West Asia Organization for Cancer Prevention (WAOCP), APOCP's West Asia Chapter. Asian Pacific Journal of Cancer Prevention 1513-7368 25 9 2024 09 01 The Dose Difference of Dominant Intraprostatic Lesions (DILs) Defined by Magnetic Resonance-Guided and arc-based Intensity Modulated Radiation Therapy (IMRT), and the Association between Dose Difference and Recurrent Prostate Cancer 3269 3275 91318 10.31557/APJCP.2024.25.9.3269 EN Amonlaya Amantakul Division of Diagnostic Radiology, Department of Radiology, Faculty of Medicine, Chiang Mai University, Chiang Mai 50200, Thailand. Medical Sciences Research, Chiang Mai University, Chiang Mai 50200, Thailand. 0000-0002-7292-7804 Thanat Kanthawang Division of Diagnostic Radiology, Department of Radiology, Faculty of Medicine, Chiang Mai University, Chiang Mai 50200, Thailand. Apichat Tantraworasin Clinical Surgical Research Center and Department of Surgery, Faculty of Medicine, Chiang Mai University, Chiang Mai 50200, Thailand. Ekkasit Tharavichitkul Division of Radiation Oncology, Department of Radiology, Faculty of Medicine, Chiang Mai University, Chiang Mai 50200, Thailand. 0000-0002-5495-1421 Journal Article 2024 05 18 Background: There is growing evidence that local recurrence after radiotherapy often occurs within the dominant intraprostatic lesions (DILs) in prostate cancer. This study aimed to evaluate the dose difference between DILs defined by Magnetic Resonance-guided and arc-based Intensity Modulated Radiation Therapy (IMRT) and to assess the association between the dose difference and biochemical recurrence-free survival. Materials and Methods: Between 2015 and 2019, 48 prostate cancer patients with DILs visible from multiparametric Magnetic Resonance Imaging (mpMRI) underwent arc-based IMRT with 70 Gy (2.5 Gy each fraction) to the prostate gland. Pretreatment mpMRI DILs contoured the prostate gland retrospectively. Results: Biochemical recurrence was 8.3%. There was a significant difference between the median dose of DILs from MRI-guided imaging, 69.22 Gy, and the median dose of the whole prostate from arc-based IMRT which was 67.09 Gy (p < 0.001*). The Kaplan-Meier survival curve compared by log-rank test showed an escalation dose of at least 2 Gy tends to improve biochemical recurrence-free survival. However, this tendency did not reach statistical significance (p = 0.2). Conclusions: The dose distribution within DILs defined by mpMRI is significantly higher than the whole prostate dose from arc-based IMRT. Escalation doses in DILs tend to improve biochemical recurrence-free survival, further validation in larger patient cohorts with extended follow-up is warranted. https://journal.waocp.org/article_91318_54d1747d048438c5b3f97568485d1675.pdf