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Background
Stereotactic body radiation therapy (SBRT) has emerged as a promising and minimally invasive treatment modality for various deep tumors including those in the lungs, prostate, rectum, kidney, cervix, and breast. Its precise targeting and high-dose delivery allow for effective local tumor control while minimizing damage to surrounding healthy tissue. However, irradiated tissues can exhibit various imaging findings including calcifications, fibrosis, ground glass opacities, vascular changes, and enhancement patterns from altered tissue density due to edema and scarring. These evolving postradiation changes may obscure visualization of residual cancer or tumor recurrence. In this case based educational exhibit, we show that PET/CT is a useful tool in distinguishing these evolving postradiation changes from new and recurring malignancy.

Educational Goals / Teaching Points
In this pictorial review, we highlight the importance of PET/CT in differentiating evolving postradiation changes vs tumor recurrence. We also highlight the importance of PET in selecting the intended biopsy site (targeting the metabolically active area).

Key Anatomic/Physiologic Issues and Imaging Findings/Techniques
Through the presentation of 10 compelling PET/CT case studies, supplemented by multimodal correlations whenever feasible, we accentuate the importance of PET/CT in distinguishing between evolving postradiation alterations and instances of tumor recurrence. Various imaging patterns and areas of tumor recurrences at different stages of post-SBRT treatment in different tumors are also highlighted.

Conclusion
The utility of PET/CT as a pivotal imaging modality cannot be overstated when it comes to discriminating evolving postradiation changes from potential tumor recurrence. Moreover, PET/CT's capability to aid in the identification of optimal biopsy sites, strategically targeting metabolically active areas, underscores its significance in enhancing clinical decision-making.