Joachim Bogner

Treatment planning comparison of conventional, 3D conformal, and intensity-modulated photon (IMRT) and proton therapy for paranasal sinus carcinoma.

PURPOSE To determine the potential improvements in patients with paranasal sinus carcinoma by comparing proton and intensity-modulated radiotherapy (IMRT) with conventional and conformal photon treatment planning techniques. METHODS AND MATERIALS In 5 patients, comparative treatment planning was performed by comparing proton plans and related conventional, conformal, and IMRT photon plans. The evaluations analyzed dose-volume histogram findings of the target volumes and organs at risk (OARs, i.e., pituitary gland, optical pathway structures, brain, nontarget tissue). RESULTS The mean and maximal doses, dose inhomogeneities, and conformity indexes for the planning target volumes were comparable for all techniques. Photon plans resulted in greater volumes of irradiated nontarget tissues at the 10-70% dose level compared with the corresponding proton plans. The volumes thereby increased by a factor of 1.3-3.1 for conventional, 1.1-3.8 for conformal, and 1.1-3.7 for IMRT. Compared with conventional techniques, conformal and IMRT photon treatment planning options similarly reduced the mean dose to the OARs. The use of protons further reduced the mean dose to the OARs by up to 65% and 62% compared with the conformal and IMRT technique, respectively. CONCLUSION Compared with conventional treatment techniques, conformal RT and IMRT similarly enabled dose reductions to the OARs. Additional improvements were obtained using proton-based treatment planning modalities.

LINAC based stereotactic radiotherapy of uveal melanoma: 4 years clinical experience

PURPOSE To study local tumor control and radiogenic side effects after fractionated LINAC based stereotactic radiotherapy for selected uveal melanoma. PATIENTS AND METHODS Between June 1997 and March 2001, 90 patients suffering from uveal melanoma were treated at a LINAC with 6 MV. The head was immobilized with a modified stereotactic frame system (BrainLAB). For stabilization of the eye position a light source was integrated into the mask system in front of the healthy or the diseased eye. A mini-video camera was used for on-line eye movement control. Tumors included in the study were either located unfavorably with respect to macula and optical disc (<3 mm distance) or presented with a thickness >7 mm. Median tumor volume was 305+/-234 mm3 (range 70-1430 mm3), and mean tumor height was 5.4+/-2.3 mm (range 2.7-15.9 mm). Total doses of 70 (single dose 14 Gy @ 80% isodose) or 60 Gy (single dose 12 Gy @ 80% isodose) were applied in five fractions within 10 days. The first fractionation results in total dose (TD) (2 Gy) of 175 Gy for tumor and 238 Gy for normal tissue, corresponding values for the second fractionation schedule are 135 and 180 Gy, respectively. RESULTS After a median follow-up of 20 months (range 1-48 months) local control was achieved in 98% (n=88). The mean relative tumor reductions were 24, 27, and 37% after 12, 24 and 36 months. Three patients (3.3%) developed metastases. Secondary enucleation was performed in seven patients (7.7%). Long term side effects were retinopathy (25.5%), cataract (18.9%), optic neuropathy (20%), and secondary neovascular glaucoma (8.8%). CONCLUSION Fractionated LINAC based stereotactic photon beam therapy in conjunction with a dedicated eye movement control system is a highly effective method to treat unfavorably located uveal melanoma. Total doses of 60 Gy (single dose 12 Gy) are considered to be sufficient to achieve good local tumor control.

