External Beam Radiotherapy Treatment Planning Research Articles

PRIMO Monte Carlo software as a tool for commissioning of an external beam radiotherapy treatment planning system.

The purpose was to validate the PRIMO Monte Carlo software to be used during the commissioning of a treatment planning system (TPS). The Acuros XB v. 16.1 algorithm of the Eclipse was configured for 6 MV and 6 MV flattening-filter-free (FFF) photon beams, from a TrueBeam linac equipped with a high-definition 120-leaf multileaf collimator (MLC). PRIMO v. 0.3.64.1814 software was used with the phase space files provided by Varian and benchmarked against the reference dosimetry dataset published by the Imaging and Radiation Oncology Core-Houston (IROC-H). Thirty Eclipse clinical intensity-modulated radiation therapy (IMRT)/volumetric modulated arc therapy (VMAT) plans were verified in three ways: 1) using the PTW Octavius 4D (O4D) system; 2) the Varian Portal Dosimetry system and 3) the PRIMO software. Clinical validation of PRIMO was completed by comparing the simulated dose distributions on the O4D phantom against dose measurements for these 30 clinical plans. Agreement evaluations were performed using a 3% global/2 mm gamma index analysis. PRIMO simulations agreed with the benchmark IROC-H data within 2.0% for both energies. Gamma passing rates (GPRs) from the 30 clinical plan verifications were (6 MV/6MV FFF): 99.4% ± 0.5%/99.9% ± 0.1%, 99.8% ± 0.4%/98.9% ± 1.4%, 99.7% ± 0.4%/99.7% ± 0.4%, for the 1), 2) and 3) verification methods, respectively. Agreement between PRIMO simulations on the O4D phantom and 3D dose measurements resulted in GPRs of 97.9% ± 2.4%/99.7% ± 0.4%. The PRIMO software is a valuable tool for dosimetric verification of clinical plans during the commissioning of the primary TPS.

External beam radiation therapy treatment factors prognostic of biochemical failure free survival: A multi-institutional retrospective study for prostate cancer

Background and purposeThe goal of this work is to identify specific treatment planning and delivery features that are prognostic of biochemical failure-free survival (BFFS) for prostate cancer patients treated with external beam radiotherapy (EBRT). Materials and methodsThis study reviewed patients diagnosed with localized prostate adenocarcinoma between 2005 and 2016, and treated with EBRT on a Varian linear accelerator at one of the four cancer centers in Alberta, Canada. BFFS was calculated using the Kaplan-Meier estimator. Patient demographics, tumor characteristics, and EBRT treatment planning and delivery factors, were collected for each patient. The patient cohort was split into a training dataset with patients from two centers and a validation dataset with patients from another two centers. A random survival forest was used to identify features associated with BFFS. ResultsThis study included 2827 patients with a median follow-up of 6.4 years. The BFFS for this cohort collectively was 84.9% at 5 years and 69.3% at 10 years. 2519 patients from two centers were used for model training and 308 patients from two different centers were used for model validation. The prognostic features were Gleason score, prostate-specific antigen (PSA) at diagnosis, clinical T stage, CTV D99, pelvic irradiation, IGRT frequency, and PTV V98. Variables including bladder volume, dose calculation algorithm, PTV D99, age at diagnosis, hip prosthesis, number of malignancies, fiducial marker usage, PTV volume, RT modality, PTV HI, rectal volume, hormone treatment, PTV D1cc, equivalent PTV margin, IGRT type, and EQD2_1.5 were unlikely to be prognostic. A random survival forest using only the seven prognostic variables was built. The Harrell’s concordance index for the model was 0.65 for the whole training dataset, 0.62 for out-of-bag samples of the training dataset, and 0.62 for the validation dataset. ConclusionEBRT features prognostic of BFFS were identified and a random survival forest was developed for predicting prostate cancer patients’ BFFS after EBRT.

