Reduction of clinical safety margins in proton therapy enabled by the clinical implementation of dual-energy CT for direct stopping-power prediction

Abstract

To quantifiy the range uncertainty in proton treatment planning using dual-energy computed tomography (DECT) for a direct stopping-power prediction (DirectSPR) algorithm and its clinical implementation. Methods and materials: To assess the overall uncertainty in stopping-power ratio (SPR) prediction of a DirectSPR implementation calibrated for different patient geometries, the influencing factors were categorized in imaging, modeling as well as others. The respective SPR uncertainty was quantified for lung, soft tissue and bone and translated into range uncertainty for several tumor types. The amount of healthy tissue spared was quantified for 250 patients treated with DirectSPR and the dosimetric impact was evaluated exemplarily for a representative brain-tumor patient. Results: For bone, soft tissue and lung, an SPR uncertainty (1rÞ of 1.6%, 1.3% and 1.3% was determined for DirectSPR, respectively. This allowed for a reduction of the clinically applied range uncertainty from currently (3.5% + 2 mm) to (1.7% + 2 mm) for brain-tumor and (2.0% + 2 mm) for prostate-cancer patients. The 150 brain-tumor and 100 prostate-cancer patients treated using DirectSPR benefitted from sparing on average 2.6 mm and 4.4 mm of healthy tissue in beam direction, respectively. In the representative patient case, dose reduction in organs at risk close to the target volume was achieved, with a mean dose reduction of up to 16% in the brainstem. Patient-specific DECT-based treatment planning with reduced safety margins was successfully introduced into clinical routine. Conclusions: A substantial increase in range prediction accuracy in clinical proton treatment planning was achieved by patient-specific DECT-based SPR prediction. For the first time, a relevant imagingbased reduction of range prediction uncertainty on a 2% level has been achieved.

Clinical use and future requirements of relative biological effectiveness: Survey among all European proton therapy centres

“…Hence, for these anatomical regions, most evidence for clinically relevant variable RBE effects is available [14][15][16][17] and more may be expected in the future. Additionally, pronounced local RBE effects may result from increasing precision in proton therapy through the reduction of range and setup uncertainty [36], as a smaller smear-out effect of the RBE is expected [6].…”

Detecting and Locating the Site of Local Relapse Using 18F-PSMA-1007 Imaging After Primary Treatment of 135 Prostate Cancer Patients—Potential Impact on PSMA-Guided Radiation Therapy

“…For adjuvant or salvage radiation therapy, these results are of great interest with regard to target volume delineation. To date, there is an increasing trend towards minimizing safety margins leading to an optimized organ at risk (OAR) sparing [23,24]. Especially when using modern radiotherapy techniques such as protons or carbon ions with a characteristically sharp dose application while sparing the surrounding healthy tissue [25], the reduction of safety margins should be exercised with a call for caution considering the close proximity of the detected relapses to neighboring organs such as the bladder or rectum.…”

Proton Therapy in the Management of Pancreatic Cancer

“…Efforts have been put into reducing the planning margins and range uncertainties and further optimizing the dose to organs at the distal end of the target [ 40 ]. Studies have shown the application of dual-energy CT (DECT) to achieve a range uncertainty of 2% (versus 3.5%) for brain and prostate cancer patients [ 41 ]. However, most DECT studies are based on static imaging or phantom.…”