A new water-equivalent 2D plastic scintillation detectors array for the dosimetry of megavoltage energy photon beams in radiation therapy

• Published in: Medical physics (Lancaster) 2011-12, Vol.38 (12), p.6763-6774
• Main Authors: Guillot, Mathieu, Beaulieu, Luc, Archambault, Louis, Beddar, Sam, Gingras, Luc
• Format: Article
• Language: English
• Subjects: ACCURACY; angular dependence; biomedical equipment; CAPACITY; Charge coupled devices; COLLIMATORS; detector array; DISTURBANCES; Dose‐volume analysis; DOSIMETRY; Dosimetry/exposure assessment; Equipment Design; Equipment Failure Analysis; IMRT; INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND TECHNOLOGY; Intensity modulated radiation therapy; IONIZATION CHAMBERS; Medical imaging; Multileaf collimators; Optical devices; OPTICAL FIBERS; OPTICAL SYSTEMS; PERTURBATION THEORY; PHANTOMS; PHOTON BEAMS; Photons; PLASTIC SCINTILLATION DETECTORS; Plastics - chemistry; POLYSTYRENE; Position sensitive detectors; Protons - therapeutic use; QUALITY ASSURANCE; Quality assurance equipment; RADIATION DOSE DISTRIBUTIONS; RADIATION DOSES; radiation therapy; RADIOLOGY AND NUCLEAR MEDICINE; RADIOTHERAPY; Radiotherapy, Conformal - instrumentation; Reproducibility of Results; Scintillation Counting - instrumentation; Scintillation detectors; Sensitivity and Specificity; solid scintillation detectors; TWO-DIMENSIONAL CALCULATIONS; VERIFICATION; Water - chemistry; water-equivalence
• ISSN: 0094-2405; 2473-4209
• DOI: 10.1118/1.3664007

Purpose: The objective of this work is to present a new 2D plastic scintillation detectors array (2D-PSDA) designed for the dosimetry of megavoltage (MV) energy photon beams in radiation therapy and to characterize its basic performance. Methods: We developed a 2D detector array consisting of 781 plastic scintillation detectors (PSDs) inserted into a plane of a water-equivalent phantom. The PSDs were distributed on a 26 × 26 cm2 grid, with an interdetector spacing of 10 mm, except for two perpendicular lines centered on the detection plane, where the spacing was 5 mm. Each PSD was made of a 1 mm diameter by 3 mm long cylindrical polystyrene scintillating fiber coupled to a clear nonscintillating plastic optical fiber. All of the light signals emitted by the PSDs were read simultaneously with an optical system at a rate of one measurement per second. We characterized the performance of the optical system, the angular dependency of the device, and the perturbation of dose distributions caused by the hundreds of PSDs inserted into the phantom. We also evaluated the capacity of the system to monitor complex multileaf collimator (MLC) sequences such as those encountered in step-and-shoot intensity modulated radiation therapy (IMRT) plans. We compared our results with calculations performed by a treatment planning system and with measurements taken with a 2D ionization chamber array and with a radiochromic film. Results: The detector array that we developed allowed us to measure doses with an average precision of better than 1% for cumulated doses equal to or greater than 6.3 cGy. Our results showed that the dose distributions produced by the 6-MV photon beam are not perturbed (within ±1.1%) by the presence of the hundreds of PSDs located into the phantom. The results also showed that the variations in the beam incidences have little effect on the dose response of the device. For all incidences tested, the passing rates of the gamma tests between the 2D-PSDA and the treatment planning system were higher than 97.5% when the standard clinical tolerances of 3% or 3 mm were used. Excellent agreement was obtained between the doses measured and calculated when we used the 2D-PSDA for monitoring a MLC sequence from a step-and-shoot IMRT plan. Conclusions: We demonstrated the feasibility of using a large number of PSDs in a new 2D-PSDA for the dosimetry of MV energy photon beams in radiation therapy. The excellent precision, accuracy, and low angular dependence of the d