Room: Exhibit Hall | Forum 5
Purpose: Daily kV IGRT may not be necessary for every prone breast patients for the sake of imaging dose and patient on-couch time. A study of ours showed that reduced kV IGRT frequency yields relatively small target dose changes but wider OAR dose variation among patients. For the optimization of kV imaging frequency, this work investigates if patient anatomy information or first several couch shift data can help predict any large OAR dose change.
Methods: 10 prone breast treatment courses for low risk of secondary cancer were involved. For each patient, three kV IGRT schemes: 1)daily-kV, 2)weekly-kV, 3)no-kV were simulated based on the daily couch shift after kV imaging is performed. When weekly-kV or no-kV scheme was utilized, the resulting dose changes relative to daily-kV were calculated for OAR structures (i.e., Dmax and Dmean for heart, ipsilateral lung and chest wall). The patient anatomy information (including breast volume, target to OAR distances) and first 3-day couch shift data were analyzed to investigate their relationship with the OAR dose changes due to different kV imaging frequency.
Results: The correlation between dose changes for different kV scheme and patient anatomy/shift data was OAR-specific. Heart dose changes were more closely correlated with patient anatomy such as breast-to-lung distance and breast volume), and their maximum correlation coefficient was 0.8 (vs. 0.7 for 3-day couch shift data). While lung dose changes had a higher correlation coefficient (maximum 0.65) with first 3-day mean couch shift data than maximum 0.4 with anatomy information. Chest wall dose changes had weak correlation with these patient data, and no other relationship was found.
Conclusion: For different kV IGRT schemes, patient anatomy and first 3-day couch shift data can help estimate dose changes for heart and lung respectively, thereby aiding clinicians in balancing the tradeoff of different kV imaging frequency.