Protection of the contralateral breast during radiation therapy for breast cancer

Conformal Radiation Therapy (3DCRT) and Intensity Modulated Radiotherapy (IMRT) improve the relationship between tumor control and complications in normal tissue. However, these techniques may cause an increase of the normal tissue volume irradiated with low doses or an increase of the doses outside the beam. The aim of this work was to measure and compare the scatter dose to the contralateral breast using both the conventional two-field technique and the 3DCRT technique with blocks. The contralateral breast dose was measured with thermoluminiscent dosimeters. The present work is divided in three parts:1)Characterization of the radiation field outside the treatment beam 2)Determination of the dose to the contralateral breast 3)Design and construction of a shield to reduce the scatter dose to the contralateral breast. Treatment using 3DCRT technique was delivered to a phantom. From one to ten 2mm thick lead sheets were placed on the dosimeters to attenuate radiation to the contralateral breast from the head, without blocking the treatment beam. Using the conventional technique the average dose to the contralateral breast was 2.09Gy,4.18%(2.9%–19%) of the 50Gy prescribed dose. The contribution of the medial field was 3.36%(2.3%–21.1%) and of the lateral field 0.86%(0.4%–3.7%). When using 3DCRT technique the average dose to the opposite breast was 5,9Gy,11.8%(7.9%–24%) of the prescribed dose. The contribution of the medial field was 10.3%(6.7%–20%) and of the lateral field 1.6%(1.1%–3.8%). A 2mm thick lead shield with a 0.2g/cm2 thick wax coat was constructed which reduced the dose from 11.8% to less than 2%. The blocks increase the dose to the contralateral breast, the highest dose being attributed to the medial field. Our shield reduced the dose, which allowed the regular use of 3DCRT with blocks. In addition, we found that this shield was comfortable for the patients and easy to position for the therapists.