| Abstrakt: |
Introduction: Intensity Modulated Radiotherapy (IMRT) and Volumetric Modulated Arc Therapy (VMAT) are primary techniques for rectal cancer treatment. In radiotherapy planning, collimator rotation is a crucial parameter, and its adjustments can lead to dosimetric variations. This study examined the influence of collimator rotation on dosimetric outcomes for different IMRT and VMAT plans for rectal cancer. Methods: CT images from 20 male rectal cancer patients were used for IMRT and VMAT treatment planning with varying collimator angles. Nine IMRT techniques (5, 7, and 9 coplanar fields with collimator angles of 0°, 45°, and 90°) and six VMAT techniques (1 and 2 full coplanar arcs with collimator angles of 0°, 45°, and 90°) were planned for each patient. Dosimetric results for target tissue (conformity index [CI] and homogeneity index [HI]) and sparing of organs at risk (OARs) (parameters from OARs dose - volume histograms [DVH]) were analyzed and compared, along with radiobiological findings. Results: The 7-fields IMRT technique showed lower bladder doses (V40Gy, V45Gy) unaffected by collimator rotation. The 9 - fields IMRT and 2 - arcs VMAT (excluding the 90 - degree collimator) exhibited the lowest V35Gy and V45Gy. A 90 - degree collimator rotation in 2 - arcs VMAT significantly increased small bowel and bladder V45Gy, femoral head doses, and HI values. Radiobiologically, the 90 - degree rotation adversely affected small bowel NTCP (normal tissue complication probability). No superiority was observed for a 45 - degree collimator rotation over 0 or 30 degrees in VMAT techniques. Conclusions: Collimator rotation minimally impacted dosimetric parameters in IMRT planning but significantly affected VMAT techniques. A 90 - degree rotation in VMAT, especially in a 2 - full arc technique, negatively impacted PTV homogeneity index, bladder dose, and small bowel NTCP. Other evaluated collimator angles did not significantly affect VMAT dosimetrical or radiobiological outcomes. [ABSTRACT FROM AUTHOR] |
