This study evaluates the accuracy of the Isogray Treatment Planning System (TPS) for fields with regular shields on the Elekta Compact linear accelerator, examining absolute and relative dose measurements across field sizes (10×10 cm², 15×15 cm², and 20×20 cm²) and shield coverages (25% and 50%). Absolute dose measurements revealed that the Isogray TPS consistently overestimated doses under shielded conditions, with discrepancies decreasing as the field size increased. In unshielded areas, the TPS demonstrated high accuracy, with dose differences within clinically acceptable limits. Relative dose measurements were evaluated using the gamma index with criteria of 3% dose difference and 3 mm distance-to-agreement. The analysis demonstrated excellent concordance for smaller fields (10×10 cm²), whereas larger fields (15×15 cm² and 20×20 cm²) exhibited significant deviations, particularly beneath the shielding structures and within the penumbral regions. These findings indicate that while the Isogray TPS performs well in open fields, it struggles to accurately model dose distributions in shielded areas, especially for larger fields. The study highlights the need for enhanced algorithms to better account for shielding effects, such as scattered radiation and secondary dose contributions. This work underscores the importance of continuous validation and algorithm optimization to improve the accuracy and reliability of treatment planning systems, ensuring both patient safety and treatment efficacy in complex radiotherapy scenarios.