Precision Of Treatment Delivery Research Articles

The use of a mini-ridge filter with cyclotron-based pencil beam scanning proton therapy.

Pencil beam scanning (PBS) proton therapy allows for far superior dose conformality compared with passive scattering techniques. However, one drawback of PBS is that the beam delivery time can be long, particularly when treating superficial disease. Minimizing beam delivery time is important for patient comfort and precision of treatment delivery. Mini-ridge filters (MRF) have been shown to reduce beam delivery time for synchrotron-based PBS. Given that cyclotron systems are widely used in proton therapy it is necessary to investigate the potential clinical benefit of mini-ridge filters in such systems. To demonstrate the clinical benefit of using a MRF to reduce beam delivery time for patients with large target volumes and superficial disease in cyclotron-based PBS proton therapy. A MRF beam model was generated by simulating the effect of a MRF on our clinical beam data assuming a fixed snout position relative to the isocenter. The beam model was validated with a series of measurements. The model was used to optimize treatment plans in a water phantom and on six patient DICOM datasets to further study the effect of the MRF and for comparison with physician-approved clinical treatment plans. Beam delivery time was measured for six plans with and without the MRF to demonstrate the reduction achievable. Plans with and without MRF were reviewed to confirm clinical acceptability by a radiation oncologist. Patient-specific QA measurements were carried out with a two-dimensional ionization chamber array detector for one representative patient's plan optimized with the MRF beam model. Results show good agreement between the simulated beam model and measurements with mean and maximum deviations of 0.06mm (0.45%) and 0.61mm (4.9%). The increase in Bragg peak width (FWHM) ranged from 2.7mm at 226MeV to 6.1mm at 70 MeV. The mean and maximum reduction in beam delivery time observed per field was 29.1s (32.2%) and 79.7s (55.3%). MRFs can be used to reduce treatment time in cyclotron-based PBS proton therapy without sacrificing plan quality. This is particularly beneficial for patients with large targets and superficial disease such as in breast cancer where treatment times are generally long, as well as patients treated with deep inspiration breath hold (DIBH).

TO ASSESS THE DOSIMETRIC IMPACT ON PROSTATE, BLADDER AND RECTUM IN CARCINOMA PROSTATE DUE TO INTERFRACTIONALANATOMICAL VARIATION IN IMAGE GUIDED RADIATION THERAPY.

ABTRACT- Prostate cancer is second most frequent cancer in men and fifth leading cause of death worldwide. Most radiotherapy patients with prostate cancer are treated with intensity modulated radiotherapy. IMRT requires high spatial accuracy in localizing the target volume and high precision in treatment delivery, because even a small geographic miss can have a large dosimetric effect. However, the patient setup position and anatomy changes daily, particularly in the prostate region, due to rectum and bladder filling. Materials Methods: We analyzed 30 patients with prostate cancer patient treated with IMRT kV CBCT was performed for each patient twice per week during the entire course of treatment. The bladder, rectum, prostate and PTV were contoured on each CBCT scan. Results: Delivered dose of prostate D95% and prostate D100% was 99.15% and 93.66% respectively and mean value of V70 for bladder was 16% and delivered value was 16.45%. Whereas the mean value of V70 of plan for rectum was 18.12% and delivered value was 27.58%. Conclusion: Interfractional variation during prostate radiotherapy can results in substantial difference between planned and delivered doses, particularly in critical structure. IG-IMRT is useful tool in assessing dosimetric changes in critical structure due to interfractional anatomical interfractional anatomical variation in prostate radiotherapy.

A Monte Carlo feasibility study for neutron based real-time range verification in proton therapy

Uncertainties in the proton range in tissue during proton therapy limit the precision in treatment delivery. These uncertainties result in expanded treatment margins, thereby increasing radiation dose to healthy tissue. Real-time range verification techniques aim to reduce these uncertainties in order to take full advantage of the finite range of the primary protons. In this paper, we propose a novel concept for real-time range verification based on detection of secondary neutrons produced in nuclear interactions during proton therapy. The proposed detector concept is simple; consisting of a hydrogen-rich converter material followed by two charged particle tracking detectors, mimicking a proton recoil telescopic arrangement. Neutrons incident on the converter material are converted into protons through elastic and inelastic (n,p) interactions. The protons are subsequently detected in the tracking detectors. The information on the direction and position of these protons is then utilized in a new reconstruction algorithm to estimate the depth distribution of neutron production by the proton beam, which in turn is correlated with the primary proton range. In this paper, we present the results of a Monte Carlo feasibility study and show that the proposed concept could be used for real-time range verification with millimetric precision in proton therapy.

