Room: Exhibit Hall
Purpose: The purpose of this study is to evaluate any effects of patient position setting variation, target motion, proton range uncertainty in resulting perturbed dose variation in treatment planning system (TPS) of pencil beam spot scanning proton therapy. IROC proton thorax/lung phantom was employed in this process.
Methods: A proton thorax/lung phantom was requested from IROC. The phantom was inserted with GAF Chromic films and couples of thermo luminescent dosimeter capsules within target and adjacent structures for imaging and dose monitoring. Various region of interest of embedded material such as PVC, PBT polystyrene as dosimeter inserts and acrylic were contoured. The relative stopping power of each material was provided. The breath hold technique was implemented to generate a single field uniform dose optimization to irradiate phantom without robustness optimization (RO). A second plan, RO was activated with 3mm setup margin and 3.5% range uncertainties for comparison. The passing rate of variant margin in setup and ranges in percentage of uncertainty rendering in target coverage were shown in final analysis table.
Results: The result of TLD measurements and 3D film profiles of thoracic lung phantom were within acceptable tolerance and met the criteria established by IROC. This result provides the base line of Plan1 (PTV +5mm margin) between lung treatment proton protocol compared to Plan2 (CTV+RO).
Conclusion: Thorax/ lung phantom provided by IROC is a useful tool to evaluate lung treatment using proton pencil beam. The further robustness optimization provides scenarios of prescribed tumor coverage from patient position setting uncertainty, range uncertainty of proton beam. Definitely the perturbed dose map provides better representation of dose statistics and clinical goal.
Not Applicable / None Entered.