Abstract
Purpose: To study the reproducibility of tangential breast treatment technique using online portal imaging system.Introduction: Treatment verification and reproducibility is an important step in radiotherapy to achieve a better tumor control. Care should be taken to ensure the same dose to be delivered in the same volume of irradiation. Electronic portal imaging technique plays a vital role in accomplishing the above task by studying the setup error and correct the same before the treatment delivery. Method and Materials: Twelve patients of carcinoma of breast were selected for this study and CT based planning was performed with simple tangential fields. The patients were then treated on a 6MV linear accelerator equipped with an electronic portal imaging device. Portal images were acquired for both medial and lateral tangential fields for 10 fractions and intra and the inter‐fraction studies were performed for all the patients. The parameters such as central lung distance (CLD), Central beam edge to skin distance, central irradiated width and cranio‐caudal distances were measured on the acquired portal image. In the intra‐fraction study lead markers were placed on the patient skin to study the breast movement during treatment. Results: The maximum variation of the marker during the treatment was 1.8 mm with a standard deviation of 0.575 mm. Similarly the CLD, CBESD, CIW and CCD were analyzed for the intra and inter‐fraction variation. Conclusion: Online portal imaging device is an important tool for ensuring the proper delivery of planned dose. Our result suggests that intra‐fraction motion of the breast has less impact on the treatment volume.