International guideline for the delineation of the clinical target volumes (CTV) for nasopharyngeal carcinoma

PurposeTarget delineation in nasopharyngeal carcinoma (NPC) often proves challenging because of the notoriously narrow therapeutic margin. High doses are needed to achieve optimal levels of tumour control, and dosimetric inadequacy remains one of the most important independent factors affecting treatment outcome. MethodA review of the available literature addressing the natural behaviour of NPC and correlation between clinical and pathological aspects of the disease was conducted. Existing international guidelines as well as published protocols specified by clinical trials on contouring of clinical target volumes (CTV) were compared. This information was then summarized into a preliminary draft guideline which was then circulated to international experts in the field for exchange of opinions and subsequent voting on areas with the greatest controversies. ResultsCommon areas of uncertainty and variation in practices among experts experienced in radiation therapy for NPC were elucidated. Iterative revisions were made based on extensive discussion and final voting on controversial areas by the expert panel, to formulate the recommendations on contouring of CTV based on optimal geometric expansion and anatomical editing for those structures with substantial risk of microscopic infiltration. ConclusionThrough this comprehensive review of available evidence and best practices at major institutions, as well as interactive exchange of vast experience by international experts, this set of consensus guidelines has been developed to provide a practical reference for appropriate contouring to ensure optimal target coverage. However, the final decision on the treatment volumes should be based on full consideration of individual patients’ factors and facilities of an individual centre (including the quality of imaging methods and the precision of treatment delivery).

Renal cancer subtypes: Should we be lumping or splitting for therapeutic decision making?

The treatment of advanced renal cell carcinoma has posed a challenge for decades, in part because of common themes related to intrinsic resistance to cytotoxic chemotherapy and the obscure biology of these cancer types. Forward movement in the treatment of the renal cell carcinomas thus can be approached in 2 ways: by splitting the tumor types along histologic and molecular features, in the hopes of coupling highly precision-focused therapy on a subset of patients who have disease with the most potential for benefit; or by lumping the various biologies and histologies together, to include the rarer renal cell carcinoma types with the more common types. The former strategy satisfies the desire for customized precision in treatment delivery, whereas the latter strategy allows clinicians to offer a wider therapeutic menu in a set of diseases we are continuing to learn about on a physiologic and molecular level. Cancer 2017;123:200-209. © 2016 American Cancer Society.

Treatment planning with functional MRI

The aim of magnetic resonance imaging (MRI) guided radiotherapy is high precision in treatment delivery. With new developments it is possible to focus the high dose irradiation on the tumor while sparing the surrounding tissue. The achievements in precision of the treatment planning and delivery warrant equally precise tumor definition. In conventional radiation therapy it is necessary to carry out a planning computed tomography (CT). For many tumors there is also need for an additional morphological MRI because of more accurate tumor definition. In standard radiotherapy the tumor volume is irradiated with a homogeneous dose. The aim of functional multiparametric MRI is to visualize and quantify biological, physiological and pathological processes at the cellular and molecular levels. Based on this information it is possible to elucidate tumor biology and identify subvolumes of more aggressive behavior. They are often radiotherapy-resistant, leading to tumor recurrence thus requiring further dose escalation. The concept of inhomogeneous tumor irradiation according to its biological behavior is called dose painting. Dose painting is technically feasible. The expected clinical benefit is motivated by selective treatment adaptations based on biological tumor characteristics. Tumors show variable response to therapy underlining the need for individual treatment plans. This approach may lead not only to higher local control but also to better sparing of normal surrounding tissue. With the clinical implementation of dose painting, improvements in the therapeutic outcome can be expected. Due to the existing technical challenges, extensive collaboration between radiation oncologists, radiologists, medical physicists and radiation biologists is needed.

