Details

Autor(en) / Beteiligte

• Carabe, Alejandro
• Moteabbed, Maryam
• Depauw, Nicolas
• Schuemann, Jan
• Paganetti, Harald

Titel

Range uncertainty in proton therapy due to variable biological effectiveness

Ist Teil von

• Physics in medicine & biology, 2012-03, Vol.57 (5), p.1159-1172

Ort / Verlag

England: IOP Publishing

Erscheinungsjahr

2012

Quelle

MEDLINE

Beschreibungen/Notizen

• Traditionally, dose in proton radiotherapy is prescribed as Gy(RBE) by scaling up the physical dose by 10%. The relative biological effectiveness (RBE) of protons is considered to vary with dose-averaged linear energy transfer (LETd), dose (d) and (α β)x. The increase of RBE with depth causes a shift of the falloff of the beam, i.e. a change of the beam range. The magnitude of this shift will depend on dose and (α β)x. The aim of this project was to quantify the dependence of the range shift on these parameters. Three double-scattered beams of different ranges incident on a computational phantom consisting of different regions of interest (ROIs) were used. Each ROI was assigned with (α β)x values between 0.5 and 20 Gy. The distribution of LETd within each ROI was obtained from a Monte Carlo simulation. The LETd distribution depends on the beam energy and thus its nominal range. The RBE values within the ROIs were calculated for doses between 1 and 15 Gy using an in-house developed biophysical model. Dose-volume histograms of the RBE-weighted doses were extracted for each ROI for a 'fixed RBE' (RBE = 1.1) and a 'variable RBE' (RBE = f (d, α β, LETd)), and the percentage difference in range was obtained from the difference of the percentage volumes at the distal 80% of the dose. Range differences in normal tissue ((α β)x = 3 Gy) of the order of 3-2 mm were obtained, respectively, for a shallow (physical range 4.8 cm) and a deep (physical range 12.8 cm) beam, when a dose of 1 Gy normalized to the mid-SOBP was delivered. As the dose increased to 15 Gy, the variable RBE decreases below 1.1 which induces ranges of about 1 mm shorter than those obtained with an RBE of 1.1. The shift in the range of an SOBP when comparing biological dose distributions obtained with a fixed or a variable RBE was quantified as a function of dose, (α β)x and physical range (as a surrogate of the initial beam energy). The shift increases with the physical range but decreases with increasing dose or (α β)x. The results of our study allow a quantitative consideration of RBE-caused range uncertainties as a function of treatment site and dose in treatment planning.