Purpose: Availability of field delivery time estimate during the treatment planning allows to better assess if a given plan is tolerable for a patient delivery time-wise and can provide an input for patient scheduling in the treatment rooms. It is also desirable to determine the deliverability of plan prior to patient specific QA or the actual treatment. The aim of this study is to evaluate a tool which can determine the plan deliverability and the treatment time of proton pencil beam therapy.
Methods: Treatment Time Calculator (TTC, Varian) algorithm has been developed and tested to estimate treatment delivery time and deliverability by considering several room-specific parameters such as minimum spot duration, layer switching time, beam currents, and beam line transmission. Fifteen deliverable (46 total fields) and 10 undeliverable treatment plans (47 total fields) of various anatomic sites were selected and tested by TTC tool. The actual delivery time of each deliverable plan were obtained for multiple fractions (average=7) from oncology information system and compared to TTC estimated time.
Results: The TTC average estimated treatment time predicted to be lower (-22.7±5.6%) than the actual delivery time as TTC reports the ideal treatment delivery and doesn’t consider daily fluctuations of the system. By applying a form factor of 23%, average difference can be reduced to 6%. Based on our daily QA records, daily treatment time can vary up to 15%. For the same plan, both calculated and measured delivery time can vary up to 30% in different treatment rooms. Additionally, prediction of treatment plan deliverability by TTC shows high sensitivity (85.0%) and specificity (99.7%).
Conclusion: Using TTC, undeliverable plans can be filtered out at the time of treatment planning and prior to delivery, which can eliminate last-minute replanning. Treatment time determination enables proper selection of treatment rooms depending on the plan configuration.
Funding Support, Disclosures, and Conflict of Interest: This project is partially supported by Varian Medical Systems. Arturs Meijers is Varian Medical Systems employee.