Role of MRI in the treatment of Prostate Cancer
Prostate gland is among the top ten leading sites of cancer in men in India. GLOBOCAN – 2018 India Cancer Fact sheet states that 28,696 new cases had been detected and 17,184 deaths related to prostate cancer have happened in the year of 2018 in India and the estimate of 5 year prevalence of prostatic malignancy was 47,558. There is a constant increase in the incidence of prostate cancer over the years. The cancer data projection estimates that there will be a doubled increase in number of cases by the year of 2020. It has also been estimated that about 1 man in 9 will be diagnosed with prostate cancer during his lifetime.
Prostate is a small-sized gland in men secreting prostatic fluid which contains enzymes, proteins and minerals that are responsible for the protection and nourishment of sperm. The prostatic fluid admixes with the seminal vesical fluid to the form semen, during ejaculation. The acini, which are the smallest structural component of the gland, are surrounded by a basement membrane separating the secretory epithelial cells from surrounding structures. Proliferation of cells through the membrane causes prostate cancer.
The management of prostate cancer can be said to be a complex issue as there are a lot of challenges involved in accurate staging and predicting the speed of disease progression. Detection of cancer at an early stage is very crucial as it allows for more treatment options. Prostatic neoplasm at an early stage tends be very slow growing and has a very long indolent course, with patients being asymptomatic until there is a rapid growth of the tumor. Once patients start having symptoms, most of them tend to be diagnosed with advanced stage of malignancy. Under such scenarios, Imaging plays a very important role in the detection and management.
MRI Imaging of Prostate was started sometime during the mid-1980’s. With the growth of technology and evolution of different image acquisition techniques, MRI is at present considered the main diagnostic imaging modality of choice as it helps in detection, localization, characterization, staging, biopsy guidance, active surveillance, post treatment follow up and restaging of prostate malignancy.
Multiparametric MRI (mpMRI) technique is considered better than routine MRI as it yields both anatomical and functional information about the tumor and its extension. In mpMRI, the conventional T1w and T2w imaging is clubbed with atleast one of the functional MR imaging techniques like Diffusion Weighted Imaging (DWI), Dynamic Contrast Enhanced -MRI, MR-Spectroscopy etc…. Other imaging modalities that can be used in concurrence with multiparametric MRI are multiparametric ultrasound (mpUS) and nuclear imaging which further assists in accurate diagnosis and treatment guidance.
However, the definite diagnosis of Prostate cancer is established histopathologically after Prostate Biopsy. TRUS (Trans Rectal Ultrasound) biopsy is a procedure in which multiple small hollow needle-core samples are removed from a man’s prostate gland and histopathological evaluation is done to determine the presence of prostate cancer. It is normally performed when the result from a PSA blood test are high. However, it’s a random and blind biopsy technique. Thus, performing MRI before prostate biopsy can help in guiding for targeted biopsies and reducing the number of tissue sample cores needed to make a diagnosis.
Role of MRI in the treatment of Prostate Cancer:
The treatment for Prostate Cancer is patient specific and the treatment options include a passive approach like active surveillance or an active approach like surgery, radiotherapy, ablative techniques like high intensity focused ultrasound ablation (HIFU), laser ablation, photo dynamic therapy (PDT), electroporation and cryoablation. Staging plays a vital role in classifying the patients into low risk, intermediate risk and high risk groups, in concordance with the Gleason score and PSA levels. MRI determines TNM stage in a patient most optimally which further can help in classifying the extent of spread of cancer for deciding the best therapy options.
MRI can confirm early-stage tumor in patients with low-risk disease clinically, thus, correctly classifying patients into active surveillance while ensuring the patients with more aggressive disease are not being denied further appropriate treatment. Multiparametric MRI correlates with Gleason grade. It is seen that, if required, multiparametric MRI can guide repeat biopsy in these patients for an accurate grading of tumor. It can classify intermediate risk patients into high- and low-risk groups on the basis of the presence or absence of extra capsular invasion (ECE) to influence further treatment.
Treatment for Prostate Cancer can be both surgical and nonsurgical in nature. For surgical patients, it is found that MRI significantly can improve the surgeon’s decision to preserve or resect the neurovascular bundle (NVB) during Radical Prostatectomy (RP). A recent study has also found that preoperative prostate MRI changed the decision to use a nerve-sparing technique during robotic-assisted laparoscopic prostatectomy in 27% (28/104) of patients in the series.
Some of the nonsurgical treatment options include radiation therapy, hormone therapy, and minimally invasive ablative therapies that use physical energy to cause tumor destruction. With the improvement of the therapies, exact localization of prostate cancer has become increasingly important. Here, the MRI plays an important role in assisting EBRT planning for locally advanced disease to determine tumor location, volume, and extent. It is important to have knowledge of the exact tumor location within the prostate as it can help direct maximal therapy to the largest focus of tumor while minimizing surrounding radiation-induced tissue damage.
Stage I tumors where the lesion is limited to the gland, have low Gleason score and low PSA levels – usually tend to be a very slowly growing tumor. In this scenario, passive treatment approach like active surveillance is considered.
In Stage II cancer where the lesion is limited to the gland, have higher Gleason score and high PSA levels. These patients are at intermediate risk to develop advanced disease. So, active therapeutic approach is needed. MRI helps in exact localization of the lesion, thus helping in considering multiple alternative therapeutic approaches other than prostatectomy/ external beam radiotherapy where there is higher chance of radiation injury to vital structures adjacent to the prostate like bladder and rectum. The alternative therapies can be placement of the brachytherapy seeds at the target site, thus reducing periprostatic toxicity to adjacent vital structures like bladder and rectum and other non-radiation focal ablative therapies like HIFU, cryoablation which are minimally invasive.
Patients with locally advanced disease (Stage III and IV) at diagnosis as characterized by MRI may require more aggressive treatment, such as whole-pelvis and prostatic radiation, adjuvant radiotherapy after surgery, or long-term androgen deprivation therapy. The extent of LNM depicted by MRI can also define the radiation field more optimally
Multi-parametric MRI is a reliable in imaging assessment of prostate cancer and helps in various aspects of prostate cancer management, including initial detection, biopsy guidance, treatment planning, and follow-up. It is considered the current standard in diagnosis, because no single MRI sequence is entirely sufficient to characterize prostate cancer. However, the optimal combination and interpretation of anatomic and functional MRI sequences still needs to be established.
Dr. Diwakar C (MBBS)