The origin of photons emitted in optical fibres under proton irradiation has been attributed to either entirely Čerenkov radiation or light consisting of fluorescence with a substantial amount of ...Čerenkov radiation. The source of the light emission is assessed in order to understand why the signal from optical fibres irradiated with protons is reportedly quenching-free. The present study uses the directional emittance of Čerenkov photons in 12 MeV and 20 MeV electron beams to validate a Monte Carlo model for simulating the emittance and transmission of Čerenkov radiation in optical fibres. We show that fewer than 0.01 Čerenkov photons are emitted and guided per 225 MeV proton penetrating the optical fibre, and that the Čerenkov signal in the optical fibre is completely negligible at the Bragg peak. Furthermore, on taking the emittance and guidance of both fluorescence and Čerenkov photons into account, it becomes evident that the reported quenching-free signal in PMMA-based optical fibres during proton irradiation is due to fluorescence.
Background and purpose: An increasing number of radiotherapy centres is now aiming for clinical implementation of intensity modulated radiotherapy (IMRT), but – in contrast to conventional treatment ...– no national or international guidelines for commissioning of the treatment planning system (TPS) and acceptance tests of treatment equipment have yet been developed. This paper bundles the experience of five radiotherapy departments that have introduced IMRT into their clinical routine.
Methods and materials: The five radiotherapy departments are using similar configurations since they adopted the commercially available Varian solution for IMRT, regarding treatment planning as well as treatment delivery. All are using the sliding window technique. Different approaches towards the derivation of the multileaf collimator (MLC) parameters required for the configuration of the TPS are described. A description of the quality control procedures for the dynamic MLC, including their respective frequencies, is given. For the acceptance of the TPS for IMRT multiple quality control plans were developed on a variety of phantoms, testing the flexibility of the inverse planning modules to produce the desired dose pattern as well as assessing the accuracy of the dose calculation. Regarding patient treatment verification, all five centres perform dosimetric pre-treatment verification of the treatment fields, be it on a single field or on a total plan procedure. During the actual treatment, the primary focus is on patient positioning rather than dosimetry. Intracavitary in vivo measurements were performed in special cases.
Result and conclusion: The configurational MLC parameters obtained through different methods are not identical for all centres, but the observed variations have shown to be of no significant clinical relevance. The quality control (QC) procedures for the dMLC have not detected any discrepancies since their initiation, demonstrating the reliability of the MLC controller. The development of geometrically simple QC plans to test the inverse planning, the dynamic MLC modules and the final dose calculation has proven to be useful in pointing out the need to remodel the single pencil beam scatter kernels in some centres. The final correspondence between calculated and measured dose was found to be satisfactory by all centres, for QC test plans as well as for pre-treatment verification of clinical IMRT fields. An intercomparison of the man hours needed per patient plan verification reveals a substantial variation depending on the type of measurements performed.
A new type of polymer gel dosimeter, which responds well to absorbed dose even when manufactured in the presence of normal levels of oxygen, was recently described by Fong et al. Phys. Med. Biol. 46, ...3105–3113 (2001) and referred to by the acronym MAGIC. The aim of this study was to investigate the feasibility of using this new type of gel for intensity-modulated radiation therapy (IMRT) verification. Gel manufacturing was carried out in room atmosphere under normal levels of oxygen. IMRT inverse treatment planning was performed using the Helios software. The gel was irradiated using a linear accelerator equipped with a dynamic multileaf collimator, and intensity modulation was achieved using sliding window technique. The response to absorbed dose was evaluated using magnetic resonance imaging. Measured and calculated dose distributions were compared with regard to in-plane isodoses and dose volume histograms. In addition, the spatial and dosimetric accuracy was evaluated using the gamma formalism. Good agreement between calculated and measured data was obtained. In the isocenter plane, the 70% and 90% isodoses acquired using the different methods are mostly within 2 mm, with up to 3 mm disagreement at isolated points. For the planning target volume (PTV), the calculated mean relative dose was
96.8±2.5%
(1 SD) and the measured relative mean dose was
98.6±2.2%.
Corresponding data for an organ at risk was
34.4±0.9%
and
32.7±0.7%,
respectively. The gamma criterion (3 mm spatial/3% dose deviation) was fulfilled for 94% of the pixels in the target region. Discrepancies were found in hot spots the upper and lower parts of the PTV, where the measured dose was up to 11% higher than calculated. This was attributed to sub optimal scatter kernels used in the treatment planning system dose calculations. Our results indicate great potential for IMRT verification using MAGIC-type polymer gel.
