PURPOSE: Brachytherapy plays an important role in radiation therapy a wide range of tumor sits such as vaginal, cervical and endometrial cancers. The purpose of this project was to design, fabricate and verify a new phantom for dosimetric verification at small distances from GYN applicators used with GZP6 cobalt-60 HDR system. METHODS: A new phantom has been designed and fabricated from 90 slabs of 18×16×0.2 cm3 Perspex to accommodate one tandem and two ovoids. The thin layer of the slabs was chosen to place GafChromic films in between the slabs for dosimetry with GZP6 cobalt-60 HDR system. For verification of this device, an assembly composed of a large ovoid size (3cm diameter) and tandem #1 with the least curvature was selected in this study. With this assembly, GafChromic films were exposed using a plan with 500 cGy dose delivery to point "A". The irradiated films were scanned. The responses of the films were converted to dose by calibrating samples of these films using a cobalt-60 teletherapy system in the range of 25 to 800 cGy dose. The measured isodose curves with the films were compared to calculated isodose lines by the treatment planning software. RESULTS: The Result of these investigations indicated differences of up to ± 23 % between the planning and measured dosimetry at different points in GYN implant with cobalt-60 HDR source of GZP6 system. Therefore, this phantom enabled us to confirm the accuracy of radiation delivery to the GYN patients with cobalt-60 HDR source of GZP6 system. CONCLUSIONS: The new phantom design could be utilized for the QA procedure of the GZP6 cobalt-60 HDR system as well as the Ir-192 HDR system to confirmation the accuracy of dose distribution in GYN implants, especially in non-traditional implants. The Radiotherapy Department of Shahid Beheshti University at Shohada hospital sponsored the purchase of the phantom materials and films used in the investigations.
