Room: ePoster Forums
Purpose: With the new proton delivery system by Hitachi, Dose Driven Continuous Scanning (DDCS), we study the benefits of direct plan conversion of a Discrete Spot Scanning (DSS) plan to DDCS. This study aims to quantify the delivery time reduction and the target dose degradation of the converted plan.
Methods: Since there are no commercial TPS available to produce DDCS plan, we developed our own software to do the conversion based on the guidelines set by the DDCS system. DDCS has a â€œbreak spotâ€? concept where if the MU of the spots are too low to allow for continuous scanning, it will perform discrete spot scanning instead. The beam current and placements of â€œbreak spotsâ€? are varied to optimise the delivery time. The concept is tested on a exported dicom plan of a head and neck case. The dose distribution of the DDCS plan is evaluated by approximating the continuous portion of the DDCS as closely spaced discrete spots; this is then imported into the TPS to compare with the original DSS plan to determine dose degradation using DVH. This procedure is repeated for the same clinical case with different spot spacings and with SFO and MFO planning techniques.
Results: There were no dose degradation in converting the DSS plan into a DDCS plan for actual proton therapy delivery - the 99% DVH target coverage differs by less than 1%. Significant delivery time reduction between 20% to 45% can be achieved by using DDCS, depending on the exact latency time for each single discrete spot scanning.
Conclusion: We have shown that direct DSS to DDCS plan conversion is feasible without having to optimise the DDCS plan. The target DVH coverage is maintained for both SFO and MFO techniques and significant delivery time reduction can be achieved especially in proton SBRT.