Clinical Outcomes and Dosimetric Evaluationof Interstitial Brachytherapyin Gynecological Malignancies.

BACKGROUND: In management of Carcinoma Cervix, Brachytherapy plays a crucial role. Most commonly used technique is Intracavitary Brachytherapy (ICBT). In cases where ICBT is not technically feasible or it may result in suboptimal dose distribution, Interstitial Brachytherapy (ISBT) is recommended. With this study we wanted to study the clinical outcome and dosimetric details of interstitial brachytherapy in gynecological cancers. MATERIALS & METHODS: We analysed clinicaloutcome and dosimetric details of interstitial brachytherapy (ISBT) done for gynecological malignancies in our institute during the period 1st January 2013 to 31st December 2020. RESULTS: Total of 42 interstitial brachytherapy (ISBT) details were analysed.37 patients had Carcinoma Cervix and 5 patients had Carcinoma Vagina. In the majority of the patients, ISBT dosage schedule was three fractions 7Gy each. D2cc to rectum, bladder, sigmoid and bowel were 4.88 Gy, 5.62 Gy, 3.57 Gy and 2.47 Gy respectively. Mean CTV volume was 129.89 cc. EQD2 dose to CTV combining EBRT and ISBT dose was 85.88 Gy. D90 and D100 to CTV from ISBT were 111.96% and 68.21 % of prescribed dose respectively. Grade III/IV toxicities were seen in 5 (12%) patients. Local control rates at 1year &2 years were 88% & 85.7% respectively. DFS at 1 year, 2 years and 3 years were 80.7%, 72.3% and 65.7% respectively. OS at 1year, 2 years, 4 years and 5 years were 92.5%, 65.5%, 59.5% and 42.3% respectively. CONCLUSION: 3D imagebased dosimetry with CT based planning using MUPIT implant is a feasible option for gynecological malignancies warranting interstitial brachytherapy. In view of good clinical outcomes in terms of toxicity profile, Local control, DFS and OS with acceptable GEC-ESTRO dosimetric data, we recommend routine use interstitial brachytherapy if facilities are available and in clinical situations were ISBT is indicated.

Beam Focal Spot Offset Determination for Linear Accelerators: A Phantom less Method.

The effectiveness of radiotherapy treatment is influenced by the position of beam focal spot; therefore, it is important to verify the beam focal spot periodically. In this study the beam focal spot offset is measured using an electronic portal imaging (EPID) based technique and co- rotational penumbra modulation technique(CPM). MATERIALS AND METHODS: This method utilizes one set of jaws and the multileaf collimator (MLC) to form a symmetric field and then a 180o collimator rotation was utilized to determine the radiation isocenter defined by the jaws and the MLC, respectively. The difference between these two isocentres is then directly correlated with the beam focal spot offset of the linear accelerator. In the current study, the method has been used for Varian ClinaciX and Elekta Versa HD linear accelerators. Since an Elektalinac with the Agility® head does not have two set of jaws, a modified method that making use of one set of diaphragms, the MLC and a full 360o collimator rotation is implemented. RESULT: The method is validated against CPM and found to be in agreement within 0.00923± 0.009360 mm ( SD) also the method has been found to be reproducible to within 0.0365 mm (SD). CONCLUSION: The method could be used for routine quality assurance (QA) to ensure that the beam focal spot offset is in tolerance.