Multisegmented Tangential Breast Fields: a Rational Way to Treat Breast Cancer

Purpose: Using three-dimensional conformal radiation therapy (3D-CRT) and multisegmented conformal radiation therapy (MS-CRT) for breast cancer treatment, the dose coverage of the planning target volume (PTV) and the radiation burden on the organs at risk (OARs) were evaluated. Material and Methods: 3D-CRT and MS-CRT were planned for 436 unilateral breasts (217 left). All patients were treated with MS-CRT between 2005 and 2007. For PTV delineation and beam orientation, supportive structures were applied. The mean PTV was 1,130 cm 3 (in ten patients > 2,200 cm 3 ). Three-dimensional planning with weight-optimized medial and lateral open fields at a total dose of 50.4/1.8 Gy was followed by multisegmented planning with a reasonably high-dose-level dose cloud to define the medial subfield, and renewed optimization. This was repeated for the lateral subfield with a final optimization. For PTV coverage evaluation, the ICRU 50 was considered: the PTV portions receiving 95–107%, < 95% and > 107% of the prescribed dose (PTV D95– 107% , PTV D 107% ), and the PTV maximal dose (PTV Dmax ). To compare the OAR radiation burdens, the mean doses to the ipsi-/contralateral lung, contralateral breast, and whole heart were documented. Results: The multisegmented plans furnished significantly (p < 0.0001) better target coverage (PTV D95–107% 82.8% vs. 90.9%, PTV D107% 5.9% vs. 0.3% and PTV Dmax 56.6 vs. 54.3 Gy). The mean OAR doses remained almost unchanged: ipsilateral lung 10.5 versus 10.4 Gy, contralateral lung 0.4 versus 0.4 Gy, contralateral breast 0.8 versus 0.8 Gy, and whole heart (for left-sided cancers) 4.8 versus 4.8 Gy. The subfields required a mean of 9.8 MU (monitor units), i.e., a mean total 7.6 MU increment. The planning took 10–20 min, and the delivery 5–10 min. Conclusion: MS-CRT is a good alternative to breast intensity-modulated radiation therapy (IMRT) and seems adequate for right-sided cancers, whereas left-sided cancers necessitate a longer follow-up of heart-related side effects before a final assessment.