Determining the contralateral breast dose during radiotherapy of breast cancer using rainbow dosimeter

External beam radiotherapy is being used regularly to treat the breast malignancy postoperatively. The contribution of the collimator leakage and scatter radiation dose to contralateral breast is of concern because of high radio sensitivity of breast tissue for carcinogenesis. This becomes more important when the age of breast 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 of radiation induced secondary breast malignancy. In present study contralateral breast dose was measured in forty cancer breast patients undergoing external beam therapy by cobalt-60 teletherapy machine. Post-operative radiotherapy was delivered by medial and lateral tangential fields daily, in addition to supraclavicular field with 200 cGy per fraction to a total dose of 5000 cGy in 25 fractions. The detectors of rainbow dosimeter were employed for these measurements.The dose at the contralateral breast measured by a rainbow dosimeter for tangential fields was between 5.34–6.40% whereas for supraclavicular field it is 1.2–1.75% of the dose. The contribution due to the medial tangential field is almost twice as that due to lateral tangential field so that maximum dose which contributes contralateral breast dose is due to medial tangential field. The goal of this investigation was to quantify the radiation dose to the contralateral breast after radiotherapy for primary breast cancer. Rainbow dosimetry is easy, accurate and convenient method to measure the contralateral breast dose.