(Sunday, 7/14/2019)
Room: ePoster Forums
Purpose: To investigate if external beam radiation plans using cylindrical shell arcs (CSA) generate comparable/improved dose savings to organs at risk (OAR) compared to the Multichannel Cylinder (MC) or interstitial high dose rate brachytherapy (HDR) for eligible vaginal cuff or endometrial cases.
Methods: The CSA plan and its analytic dose model for external beam radiation have been developed and tested with CIRS phantom plans for multiple single-channel cylinder diameters with and without interstitial needles; plans of multi-channel cylinder cases have been created. The CSA plan uses the HDR cylinder for target localization; photon jaws and MLCs are conformed outside of the cylindrical surface to decrease doses outside the target. One or two shell arcs are used with VMAT for dose optimization purposes and patient set up is based on the cylinder.
Results: The CSA plans resulted in less dose delivered to surrounding OARs compared to the single- channel or multichannel cylinder at distances of 0.75cm, 1.4cm and 1.75 cm from surface for single- and multi-channel cylinder diameters of 2.5cm, 3cm and 3.5 cm, respectively. It also generated comparable plan quality to an interstitial HDR if the high risk CTV is less than 1.25cm, 1.9cm and 2.25cm from the cylinder surface with similar cylinder diameters to those described above. The comparison of the VMAT plans with brachytherapy plans showed that VMAT plans were superior for larger targets.
Conclusion: CSA generated plans with comparable dosimetric quality to those developed for HDR brachytherapy for multiple diameters of single-channel and multi-channel cylinders with or without interstitial needles. This less invasive treatment approach has the potential to be used as an alternative treatment modality to HDR MC or interstitial brachytherapy for limited para-vaginal extension.
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