Validating dose rate calibration of radiotherapy photon beams through IAEA/WHO postal audit dosimetry service

In external beam radiation therapy (EBRT), the quality assurance (QA) of the radiation beam is crucial to the accurate delivery of the prescribed dose to the patient. One of the dosimetric parameters that require monitoring is the beam output, specified as the dose rate on the central axis under reference conditions. The aim of this project was to validate dose rate calibration of megavoltage photon beams using the International Atomic Energy Agency (IAEA)/World Health Organisation (WHO) postal audit dosimetry service. Three photon beams were audited: a 6 MV beam from the low-energy linac and 6 and 18 MV beams from a dual high-energy linac. The agreement between our stated doses and the IAEA results was within 1% for the two 6 MV beams and within 2% for the 18 MV beam. The IAEA/WHO postal audit dosimetry service provides an independent verification of dose rate calibration protocol by an international facility

Acute toxicity and local response using three fractions of high dose rate (HDR) brachytherapy for curative treatment of carcinoma cervix

To determine the acute vaginal mucosal toxicity and clinical response of cervical cancer after definitive treatment with external beam radiotherapy (EBRT) and three fractions each of 8 Fray (Gy) high dose rate intracavitary brachytherapy (HDR-BT).Study design: Descriptive study.Place and duration: Radiation Oncology Section, Department of Oncology, The Aga Khan University Hospital, Karachi, Pakistan from January 2008 till December 2015.Methodology: Protocol was formulated for carcinoma cervix to complete treatment in 7 weeks. Patients were treated with chemotherapy and pelvic EBRT to a total dose of 45 Gy/25 fractions, followed by three intracavitary HDR brachytherapy fractions of 8 Gy each. Vaginal toxicity and local clinical response was assessed at the end of treatment, at 4 and 8 weeks.Results: A total of 57 patients were treated with HDR brachytherapy and 49 patients were evaluated for assessment of toxicity and response. According to FIGO staging system, two had stage IB2, one had IIA, thirty-six had IIB, seven had IIIB, one had IVA disease and two had IVB with para aortic nodes. Concurrent gemcitabine and cisplatin were given to 26 (46%); whereas, 28 (49%) received concurrent cisplatin alone. Grade III acute vaginal mucosal toxicity was seen in 52 and Grade IV acute vaginal mucosal toxicity was observed in 08 patients. At completion of treatment, 40 patients had complete clinical response, at 4 weeks follow-up, complete regression of disease was found in 3 more and at 8 weeks none had clinical residual disease.Conclusion: This regimen of HDR brachytherapy treatments is feasible, efficacious, and well-tolerated for carcinoma cervix in a setup with cost constraints. Long term toxicity and disease control remains to be reported with longer follow-up. Key Words: Carcinoma cervix, High dose rate brachytherapy, Acute toxicity, Local response, External beam radiation therapy, Intracavitary brachytherapy

A new approach to measure dwell position inaccuracy in HDR ring applicators - quantification and corrective QA.

As part of quality assurance (QA) in high dose rate brachytherapy, it is necessary to verify that the source dwell positions correspond to the radiographic markers used in simulation and treatment planning. The procedure is well established for linear tandem applicators. However, with the advent of ring applicators, this has become more critical and challenging. This work describes a new approach to determine positional inaccuracies for ring applicators in which the dummy markers are imaged just once and their dwell positions characterized with respect to an applicator-defined axis. The radiograph serves as a reference for dummy markers for comparison with all subsequent measurements in which the active sources are autoradiographed at different offsets - thus obviating the back-and-forth transferring of setup between afterloader and simulator. The method has been used specifically to characterize the Varian GammaMed 60degrees ring applicator, but it may be adapted to any other applicator. The results show that an offset of 1-2 mm minimizes the overall inaccuracy to within 2 mm