IPEM Topical Report: an international IPEM survey of MRI use for external beam radiotherapy treatment planning

Introduction/Background. Despite growing interest in magnetic resonance imaging (MRI), integration in external beam radiotherapy (EBRT) treatment planning uptake varies globally. In order to understand the current international landscape of MRI in EBRT a survey has been performed in 11 countries. This work reports on differences and common themes identified. Methods. A multi-disciplinary Institute of Physics and Engineering in Medicine working party modified a survey previously used in the UK to understand current practice using MRI for EBRT treatment planning, investigate how MRI is currently used and managed as well as identify knowledge gaps. It was distributed electronically within 11 countries: Australia, Belgium, Denmark, Finland, France, Italy, the Netherlands, New Zealand, Sweden, the UK and the USA. Results. The survey response rate within the USA was <1% and hence these results omitted from the analysis. In the other 10 countries the survey had a median response rate of 77% per country. Direct MRI access, defined as either having a dedicated MRI scanner for radiotherapy (RT) or access to a radiology MRI scanner, varied between countries. France, Italy and the UK reported the lowest direct MRI access rates and all other countries reported direct access in ≥82% of centres. Whilst ≥83% of centres in Denmark and Sweden reported having dedicated MRI scanners for EBRT, all other countries reported ≤29%. Anatomical sites receiving MRI for EBRT varied between countries with brain, prostate, head and neck being most common. Commissioning and QA of image registration and MRI scanners varied greatly, as did MRI sequences performed, staffing models and training given to different staff groups. The lack of financial reimbursement for MR was a consistent barrier for MRI implementation for RT for all countries and MR access was a reported important barrier for all countries except Sweden and Denmark. Conclusion. No country has a comprehensive approach for MR in EBRT adoption and financial barriers are present worldwide. Variations between countries in practice, equipment, staffing models, training, QA and MRI sequences have been identified, and are likely to be due to differences in funding as well as a lack of consensus or guidelines in the literature. Access to dedicated MR for EBRT is limited in all but Sweden and Denmark, but in all countries there are financial challenges with ongoing per patient costs. Despite these challenges, significant interest exists in increasing MR guided EBRT planning over the next 5 years.

IPEM Topical Report: A 2018 IPEM survey of MRI use for external beam radiotherapy treatment planning in the UK

The benefits of integrating MRI into the radiotherapy pathway are well published, however there is little consensus in guidance on how to commission or implement its use. With a view to developing consensus guidelines for the use of MRI in external beam radiotherapy (EBRT) treatment planning in the UK, a survey was undertaken by an Institute of Physics and Engineering in Medicine (IPEM) working-party to assess the current landscape of MRI use in EBRT in the UK.A multi-disciplinary working-party developed a survey to understand current practice using MRI for EBRT treatment planning; investigate how MRI is currently used and managed; and identify knowledge gaps. The survey was distributed electronically to radiotherapy service managers and physics leads in 71 UK radiotherapy (RT) departments (all NHS and private groups).The survey response rate was 87% overall, with 89% of NHS and 75% of private centres responding. All responding centres include EBRT in some RT pathways: 94% using Picture Archiving and Communication System (PACS) images potentially acquired without any input from RT departments, and 69% had some form of MRI access for planning EBRT. Most centres reporting direct access use a radiology scanner within the same hospital in dedicated (26%) or non-dedicated (52%) RT scanning sessions. Only two centres reported having dedicated RT MRI scanners in the UK, lower than reported in other countries. Six percent of radiotherapy patients in England (data not publically available outside of England) have MRI as part of their treatment, which again is lower than reported elsewhere. Although a substantial number of centres acquire MRI scans for treatment planning purposes, most centres acquire less than five patient scans per month for each treatment site. Commissioning and quality assurance of both image registration and MRI scanners was found to be variable across the UK. In addition, staffing models and training given to different staff groups varied considerably across the UK, reflecting the current lack of national guidelines.The primary barriers reported to MRI implementation in EBRT planning included costs (e.g. lack of a national tariff for planning MRI), lack of MRI access and/or capacity within hospitals. Despite these challenges, significant interest remains in increasing MRI-assisted EBRT planning over the next five years.

A method to predict patient-specific table coordinates for quality assurance in external beam radiation therapy.

PurposeWhile external beam radiotherapy treatment planning determines nearly every mechanical and dosimetric parameter of the linear accelerator (LINAC), the table coordinates in all three dimensions are generally unknown until initial patient setup at the LINAC. Knowing these parameters in advance could help verify the direction of patient shifts and prevent wrong‐site errors. This study aims to determine the feasibility and accuracy of table coordinate prediction for indexed immobilization devices.MethodsA total of 303 table coordinates were predicted for patients on Varian and Elekta linear accelerators with immobilization devices including Orfit mask with baseplate, wingboard, breastboard and BodyFix. Predictions were made for all three spatial dimensions except for Body Fix setups due to the lack of a radiographically apparent indexing‐related landmark. Coordinates were predicted by measuring baseline table coordinates in all dimensions at specified landmark positions.ResultsPredictions were accurate within 2 cm for 86% of coordinates (71% within 1 cm). Table coordinates were predicted most accurately for head and neck patients with a base plate and the most difficult prediction was in the lateral direction for breastboard patients.ConclusionsWith proper indexing, table coordinates can be predicted with reasonable accuracy. The data suggest an action of level of 2 cm with certain exceptions for specific immobilization devices and directions.

