Cardiac avoidance in breast radiotherapy: a comparison of simple shieldingtechniques with intensity-modulated radiotherapy

Background and purpose: Adjuvant breast radiotherapy (RT) is now part of th e routine care of patients with early breast cancer. However, analysis of t he Early Breast Cancer Trialists' Collaborative suggests that patients with the lowest risk of dying of breast cancer are at significant risk of cardi ac mortality due to longer relapse-free survival. Patients with a significa nt amount of heart in the high-dose volume have been shown to be at risk of fatal cardiac events. This study was designed to assess whether conformal planning or intensity-modulated radiotherapy (IMRT) techniques allow reduce d cardiac irradiation whilst maintaining full target coverage. Material and methods: Ten patients with early breast cancer were available for computed tomography (CT) planning. Each had at least 1 cm maximum heart depth within the posterior border of conventional tangents. For each patie nt, plans were generated and compared using dose volume histograms for plan ning target volume (PTV) and organs at risk. The plans included conventiona l tangents with and without shielding. The shielding was designed to either completely spare the heart or to shield as much heart as possible without compromising PTV coverage. IMRT plans were also prepared using two- and fou r-field tangential and six-field arc-like beam arrangements. Results: PTV homogeneity was better for the tangential IMRT techniques. For all patients, cardiac irradiation was reduced by the addition of partial c ardiac shielding to conventional tangents, without compromise of PTV covera ge. The two- and four-field IMRT techniques also reduced heart doses. The a verage percentage volume of heart receiving > 60% of the prescription dose was 4.4% (range 1.0-7.1%) for conventional tangents, 1.5% (0.2-3.9%) for pa rtial shielding, 2.3% (0.5-4.6%) for the two-field IMRT technique and 2.2% (0.4-5.6%) for the four-field IMRT technique. For patients with larger maxi mum heart depths the four-field IMRT plan achieved greater heart sparing th an the partial shielding, although irradiation of the contralateral breast was increased. Full cardiac shielding resulted in the most complete heart s paring but with compromise of the PTV coverage; the mean volume receiving l ess than 95% of the prescription dose was 4% (range 1.5-8.7%). Conclusion: All patients undergoing adjuvant tangential breast RT in whom t he heart is seen to be in the high-dose volume should be considered for the addition of cardiac-sparing lead blocks. Three-dimensional CT planning and alternative beam arrangements with IMRT optimization enables more complete cardiac sparing without compromise of PTV coverage in certain patients. (C ) 2001 Elsevier Science Ireland Ltd. All rights reserved.