Abstract
Background and purpose: Adjuvant breast radiotherapy (RT) is now part of the routine care of patients with
early breast cancer. However, analysis of the Early Breast Cancer Trialists’ Collaborative
suggests that patients with the lowest risk of dying of breast cancer are at significant
risk of cardiac mortality due to longer relapse-free survival. Patients with a significant
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 reduced 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 patient, plans were generated and compared using dose
volume histograms for planning target volume (PTV) and organs at risk. The plans included
conventional 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 four-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 cardiac shielding to conventional
tangents, without compromise of PTV coverage. The two- and four-field IMRT techniques
also reduced heart doses. The average 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 partial 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 maximum heart depths the
four-field IMRT plan achieved greater heart sparing than the partial shielding, although
irradiation of the contralateral breast was increased. Full cardiac shielding resulted
in the most complete heart sparing but with compromise of the PTV coverage; the mean
volume receiving less than 95% of the prescription dose was 4% (range 1.5–8.7%).
Conclusion: All patients undergoing adjuvant tangential breast RT in whom the 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.
Keywords
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Article info
Publication history
Accepted:
April 9,
2001
Received in revised form:
March 16,
2001
Received:
September 19,
2000
Identification
Copyright
© 2001 Elsevier Science Ireland Ltd. Published by Elsevier Inc. All rights reserved.
