Claire McCarthy

Inter-fraction motion and dosimetric consequences during breast intensity-modulated radiotherapy (IMRT)

BACKGROUND AND PURPOSE Intensity-modulated radiotherapy (IMRT) can improve dose homogeneity within the breast planned target volume (PTV), but may be more susceptible to patient/organ motion than standard tangential radiotherapy (RT). We used daily cone-beam CT (CBCT) imaging to assess inter-fraction motion during breast IMRT and its subsequent impact on IMRT and standard RT dose homogeneity. MATERIALS AND METHODS Ten breast cancer patients selected for IMRT were studied. CBCT images were acquired immediately after daily treatment. Automatic image co-registration was used to determine patient positioning variations. Daily PTV contours were used to calculate PTV variations and daily delivered IMRT and theoretically planned tangential RT dose. RESULTS Group systematic (and random) setup errors detected by CBCT were 5.7 (3.9)mm laterally, 2.8 (3.5)mm vertically and 2.3 (3.2)mm longitudinally. Rotations >2 degrees in any axis occurred on 53/106 (50%) occasions. Daily PTV volume varied up to 23%. IMRT dose homogeneity was superior at planning and throughout the treatment compared with standard RT (1.8% vs. 15.8% PTV received >105% planned mean dose), despite increased motion sensitivity. CONCLUSIONS CBCT revealed inadequacies of current patient positioning and verification procedures during breast RT and confirmed improved dose homogeneity using IMRT for the patients studied.

Ultrasound Imaging to Assess Inter- and Intra-fraction Motion during Bladder Radiotherapy and its Potential as a Verification Tool

AIMS Organ motion is the principle source of error in bladder cancer radiotherapy. The aim of this study was to evaluate ultrasound bladder volume measurement as a surrogate measure of organ motion during radiotherapy: (1) to assess inter- and intra-fraction bladder variation and (2) as a potential treatment verification tool. MATERIALS AND METHODS Twenty patients receiving radical radiotherapy for bladder cancer underwent post-void ultrasound bladder volume measurement at the time of radiotherapy treatment planning (RTP), and immediately before (post-void) and after receiving daily fractions. RESULTS Ultrasound bladder volume measurement was found to be a simple and acceptable method to estimate relative bladder volume changes. Six patients showed significant changes to post-void bladder volume over the treatment course (P<0.05). The mean inter-fraction post-void bladder volume of five patients exceeded their RTP ultrasound bladder volume by more than 50%. Intra-fraction bladder volume increased on 275/308 (89%) assessed fractions, with the mean intra-fraction volume increases of seven patients exceeding their RTP ultrasound bladder volume by more than 50%. CONCLUSIONS Both day-to-day bladder volume variation and bladder filling during treatment should be considered in RTP and delivery. Ultrasound may provide a practical daily verification tool by: supporting volume limitation as a method of treatment margin reduction; allowing detection of patients who may require interventions to promote bladder reproducibility; and identifying patients with prominent volume changes for the selective application of more advanced adaptive/image-guided radiotherapy techniques.

Verification kilovoltage cone beam CT (CBCT) in monitoring delivered doses and dose guided radiotherapy in oesophago-gastric cancers

Breast radiotherapy is planned on image data acquired pre-treatment, however the delivered distribution of radiation may vary from the plan due to changes in position and shape of the breast at the different fractions of treatment. This study uses anatomical information from repeated cone beam CT (CBCT) imaging at the point of treatment to assess the delivered dose distribution at different fractions of treatment.