Room: Exhibit Hall | Forum 1
Purpose: To present the results of case studies on strategies used to mitigate the effect of RBE uncertainties in the proton therapy treatment plans for targets in the brain.
Methods: Uncertainties in the value of relative biological effectiveness (RBE) of proton beam, especially in the distal dose fall off region, is an important consideration in designing safe treatment plans for proton therapy. Because of the close proximity of organs at risk (OARs) to targets in many brain cancer patients, it is especially challenging to mitigate the effect of RBE uncertainties on doses given to them. Some of the strategies to reduce the effect of RBE uncertainties are to use: (1) suitable beam angles to minimize the dose to OARs from the distal fall off region of the field dose, (2) beam specific PTVs (BSPTV) to force the beam stop further away from the OARs, (3) reduced biological effective doses (BEDs) to OARs by considering approximate higher RBE values in the longitudinal penumbral (LP) region of proton beam, and (4) multiple plans with different beam angles to spread the dose from LP region to different locations.
Results: It is found that use of the above strategies helped to reduce the BED of OARs so as to meet their required dose volume constraints. In many cases use of multiple plans with different beam angles led to reduced doses to the OARs compared to one plan with limited beam angles while keeping the treatment delivery time same. Results for clinical cases will be presented.
Conclusion: A combination of beam angle selection, use of BSPTV, use of multiple plans and use of reduced BED dose constraints on OARs located in the longitudinal penumbra region of the proton beam are found to mitigate the RBE uncertainties in proton therapy plans for targets in brain.