Room: ePoster Forums
Purpose: To find whether the OAR's spatial position can influence the verification plans' passing rates by using Delta4 and COMPASS.
Methods: 17 UCC IMRT plans were verified both by Delta4 and COMPASS. The dose error (DE%) and gamma index were measured from PTV(Dâ‚‰â‚…,Dmean), bladder(Dâ‚‚cc,Dmean), rectum(Dâ‚‚cc,Dmean), and the femoral heads(Dâ‚‚cc,Dmean) both left and right used for quantification. Two parallel measurements were performed with: 1) both Delta4 and COMPASS geometry center overlap with the iso-center; 2) only Delta 4's geometry center shifted 5 cm from the iso-center left hand side reference the LINAC .
Results: For parallel measurement 1, all the plans' DE% of the PTV, bladder and rectum are all less than 5% averagely meanwhile the gamma index of the PTV(Dâ‚‰â‚…,Dmean),bladder(Dâ‚‚cc,Dmean) and rectum(Dâ‚‚cc,Dmean) are higher than 95% no matter Delta 4 or COMPASS was used. However for the femoral heads, the gamma indexs are all higher than 95% for both Delta 4 and COMPASS but the Delta 4 based DE% of Dmean was higher than 15% compared with that being less than 5% for COMPASS. For parallel measurement 2, the Gamma index of all the structures include the left femoral heads were higher than 95% for both Delta4 and the DE% was less than 5%. For the left femoral heads, the Dmeansâ€™ DE% is less than 5% and Gamma index is larger than 95%.
Conclusion: The verification plans' passing rates can be influenced by the OARs' spatial position for Delta4 measurement, especially for these located far from Delta4's geometrical center such as the femoral heads. It reveals that we should take into account of the OARs' relative spatial position to Delta4's geometrical center. If abnormality occurs with these OAR, then other evaluation parameters such as the Dâ‚‚cc should be used for further plan verification.