Abstract
High-dose-rate (HDR) brachytherapy is an effective internal radiation therapy procedure for treating malignant neoplasms. This technique is widely used in breast cancer treatments to destroy residual cancer cells surrounding the lumpectomy cavity following surgery. This is done by inserting a balloon catheter into the cavity that is inflated with saline as well as a medium of radiographic contrast. Then the radioactive isotope is positioned into the center of the balloon using an HDR unit to deliver the prescribed dose to a volume surrounding the balloon. Most of the currently available treatment planning systems (TPS) for brachytherapy, including Nucletron Oncentra, estimate dose using proprietary algorithms which use a pre-calculated dose metric derived from Ir-192 placed in a water phantom. However, they do not take into account variations in attenuation due to inhomogeneities in different tissues. This may lead to several questions: do these TPS estimate absorbed dose correctly within the target tissue? What are the effects on breast-air interface within the target volume? Does a radiographic contrast medium in the balloon alter the dose distribution calculated by TPS? These uncertainties and doses can be quantified by using the data recorded in a tissueequivalent patient phantom which is aided by a PN junction commercial diode detector and an electrometer. During this investigation, we used a cubical water phantom and Mammosite® single lumen balloon system to measure effects on breast-air interface, the diode detector was placed on the phantom wall to simulate the tissue air interface. Measured data were compared with predictions from the Oncentra TPS for the same geometry. These results may help quantify uncertainties in the predicted versus actual skin doses used during the treatments. This in turn could increase the clinicians’ predictive power regarding potential excessive skin dose that could cause toxicity in patients.
Highlights
1.1 Breast Cancer statistics Among the many types of cancer, breast cancer is the type that causes the most deaths among women worldwide [1]
4.1 Effect of Contrast Material The dwell times calculated with the treatment planning system for 100 cGy radiation dose at 5 cm from the MammoSite® catheter axis were recorded for different contrast concentrations; and the dwell time data were normalized to 0% contrast
4.2 Effect of Breast Air Interface The dwell times calculated by the treatment planning system for 100 cGy radiation dose at 5c m from the MammoSite® catheter axis were recorded for different over-lying water thicknesses; and data were normalized to over-lying water thickness d, where d is equal to 7cm
Summary
1.1 Breast Cancer statistics Among the many types of cancer, breast cancer is the type that causes the most deaths among women worldwide [1]. In 2013, the United States alone reported 232,340 new breast cancer cases and 39,620 deaths due to breast cancer [2]. It can be inferred using the rates from 2007-2009 that 12.38% of women born today will be diagnosed with breast cancer during their lifetime [3]. This means that one in eight women are going to be diagnosed with cancer during their life [4]. The increasing rate of survival is thought to be due to advanced treatment options and early diagnosis
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