COMPARATIVE ANALYSIS OF DOSE DISTRIBUTIONS AND ORGAN DOSES IN 3D-CRT, IMRT AND VMAT ACCORDING TO QUANTEC AND RTOG PROTOCOLS: PLANNING FEATURES, ADVANTAGES AND LIMITATIONS

The study was conducted at the Center of Nuclear Medicine and Oncology (Semey) and is devoted to a comparative dosimetric analysis of external beam radiotherapy planning parameters for locally advanced cervical cancer. Three- dimensional conformal radiotherapy (3D-CRT), intensity-modulated radiation therapy (IMRT), and volumetric modulated arc therapy (VMAT) were compared in terms of dose distribution quality and dose burden to organs at risk. Treatment planning was performed for 25 patients using a TrueBeam linear accelerator with daily patient setup verification based on IGRT/CBCT. Plan quality was evaluated using dose–volume histograms, including D95% for the planning target volume (PTV), conformity index (CI) and homogeneity index (HI), as well as absolute dose parameters (Dmean, Dmax) for organs at risk, in accordance with RTOG criteria and QUANTEC recommendations. The analysis demonstrated that VMAT provided the most favorable dosimetric performance, with a high conformity index (CI = 1,03±0,02) and a low homogeneity index (HI = 0,09±0,02), ensuring more uniform and accurate PTV coverage compared with IMRT and 3D-CRT. A key finding was a substantial reduction in dose burden to pelvic organs at risk: VMAT resulted in an average 25–30% reduction in overall dose compared with 3D-CRT, while the mean dose to the rectum (Dmean) decreased to 33,0 Gy. In addition, VMAT significantly reduced the average treatment delivery time to 5–7 minutes, thereby lowering the risk of intrafraction motion. The obtained results confirm the dosimetric advantages of VMAT and substantiate its feasibility for routine clinical use in a regional oncology center.

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