Background and purpose: A new multi-channel vaginal cylinder has been constructed. The dose distribution is compared to that of a central channel cylinder.
Patients and methods: The source channels of the multi-channel cylinder are placed close to the treatment volume, which means that the dose gradient in the radial direction is steep. Therefore the dose is enhanced close to the cylinder surface and lowered at larger distances as compared to the central channel cylinder. Three patients were each CT-scanned twice with a vaginal cylinder in situ. CT-based 3D dose-planning studies were used to calculate the dose distribution. Dose-volume histograms (DVHs) were generated for rectum and bladder, and a quantification of high dose volumes was calculated from the DVHs. Dose to the vaginal mucosa was calculated.
Results: The dose to the critical organs depends on the depth of normalization. When the dose is normalized on the cylinder surface the hot spot dose to bladder and rectum is reduced by 16 and 17%, respectively, whereas mucosal dose remains the same. When the dose is normalized at 5 mm depth the hot spot dose to bladder and rectum is reduced by 1 and 3%, respectively, whereas mucosal dose is enhanced by 17%.
Conclusions: The multi-channel cylinder makes it possible to spare the rectum and the bladder at the expense of enhanced mucosal dose.