Poster Presentations Archive

UK & Ireland Prostate Brachytherapy Conference 2022

Abstract number 6

Independent DVH QA test of a Brachytherapy Treatment Planning System 

Esteve S
Northern Ireland Cancer Centre, Belfast 

PURPOSE: To develop a test to independently verify Dose Volume Histogram (DVH) calculations on a Low-Dose-Rate Brachytherapy Treatment Planning System. 

METHODS: An in-house program was developed with Matlab to calculate dose points following the TG43 algorithm with 2D anisotropy and radial functions. A 5cm cube was created with 1x1x1mm3 voxels. 2 I125 (AgX100) sources of 100U air kerma strength were placed on opposite corners. Doses were calculated from each source to the centre of every voxel. The dose was considered uniform within each voxel. Contributions from both seeds were added and a differential dose-volume-histogram (DVH) was calculated based on voxel doses. Dummy images were acquired on Variseed TPS with a BK FlexFocus scanner and BK transrectal probe. A 5cm cube was ‘contoured’ with the aid of the Digital Ultrasound template visible on each 1mm slice. 2 Seeds were placed on opposite corners and the resulting DVH of this structure was exported as a text file. The calculated and planned DVHs were compared and a parameter was defined to quantify the agreement between both curves. Dose and volume differences were calculated for each point and thresholds were set to evaluate differences higher than 2%. 

RESULTS: There was excellent agreement between both DVHs. All points passed with differences less than 1%. 

CONCLUSION: The test can be part of a routine QA program or for post-upgrades checks. The code can be modified to include more seeds or simple structures. Future work will include the verification of clinical margins that are used in prostate brachytherapy