Radioterapija raka prostate vođena magnetskom rezonancom: nova paradigma liječenja

Radiotherapy is one of the key treatment modalities for primary prostate cancer. During the last decade, significant advances were made in radiotherapy technology leading to increasing both physical and biological precision. Being a loco-regional treatment approach, radiotherapy requires accurate target dose deposition while sparing surrounding healthy tissue. Conventional radiotherapy is based on computerized tomography (CT) images both for radiotherapy planning and image-guidance, however, shortcomings of CT as soft tissue imaging tool are well known. Nowadays, our ability to further escalate radiotherapy dose using hypofractionation is limited by uncertainties in CT-based image guidance and verification. Magnetic resonance imaging (MRI) is a well established imaging method for pelvic organs. In prostate cancer specifically, MRI accurately depicts prostate zonal anatomy, rectum, bladder, and pelvic floor structures with previously unseen precision owing to its sharp soft tissue contrast. The advantages of including MRI in the clinical workflow of prostate cancer radiotherapy are multifold. MRI allows for true adaptive radiotherapy to unfold based on daily MRI images taken before, during and after each radiotherapy fraction. It enables accurate dose escalation to the prostate and intraprostatic tumor lesions. Technically, MRI high-strength magnetic field and linear accelerator high energy electromagnetic beams are hardly compatible, and important efforts were made to overcome these technical challenges and integrate MRI and linear accelerator into one single treatment device, called MRI-linac. Different systems are produced by two leading vendors in the field and currently, there are around 100 MRI-linacs worldwide in clinical operations. In this narrative review paper, we discuss historical perspective of image guidance in radiotherapy, basic elements of MRI, current clinical developments in MRI-guided prostate cancer radiotherapy, and challenges associated with the use of MRI-linac in clinical practice.Radioterapija je temelj liječenja raka prostate. Radioterapija je zadnjih godina značajno napredovala što je omogućilo njenu preciznost. Radioterapija zahtjeva točnu isporuku radioterapijske doze na tumor uz maksimalnu poštedu okolnog zdravog tkiva. Konvencionalna radioterapija se bazira na slikama kompjuterizirane tomografije (CT) za sve faze radioterapijskog procesa, iako su slike CT-a slabe rezolucije za prikaz mekih tkiva. Danas je naša sposobnost da još više podižemo radioterapijsku dozu limitirana nedovoljnom jasnoćom CT slika. Magnetska rezonanca (MR) za razliku od CT-a ima odličan kontrast za meka tkiva zdjelice te odlično oslikava prostatu i zdjelične strukture. Mnoge su prednosti uključenja MR u radioterapijski proces raka prostate. MR omogućava pravu adaptivnu radioterapiju na osnovi MR slika uzetih prije, tijekom i nakon radioterapije. Omogućuje eksalaciju doze na intraprostatičke tumorske strukture. Napredak tehnike je omogućio integraciju snažnog magnetskog polja MR-a i visokoenergetskih X-zraka linearnog akceleratora u jedan jedinstveni uređaj - MRI-linac. Dva su MR-linac komercijalna sustava dostupna na tržištu, a u svijetu ima instalirano preko 100 ovakvih uređaja. U ovom preglednom članku razmatramo razvoj slikovnog vođenja u radioterapiji, trenutno stanje magnetom vođene radioterapije raka prostate, kao i izazove u primjeni ove inovativne metode