Mladen Kasabašić

Survey of mammography practice in Croatia: equipment performance, image quality and dose

A national audit of mammography equipment performance, image quality and dose has been conducted in Croatia. Film-processing parameters, optical density (OD), average glandular dose (AGD) to the standard breast, viewing conditions and image quality were examined using TOR(MAM) test object. Average film gradient ranged from 2.6 to 3.7, with a mean of 3.1. Tube voltage used for imaging of the standard 45 mm polymethylmethacrylate phantom ranged from 24 to 34 kV, and OD ranged from 0.75 to 1.94 with a mean of 1.26. AGD to the standard breast ranged from 0.4 to 2.3 mGy with a mean of 1.1 mGy. Besides clinical conditions, the authors have imaged the standard phantom in the referent conditions with 28 kV and OD as close as possible to 1.5. Then, AGD ranged from 0.5 to 2.6 mGy with a mean of 1.3 mGy. Image viewing conditions were generally unsatisfying with ambient light up to 500 lx and most of the viewing boxes with luminance between 1000 and 2000 cd per m(2). TOR(MAM) scoring of images taken in clinical and referent conditions was done by local radiologists in local image viewing conditions and by the referent radiologist in good image viewing conditions. Importance of OD and image viewing conditions for diagnostic information were analysed. The survey showed that the main problem in Croatia is the lack of written quality assurance/quality control (QA/QC) procedures. Consequently, equipment performance, image quality and dose are unstable and activities to improve image quality or to reduce the dose are not evidence-based. This survey also had an educational purpose, introducing in Croatia the QC based on European Commission Guidelines.

Rotation of the Sacrum During Bellyboard Pelvic Radiotherapy

Patients with cervical, uterine, and rectal carcinomas are usually treated in the prone position using the bellyboard positioning device. Specific and uncomfortable prone position gives rise to uncertainties in the daily set-up of patients during the treatment. During investigation of translational movements, rotational movements of the pelvis are observed and investigated. The film portal imaging is used to discover patient positioning errors during treatment. We defined the rotational set-up errors by angle deviations of the sacrum. Thirty-six patients were included in the study; 15 patients were followed during the whole treatment and 21 during the first 5 consecutive treatment days. The image acquisitions were completed in 84%. Systematic and random positioning errors were analyzed in 725 images. Approximately half of the patients had adjusted to the bellyboard in the first few fractions, with sacrum angles remaining the same for the rest of the treatment. The other half had drifts of the sacrum angle during the whole treatment. The rotation of the sacrum during treatment ranged up to 14 degrees , causing the usual set-up verification and correction procedure to result in errors up to 15 mm. Rotational movements of the patient pelvis during bellyboard pelvis radiotherapy can introduce considerable patient position error.

Dosimetric verification of compensated beams using radiographic film

Dosimetric verification of compensated beams using radiographic film Introduction. External photon beam modulation using compensators in order to achieve a desired dose distribution when brachytherapy treatment is followed by external beam radiation is a well-established technique. A compensator modulates the central part of the beam, and the dose beneath the thickest part of the compensator is delivered mostly by scattered, low energy photons. A two-dimensional detector with a good spatial resolution is needed for the verification of those beams. In this work, the influence of different types of detectors on the measured modulated dose distributions was examined. Materials and methods. Dosimetric verification was performed using X-Omat V, Eastman Kodak radiographic films at different depths in a solid water phantom. The film measurements were compared with those made by ionization chambers. Photon beams were also modelled using EGSnrc Monte Carlo algorithm to explain the measured results. Results. Monte Carlo calculated over-response of the film under the thickest part of the compensator was over 15%, which was confirmed by measurements. The magnitude of over-response could be associated with changes in the spectra of photon energy in the beam. Conclusions. The radiographic film can be used for the dosimetry of compensated high energy photon beams, with limitations in volumes where photon spectra are hardly degraded.

Implementing of the offline setup correction protocol in pelvic radiotherapy: safety margins and number of images

Implementing of the offline setup correction protocol in pelvic radiotherapy: safety margins and number of images Background. Patient positioning errors in pelvic radiotherapy at Department of Oncology and Radiotherapy in Osijek are explored in order to establish the offline setup correction protocol and determine the safety margins. Material and methods. Film portal imaging is used during the whole treatment in order to find patient positioning errors. Eleven patients are included in the study and 420 images are analyzed. Setup errors are found by measuring distances between the center of the field and bony landmarks. Systematic and random errors are analyzed. Results. Safety margins that should be employed at our department are 11 mm, 13 mm and 14 mm in mediolateral, craniocaudal and anteroposterior direction, respectively. Time trend is found only in an aged, obese patient with a hip problem. No action level offline setup protocol was employed by taking and averaging first four images in mediolateral and craniocaudal and 5 images in anteroposterior direction. Conclusions. Since time trend is found only in a patient who was hard to position because of his age, obesity and the hip problem, we decided that such patients are to be positioned without a bellyboard and in supine position. Time trends are not found in all of the other patients so we employed the offline setup error protocol by averaging setup errors from the first few consecutive images. Safety margins that will ensure 90% probability of depositing at least 95% of the prescribed dose in the target are calculated. Safety margins and number of images that should be taken showed that the most inaccurate positioning was in the anteroposterior direction.

[Influence of daily set-up errors on dose distribution during pelvis radiotherapy].

