Session Item

This work reports on the commissioning and clinical beam characterization of proton pencil beam scanning system, ProBeam Compact (Varian Medical System, Palo Alto, CA) at the first proton compact gantry in Thailand. 

ProBeam Compact proton therapy system is a single room combined with the 360-degree gantry system and robotic couch, using the cyclotron accelerated proton beam for the pencil beam scanning technique. The proton system commissioning and clinical beam characterization of (1) radiation safety and interlock verification, (2) gantry and patient table mechanical testing, (3) CBCT and kV image acquisition, 4) proton beam characterization and data commissioning for Eclipse proton algorithms (Eclipse proton V.15.6, Varian Medical System) and (5) dosimetric validation and end to end test in the clinical condition were performed and discussed. 

Radiation safety was monitored and reported within the tolerance limit for all areas. The safety access control feature and emergency stop were well operated. The gantry and patient table mechanical tests showed a good performance within the acceptance criteria. The CBCT and kV image acquisitions were well functionally and suitable for the image-guided therapy procedure. For proton beam characterization, the results were in good agreement with the published work and theoretical calculation. Proton integral depth dose, in-air spot profile (figure 1),and the absolute dose calibration, together with the calibration curve of CT-HU and relative stopping power (figure 2) were successfully obtained and modeled into the Eclipse proton treatment planning system. According to the dosimetric validations, dose distributions with and without range shifter were comparable between dose calculations and measurements within the acceptable clinical criteria (within 3%). 

The first proton therapy center in Thailand was successfully commissioned. The acceptable verification results and the dosimetric validations ensured that the proton therapy system is ready for clinical use.