Comparative treatment planning on localized prostate carcinoma : Conformal photon- versus proton-based radiotherapy

Purpose:To assess the potential benefit of proton–beam therapy in comparison to 3–D conformal photon therapy and photon– based intensity–modulated radiotherapy (IMRT) in prostate carcinoma for various stages of disease.Material and Methods:In five patients a 3–D conformal proton–based (two lateral beams) irradiation technique was compared with 3–D conformal photon–beam radiotherapy (four–field box) and IMRT (seven beams). For each patient different target volumes (CTVs) were defined according to early, intermediate and advanced stages of disease: CTV I consisted of the prostate gland, CTV II encompassed prostate and basis of seminal vesicles, and CTV III the prostate and seminal vesicles. Corresponding planning target volumes PTV I–III were defined by uniformly adding a margin of 5 mm to CTV I–III. Dose–volume histograms (DVHs) were analyzed for the different PTVs and various organs at risk (OARs), i.e., rectal wall, bladder, both femoral heads. In addition, maximum and mean doses were derived for the various structures and irradiated non–target tissue volumes were compared for PTV I–III and the different irradiation techniques. Finally, dose conformity and target dose homogeneity were assessed.Results:With photon– and proton–based radiotherapy techniques similar dose distributions were determined for PTV I–III: mean and maximum PTV dose values were between 99–104% and 102–107% of the normalized total doses (70 Gy), respectively. Conformity indices varied from 1.4 to 1.5 for the photon techniques, whereas for proton–beam radiotherapy values ranged from 1.1 to 1.4. Both the 3–D conformal and the IMRT photon treatment technique resulted in increased mean doses (~ 40–80%) for OARs when compared to protons. With both photon techniques non–target tissue volumes were irradiated to higher doses (mean dose difference ≥ 70%) compared to proton–beam radiotherapy. Differences occurred mainly at the low and medium dose levels, whereas in high dose levels similar values were obtained. In comparison to conformal 3–D treatments IMRT reduced doses to OARs in the medium dose range, especially for the rectal wall.Conclusion:IMRT enabled dose reductions to OARs in the medium dose range compared to 3–D conformal radiotherapy. A rather simple two–field proton–based treatment technique further reduced doses to OARs compared to photon–beam radiotherapy. The advantageous dose distribution of proton–beam therapy for prostate cancer may result in reduced side effects, which needs to be confirmed in clinical studies.Ziel:Im Rahmen einer planungstechnischen Studie wurde für die Behandlung des primären Prostatakarzinoms die Dosisverteilung einer konformalen Protonentechnik mit intensitätsmodulierten (IMRT) und konformalen Photonentechniken verglichen und analysiert. Material und Methodik:Bei fünf Patienten wurde eine konformale Zwei–Felder–Protonentechnik mit einer konformalen Photonentechnik (Vier–Felder–Becken–Box) und einer Sieben–Felder–IMRT–Technik verglichen. Dabei wurden für jeden Patienten entsprechend frühen, intermediären sowie fortgeschrittenen Tumorstadien verschiedene Zielvolumina (CTV) definiert; CTV I: Prostata, CTV II: Prostata und Samenblasenbasis, CTV III: Prostata und Samenblasen. Für die Planungszielvolumina PTV I–III wurde jeweils ein isotroper Sicherheitssaum von 5 mm gewählt. Mittels Dosis–Volumen–Histogramm–(DVH–)Auswertung wurden mittlere und maximale Dosiswerte im Bereich der unterschiedlichen PTV sowie der Risikoorgane (Rektumwand, Harnblase, Hüftköpfe beidseits) verglichen. Zusätzlich wurden die Volumina des bestrahlten Normalgewebes, der PTV und Risikoorgane in unterschiedlichen Dosisbereichen bewertet.Ergebnisse:Die Dosisverteilungen in PTV I–III zeigten für die unterschiedlichen Planungsvarianten mit mittleren Dosen von 99–104% bzw. maximalen Dosiswerten von 102–107% (normiert auf Gesamtdosis 70 Gy) vergleichbare Werte. Die Konformalitätsindizes variierten zwischen 1,4 und 1,5 für die Photonentechniken und zwischen 1,1 und 1,4 für die Protonentherapie. Im Vergleich zur Protonentherapie ergaben sich bei den Photonentechniken erhöhte mittlere Dosiswerte (~ 40–80%) für die evaluierten Risikoorgane, sowie ein Anstieg (Differenz mittlere Dosis ≥ 70%) des bestrahlten Normalgewebevolumens. Die Unterschiede zwischen den Photonen– und Protonentechniken dominierten in den niedrigen und mittleren Dosisbereichen, während im Hochdosisbereich vergleichbare Dosisverteilungen erzielt wurden. Beim Vergleich der konformalen Photonentherapie mit der IMRT zeigte Letztere eine geringere Risikoorganbelastung im mittleren Dosisbereich, im Speziellen im Bereich der Rektumwand.Schlussfolgerung:Im Vergleich zur 3–D–gestützten konformalen Photonentherapie konnte mit Hilfe der IMRT die Dosisbelastung an den Risikoorganen in den mittleren Dosisbereichen reduziert werden. Der Einsatz einer Zwei–Felder–Protonentechnik führte zu einer weiteren Dosisreduktion in den Risikoorganen. Diese verbesserte Dosisverteilung von Protonen bei der Behandlung des primären Prostatakarzinoms könnte zu einer Reduktion therapieassoziierter Nebenwirkungen führen, was in zukünftigen klinischen Studien zu belegen ist.

