Application of 3D printed compensators for pediatric patients in treatment planning of shallow situated H&N tumours
T. Kajdrowicz(1), A. Wochnik(1), J. Swakoń(1), D. Krzempek(1), K. Małecki(2), B. Michalec(1), G. Mierzwińska(1), P. Olko(1), K. Krzempek(1) and R. Kopeć(1)
(1) Institute of Nuclear Physics Polish Academy of Sciences PL-31342 Krakow, Poland
(2) University Children’s Hospital of Krakow, Poland
Cyclotron PT facilities deliver lowest energy of proton beam between 60 and 100 MeV. Treatment of superficial lesions requires range shifter (RS), increasing spot size, widening lateral penumbra and lowering plan conformity, resulting in decrease of target coverage if sparing organs at risk (OAR). We investigated 3D-printed compensators for pediatric patients to improve dose distribution in treatment planning of shallow situated H&N tumours.
Materials and methods
Cyclotron Centre Bronowice (CCB IFJ PAN, Kraków, Poland) is equipped with IBA Proteus-235 system with RS placed at nozzle exit. Treatment plans for five children with shallow situated H&N cancer were optimized with RS and with compensators printed using Fused-Fiber-Filament (FFF) technology with polylactide (PLA) material. Compensators were examined for homogeneity and range uncertainties. Treatment plans were compared for coverage, conformity and OAR sparing. Influence of intra-fractional patient positioning errors on plan robustness was estimated.
Analysis of 3D-printed compensators homogeneity allowed for plan range uncertainties estimations. Appropriate overwrite Hounsfield unit (HU) values were determined. Variations in compensator homogeneity altered its water equivalent ratio (WER) by not more than 3.5 % being within the limit for plan robustness evaluation. Usage of 3D-printed compensators showed higher conformity and resulted in better sparing of OARs. Appropriate placement of ball-bearing markers within compensator structure led to patient positioning errors similar to standardized procedures.
Application of 3D-printed compensators led to more conformal dose distribution as compared to RS placed at nozzle, which allowed to meet clinical objectives. Dedicated QA procedure permitted to keep the plan range uncertainty evaluation unaffected.