Medical Physics Seminar - Seminario de Física Médica
Title: Benefits of range uncertainty reductions in proton therapy and interplay with proton arc therapy implementation
Author: Sebastian Tattenberg, PhD
Affiliation: TRIUMF, Vancouver, BC, Canada and Northern Ontario School of Medicine (NOSM) University, Sudbury, ON, Canada
Motivation: Conventional external beam radiotherapy for cancer is generally photon-based, but due to higher dose conformality to the tumor, proton therapy treatments have experienced rapidly-growing interest. However, uncertainties in the in vivo proton range remain a considerable hurdle.
Methods: Based on a total of 25 patients with tumors in the brain or the head & neck region, the benefits of a range uncertainty reduction from the current clinical level of approximately 3.5% to a potentially achievable level of 1% were quantified. In addition, proton arc therapy (PAT) treatment plans utilizing a much higher number of irradiation directions (72 rather than 4) were created for a sub-set of five patients. The benefit of PAT implementation was then determined and compared to range uncertainty reduction benefits prior or subsequently to PAT implementation.
Results: A 3.5% to 1% range uncertainty reduction reduced evaluated normal tissue complication probabilities (NTCPs) by up to 3.2 percentage points (pp). The benefits of novel proton beam arrangements which only become feasible as range uncertainties are reduced often exceeded the direct benefits of range uncertainty reductions. In the five patient sub-set, the mean NTCP reduction achieved via PAT implementation (2.5 pp) was four times higher than the mean benefit of a 3.5% to 1% range uncertainty reduction (0.6 pp). PAT implementation did not, however, reduce the benefits associated with reducing proton range uncertainties.
Conclusion: Proton range uncertainty reductions were associated with considerable dosimetric benefits, parts of which resulted from the feasibility of novel beam arrangements at lower range uncertainties. The benefits of PAT implementation exceeded the benefits of a 3.5% to 1% range uncertainty reduction significantly. However, PAT implementation did not reduce range uncertainty reduction benefits. Range uncertainty reductions are therefore expected to remain beneficial even if achieved subsequently to or in tandem with PAT implementation.
Online link: https://conectaha.csic.es/b/fer-gny-a0x-omp. The room access code will be sent per e-mail.
Ana Ros y Fernando Hueso