Development and application of a real-time monitoring and feedback system for deep inspiration breath hold based on external marker tracking

Respiration can cause tumor movements in thoracic regions of up to 3 cm. To minimize motion effects several approaches, such as gating and deep inspiration breath hold (DIBH), are still under development. The goal of our study was to develop and evaluate a noninvasive system for gated DIBH (GDIBH) based on external markers. DIBH monitoring was based on an infrared tracking system and an in-house-developed software. The in-house software provided the breathing curve in real time and was used as on-line information for a prototype of a feedback device. Reproducibility and stability of the breath holds were evaluated without and with feedback. Thirty-five patients undergoing stereotactic body radiotherapy (SBRT) performed DIBH maneuvers after each treatment. For 16 patients dynamic imaging sequences on a multislice CT were used to determine the correlation between tumor and external markers. The relative reproducibility of DIBH maneuvers was improved with the feedback device (74.5% +/- 17.1% without versus 93.0% +/- 4.4% with feedback). The correlation between tumor and marker was good (Pearson correlation coefficient 0.83 +/- 0.17). The regression slopes showed great intersubject variability but on average the internal margin in a DIBH treatment situation could be theoretically reduced by 3 mm with the feedback device. DIBH monitoring could be realized in a noninvasive manner through external marker tracking. We conclude that reduction of internal margins can be achieved with a feedback system but should be performed with great care due to the individual behavior of target motion.

