The electron energy (range 6-16 MeV) was chosen so that
the 95'Yn isodose surface encompassed the whole target
volume. The dose planning was calculated on the central
CT slice and in some cases on additional slices if the chest
wall was uneven. Correction for lung density was based on
the CT images' data. In 16 patients two different electron
energies were used because of large differences between the
thickness of the chest wall and the sternal region. Bolus
material was used in 109 (80%) of the cases to even-out
smaller differences in the thickness of the chest wall.
The patients treated after surgery for local recurrence of
the disease were usually treated with an additional small
boost electron field against the scar. The electron energies
were usually lower than for the main treatment of the
chest wall and the scar was treated up to 60 Gy.
The upper internal mammary, axillary, and supraclavicular
lymph nodes were treated with an anterior 8 MV
photon beam as well as the most lateral part of the chest
wall. The prescribed dose per fraction was 2.0 Gy at a 3-cm
depth in the supraclavicular fossa. To achieve 2.0 Gy in the
centre of the axilla, without getting a substantial overdose
in the anterior part, a small posterior axillary 8 MV photon
beam was added based upon the thickness of the axilla. The
reference dose per fraction of these fields was in the order
of 0.37 Gy. This part was planned manually.
The patient was placed in the supine position with the
chest elevated (27") to obtain a horizontal treatment surface.
A special support was used and the arm on the
treated side was abducted to a 90-degree angle at the
shoulder joint. The patient's position was slightly different
at the dose-planning CT (17" elevation) owing to technical
circumstances. As an example, an original dose distribution
calculated in the central plane (at the level of the
mamilla) for the electron beam and the lateral part of the
photon beam is shown in Fig. la.
Partial mastectomy. The target volume was defined as
the ipsilateral internal mammary, axillary, and supraclavicular
lymph nodes, the chest wall, and the breast. The
prescribed dose to the breast was 50 Gy. The prescribed
dose to the rest of the target volume was 46 Gy, given in
2.0 Gylfraction, 5 fractions/week.
The lower internal mammary lymph nodes (IMN), the
chest wall, and the breast were in most cases treated with
two opposing tangential photon beams (range 4-8 MV).
As an example, an original dose distribution calculated in
the central plane is shown in Fig. lb. The minimum dose
accepted within the target volume was specified as 95% of
the prescribed dose. In many treatments a special lead
shielding was used to conform these beams to the target
volume, thereby sparing the heart and/or the lower part of
the lung.