The experimental arm Stereotactic Body Radiotherapy (SBRT) boost regimen will consist of two fractions of 700 cGy each total of 14Gy in 2 fractions, delivered at 1st and 2nd week of the treatment.In the proposed protocol, the pelvic field dose will be delivered as 45 Gy in 25 fractions, while the nodal boost will be delivered as SBRT 14 Gy in 2 fractions, typically at the first and second weeks of treatment, subject to plan evaluation and organ-at-risk constraints. This sequencing is consistent with the concept of combining broad pelvic coverage with ablative focal escalation.

Patients will be immobilized supine with an abdominopelvic thermoplastic shell, and simulation will be performed using contrast-enhanced planning CT with MRI and PET-CT fusion where available. Bladder and bowel preparation will be standardized before simulation and treatment to improve reproducibility and reduce interfraction variation.

Patients in the standard arm will receive conventional radical chemoradiation for locally advanced carcinoma cervix with pelvic external beam radiotherapy and concurrent weekly cisplatin, followed by brachytherapy. Pelvic radiotherapy will be delivered to a dose of 45 Gy in 25 fractions over 5 weeks, using IMRT/VMAT or fixed-field technique, with standard contouring of elective pelvic target volumes and gross disease. The nodal boost will be delivered as a conventional Simultaneous Integrated Boost (SIB) to the involved pelvic node(s) during the course of external beam radiotherapy. A total dose of 55 Gy or 57.5 Gy in 25 fractions, delivered in a simultaneous integrated manner according to nodal size, location, and institutional planning constraints. Treatment will be planned with appropriate image guidance, and organs at risk will be respected according to predefined dose constraints. Toxicity will be monitored during treatment and follow-up, and graded using CTCAE version 5.0.

Experimental Arm: Stereotactic Body Radiotherapy Boost to Involved Pelvic Lymph Nodes Participants in the experimental arm will receive definitive radical chemoradiation for stage IIIC carcinoma cervix with a stereotactic body radiotherapy (SBRT) boost to the radiologically involved pelvic lymph node(s). The purpose of this intervention is to intensify the dose to gross nodal disease while maintaining acceptable doses to nearby organs at risk, including bowel, rectum, bladder, sigmoid, spinal cord, kidneys, femoral heads, duodenum, and active bone marrow. The SBRT boost is integrated with standard pelvic external beam radiotherapy and concurrent chemotherapy, followed by brachytherapy as per institutional curative protocol.

The primary outcome measure is the incidence of grade 3 or higher treatment-related adverse events, specifically acute gastrointestinal and genitourinary toxicity, assessed within 30 days of completion of treatment using CTCAE version 5.0.

Incidence of grade 3 or higher acute gastrointestinal and genitourinary toxicity, assessed at 6 months of completion of external-beam chemoradiation, using CTCAE version 5.0.