Comparative Treatment Planning on Localized Prostate Carcinoma

Purpose:To assess the potential benefit of proton–beam therapy in comparison to 3–D conformal photon therapy and photon– based intensity–modulated radiotherapy (IMRT) in prostate carcinoma for various stages of disease.Material and Methods:In five patients a 3–D conformal proton–based (two lateral beams) irradiation technique was compared with 3–D conformal photon–beam radiotherapy (four–field box) and IMRT (seven beams). For each patient different target volumes (CTVs) were defined according to early, intermediate and advanced stages of disease: CTV I consisted of the prostate gland, CTV II encompassed prostate and basis of seminal vesicles, and CTV III the prostate and seminal vesicles. Corresponding planning target volumes PTV I–III were defined by uniformly adding a margin of 5 mm to CTV I–III. Dose–volume histograms (DVHs) were analyzed for the different PTVs and various organs at risk (OARs), i.e., rectal wall, bladder, both femoral heads. In addition, maximum and mean doses were derived for the various structures and irradiated non–target tissue volumes were compared for PTV I–III and the different irradiation techniques. Finally, dose conformity and target dose homogeneity were assessed.Results:With photon– and proton–based radiotherapy techniques similar dose distributions were determined for PTV I–III: mean and maximum PTV dose values were between 99–104% and 102–107% of the normalized total doses (70 Gy), respectively. Conformity indices varied from 1.4 to 1.5 for the photon techniques, whereas for proton–beam radiotherapy values ranged from 1.1 to 1.4. Both the 3–D conformal and the IMRT photon treatment technique resulted in increased mean doses (~ 40–80%) for OARs when compared to protons. With both photon techniques non–target tissue volumes were irradiated to higher doses (mean dose difference ≥ 70%) compared to proton–beam radiotherapy. Differences occurred mainly at the low and medium dose levels, whereas in high dose levels similar values were obtained. In comparison to conformal 3–D treatments IMRT reduced doses to OARs in the medium dose range, especially for the rectal wall.Conclusion:IMRT enabled dose reductions to OARs in the medium dose range compared to 3–D conformal radiotherapy. A rather simple two–field proton–based treatment technique further reduced doses to OARs compared to photon–beam radiotherapy. The advantageous dose distribution of proton–beam therapy for prostate cancer may result in reduced side effects, which needs to be confirmed in clinical studies.Ziel:Im Rahmen einer planungstechnischen Studie wurde für die Behandlung des primären Prostatakarzinoms die Dosisverteilung einer konformalen Protonentechnik mit intensitätsmodulierten (IMRT) und konformalen Photonentechniken verglichen und analysiert. Material und Methodik:Bei fünf Patienten wurde eine konformale Zwei–Felder–Protonentechnik mit einer konformalen Photonentechnik (Vier–Felder–Becken–Box) und einer Sieben–Felder–IMRT–Technik verglichen. Dabei wurden für jeden Patienten entsprechend frühen, intermediären sowie fortgeschrittenen Tumorstadien verschiedene Zielvolumina (CTV) definiert; CTV I: Prostata, CTV II: Prostata und Samenblasenbasis, CTV III: Prostata und Samenblasen. Für die Planungszielvolumina PTV I–III wurde jeweils ein isotroper Sicherheitssaum von 5 mm gewählt. Mittels Dosis–Volumen–Histogramm–(DVH–)Auswertung wurden mittlere und maximale Dosiswerte im Bereich der unterschiedlichen PTV sowie der Risikoorgane (Rektumwand, Harnblase, Hüftköpfe beidseits) verglichen. Zusätzlich wurden die Volumina des bestrahlten Normalgewebes, der PTV und Risikoorgane in unterschiedlichen Dosisbereichen bewertet.Ergebnisse:Die Dosisverteilungen in PTV I–III zeigten für die unterschiedlichen Planungsvarianten mit mittleren Dosen von 99–104% bzw. maximalen Dosiswerten von 102–107% (normiert auf Gesamtdosis 70 Gy) vergleichbare Werte. Die Konformalitätsindizes variierten zwischen 1,4 und 1,5 für die Photonentechniken und zwischen 1,1 und 1,4 für die Protonentherapie. Im Vergleich zur Protonentherapie ergaben sich bei den Photonentechniken erhöhte mittlere Dosiswerte (~ 40–80%) für die evaluierten Risikoorgane, sowie ein Anstieg (Differenz mittlere Dosis ≥ 70%) des bestrahlten Normalgewebevolumens. Die Unterschiede zwischen den Photonen– und Protonentechniken dominierten in den niedrigen und mittleren Dosisbereichen, während im Hochdosisbereich vergleichbare Dosisverteilungen erzielt wurden. Beim Vergleich der konformalen Photonentherapie mit der IMRT zeigte Letztere eine geringere Risikoorganbelastung im mittleren Dosisbereich, im Speziellen im Bereich der Rektumwand.Schlussfolgerung:Im Vergleich zur 3–D–gestützten konformalen Photonentherapie konnte mit Hilfe der IMRT die Dosisbelastung an den Risikoorganen in den mittleren Dosisbereichen reduziert werden. Der Einsatz einer Zwei–Felder–Protonentechnik führte zu einer weiteren Dosisreduktion in den Risikoorganen. Diese verbesserte Dosisverteilung von Protonen bei der Behandlung des primären Prostatakarzinoms könnte zu einer Reduktion therapieassoziierter Nebenwirkungen führen, was in zukünftigen klinischen Studien zu belegen ist.

