Clinical use of electronic portal imaging to analyse tumor motion variation during a 3D-conformal prostate cancer radiotherapy using online target verification and implanted markers

Abstract

Purpose: To evaluate the daily treatment setup variation and the interfraction and intrafraction prostate motion with portal imaging and implanted fiducial markers during irradiation with a 3D conformal radiotherapy for localized prostate cancer patients. Methods : By remote verification, shifts from isocenteric positioning and inter/intra-fraction prostate motion were investigated for 34 patients treated supine with escalated dose conformal radiotherapy. To limit the effect of inter-fraction prostate motion, patients were planned and treated with an empty rectum and a comfortably full bladder. Daily pre-therapy and treatment electronic portal images were obtained for anterior and lateral treatment fields according to an on-line target localization protocol using three gold markers. From these images, random and systematic set-up errors were measured by matching corresponding patients’ gold markers on reference digitally reconstructed radiographs (DRR). Superior-inferior, anterior-posterior and lateral motions were measured from the displacement of the gold markers implanted into the prostate before planning. A planning target volume (PTV) was derived to account for the measured prostate motion and field placement deviations. Results: Analysis of 1,278 portal images to determine changes in the radiation field during the course of treatment. From the data, random isocenter positioning deviations were 2.66 mm, 2.78 mm and 2.59 mm for vertical, lateral and longitudinal movements respectively. The systematic deviations were 3.15 mm, 3.09 mm and 2.52 mm for vertical, lateral and longitudinal movements respectively. From the verification process, it was realized that 44.7%, 42.8% and 31.4% of the vertical, lateral and longitudinal prostate migrations respectively needed correction/shift. Conclusion : Random set-up errors were small using real-time isocenter placement corrections. Inter-fraction prostate motion remained the largest source of treatment error, and observed motion was greatest at the laterals. In the absence of real-time pre-treatment imaging of the prostate position, using sequential portal films of implanted gold markers, portions of the PTV is missed and surrounding tissues not spared. This research improves quality assurance by confirming the prostate position within the treatment field over the course of therapy. ----------------------------- Cite this article as : Acquah GF, Gustavsson M, Doudoo CO, Agbeve RK, Schiestl B. Clinical use of electronic portal imaging to analyze tumor motion variation during a 3D-conformal prostate cancer radiotherapy using online target verification and implanted markers. Int J Cancer Ther Oncol 2014; 2 (4):02044. DOI : 10.14319/ijcto.0204.4