DosimetryDosimetric evaluation of prostate rotations and their correction by couch rotations
Section snippets
Patient data
CT-scans of 5 consecutive patients with prostate cancer were selected. The prostate, the base of the seminal vesicles, rectum, bladder and femoral heads were contoured according to our clinical protocol. The base of the seminal vesicles was defined as the first 2 cm of the seminal vesicles from the base of the prostate in the sagittal view. The clinical target volume (CTV) contained the prostate and the base of the seminal vesicles. No-margin was added in order to explore the maximum effect of
Results
On average the rotation correction could reduce the systematic rotation error fully in 50% of all rotations around the left–right axis and in 75% of all rotations around the anterior–posterior and cranial–caudal axis. For the combined systematic and random rotations, i.e. for each treatment, these numbers were 35%, 70%, and 62%, respectively.
In the five patients considered we observed similar behaviour in the results, which allows us to discuss them jointly. For clarity the results of a single
Discussion
The dosimetric effects of rotations and consequently the corrections of those rotations turn out to be modest. Averaged over 5 patients, the coverage for the idealised seminal vesicles is improved from 92.6% (range 89.9–96.0%) to 95.9% (range 94.7–98.1%). The gain for the idealised prostate was less: the deteriorated coverage of 95.9% (range 94.4–97.0%) could be improved to 97.5% (range 95.5–98.4%). That this effect is small is due to the more or less spherical shape of the prostate_95 and the
Conclusion
The dosimetric effect of prostate rotations was studied and it is concluded that prostate rotations have no large impact on prostate coverage. The coverage of the seminal vesicles on the other hand can in extreme cases deteriorate more. With on-line correction of rotations the dose coverage of the target generally improves. For organs at risk near the target, the dose distribution could be improved as well as deteriorated. Most importantly, the dose to organs at risk at large distances from the
Acknowledgement
The authors thank Nucletron B.V. for the research module of PLATO-RTS that was used for the simulations.
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The dosimetric impact of prostate rotations during electromagnetically guided external-beam radiation therapy
2013, International Journal of Radiation Oncology Biology PhysicsCitation Excerpt :Van Hertin et al (9), in contrast, concluded that prostate rotations around RL axis have minimal impact on prostate coverage given that translations were managed. This conclusion was based on evaluating dosimetric impact of prostate rotations using simulated treatment plans with different rotation errors (9). This disagreement could be attributed to using simulated rotational errors on 5 patients’ CT data vs real rotations measured in 26 patients or the nature of simulated error.
Electromagnetic detection and real-time DMLC adaptation to target rotation during radiotherapy
2012, International Journal of Radiation Oncology Biology PhysicsCitation Excerpt :As with translational motion, rotational motion can severely compromise target dose coverage and normal tissue sparing if it is not accounted for. Rotation may cause part of the target volume to move out of the treatment field and result in underdose (13, 14). Recently, Li et al. (15) found that the dosimetric discrepancies caused by prostate rotation were more significant than those caused by translational intrafractional motion.
Dosimetric consequences of rotational errors in radiation therapy of pediatric brain tumor patients
2012, Radiotherapy and OncologyPosition verification for the prostate: Effect on rectal wall dose
2011, International Journal of Radiation Oncology Biology PhysicsCitation Excerpt :Engels et al. (39) reported increased biochemical failure in patients with a distended rectum on the planning CT scan, despite image guidance by implanted markers because of inadequate margins. Intrafraction motion (12, 37), delineation uncertainty (12, 40, 41), and rotations (42) are examples of the other factors to be accounted for when devising margins. In the present study, we obtained daily EPIs for both the on-line and the off-line protocols.