Dosimetric verification of IMPT using a commercial heterogeneous phantom

Abstract

The purpose of this study was to propose a verification method and results of intensity‐modulated proton therapy (IMPT), using a commercially available heterogeneous phantom. We used a simple simulated head and neck and prostate phantom. An ionization chamber and radiochromic film were used for measurements of absolute dose and relative dose distribution. The measured doses were compared with calculated doses using a treatment planning system. We defined the uncertainty of the measurement point of the ionization chamber due to the effective point of the chamber and mechanical setup error as 2 mm and estimated the dose variation base on a 2 mm error. We prepared a HU‐relative stopping power conversion table and fluence correction factor that were specific to the heterogeneous phantom. The fluence correction factor was determined as a function of depth and was obtained from the ratio of the doses in water and in the phantom at the same effective depths. In the simulated prostate plan, composite doses of measurements and calculations agreed within ±1.3% and the maximum local dose differences of each field were 10.0%. Composite doses in the simulated head and neck plan agreed within 4.0% and the maximum local dose difference for each field was 12.0%. The dose difference for each field came within 2% when taking the measurement uncertainty into consideration. In the composite plan, the maximum dose uncertainty was estimated as 4.0% in the simulated prostate plan and 5.8% in the simulated head and neck plan. Film measurements showed good agreement, with more than 92.5% of points passing a gamma value (3%/3 mm). From these results, the heterogeneous phantom should be useful for verification of IMPT by using a phantom‐specific HU‐relative stopping power conversion, fluence correction factor, and dose error estimation due to the effective point of the chamber.

Dosimetric response of a glass dosimeter in proton beams: LET-dependence and correction factor

“…The uncertainties in this study are primarily the positional uncertainty in both the ionization chamber and RGD measurements. The effective measurement point of the ionization chamber is assumed to be approximately 1 mm toward the source [43]; however, the effective measurement point of an RGD has not been investigated and verified. The position of the effective center of an RGD may be different from that of the ionization chamber because an RGD contains high atomic number materials.…”

Evaluating the usefulness of the direct density reconstruction algorithm for intensity modulated and passively scattered proton therapy: Validation using an anthropomorphic phantom

“…3.0.1 Hitachi, Ltd., Ibaraki, Japan), a treatment planning system commercially available in Japan, which is the first system to use a triple Gaussian kernel model for dose calculation. [20,21]; the dose calculation grid was 2 mm. Fig.…”

Development of an Anthropomorphic Heterogeneous Female Pelvic Phantom and Its Comparison with a Homogeneous Phantom in Advance Radiation Therapy: Dosimetry Analysis

“…Phantoms, which have been in use since the inspection of radiotherapy, are substitutes that conform to the real-body scenario. Although the majority of the human body consists of water, physical phantoms that are made of water or solid water-equivalent materials have mostly been used for PSQA [ 15 , 16 ]. These phantoms were used because of their cost effectiveness, universal availability, uniform density of 1 g/cc, and simpler designs.…”