Impact of a micromultileaf collimator on stereotactic radiotherapy of uveal melanoma

PURPOSE To evaluate the impact of a micro multileaf collimator (mMLC) on Linac-based stereotactic radiotherapy (SRT) of uveal melanoma by comparing circular arc with static conformal, dynamic arc, and intensity-modulated SRT. MATERIALS AND METHODS Forty uveal melanoma patients were selected from approximately 100 patients treated with SRT since 1996. For each patient, four treatment plans (BrainSCAN XL, V5.0) were made: conventional arc, static conformal, dynamic arc plan, and intensity-modulated radiotherapy (IMRT). The goal of treatment planning was to fully encompass the planning target volume (PTV) by the 80% isodose while minimizing doses to the optic nerve and lens. The following parameters were evaluated: target conformity; target homogeneity; ratio of the target volume and 50% isodose volume; normal tissue receiving doses >/=80%, >/=50%, and >/=20%; central nervous system volume irradiated to >/=20%; optical nerve volume irradiated >/=50%, D(max) of the lens; lens volume receiving >/=20%; and monitor units. RESULTS PTVs ranged from 0.68 to 4.90 cm(3) (mean 1.97 +/- 0.97 cm(3)). The average reduction of the prescription isodose volume was 1-1.5 cm(3) for conformal (range 2.6-0.3 cm(3)), dynamic arc (range 2.5-0.3 cm(3)), and IMRT plans (range 3.9-0.1 cm(3)), compared with conventional arc therapy. Central nervous system volumes irradiated to doses >/=20% were smallest for conventional or dynamic arc treatments. Average target dose homogeneity values were 1.74 +/- 0.50 for arc, 1.27 +/- 0.02 for static mMLC, 1.26 +/- 0.01 for dynamic arc, and 1.15 +/- 0.03 for IMRT plans. IMRT helped to reduce doses to the lens but did not provide an advantage for optical nerve sparing. When applying IMRT, the monitor units increased by approximately one-third compared with static mMLC-based SRT. CONCLUSIONS Conformal mMLC and dynamic arc SRT are the treatment options of choice for Linac-based SRT of uveal melanoma. They present dosimetric advantages, while being highly efficient in treatment planning and delivery.

Automatic real-time surveillance of eye position and gating for stereotactic radiotherapy of uveal melanoma

A new prototype (hardware and software) for monitoring eye movements using a noninvasive technique for gated linac-based stereotactic radiotherapy (SRT) of uveal melanoma was developed. The prototype was tested within the scope of a study for 11 patients. Eye immobilization was achieved by having the patient fixate a light source integrated into the system. The system is used in conjunction with a Head&Neck mask system for immobilization, and uses infrared tracking technology for positioning (both BrainLAB AG Heimstetten/Germany). It was used during CT and MR image acquisition as well as during all of five treatment fractions (6 MeV, 5 x 12 Gy to 80% isodose) to guarantee identical patient setup and eye rotational state during treatment planning and treatment delivery. Maximum temporal and angular deviations tolerated during treatment delivery can be chosen by the physician, the radiation then being interrupted automatically and instantaneously if those criteria are being exceeded during irradiation. A graphical user interface displays life video images of the treated eye and information about the current and previous rotational deviation of the eye from its reference treatment position. The physician thus has online access to data directly linked to the success of the treatment and possible side effects. Mean angular deviations during CT/MR scans and treatment deliveries ranged from 1.61 degrees to 3.64 degrees (standard deviations 0.87 degrees to 2.09 degrees ) which is in accordance with precision requirements for SRT. Typical situations when preset deviation criteria were exceeded are slow drifts (fatigue), sudden large eye movements (irritation), or if patients closed their eyes (fatigue). In these cases radiation was reliably interrupted by the gating system. In our clinical setup the novel system for computer-controlled eye movement gated treatments was well tolerated by all patients. The system yields quantitative real-time information about the eyes rotational state with respect to a reference position (treatment planning situation). Together with the possibility of performing movement-gated treatments of uveal melanoma, the system thus greatly improves the quality of this treatment.

