A comparison of dosimetric variance for external-beam partial breast irradiation using three-dimensional and four-dimensional computed tomography

Comparison of two different respiratory monitoring systems with 4D-CT images for target volume definition in patients undergoing para-aortic nodal irradiation

OBJECTIVE

Today, respiratory movement can be monitored and recorded with different methods during a simulation on a four-dimensional (4D) computed tomography (CT) device to be used in radiotherapy planning. A synchronized respiratory monitoring system (RPM) with an externally equipped device is one of these methods. Another method is to create 4D images of the patient's breathing phases without the need for extra equipment, with an anatomy-based software program integrated into the CT device. Our aim is to compare the RPM system and the software system (Deviceless) which are two different respiratory monitoring methods used in tracking moving targets during 4D-CT imaging and to assess their clinical usability.

METHODS

Ten patients who underwent paraaortic nodal irradiation were enrolled. The simulation was performed using intravenous contrast material on a 4D-CT device with both respiratory monitoring methods. The right/left kidneys and renal arteries were chosen as references to evaluate abdominal organ movement. It was then manually contoured one by one on both sets of images. The images were compared volumetrically and geometrically after rigid reconstruction. The similarity between the contours was determined by the Dice index. Wilcoxon test was used for statistical comparisons.

RESULTS

The motion of the kidneys in all three directions was found to be 0.0 cm in both methods. The shifts in the right/left renal arteries were submillimetric. The Dice index showed a high similarity in both kidney and renal artery contours.

CONCLUSION

In our study, no difference was found between RPM and Deviceless systems used for tracking and detection of moving targets during simulation in 4D-CT. Both methods can be used safely for radiotherapy planning according to the available possibilities in the clinic.

Analysis of the variability among radiation oncologists in delineation of the postsurgical tumor bed based on 4D-CT

OBJECTIVE

This study investigated interobserver and intraobserver variability in radiation oncologists' definition of the tumor bed (TB) after breast-conserving surgery (BCS).

RESULTS

The TB volume, CVS and number of surgical clips were not significantly related to intraobserver variability. Moreover, no correlation was noted between CT slice thickness and interobserver variability (Δinter, DSCinter) in TB delineation, and no significant difference was noted among the three groups. The TB volume was negatively correlated with Δinter. DSCinter improved significantly with increased TB volume and decreased Δinter. DSCinter also increased significantly in patients with a CVS of 3 to 5 compared with patients with a CVS of 1 to 2. DSCinter was thus positively correlated with the CVS, with a correlation coefficient of 0.451. The use of 7 to 9 surgical clips neither decreased Δinter nor increased DSCinter.

MATERIALS AND METHODS

Five or more surgical clips were placed at the TB during lumpectomy. The TB was delineated on the end expiration scan. The data were stratified based on the cavity visualization score (CVS), CT slice thickness and surgical clip number. The Dice similarity coefficient (DSC) and inter(intra)observer variability (Δinter and Δintra) in different groups were evaluated and compared.

CONCLUSIONS

Inter(intra)observer variability in TB delineation was decreased for breast cancer patients implanted with 5 or more surgical clips in the cohort with a higher CVS and a larger TB. The use of more than 6 surgical clips did not significantly improve TB delineation, so 5 to 6 surgical clips are likely adequate to delineate the TB.

[Respiratory synchronization and breast radiotherapy]

Adjuvant radiation therapy following breast cancer surgery continues to improve locoregional control and overall survival. But the success of highly targeted-conformal radiotherapy such as intensity-modulated techniques, can be compromised by respiratory motion. The intrafraction motion can potentially result in significant under- or overdose, and also expose organs at risk. This article summarizes the respiratory motion and its effects on imaging, dose calculation and dose delivery by radiotherapy for breast cancer. We will review the methods of respiratory synchronization available for breast radiotherapy to minimize the respiratory impact and to spare organs such as heart and lung.