Utjecaj pogreške u položaju bolesnika tijekom zračenja zdjelice na raspodjelu doze Radioterapija megavoltnim snopovima fotona linearnog akceleratora oblik je lokalnog onkološkog liječenja. Njezin je cilj predati propisanu apsorbiranu dozu ciljnom volumenu, uz što nižu dozu okolnomu zdravom tkivu. Proces se sastoji od niza koraka u kojima sudjeluje tim stručnjaka iz različitih područja. Veliki broj postupaka i ljudi uključenih u radioterapijski proces, nepouzdanosti uređaja te pomaci bolesnika i unutrašnjih organa tijekom terapije mogu uzrokovati odstupanja između planirane i stvarne raspodjele doze. U ovom radu procijenili smo utjecaj pogreške položaja bolesnika tijekom terapije na raspodjelu doze, te na veličine koje služe za procjenu kvalitete plana. Pogreške u položaju bolesnika ispitane su u skupini od 35 bolesnika. Te smo pogreške simulirali na pet bolesnika, koristeći se 3D programom za planiranje XiO (CMS Inc., St. Louis, MO, Elekta). Ispitali smo razlike u raspodjeli doze između planiranog i stvarnog položaja. Dodatno, utjecaj pogrešaka na odabir plana zračenja provjerili smo analizirajući promjene u dozno-volumnom histogramu (DVH), pokrivenost planiranog volumena (engl. PTV conformity index, CIPTV) i jednoličnost raspodjele doze u ciljnom volumenu (engl. homogeneity index, HI). Simulacije pokazuju da promjene u položaju bolesnika mogu uzrokovati značajne razlike između planirane i stvarne raspodjele doze. Kod nekih bolesnika ako se ne korigiraju pogreške, CIPTV postaje manji od 97% što znači da plan više nije prihvatljiv za zračenje. Iznenađuje da HI nije ovisan o pomacima bolesnika kao CIPTV. Rezultati pokazuju potrebu za smanjenjem pogrešaka, što se može postići provođenjem kontrole kvalitete u radioterapiji. Influence of Daily Set-Up Errors on Dose Distribution During Pelvis Radiotherapy An external beam radiotherapy (EBRT) using megavoltage beam of linear accelerator is usually the treatment of choice in cancer patients. The goal of EBRT is to deliver the prescribed dose to the target volume, with as low as possible dose to the surrounding healthy tissue. A large number of procedures and different professions involved in radiotherapy, uncertainty of equipment and daily patient set-up errors can cause a difference between the planned and delivered dose. We investigated a part of this difference caused by measuring daily patient set-up errors for 35 patients. These set-up errors were simulated on five patients, using 3D treatment planning software XiO. The simulation investigated differences in dose distributions between the planned and shifted geometry. Additionally, we investigated the influence of the error on treatment plan selection by analysing changes in dose volume histograms, planning target volume conformity index (CIPTV), and homogeneity index (HI). Simulations showed that patient daily set-up errors can cause significant differences between the planned and actual dose distributions. Moreover, for some patients, those errors could affect the choice of treatment plan since CIPTV fell under 97%. Surprisingly, HI was not as sensitive to set-up errors as CIPTV. Our results have confirmed the need to minimise daily set-up errors through quality assurance programmes.

Survey of equipment quality control in radiotherapy centres in croatia: first results.

Survey of Equipment Quality Control in Radiotherapy Centres in Croatia: First Results Implementation of advanced radiation therapy techniques in clinical practice can greatly improve tumour control and normal tissue sparing. An important part of this implementation is quality control (QC) of every part of the radiotherapy process, as it helps to detect errors and provides instant remedy. This increases the probability of successful radiation treatment and ensures patient radiation safety. Every radiotherapy quality assurance (QA) programme is based on quality control of radiotherapy equipment. The aim of our survey was to review QC practices in a number of radiotherapy centres in Croatia. As a first step, we defined a set of tests to check different parameters of linear accelerators and simulators in these centres. The tests were defined and performed according to protocols developed at two university hospitals. Test results varied largely between the centres. This calls for harmonisation of QC protocols. Utvrđivanje stanja kontrole kvalitete opreme radioterapijskih centara u Hrvatskoj: prvi rezultati Uvođenje naprednih radioterapijskih tehnika u kliničku praksu ima golem utjecaj na bolju kontrolu tumora i poštedu zdravog tkiva. Veliku ulogu u tome ima postojanje protokola za kontrolu kvalitete za svaki dio radioterapijskog procesa. Provođenje protokola ključno je za detektiranje pogrešaka i njihovo trenutačno ispravljanje. Time se povećava vjerojatnost za željeni ishod radioterapije i osigurava zaštita pacijenta od neželjenog zračenja. Osnova osiguranja kvalitete u radioterapiji jest kontrola kvalitete samog uređaja. U sklopu projekata financiranih od Međunarodne agencije za atomsku energiju, istraživali smo postojanje protokola za kontrolu kvalitete radioterapijske opreme. Pokazalo se da se testovi kontrole kvalitete provode u svim centrima u Hrvatskoj, no među njima postoje razlike. Također, pisani su protokoli bili rijetko prisutni. Pregled prakse u kontroli kvalitete i razmjena iskustva pomogli bi u razvoju protokola za kontrolu kvalitete na nacionalnom nivou. Kao prvi korak definirali smo niz testova za provjeru raznih parametara na linearnim akceleratorima i klasičnim simulatorima u radioterapijskim centrima u Hrvatskoj. Testovi su definirani i izvedeni u skladu s protokolima razvijenim u naše dvije bolnice. Sljedeći korak planiran je tijekom ove godine, a odnosi se na verifikaciju sustava za planiranje u kliničkim uvjetima prema protokolu izrađenom u KBC-u Rijeka. U radu iznosimo pregled provedenih testova, uređaja i računalnih programa za analizu kojima smo se koristili, kao i cjelokupne rezultate.