VMAT - volumetrična modulirana ločna terapija VMAT - Volumetric Modulated Arc Therapy

Abstract

Volumetrična modulirana ločna terapija (angl. Volumetric Modulated Arc Therapy, VMAT) je ena izmed najsodobnejših obsevalnih tehnik, ki jo od marca 2011 uporabljamo tudi v Sektorju radioterapije na Onkološkem inštitutu v Ljubljani. Temeljna značilnost VMAT je, da linearni pospeševalnik seva fotonski snop ves čas kroženja glave obsevalnika okoli bolnikovega telesa. Pri tem sočasno prihaja do spreminjanja 3 parametrov: oblike obsevalnega polja, hitrosti vrtenja roke oz. glave obsevalnika ter hitrosti doze izsevanega fotonskega snopa. Nasprotno pa pri intenzitetno moduliranem obsevanju (angl. Intensity Modulated RadioTherapy, IMRT) uporabljamo statična obsevalna polja in je hitrost doze ves čas nespremenjena. Najpomembnejši prednosti VMAT pred IMRT sta krajše obsevanje in s tem manjša verjetnost, da se bo bolnik (ali tarča, tj. tumor v njem) na mizi obsevalnika premaknil, ter manjša dozna obremenitev zdravih tkiv v okolici tarče, pri čemer sta konformnost porazdelitve doze v območju tarče in stopnja zaščite zdravih organov in tkiv v okolici najmanj primerljiva s tisto, ki jo dosežemo z IMRT, v nekaterih primerih (obsevanje območja medenice) pa celo izboljšani. V prispevku predstavljamo VMAT: njene značilnosti, potek, indikacije za izbiro in nevarnosti, s katerimi se srečamo pri tako natančnem obsevanju.

Abstract (Eng)

Volumetric Modulated Arc Therapy (VMAT) Volumetric Modulated Arc Therapy (VMAT) is one of the most advanced radiation therapy techniques, which has been used by the Division of Radiation Oncology at the Institute of Oncology in Ljubljana since March 2011. The fundamental characteristic of VMAT is that the linear accelerator delivers the photon beam for the entire duration of the treatment head’s rotation around the patient’s body. While doing so, it simultaneously changes 3 parameters: the shape of the radiation field, the treatment head’s rotation speed and the dose speed of the delivered photon beam. On the contrary, the Intensity Modulated Radiotherapy (IMRT) utilises static radiation fields and delivers the dose at a constant speed. Compared to IMRT, the most important strengths of VMAT are shorter irradiation time, which makes it less likely that the patient (or target - the tumour) will move on the table of the irradiation device, and a lower dose burden to healthy tissues around the target so that the conformity of the dose distribution in the target region and the level of protection of the healthy organs and tissues surrounding it are comparable to those provided by IMRT or, in some cases (irradiation of the pelvic region), even more improved. The article presents VMAT: its features, course of treatment, indications for the selection and the hazards associated with such an accurate radiation therapy.