Radiotherapy (RT) for breast cancer results in scattered radiation
doses to the contralateral breast (CB) which is found to be associated
with an increased risk of secondary malignancy. This study investigates
the dosimetric and volumetric changes in CB as a consequence of changes
during the breathing cycle.
Patients- Methods: Ten patients with breast carcinoma underwent breast
conservative surgery or mastectomy receiving RT are included. For this
study, planning CT (computerized tomography) images were obtained
during deep inspiration (I) and end of expiration (E), as well as free breathing
(FB) in order to simulate respiratory cycle. I and E images were registered
to FB. Targets and CB were contoured by the same Radiation Oncologist
on 3 image series. Three dimensional conformal or IMRT planning
was done to obtain dose - volume information. Treatment plans and dose
calculations were constructed using CT images taken during FB. Then, plan
was exported to I and E image series. The significance of dose and volume
changes was investigated.
Results: Mean breast doses changed marginally between FB and I (p=0,057)
while not significant between FB and E (p=0.58). There was a significant
variation between I and F, and I and E for 1% of CB volume receiving maximum
dose (p=0.008 and p=0.03) while it was not significant between
FB and E (p=0.35). Intended dose constrains for CB were achieved for all
patients as mean CB doses were less than 1 Gy and max CB doses were less
than 3.5 Gy. However, these limitations exceeded during I phase in 6 out
of 10 patients regarding maximum CB doses and 1 out of 10 patients for
mean CB dose.
Conclusion: Contralateral breast dose changes should be considered together
with heart and lung dose changes during the different phases of respiratory
cycle because maximum CB dose could exceed the upper limit in 60%
of patients during I.