The CT number accuracy of a novel commercial metal artifact reduction algorithm for large orthopedic implants

Philips Healthcare released a novel metal artifact reduction algorithm for large orthopedic implants (O‐MAR). Little information was available about its CT number accuracy. Since CT numbers are used for tissue heterogeneity corrections in external beam radiotherapy treatment planning, we performed a phantom study to assess the CT number accuracy of O‐MAR. Two situations were simulated: a patient with a unilateral metallic hip prosthesis and a patient with bilateral metallic hip prostheses. We compared the CT numbers in the O‐MAR reconstructions of the simulations to those in the nonO‐MAR reconstruction and to those in a metal‐free baseline reconstruction. In both simulations, the CT number accuracy of the O‐MAR reconstruction was better than the CT number accuracy of the nonO‐MAR reconstruction. In the O‐MAR reconstruction of the unilateral simulation, all CT numbers were accurate within ±5HU (AAPM criterion). In the O‐MAR reconstruction of the bilateral simulation, CT numbers were found that differed more than ±5HU from the metal‐free baseline values. However, none of these differences were clinically relevant.PACS numbers: 87.57.Q‐, 87.57.cp

MO‐E‐342‐03: Radionuclide Therapy and Dosimetry in Nuclear Medicine

Advances in our understanding of the molecular biology of cancer and other diseases have identified molecules and signaling pathways that we can now visualize, in vivo, for diagnosis, staging, and to identify optimal therapy and monitor patient response to therapy. These advances have also helped identify targets for targeted radionuclide therapy, making it possible to target radiation at the cellular and molecular level. Planning for this treatment approach is similar, in principle, to external beam radiotherapy treatment planning, but substantially different in practice. Dosimetry for systemic or locoregional administration of a therapeutic radiopharmaceutical requires an understanding of its biodistribution and pharmacokinetics, this must be coupled with a methodology for translating total number of radionuclide disintegration in a particular anatomical volume to the absorbed dose to the volume. Advances in imaging and computing technology over the past 20 to 30 years have fostered corresponding advances in the implementation of the basic radionuclide dosimetry scheme outlined above. Dosimetry in nuclear medicine is evolving from a standard anatomical model‐based calculation that provides mean absorbed dose over a target organ volume to a calculation that provides the spatial distribution of absorbed dose over the individual patient target and organ geometry and that also incorporates radiobiological modeling as a step towards assessing the biological consequences of the dose distribution. The evolution of nuclear medicine dosimetry as well as recently approved and emerging radionuclide‐based therapeutics will be reviewed.

Sci-Thur PM Therapy-03: Automated Monte Carlo Simulation and Validation of an External Beam Radiotherapy Treatment Plan

We present the implementation of an integrated EGSnrc‐based Monte Carlo(MC) system as a tool for the verification of Varian's Eclipse clinical external beam radiotherapytreatment planning system (TPS). Once a TPS plan is generated an automated and fully integrated MC simulation is performed based on the information contained in the DICOM RT Plan, RT Sset, RT Dose and CTimage set. MC simulation parameters are determined from information extracted from the RT Plan. The CTimage set is then used to generate a virtual phantom in a manner analogous to that of CTcreate (the relevant EGSnrc program), but with the added advantage of incorporating the structures in RT Sset for volume definition within the phantom. The MC simulation is broken into stages that progress from the target in the head of the accelerator, through the various stages of collimation, and into the phantom using both BEAMnrc and DOSXYZnrc on a dedicated cluster. Using RT Dose, we are then able to compare absolute dose differences between the approaches quantitatively in 3D using a χ metric. To illustrate the process, we compare dose distributions for an unblocked four field pelvic treatment generated both using Eclipse and the MC system. Significant differences (> 4%) between the MC and TPS dose matrixes are observed in the vicinity of the bony anatomy.