During the course of radiation treatment, standard quality control measures are used to monitor the accuracy of delivery of radiation and adherence to the planned treatment protocol. In addition to the routine machine calibration checks, other measures include: (i) clinical examination, (ii) verification of patient position on the treatment couch, and (iii) port film (fig 3) checks of the treatment field.
In spite of undertaking the above-mentioned quality control measures, in the case of radiation delivery to the breast with a tissue expander in place, subtle changes in the prosthesis can escape detection. This can lead to serious dosimetric inaccuracies causing over and/or under dosing of the treatment volume. This will result in failure of loco-regional control apart from poor cosmesis.
Figure 3. Normal simulation film revealing that the whole “breast mound” is completely and adequately in the planned radiation port.
In the radiation treatment of an augmented breast with a temporary tissue expander, failure of radiation therapy to prevent loco-regional relapse can be attributed to deviations from the prescribed dose distribution and planned treatment volume. This can be due to: (i) fluctuations in shape and volume of tissue expander during the course of therapy, (ii) possible damage to the tissue expander, (iii) changes occurring to the surrounding structures such as ribs and chest wall (iv) presence of seroma, infection, necrosis and capsular contracture (v) spontaneous changes (expansion or deflation) occurring in the prosthesis. There is a need for establishing quality control parameters in patients with temporary tissue expanders who are candidates for radiation treatment.
Figure 4. Mechanical stress and strain of the prosthesis during radiation can cause the prosthesis to expand anteriorly abnormally. This can lead to dosimetric discrepancy.