1
|
Decabooter E, Roijen E, Martens J, Unipan M, Bosmans G, Vilches-Freixas G. Quality assurance of scanned proton beams at different gantry angles using an ionization chamber array in a rotational phantom. Phys Med 2022; 104:67-74. [PMID: 36370605 DOI: 10.1016/j.ejmp.2022.10.014] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/29/2022] [Revised: 09/23/2022] [Accepted: 10/22/2022] [Indexed: 11/11/2022] Open
Abstract
PURPOSE To implement a single set-up monthly QA procedure for 9 different beam parameters at different gantry angles and evaluate its clinical implementation over a 12 month period. METHODS We developed a QA procedure using an array detector (PTW Octavius 1500XDR) embedded in a rotational unit (PTW Octavius 4D) at our proton facility. With a single set-up we can monitor field central axis position, field symmetry, field size, flatness, penumbrae, output, spot size, spot position and range at different gantry angles (AAPM TG 224). The set-up is irradiated with homogenous 2D fields with dynamic aperture and spot patterns at five gantry angles. A modular top is used to check the range consistency. Absolute γ analysis were performed to compare measured dose distributions to calculated dose. All other parameters are directly extracted from the measurements. Additionally, the sensitivity of the set-up to small changes in beam parameters were compared to the Lynx detector (IBA). RESULTS Over a 12 month period, output, symmetry, and flatness were within ± 2 %; FWHM, spot positions, penumbra widths, and central axis fields were within ± 1 mm. Range differences were all within 1/2 of the energy spacing (±0.6 MeV) relative to baseline. Most (2 %, 2 mm) γ-analysis showed agreement scores higher than 90 %. The sensitivity is comparable to the Lynx detector and measurement time is reduced by 40 %. CONCLUSION The time-efficient monthly QA procedure that we developed can accurately be used to measure a large range of beam parameters at different gantry angles, within the TG 224 AAPM recommendations.
Collapse
Affiliation(s)
- Esther Decabooter
- Department of Radiation Oncology (Maastro Clinic), GROW School for Oncology, Maastricht University Medical Centre+, Maastricht, the Netherlands.
| | - Erik Roijen
- Department of Radiation Oncology (Maastro Clinic), GROW School for Oncology, Maastricht University Medical Centre+, Maastricht, the Netherlands
| | - Jonathan Martens
- Department of Radiation Oncology (Maastro Clinic), GROW School for Oncology, Maastricht University Medical Centre+, Maastricht, the Netherlands
| | - Mirko Unipan
- Department of Radiation Oncology (Maastro Clinic), GROW School for Oncology, Maastricht University Medical Centre+, Maastricht, the Netherlands
| | - Geert Bosmans
- Department of Radiation Oncology (Maastro Clinic), GROW School for Oncology, Maastricht University Medical Centre+, Maastricht, the Netherlands
| | - Gloria Vilches-Freixas
- Department of Radiation Oncology (Maastro Clinic), GROW School for Oncology, Maastricht University Medical Centre+, Maastricht, the Netherlands
| |
Collapse
|
2
|
Kretschmer J, Brodbek L, Looe HK, van der Graaf E, Jan van Goethem M, Kiewiet H, Olivari F, Meyer C, Poppe B, Brandenburg S. Investigating the lateral dose response functions of point detectors in proton beams. Phys Med Biol 2022; 67. [DOI: 10.1088/1361-6560/ac783c] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/20/2022] [Accepted: 06/13/2022] [Indexed: 11/11/2022]
Abstract
Abstract
Objective. Point detector measurements in proton fields are perturbed by the volume effect originating from geometrical volume-averaging within the extended detector’s sensitive volume and density perturbations by non-water equivalent detector components. Detector specific lateral dose response functions K(x) can be used to characterize the volume effect within the framework of a mathematical convolution model, where K(x) is the convolution kernel transforming the true dose profile D(x) into the measured signal profile of a detector M(x). The aim of this work is to investigate K(x) for detectors in proton beams. Approach. The K(x) for five detectors were determined by iterative deconvolution of measurements of D(x) and M(x) profiles at 2 cm water equivalent depth of a narrow 150 MeV proton beam. Monte Carlo simulations were carried out for two selected detectors to investigate a potential energy dependence, and to study the contribution of volume-averaging and density perturbation to the volume effect. Main results. The Monte Carlo simulated and experimentally determined K(x) agree within 2.1% of the maximum value. Further simulations demonstrate that the main contribution to the volume effect is volume-averaging. The results indicate that an energy or depth dependence of K(x) is almost negligible in proton beams. While the signal reduction from a Semiflex 3D ionization chamber in the center of a gaussian shaped field with 2 mm sigma is 32% for photons, it is 15% for protons. When measuring the field with a microDiamond the trend is less pronounced and reversed with a signal reduction for protons of 3.9% and photons of 1.9%. Significance. The determined K(x) can be applied to characterize the influence of the volume effect on detectors measured signal profiles at all clinical proton energies and measurement depths. The functions can be used to derive the actual dose distribution from point detector measurements.
