Estimation of geometric uncertainties in radiotherapy

Abstract

<p>Uvod:Cilj ovo gistraživanja je procjena trodimensionalne gre&scaron;ke poyicioniranja i kalkulacija odgovarajuće margine za planirani volumen.<br />Metoda:Trideset pet pacijenata su uključena u istraživanje,Ukupan broj analiziranih portalnih snimaka je 632. Populaciona sistematska i slučajna gre&scaron;ka za pacijente sa kancerom glave i vrata je evaluirana u sva tri smjera vertikalno, logintudinalno i lateralno . Na osnovu van Herk formule izračunata je odgovarajuća margina.<br />Rezultati: Standardna devijacija sistematske gre&scaron;ke pozicioniranja je u interval od 1.51 do 1.93 mm, za slučajne gre&scaron;ke SD je od 1.77 do 1.86 mm. Vrijednost 3d Vektora pomjeranja je 2.66. PTV margina prema Van Herku je u interval od 2 mm- 6.2 mm u smjerovima računanja margine.<br />Zaključak: Eksapanzija CTV za 6 mm na PTV obezbjeđuje da 90 % pacijenata u centru primi najmanje 95% propisane doze na CTV.</p>

<p>Introduction: The aim of this study was to<br />evaluate three-dimensional (3D) set-up errors<br />and propose optimum margins for planning<br />target volume (PTV) coverage in head and neck<br />radiotherapy.<br />Methods: Thirty-five patients were included in<br />the study. The total number of portal images<br />studied was 632. Population systematic (S) and<br />random (s) errors for the patients with head and<br />neck cancer were evaluated based on the portal<br />images in the caudocranial longitudinal (CC)<br />and left-right lateral (LR) direction measured in<br />the anterior-posterior (AP) field, as well as from<br />the images in the caudocranial longitudinal<br />(CC) and dorsoventral lateral (DV) direction<br />measured in the lateral (LAT) field. The values<br />for the clinical-to-planning target volume<br />(CTVPTV) margins were calculated using<br />ICRU Report 62 recommendations, along with<br />Stroom&rsquo;s and van Herk&rsquo;s formulae.<br />Results: The standard deviations of systematic<br />set-up errors (S) ranged from 1.51 to 1.93 mm<br />while the standard deviations of random set-up<br />(s) errors fell in between 1.77 and 1.86 mm.<br />The mean 3D vector length of displacement was<br />2.66 mm. PTV margins calculated according to<br />ICRU, Stroom&rsquo;s and van Herk&rsquo;s models were<br />comprised between 1.95 and 6.16 mm in the<br />three acquisition directions.<br />Discussion and conclusions: Based on our<br />results we can conclude that a 6-mm extension<br />of CTV to PTV margin, as the lower limit, is<br />enough to ensure that 90% of the patients<br />treated for head and neck cancer will receive a<br />minimum cumulative CTV dose greater than or<br />equal to 95% of the prescribed dose.</p>