World-wide incidence rate of prostate cancer has progressively increased with time especially with the increased proportion of elderly population. Early detection of prostate cancer when it is confined to the prostate gland has the best chance of successful treatment and increase in surviving rate. Prostate cancer occurrence rate varies over the three prostate regions, peripheral zone (PZ), transitional zone (TZ), and central zone (CZ) and this characteristic is one of the important considerations is development of segmentation algorithm. In fact, the occurrence rate of cancer PZ, TZ and CZ regions is respectively. at 70-80%, 10-20%, 5% or less. In general application of medical imaging, segmentation tasks can be time consuming for the expert to delineate the region of interest, especially when involving large numbers of images. In addition, the manual segmentation is subjective depending on the expert's experience. Hence, the need to develop automatic segmentation algorithms has rapidly increased along with the increased need of diagnostic tools for assisting medical practitioners, especially in the absence of radiologists. The prostate gland segmentation is challenging due to its shape variability in each zone from patient to patient and different tumor levels in each zone. This survey reviewed 22 machine learning and 88 deep learningbased segmentation of prostate MRI papers, including all MRI modalities. The review coverage includes the initial screening and imaging techniques, image pre-processing, segmentation techniques based on machine learning and deep learning techniques. Particular attention is given to different loss functions used for training segmentation based on deep learning techniques. Besides, a summary of publicly available prostate MRI image datasets is also provided. Finally, the future challenges and limitations of current deep learningbased approaches and suggestions of potential future research are also discussed.
INDEX TERMS MRI, prostate cancer, deep learning, automatic algorithms, prostate gland
I. INTRODUCTIONP ROSTATE cancer is a significant global public health issue and has ranked as the second world's prevalent cancers in male after lung cancer. Diagnosis of prostate cancer has become a challenging task with a progression rate of 1 in 6 men affected throughout their lives, and 1 in 36 died from the disease, being the second most common cause of death among men [1], [2]. According to the study in [3], prostate cancer ratio is the highest in the United States (USA) at 21% whereas it ranges from 1 to 9 in 100,00 men in Northern Europe, North America, New Zealand, and Australia. In 2019, among the various types of cancer, including breast cancer, lung cancer, colon, and rectum cancer, prostate 13 cancer has recorded 174,650 new prostate cancer cases, and 14 31,620 cancer deaths in the U.S. [4]. The survival rate of 15 individuals affected with prostate cancer is relatively high. 16 However, human aging factors would exacerbate the disease 17 and spread cancer to other organs if left un...