A noninvasive eye fixation and computer-aided eye monitoring system for linear accelerator–based stereotactic radiotherapy of uveal melanoma

PURPOSE To introduce a noninvasive eye fixation and computer-aided eye monitoring system for linear accelerator-based stereotactic radiotherapy for uveal melanoma. METHODS AND MATERIALS At the Department of Radiotherapy and Radiobiology, University of Vienna, stereotactic radiotherapy is offered to patients with uveal melanoma considered unsuitable for (106)Ru brachytherapy or local resection. For the present feasibility study, 8 patients were carefully selected according to their ability to fixate a small light source with the diseased eye and whether they had a rather small head to meet the limited geometric space available. A polymethyl methacrylate tube was attached to a stereotactic mask system in craniocaudal orientation supporting a 45 degrees mirror, which was placed in front of the diseased eye. At the other end of the tube, the patient was given a small fixation light, and a small camera was positioned beneath, which was shielded for use during MRI. A computer interface calculated and visualized the spatial difference of the actual and a given reference pupil position, which was defined before CT scanning, during the MRI sequences, and during treatment delivery at the linear accelerator. RESULTS The described system can be attached to a conventional stereotactic mask system with minor modifications. Because of the large distance between the eye and the fixation light, the optical fixation system was well tolerated by all patients, and a stable position of the eye was obtained. The camera system can be used during CT and MRI without interference. Absorption of the 6-MV photon beam by the mirror and the polymethyl methacrylate tube was negligible. The computer interface designed to determine the pupil position uses an image-processing algorithm that correlates a template of the reference image with the actual image of the eye. Provided sufficient illumination of the pupil, the correlation function showed a pronounced minimum at the reference position. The precision of the algorithm was tested by phantom measurements. For a given 1 mm or 2 mm displacement, the interface reported a mean shift of 0.96 +/- 0.18 mm or 2.07 +/- 0.11 mm, respectively. CONCLUSION The results of this study demonstrated the feasibility of a new optical fixation system for linear accelerator-based stereotaxis. The artifact-free application of the camera system during image acquisition and irradiation and the use of the computer interface, which automatically monitored eye movements with submillimeter precision, provided large improvements compared with existing techniques. Given well-defined interruption criteria and accelerated image processing, the described system has a high potential to perform automatically gated treatment beam delivery in the near future.