Collapse
|
3
|
Ricci JC, Hsi WC, Su Z, Mund K, Dawson R, Indelicato DJ. The root cause analysis on failed patient-specific measurements of pencil beam scanning protons using a 2D detection array with finite size ionization chambers. J Appl Clin Med Phys 2021; 22:175-190. [PMID: 34312997 PMCID: PMC8364270 DOI: 10.1002/acm2.13343] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/17/2020] [Revised: 04/21/2021] [Accepted: 06/03/2021] [Indexed: 02/01/2023] Open
Abstract
The aim of this report is to present the root cause analysis on failed patient‐specific quality assurance (QA) measurements of pencil beam scanning (PBS) protons; referred to as PBS‐QA measurement. A criterion to fail a PBS‐QA measurement is having a <95% passing rate in a 3.0%‐3.0 mm gamma index analysis. Clinically, we use a two‐dimensional (2D) gamma index analysis to obtain the passing rate. The IBA MatriXX PT 2D detection array with finite size ionization chamber was utilized. A total of 2488 measurements performed in our PBS beamline were cataloged. The percentage of measurements for the sites of head/neck, breast, prostate, and other are 53.3%, 22.7%, 10.5%, and 13.5%, respectively. The measurements with a passing rate of 100 to >94%, 94 to >88%, and <88% were 93.6%, 5.6%, and 0.8%, respectively. The percentage of failed measurements with a <95% passing rate was 10.9%. After removed the user errors of either re‐measurement or re‐analysis, 8.1% became acceptable. We observed a feature of >3% per mm dose gradient with respect to depth on the failed measurements. We utilized a 2D/three‐dimensional (3D) gamma index analysis toolkit to investigate the effect of depth dose gradient. By utilizing this 3D toolkit, 43.1% of the failed measurements were improved. A feature among measurements that remained sub‐optimal after re‐analysis was a sharp >3% per mm lateral dose gradient that may not be well handled using the detector size of 5.0 mm in‐diameter. An analysis of the sampling of finite size detectors using one‐dimensional (1D) error function showed a large dose deviation at locations of low‐dose areas between two high‐dose plateaus. User error, large depth dose gradient, and the effect of detector size are identified as root causes. With the mitigation of the root causes, the goals of patient‐specific QA, specifically detecting actual deviation of beam delivery or identifying limitations of the dose calculation algorithm of the treatment planning system, can be directly related to failure of the PBS‐QA measurements.
Collapse
Affiliation(s)
- Jacob C Ricci
- Department of Radiation Oncology, University of Florida College of Medicine, Gainesville, FL, USA.,Department of Radiation Oncology, University of Florida Health Proton Therapy Institute, Jacksonville, FL, USA
| | - Wen C Hsi
- Department of Radiation Oncology, University of Florida College of Medicine, Gainesville, FL, USA.,Department of Radiation Oncology, University of Florida Health Proton Therapy Institute, Jacksonville, FL, USA
| | - Zhong Su
- Department of Radiation Oncology, University of Florida College of Medicine, Gainesville, FL, USA.,Department of Radiation Oncology, University of Florida Health Proton Therapy Institute, Jacksonville, FL, USA
| | - Karl Mund
- Department of Radiation Oncology, University of Florida College of Medicine, Gainesville, FL, USA
| | - Robert Dawson
- Department of Medical Physics, University of Florida College of Medicine, Gainesville, FL, USA.,Department of Radiation Oncology, Ackerman Cancer Center, Jacksonville, FL, USA
| | - Daniel J Indelicato
- Department of Radiation Oncology, University of Florida College of Medicine, Gainesville, FL, USA.,Department of Radiation Oncology, University of Florida Health Proton Therapy Institute, Jacksonville, FL, USA
| |
Collapse
|