Ciência e terapia do câncer

Reduction of Dose to the Contralateral Breast by use of Lead Shield in Radiation Therapy for post-op Ca Breast Patients

Abstract

Richa Verma

Introduction: Breast cancer is the most common cause of cancer in women in India. India ranks number one in the number of healthy life years lost (DALY- Disability Adjusted Life Years ) due to breast cancer. Surgery, radiation therapy and chemotherapy (+/- hormonal therapy) constitute the multimodality approach for treatment of breast cancer. Radiation therapy is recommended as a treatment of choice for post-operative ca breast patients. Radiation doses to nearby critical normal structures like heart, lungs, and contralateral breast (CLB) increases risk of second malignancies due to increasing life expectancy of the patient. During external beam therapy unwanted radiations produced due to leakage from collimator and scatter from primary beam . It appears prudent to be aware of these potential risk and efforts must be made to maintain a dose to CLB as low as reasonably achievable. In this study, we measured doses to the CLB and studied reduction in dose achieved by use of of a 2mm lead shield. Materials and Methods: Ten number of post-operative Ca-Breast patients were taken for our study. All the patients underwent 3D conformal radiotherapy in Linear Accelerator(Make: Varian Medical Systems, Model: Clinac 2100CD) which has multi leaf collimator 40 pairs. Forward IMRT Treatment plans were performed in Eclipse Treatment planning system (Make: Varian Medical Systems, Version 13.8)As the intent is to measure the contralateral breast dose the TLD discs ( Type; CaSo4;Dy, 13mm dia, 0.8mm thick) were placed over the CB; Customized lead shields were prepared to study the reduction of dose to CB. Measurements were made with the TLD Discs with the presence and the absence of customized lead shield over the CB and doses were calculated with the help of TLD Reader (Make: Nucleonix, Hyderabad). Here we present a case of 10 ca breast patients who received radiotherapy post operatively. Radiation therapy of 40.05 Gy was planned in 15 fractions, 5 days a week, using the Eclipse Treatment Planning System version 8.9.15, with a pencil beam convolution algorithm and 6 MV photon beam. Plans were transferred to a linear accelerator (Varian 2300 CD) for execution of treatment. Twenty-four CaSO4 thermoluminescent dosimeter discs (TLDs) were used for dose measurement over the CLB. The dose was measured for each patient without a lead shield for 7 fractions and with lead shield for 7 fractions. Results: Mean doses/fractions received by the CLB without and with a lead shield were 12.62 ± 1.29 cGy and 6.42 ± 2.62 cGy, respectively, with total doses of 208.326 ± 32.43 cGy (5.14% of prescribed dose) and 113.7 ± 65.62 cGy (2.83% of prescribed dose). The average reduction in mean dose with a 2mm thick lead shield was 53.10 ± 17.18%, in the range of 20 to 80% and statistically significant (p < 0.001) Conclusion: The above study was performed for 10 number of cases and it was evident in all the patients the dose to CB has reduced to less than 50% (p value <0.05). The lead sheets were customized for individual patients and it was an effective parameter in CB dose reduction. The lead sheets are in- house customized and can be easily made in every department with minimal cost. This study will be further extended for more number of cases with increment in lead thickness. We may find an optimum lead thickness that reduces significant dose to CB without creating discomfort to the patients.