Inverse Planning – a Comparative Intersystem and Interpatient Constraint Study

Purpose:To compare commercial treatment-planning systems (TPS) for inverse planning (IP) and to assess constraint variations for specific IMRT indications.Material and Methods:For IP, OTP, XiO and BrainSCAN were used and step-and-shoot intensity-modulated radiotherapy (IMRT) delivery was assumed. Based on identical constraints, IP was performed for a prostate, head and neck, brain, and gynecologic case. IMRT plans were compared in terms of conformity/homogeneity, dose-volume histograms (DVHs), and delivery efficiency. For ten patients each of a class of indications, constraint variations were evaluated.Results:IMRT plans were comparable concerning minimum target dose, homogeneity, conformity, and maximum doses to organs at risk. Larger differences were seen in dose gradients outside the target, monitor units, and segment number. Using help structures proved efficient to shape isodoses and to reduce segmentation workload. For IMRT class solutions, IP constraint variations depended on anatomic site.Conclusion:IP systems requiring doses as input and having objective functions based on physical parameters had a very similar performance. Constraint templates can be established for a class of IMRT indications.Ziel:Die Funktionalität der inversen Planung (IP) von kommerziellen Bestrahlungsplanungssystemen (TPS) sowie die Unterschiede von Dosiszielgrößen bei typischen IMRT-Indikationen (intensitätsmodulierte Strahlentherapie) wurden untersucht.Material und Methodik:Für die IP fanden OTP, XiO und BrainSCAN Verwendung, und eine „Step-and-shoot“-IMRT wurde angenommen. Basierend auf gleichen Zielgrößenvorgaben wurde für je einen Fall mit Prostatakarzinom, Hirntumor, HNO-Tumor sowie gynäkologischem Tumor eine IP durchgeführt. Die IMRT-Pläne wurden anhand von Dosis-Volumen-Histogrammen (DVHs), Konformität, Homogenität und Bestrahlungseffizienz bewertet. Für je zehn Patienten mit bestimmten Indikationen wurde die Schwankung der IP-Zielgrößen untersucht.Ergebnisse:Mit allen drei TPS konnten ähnliche IMRT-Pläne mit vergleichbarer Zielgebietsauslastung, Dosishomogenität, Konformität und maximaler Dosisbelastung der Risikoorgane erstellt werden. Größere Unterschiede wurden hinsichtlich des Dosisgradienten außerhalb des Zielgebiets, der Monitoreinheiten sowie der Segmentzahlen beobachtet. Die Verwendung von Hilfsstrukturen erwies sich als zeitsparend. Für eine IMRT-Indikation schwanken die Zielgrößenvorgaben in Abhängigkeit von der Patientenanatomie.Schlussfolgerung:Mit TPS, deren Zielgrößen und Zielfunktionen auf physikalischen Dosen beruhen, konnten ähnliche IMRT-Pläne erzielt werden. Für IMRT-Konzepte lassen sich Standardzielvorgaben festlegen.

Registration of DRRs and portal images for verification of stereotactic body radiotherapy: a feasibility study in lung cancer treatment

Image guidance has become a pre-requisite for hypofractionated radiotherapy where the applied dose per fraction is increased. Particularly in stereotactic body radiotherapy (SBRT) for lung tumours, one has to account for set-up errors and intrafraction tumour motion. In our feasibility study, we compared digitally reconstructed radiographs (DRRs) of lung lesions with MV portal images (PIs) to obtain the displacement of the tumour before irradiation. The verification of the tumour position was performed by rigid intensity based registration and three different merit functions such as the sum of squared pixel intensity differences, normalized cross correlation and normalized mutual information. The registration process then provided a translation vector that defines the displacement of the target in order to align the tumour with the isocentre. To evaluate the registration algorithms, 163 test images were created and subsequently, a lung phantom containing an 8 cm(3) tumour was built. In a further step, the registration process was applied on patient data, containing 38 tumours in 113 fractions. To potentially improve registration outcome, two filter types (histogram equalization and display equalization) were applied and their impact on the registration process was evaluated. Generated test images showed an increase in successful registrations when applying a histogram equalization filter whereas the lung phantom study proved the accuracy of the selected algorithms, i.e. deviations of the calculated translation vector for all test algorithms were below 1 mm. For clinical patient data, successful registrations occurred in about 59% of anterior-posterior (AP) and 46% of lateral projections, respectively. When patients with a clinical target volume smaller than 10 cm(3) were excluded, successful registrations go up to 90% in AP and 50% in lateral projection. In addition, a reliable identification of the tumour position was found to be difficult for clinical target volumes at the periphery of the lung, close to backbone or diaphragm. Moreover, tumour movement during shallow breathing strongly influences image acquisition for patient positioning. Recapitulating, 2D/3D image registration for lung tumours is an attractive alternative compared to conventional CT verification of the tumour position. Nevertheless, size and location of the tumour are limiting parameters for an accurate registration process.