carcinoma were selected for this dosimetric planning study. We designed CR, 3DCRT and DMPO-IMRT plans for each patient. The prescribed dose was 50 Gy/2 Gy/25 f, 95% of PTV received the prescription dose. Doses were computed with a commercially available treatment planning system using convolution/superimposition (CS) algorithm. Plans were compared according to dose-volume histogram (DVH) analysis in terms of PTV homogeneity and conformity indices (HI and CI) as well as OARs dose and volume parameters.

Results: Both the HI and CI of the PTV showed statistically significant difference between CR, 3DCRT and DMPO-IMRT with those of DMPO-IMRT were best (P < 0.05). Compared with CR, 3DCRT showed smaller exposed volumes of ipsilateral lung, contralateral breast and heart while DMPO-IMRT indicated larger exposed volumes of ipsilateral lung (except for V20 and V30), contralateral breast and heart. In addition, DMPO-IMRT demonstrated an increase of exposed volume of ipsilateral lung (except for V30), contralateral breast and heart compared with 3DCRT.

Conclusions: In WBI of breast cancer after conservative surgery, 3DCRT and DMPO-IMRT improved the homogeneity and conformity of the PTV compared with CR. Meanwhile, 3DCRT reduced the irradiated volumes of OARs at all dose levels listed in our study while DMPO-IMRT reduced the irradiated volumes of OARs in high-dose areas but increased the irradiated volumes of OARs in low-dose areas.