Technical Note: Reconstruction of physical and biological dose distributions of carbon‐ion beam through deconvolution of longitudinal dosimeter responses

Purpose This is a theoretical simulation study for proof of concept of radiochromic film dosimetry to measure physical and biological doses without plan‐based quenching correction for patient‐specific quality assurance of carbon‐ion radiotherapy. Methods We took a layer‐stacking carbon‐ion beam comprised of range‐shifted beamlets. The dosimeter response was simulated according to an experimental quenching model. The beam model followed a treatment planning system. The beam was decomposed into finely arranged beamlets with weights estimated by deconvolution of longitudinal dosimeter responses. The distributions of physical and biological doses were reconstructed from the estimated weights and were compared with the plan. We also evaluated the sensitivity to measurement errors and to erratic delivery with an undelivered beamlet. Results The reconstructed physical and biological doses accurately reproduced the simulated delivery with errors approximately corresponding to the measurement errors. The erratic beam delivery was easily detectable by comparison of biological dose distribution to the plan. Conclusions We have developed a method to measure physical and biological doses by longitudinal dosimetry of quenched response without using plan data. The method only involves a general optimization algorithm, a radiobiology model, and experimental beamlet data, and requires no extra corrections. Theoretically, this approach is applicable to various dosimeters and to proton and ion beams of any delivery method, regardless of quenching or biological effectiveness.