Purpose: Primarily, to compare proton therapy (PT) treatment quality between upright and supine positions for three pelvic PT indications; secondarily, to develop the digital phantoms needed for these comparisons.
Methods: A digital anthropomorphic XCAT2 phantom was used as a patient model for treatment planning studies. Four XCAT2 models were modified from supine into the upright position, with a backrest angle of 20˚. In addition, extensive investigations, using Finite Element Method (FEM) simulations, determined the impact of gravitational force on translation and deformation of internal abdominal and pelvic organs. Treatment planning studies evaluated two male and two female phantoms (varying weight, height, and age) in supine and upright positions. In total: two prostate, four bladder, and four osteosarcoma cases of the pelvis area were studied. Afterward, upright and supine position plans were compared by assessing the respective Dose Volume Histogram metrics.
Results: FEM results showed minimal deformation of pelvic organs in the upright compared to supine position. Upright position plan quality was preserved in all cases compared to the supine position. Quantitatively, for Planning Target Volumes, D_95% the difference between upright a supine positions was a maximum of 30 cGy. For prostate treatment, femoral head sparing was noted to be significantly improved for prostate treatment in the upright position - i.e. an average dose delivered to the right femoral head decreased from 1541 cGy to 20 cGy. Bladder and osteosarcoma cases results were varying in this regard.
Conclusion: This work indicates the potential of pelvic PT delivered in the upright position. Observed performance of the treatment plans for bladder, prostate, and pelvic osteosarcoma cases, showed no decrease in the plan quality for the presented cases. Follow-up treatment planning studies will be performed with volunteers using CT scans. The phantoms will also be further validated using ultrasonography scans of volunteers.
Funding Support, Disclosures, and Conflict of Interest: Wioletta Kozlowska and Ondrej Sevela are employees of ADAM SA and participate in the employee share option program of Advanced Oncotherapy (AVO). Jonathan Farr holds a senior management position at ADAM SA and is a shareholder in AVO. Alena Zemanova and William Larsen are employees of ADAM SA.
TH- External Beam- Particle/high LET therapy: Proton therapy – treatment planning/virtual clinical studies