Radiation Doses to Contralateral Breast During Irradiation of Breast Cancer
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- Category: Vol. 77, June 2009
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Radiation Doses to Contralateral Breast During Irradiation of Breast Cancer,ADEL G. WAHBA and REHAM SAFWAT
Abstract
Aims: External beam radiotherapy is being used regularly to treat the breast malignancy postoperatively. The contribution of collimator leakage and scatter radiation dose, as well as the dose of the treatment fields, to contralateral breast is of concern because of high radio sensitivity of breast tissue for carcinogenesis. This becomes more important when the treated cancer breast patient is younger than 45 years and therefore the contralateral breast must be treated as organ at risk. Quantification of contralateral dose during primary breast irradiation is helpful to estimate the risk and reduce scatter dose to the contralateral breast.
Materials and Methods: In present study contralateral breast dose was measured in 30 cancer breast patients under-going extenal beam therapy. Postoperative radiotherapy was delivered by medial and lateral tangential fields daily, in addition to supraclavicle field with 200cGy/F to a total dose of 5000cGy in 25 fractions. A themoluminescence dosimeter chips were employed for these measurements. TLD chips were put on the surface of skin of contralateral breast, on the level of nipple, with and without shield, TLD chips were removed and measured for dose after 2h on Harshaw reader 5500.
Results: The dose at the contralateral breast nipple mea-sured by TLD chips and it was between 4.5 and 17% of the total primary breast dose which is 5000cGy in 25 fractions. Further it was observed that the maximum contribution of contralateral breast dose was due to medial tangential half blocked field (in Kds2). Dose was reduced to one third of the scatter dose to the contralateral breast using 2mm of lead shield and some modifications in the treatment technique.
Conclusion: Thermoluminescence dosimetry is quite easy, accurate and convenient method to measure the contralateral breast dose. Reduction in unwanted scatter dose to the con-tralateral breast is in accord with the philosophy of keeping radiation exposure as low as reasonably achievable and might be of most benefit for young patients.