In-vivo dosimetry with EBT-3 gafchromic films and thermoluminescent dosimeters in breast cancer radiotherapy treatments

Purpose: Breast cancer is the first common cancer and one of the deadliest cancers among women worldwide. The treatment of cancer patients using radiotherapy involves many risk factors which can lead to severe complications. The aim of this study was to investigate measured doses received by breast cancer patients during external beam radiotherapy (EBT) treatment and compare to doses prescribed, using EBT-3 films and TLDs as detectors. Dosimetric evaluation of entrance doses during patient irradiation and scattered doses to sensitive organs for patients requiring postmastectomy radiotherapy (PMRT) were carried-out. Method: Total of 183 field measurements for left and right breasts were performed on a male and 60 females undergoing PMRT. Measurements of delivered doses to patients were performed by applying both EBT-3 film and TLD chips directly on patient skin along the central beam axis, and on the sensitive selected organs during irradiations to measure scattered radiations. Irradiated films were scanned with a flatbed scanner and analysed with ImageJ software. The TLDs were read using Hawshaw 6600 TLD reader. Result: The percentage error between measured and prescribed doses ranged from 0.07%—8.76%, < 0.38%—9.61% and < 0.1%—11.51% for the supraclavicular, medial tangential and lateral tangential irradiations respectively. Results obtained show that the overall tolerance errors of ± 7% for breast irradiation in dosimetry was achieved in 99.45% and 86.33% of all the cases studied for EBT-3 films and TLDs respectively. Analysis of the results obtained from the scatter received by selected sensitive organs (eye, thyroid, sternum, contralateral breast, shoulder (acromioclavicular joint (ACJ)) and lung as Organ at Risk (OAR) using TLDs, shows that almost all sensitive organ absorbed doses were less than the required limit of 0.1 Gy, except the absorbed doses obtained to the thyroid and lung that were estimated to be 0.151 Gy and 0.1233 Gy. At a p-value < 0.05, there was a statistically significant difference in the mean value of measured doses on patients between EBT-3 films and TLDs for all the three field sites used in breast irradiation. While almost all measured dose with EBT-3 were within the tolerance limit, TLDs measurements gave a relatively higher dose compared to EBT-3 films. Conclusion: The level of accuracy between prescribed and measured doses is seen generally as acceptable in the study. EBT-3 film was found most accurate detector that we recommend for use in IVD. The study also shows that errors are reduced by applying various correction factors (field size, SSD, angle dependence, wedge, tray) while determining the patient received dose (depth dose). This study served as part of patient quality assurance at the radiotherapy centre as recommended by national regulatory bodies and international requirements.