Rationale for External Beam APBI

Data supporting the concept of PBI result from major randomized studies that have evaluated the role of adjuvant radiation therapy in breast conservation (Clark et al. 1996; Liljegren et al. 1994; Veronesi et al. 2001). These studies are reviewed elsewhere in this textbook, but basically demonstrate that ipsilateral breast recurrences largely occur at the original tumor bed and the ipsilateral breast elsewhere failure rate is similar to the contralateral breast new primary rate (1.5-4% at 13 years) (Perera et al. 1995; Vicini et al. 2004). Based on these data, the partial breast target volume comprising the lumpectomy cavity with a margin may be adequate in reducing the risk of local recurrence in women with small, adequately resected tumors. With hypofractionated radiation therapy, reducing the target volume from the whole breast to the cavity with a margin is intended to reduce late toxicity including telangiectasias and fibrosis, which are more prominent when the whole breast is treated with a hypofractionated schedule. APBI is now a potential adjuvant treatment option for patients with early-stage breast cancer who, due to comorbid conditions and/or age, and/or logistics, are not suitable candidates for 6-7 weeks of daily radiation therapy, but would benefit from adjuvant treatment based on life expectancy. However, some patients who are candidates for PBI are not appropriate candidates for brachytherapy applicators such as the MammoSite balloon or interstitial needles (due to the location of the lumpectomy cavity, or size, shape, ratio of breast/cavity volumes), or would rather undergo a non-invasive treatment approach. In such patients, 3D confor-mal APBI may be most applicable.

Table 11.1 APBI: external beam radiotherapy studies (Rosenstein et al. 2004)

(ยป)

Age (years)

Tumor size (cm)

Dose fractionation

Median follow-up

(months)

Christie Hospital

353

<70

<4

5 Gy X 8 in 10 days

96

New York University

47

Postmenopausal

<2

6 Gy X 5 in 10 days

Beaumont

Hospital

31

50

<3

3.4 Gy X 10 in 5 days or 3.85 Gy X 10 in 5 days

10

Technique

Field

Tumor bed

Margin

Ipsilateral

arrange

definition

(cm)

breast

ment

(CTV)

recurrence rate (%)

Supine,

Single elec

Tumor bed

0

6(21/355)

10-MeV

tron beam

at surgery

electrons

Prone, 6-MV

Two

Architectural

1.5-2

0

photons

coplanar mini tangents

distortion on CT

Supine, 6-

Three to five

Architectural

1-1.5

-

MV, 18-MV

noncoplanar

distortion

photons

beams

and surgical clips on CT

0 0

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