OverviewClinical Application of Image-guided Radiotherapy in Bladder and Prostate Cancer
Section snippets
Statement of Search Strategies Used and Sources of Information
Both authors independently searched MEDLINE using technique-specific terms up to 11 January 2010. Further papers were extracted from the references of papers identified from this MEDLINE search strategy.
Radiotherapy Delivery — the Problem of Motion
The core issue is variation in bladder volume and shape, although changes in bowel and rectal volume can also have clinical relevance. Henry et al. [19], in a study with repeat cone-beam computed tomographic imaging (CBCT) during a course of radiotherapy, showed that there are both systematic (Σ) and random (σ) variations in bladder volume, with some patients exhibiting systematic reductions in bladder volume. Changes in bladder volume result in three-dimensional changes in the bladder shape
Radiotherapy Delivery — the Problem of Motion
The considerable internal organ motion of the prostate is primarily due to changes in rectal volume. This has now been shown to impact on tumour control. Two studies in the pre-IGRT era showed that the reduction in biochemical control associated with a large rectal volume at computer tomography planning (over 25 and 20%, respectively, in certain risk groups) was greater than the benefit seen within the dose escalation studies [52], [53]. A large rectal cross-sectional area has also been
Conclusion
Bladder cancer and prostate cancer are two malignancies where significant target motion occurs, necessitating the use of margins to account for this. The causes and solutions are different: for bladder cancer, changes in the shape of the target volume require changes to the volume treated; for prostate cancer, a three-dimensional vector displacement requires accurate alignment of the isocentre. Historically these margins have been population derived yet this is now known to be suboptimal —
Acknowledgements
We would like to thank Dr Nachi Palaniappan for identifying two recent references on bladder IGRT.
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