IMRT in a pregnant patient: how to reduce the fetal dose? Josipović, Mirjana; Nyström, Håkan; Kjaer-Kristoffersen, Flemming
Medical dosimetry : official journal of the American Association of Medical Dosimetrists,
2009-Winter, Letnik:
34, Številka:
4
Journal Article
Recenzirano
The purpose of our study was to find a solution for fetal dose reduction during head-and-neck intensity modulated radiation therapy (IMRT) of a pregnant patient. The first step was optimization of ...the IMRT treatment plan with as few monitor units (MUs) as possible, while maintaining an acceptable dose distribution. The peripheral dose originating from the final IMRT plan was measured at distances reaching from the most proximal to the most distal fetal position, along the accelerator's longitudinal axis, using an anthropomorphic phantom extended with water-equivalent plastic. The measured peripheral dose was divided into leakage, and internal and collimator scatter, to find the degree to which each component influences the peripheral dose to build an appropriate shield. Collimator scatter was the greatest contributor to the peripheral dose throughout the range of the growing fetus. A shield was built and placed beneath the accelerator head, extending caudally from the field edge, to function as an extra collimator jaw. This shield reduced the fetal dose by a factor of 3.5. The peripheral dose components were also measured for simple rectangular fields and also here the collimator scatter was the greatest contributor to the peripheral dose. Therefore, the shielding used for the IMRT treatment of our patient could also be used when shielding in conventional radiotherapy. It is important for a radiation therapy department to be prepared for treatment of a pregnant patient to shield the fetus efficiently.
The origin of photons emitted in optical fibres under proton irradiation has been attributed to either entirely erenkov radiation or light consisting of fluorescence with a substantial amount of ...erenkov radiation. The source of the light emission is assessed in order to understand why the signal from optical fibres irradiated with protons is reportedly quenching-free. The present study uses the directional emittance of erenkov photons in 12 MeV and 20 MeV electron beams to validate a Monte Carlo model for simulating the emittance and transmission of erenkov radiation in optical fibres. We show that fewer than 0.01 erenkov photons are emitted and guided per 225 MeV proton penetrating the optical fibre, and that the erenkov signal in the optical fibre is completely negligible at the Bragg peak. Furthermore, on taking the emittance and guidance of both fluorescence and erenkov photons into account, it becomes evident that the reported quenching-free signal in PMMA-based optical fibres during proton irradiation is due to fluorescence.
Particle therapy is becoming increasingly available world-wide for precise tumor targeting, its favorable depth dose deposition, and increased biological damage to tumor tissue compared to ...conventional photon therapy. As demand increases for improved robustness and conformality, next-generation secondary dose calculation engines are needed to verify treatment plans independently and provide estimates for clinical decision-making factors, such as dose-averaged linear energy transfer (LET
) and relative biological effectiveness (RBE).
FRoG (Fast dose Recalculation on GPU) has been installed and commissioned at the Danish Centre for Particle Therapy (DCPT). FRoG was developed for synchrotron-based facilities and has previously demonstrated good agreement with gold-standard Monte Carlo simulations and measurements. In this work, additions and modifications to FRoG's pencil beam algorithm to support the ion beam delivery with cyclotron-based technology as used at the DCPT, range shifter (RS) implementation, and robustness analysis methods are presented. FRoG dose predictions are compared to measurements and predictions of the clinical treatment planning system (TPS) Eclipse (Varian Medical Systems, Palo Alto, United States of America, CA, v.13.7.16) in both homogenous and heterogeneous scenarios using a solid-water/water and a half-head anthropomorphic phantom, respectively. Additional capabilities of FRoG are explored by performing a plan robustness analysis, analyzing dose and LET
for ten patients.
Mid-target measurements in spread-out Bragg Peaks (SOBP) were on average within -0.19% ± 0.30% and ≤0.5% of FRoG predictions for irradiations without and with RS, respectively. Average 3%/2mm 3D γ-analysis passing rates were 99.1% for ~200 patient plan QA comparisons. Measurement with an anthropomorphic head-phantom yielded a γ-passing rate >98%. Overall, maximum target differences in D
of <2% between the TPS and FRoG were observed for patient plans. The robustness analysis study accounting for range, delivery, and positioning uncertainties revealed small differences in target dose and a maximum LET
VH
(LET
received by 2% of the volume having dose larger than 1% of maximum dose) values below 10.1 keV/µm to the brain stem.
We demonstrate that auxiliary dose calculation systems like FRoG can yield excellent agreement to measurements comparable to clinical beam models. Through this work, application of FRoG as a secondary engine at third party cyclotron-based particle treatment facilities is now established for dose verification as well as providing further insight on LET
and variable RBE distributions for protons, currently absent from the standard clinical TPS.
A study of the performance of five commercial radiotherapy treatment planning systems (TPSs) for common treatment sites regarding their ability to model heterogeneities and scattered photons has been ...performed. The comparison was based on CT information for prostate, head and neck, breast and lung cancer cases. The TPSs were installed locally at different institutions and commissioned for clinical use based on local procedures. For the evaluation, beam qualities as identical as possible were used: low energy (6 MV) and high energy (15 or 18 MV) x-rays. All relevant anatomical structures were outlined and simple treatment plans were set up. Images, structures and plans were exported, anonymized and distributed to the participating institutions using the DICOM protocol. The plans were then re-calculated locally and exported back for evaluation. The TPSs cover dose calculation techniques from correction-based equivalent path length algorithms to model-based algorithms. These were divided into two groups based on how changes in electron transport are accounted for ((a) not considered and (b) considered). Increasing the complexity from the relatively homogeneous pelvic region to the very inhomogeneous lung region resulted in less accurate dose distributions. Improvements in the calculated dose have been shown when models consider volume scatter and changes in electron transport, especially when the extension of the irradiated volume was limited and when low densities were present in or adjacent to the fields. A Monte Carlo calculated algorithm input data set and a benchmark set for a virtual linear accelerator have been produced which have facilitated the analysis and interpretation of the results. The more sophisticated models in the type b group exhibit changes in both absorbed dose and its distribution which are congruent with the simulations performed by Monte Carlo-based virtual accelerator.
