Pre-operative CT to improve delineation of the tumorbed in radiotherapy for breast cancer.

Whole breast irradiation with 50 Gy after lumpectomy for breast cancer has been
shown to reduce the local recurrence rate with a factor 3 to 4. An additional
boost of 16 Gy to the tumorbed has been shown to improve the local control rate
even further with a factor 2. However, this boost dose appears to reduce not
only the local recurrences in the tumorbed, but also elsewhere in the breast,
suggesting that the boost may not always be delivered at the correct region. In
addition, even with the boost dose of 16 Gy, the local recurrence rate in young
patients < 40 yr is still quite high - with the majority of recurrences in the
tumorbed. Consequently, further improvement of the local control, especially in
young women, is still an important aim to pursue, in order to maintain breast
conserving therapy (BCT) as an acceptable treatment option in young women. One
way to improve local control may be to increase the dose [Young Boost Trial],
but also to improve the definition of the tumorbed, i.e. the target volume for
boost irradiation. We expect that visualization of the tumor priro to surgery
on a CT scan made in radiation treatment position will improve the definition
of the target volume for boost irradiation.

The aim of this study is to investigate the effect of incorporating a CT-thorax
in the target volume delineation process on 1) percentage of the target volume
that receives less than 85% of the prescribed dose, 2) the size of the
irradiated boost volumes, and 3) the interobserver variation in target volume
delineation.

A CT scan of the thorax will be made < 3 weeks prior to surgery, with the
patient in radiation treatment position. After breast conserving surgery,
patients will be referred for post-operative radiotherapy according to the
standard guidelines. Prior to radiotherapy, a standard CT thorax scan will be
made for treatment planning.
The planning target volume (PTV) for the boost will be delineated according to
the MAASTRO protocol, by three independent observers (PTV-1A-C), using the
planning CT only. Delineation of the boost will be repeated after 3D
registration of the pre-operative CT scan with the planning CT-scan (PTV-2A-C).
Thereafter, consensus will be obtained for the PTV-1A-C and the PTV-2A-C,
resulting in one PTV-1 and one PTV-2 for each patient. Radiation treatment
plans (RT-plans) will subsequently be designed for PTV-1 and PTV-2. Coverage of
the treatment plans by the 85% isodose for both PTV-1- and PTV-2, and the
irradiated volumes (percentage of the volume receiving 95% or more (V95)) will
be calculated. Patients will be treated with the treatment plan for PTV-2.

Both a contrast enhanced CT and a CT without contrast will be made to
investigate in which patients contrast enhancement has additional value.

Patients will only be included after written informed consent. The preoperative
CE-CT-thorax-scan yields little additional radiation exposure, which will
however be negligible compared to the radiation treatment to be given because
of the breast cancer. In addition, there is a small risk on an allergic
reaction to the intravenous contrast, and on renal complications. Therefore,
renal function will be checked prior to giving contrast. A kreatinine clearance
< 60 ml/min will be a contra-indication for contrast. The pre-operative CT-scan
will be made in MAASTRO clinic, requiring an additional visit to MAASTRO
clinic. A possible benefit may be that the pre-operative CE-CT thorax may
improve the definition of the target volume, and thereby 1) reduce the risk on
a local recurrence, and 2) reduce the size of the irradiated volume, thereby
improving the cosmetic outcome. A possible drawback may be that the size of the
irradiated volume increases, which may detoriate the cosmetic outcome.