Range uncertainty reductions in proton therapy may lead to the feasibility of novel beam arrangements which improve organ‐at‐risk sparing

Abstract

In proton therapy, dose distributions are currently often conformed to organs at risk (OARs) using the less sharp dose fall-off at the lateral beam edge to reduce the effects of uncertainties in the in vivo proton range. However, range uncertainty reductions may make greater use of the sharper dose fall-off at the distal beam edge feasible, potentially improving OAR sparing. We quantified the benefits of such novel beam arrangements. Methods: For each of 10 brain or skull base cases, five treatment plans robust to 2 mm setup and 0%-4% range uncertainty were created for the traditional clinical beam arrangement and a novel beam arrangement making greater use of the distal beam edge to conform the dose distribution to the brainstem. Metrics including the brainstem normal tissue complication probability (NTCP) with the endpoint of necrosis were determined for all plans and all setup and range uncertainty scenarios. Results: For the traditional beam arrangement, reducing the range uncertainty from the current level of approximately 4% to a potentially achievable level of 1% reduced the brainstem NTCP by up to 0.9 percentage points in the nominal and up to 1.5 percentage points in the worst-case scenario. Switching to the novel beam arrangement at 1% range uncertainty improved these values by a factor of 2, that is, to 1.8 percentage points and 3.2 percentage points, respectively. The novel beam arrangement achieved a lower brainstem NTCP in all cases starting at a range uncertainty of 2%. Conclusion:The benefits of novel beam arrangements may be of the same magnitude or even exceed the direct benefits of range uncertainty reductions. Indirect effects may therefore contribute markedly to the benefits of reducing proton range uncertainties.

A hybrid multi-particle approach to range assessment-based treatment verification in particle therapy

“…This ensures that the prescribed dose is delivered to the tumour, but at the expense of an extra dose to the surrounding healthy tissue. In addition, selection of beam angles is limited to avoid the risk of overshoots to high-risk organs 4 , 5 . Thus, it is highly desirable to increase the accuracy and adaptation potential of PT, especially for moving tumors and patients with implants or target regions affected by anatomical changes.…”

Potential benefits of using radioactive ion beams for range margin reduction in carbon ion therapy

“…Reduction of target margins that are associated with range uncertainties, enabled by the use of 11 C beams, apart from reducing the doses to the adjacent structures by default, might further improve the flexibility and quality of treatment by enabling irradiation from different angles. A recent study 22 has shown further brainstem NTCP decrease from using novel proton beam arrangements, enabled by the reduced range margins. As the authors have shown, new beam arrangements might also enable the possibility of redistributing the LET distributions in the target and increasing its mean value.…”

Range margin reduction in carbon ion therapy: potential benefits of using radioactive ion beams

“…Reduced range uncertainties guaranteed with 11 C beams, apart from reducing the doses to the adjacent structures by default, might further improve the exibility and quality of treatment by enabling irradiation from different angles. A recent study 22 has shown further brainstem NTCP decrease from using novel proton beam arrangements, enabled by the reduced range margins. As the authors have shown, new beam arrangements might also enable the possibility of redistributing the LET distributions in the target and increasing its mean value.…”