Purpose
Particle therapy is becoming increasingly available world‐wide for precise tumor targeting, its favorable depth dose deposition, and increased biological damage to tumor tissue compared to ...conventional photon therapy. As demand increases for improved robustness and conformality, next‐generation secondary dose calculation engines are needed to verify treatment plans independently and provide estimates for clinical decision‐making factors, such as dose‐averaged linear energy transfer (LETd) and relative biological effectiveness (RBE).
Method
FRoG (Fast dose Recalculation on GPU) has been installed and commissioned at the Danish Centre for Particle Therapy (DCPT). FRoG was developed for synchrotron‐based facilities and has previously demonstrated good agreement with gold‐standard Monte Carlo simulations and measurements. In this work, additions and modifications to FRoG’s pencil beam algorithm to support the ion beam delivery with cyclotron‐based technology as used at the DCPT, range shifter (RS) implementation, and robustness analysis methods are presented. FRoG dose predictions are compared to measurements and predictions of the clinical treatment planning system (TPS) Eclipse (Varian Medical Systems, Palo Alto, United States of America, CA, v.13.7.16) in both homogenous and heterogeneous scenarios using a solid‐water/water and a half‐head anthropomorphic phantom, respectively. Additional capabilities of FRoG are explored by performing a plan robustness analysis, analyzing dose and LETd for ten patients.
Results
Mid‐target measurements in spread‐out Bragg Peaks (SOBP) were on average within −0.19% ± 0.30% and ≤0.5% of FRoG predictions for irradiations without and with RS, respectively. Average 3%/2mm 3D γ‐analysis passing rates were 99.1% for ~200 patient plan QA comparisons. Measurement with an anthropomorphic head‐phantom yielded a γ‐passing rate >98%. Overall, maximum target differences in D02% of <2% between the TPS and FRoG were observed for patient plans. The robustness analysis study accounting for range, delivery, and positioning uncertainties revealed small differences in target dose and a maximum LETdVH02% (LETd received by 2% of the volume having dose larger than 1% of maximum dose) values below 10.1 keV/µm to the brain stem.
Conclusion
We demonstrate that auxiliary dose calculation systems like FRoG can yield excellent agreement to measurements comparable to clinical beam models. Through this work, application of FRoG as a secondary engine at third party cyclotron‐based particle treatment facilities is now established for dose verification as well as providing further insight on LETd and variable RBE distributions for protons, currently absent from the standard clinical TPS.
Abstract Purpose The aim of this study was the clinical evaluation of an independent dose and monitor unit verification (MUV) software which is based on sophisticated semi-analytical modelling. The ...software was developed within the framework of an ESTRO project. Finally, consistent handling of dose calculation deviations applying individual action levels is discussed. Materials and methods A Matlab-based software (“MUV”) was distributed to five well-established treatment centres in Europe (Vienna, Graz, Basel, Copenhagen, and Umeå) and evaluated as a quality assurance (QA) tool in clinical routine. Results were acquired for 226 individual treatment plans including a total of 815 radiation fields. About 150 beam verification measurements were performed for a portion of the individual treatment plans, mainly with time variable fluence patterns. The deviations between dose calculations performed with a treatment planning system (TPS) and the MUV software were scored with respect to treatment area, treatment technique, geometrical depth, radiological depth, etc. Results In general good agreement was found between calculations performed with the different TPSs and MUV, with a mean deviation per field of 0.2 ± 3.5% (1 SD) and mean deviations of 0.2 ± 2.2% for composite treatment plans. For pelvic treatments less than 10% of all fields showed deviations larger than 3%. In general, when using the radiological depth for verification calculations the results and the spread in the results improved significantly, especially for head-and-neck and for thorax treatments. For IMRT head-and-neck beams, mean deviations between MUV and the local TPS were −1.0 ± 7.3% for dynamic, and −1.3 ± 3.2% for step-and-shoot IMRT delivery. For dynamic IMRT beams in the pelvis good agreement was obtained between MUV and the local TPS (mean: −1.6 ± 1.5%). Treatment site and treatment technique dependent action levels between ±3% and ±5% seem to be clinically realistic if a radiological depth correction is performed, even for dynamic wedges and IMRT. Conclusion The software MUV is well suited for patient specific treatment plan QA applications and can handle all currently available treatment techniques that can be applied with standard linear accelerators. The highly sophisticated dose calculation model implemented in MUV allows investigation of systematic TPS deviations by performing calculations in homogeneous conditions.
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