Abstract
Dose painting by numbers (DPBN) require a high degree of dose modulation to fulfill the image-based voxel wise dose prescription. The aim of this study was to assess the dosimetric accuracy of 18F-fluoro-2-deoxy-glucose positron emission tomography(18F-FDG-PET)-based DPBN in an anthropomorphic lung phantom using alanine dosimetry. A linear dose prescription based on 18F-FDG-PET image intensities within the gross tumor volume (GTV) of a lung cancer patient was employed. One DPBN scheme with low dose modulation (Scheme A; minimum/maximum fraction dose to the GTV 2.92/4.26Gy) and one with a high modulation (Scheme B; 2.81/4.52Gy) were generated. The plans were transferred to a computed tomograpy (CT) scan of a thorax phantom based on CT images of the patient. Using volumetric modulated arc therapy (VMAT), DPBN was delivered to the phantom with embedded alanine dosimeters. A plan was also delivered to an intentionally misaligned phantom. Absorbed doses at various points in the phantom were measured by alanine dosimetry. A pointwise comparison between GTV doses from prescription, treatment plan calculation and VMAT delivery showed high correspondence, with a mean and maximum dose difference of <0.1Gy and 0.3Gy, respectively. No difference was found in dosimetric accuracy between scheme A and B. The misalignment caused deviations up to 1Gy between prescription and delivery. DPBN can be delivered with high accuracy, showing that the treatment may be applied correctly from a dosimetric perspective. Still, misalignment may cause considerable dosimetric erros, indicating the need for patient immobilization and monitoring.
Highlights
The concept of biologic image guided radiotherapy (RT) dose de livery – dose painting – was introduced in the early 2000 s [1]
The strategy is to use biologic imaging such as magnetic resonance imaging (MRI) or positron emission tomography (PET) to prescribe a heteroge neous dose delivery to the target volume, based on the assumption that the images reflect the inherent radiosensitivity of the tumour
While dose painting by contours (DPBC) is relatively straightforward to implement in commercial treatment planning systems (TPS), dose painting by numbers (DPBN) relies on in-house add-ons or research versions of the TPS [2,3,4,5]
Summary
The concept of biologic image guided radiotherapy (RT) dose de livery – dose painting – was introduced in the early 2000 s [1]. Dose painting by numbers (DPBN) require a high degree of dose modulation to fulfill the image-based voxel wise dose prescription. The aim of this study was to assess the dosimetric accuracy of 18Ffluoro-2-deoxy-glucose positron emission tomography(18F-FDG-PET)-based DPBN in an anthropomorphic lung phantom using alanine dosimetry. Materials and methods: A linear dose prescription based on 18F-FDG-PET image intensities within the gross tumor volume (GTV) of a lung cancer patient was employed. Results: A pointwise comparison between GTV doses from prescription, treatment plan calculation and VMAT delivery showed high correspondence, with a mean and maximum dose difference of
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