Radiotherapy for craniopharyngioma

Radiotherapy remains the mainstay of multidisciplinary management of patients with incompletely resected and recurrent craniopharyngioma. Advances in imaging and radiotherapy technology offer new alternatives with the principal aim of improving the accuracy of treatment and reducing the volume of normal brain receiving significant radiation doses. We review the available technologies, their technical advantages and disadvantages and the published clinical results. Fractionated high precision conformal radiotherapy with image guidance remains the gold standard; the results of single fraction treatment are disappointing and hypofractionation should be used with caution as long term results are not available. There is insufficient data on the use of protons to assess the comparative efficacy and toxicity. The precision of treatment delivery needs to be coupled with experienced infrastructure and more intensive quality assurance to ensure best treatment outcome and this should be carried out within multidisciplinary teams experienced in the management of craniopharyngioma. The advantages of the combined skills and expertise of the team members may outweigh the largely undefined clinical gain from novel radiotherapy technologies.

The best method for dose escalation: Prostate brachytherapy

The best method for dose escalation: Prostate brachytherapy

Marker-less intra-fraction organ motion tracking using hybrid ASM

Aim External beam radiation therapy attempts to deliver a high dose of ionizing radiation to destroy cancerous tissue, while sparing healthy tissues and organs at risk (OAR). Recent advances in intensity modulated radiotherapy treatment call for a greater understanding of uncertainties in the treatment process and more rigorous protocols leading to greater precision in treatment delivery. The degree to which this can be achieved depends largely on the cancer site. The treatment of organs comprises soft tissue (e.g. in the abdomen) and those subject to rhythmic movements (e.g. lungs) causing inter and intra-fraction motion artifacts that are particularly problematic. Various methods have been developed to tackle the problems caused by organ motion during radiotherapy treatment, e.g. Real-time position management respiratory gating (Varian) and synchronized moving aperture radiation therapy, developed by researchers at Harvard Medical School.

USE OF ELECTROMAGNETIC GUIDANCE BRONCHOSCOPY FOR INSERTION AND FIXATION OF FIDUCIAL MARKERS FOR SETUP AND TRACKING OF A LUNG TUMOR DURING RADIATION THERAPY

INTRODUCTION: With recent advances in the precision of treatment delivery, radiation therapy has become more accurate, integrating high-resolution real-time imaging with radiation delivery for the treatment of lung cancer. The latest development in this field is Image-Guided Radiation Therapy (IGRT) with real time tumor tracking, promising to improve efficacy and reduce morbidity. This technique can be enhanced by implanting radio-opaque markers, however the marker insertion technique has not yet been widely established.

An image registration scheme applied to verification of radiation therapy.

The introduction of modern conformal radiation therapy techniques requires high geometric precision in treatment delivery which must be verified. For that purpose we have developed an automated system based on registration of portal and simulation (or planning) image pairs. The image registration is performed on anatomical features which are automatically extracted from the portal image. The portal image is then registered with a planning or simulation radiographic image which represents the geometric prescription for the treatment, using an optimized version of the chamfer matching algorithm. Subsequently, the magnitude of the radiation field displacement during treatment is measured by registering the prescribed and treated field boundaries. Algorithms based on chamfer matching and polygon matching have been used for the field boundary registration. Performance of the entire scheme was evaluated on a series of 15 portal images of a pelvic phantom representing various known degrees of the radiation field displacement. The measurements of the radiation field displacements performed by the automated system proved very reliable and after correction for systematic bias agreed to within 1.5 mm or 1 degree with the displacements applied. Second test series involved comparisons between the automated registrations and those performed manually/visually by an experienced human observer, on 31 portal images acquired during treatments of 18 pelvic patients. These tests showed close agreement (in 80% of cases discrepancies were smaller than 1.5 mm or 1.5 degrees) between the automated scheme and the human observer. It is concluded that the developed scheme would be suitable for online geometric verification of radiation therapy treatments.

Ion beams for cancer treatment — a perspective

Clinical use of proton and light-ion beams for cancer treatment is burgeoning worldwide. Various accelerator types, including synchrotrons, cyclotrons, and linacs, will be used for hospital-based proton facilities dedicated to therapy. When compared with conventional radiotherapy, the proton modality turns out to be a viable option that is not only therapeutically superior but also more cost-effective. To achieve full potential of proton treatments, further technological developments such as in better tumor delineation and increased precision in treatment delivery are needed.

56 Clinical implementation of radiosurgery using a multileaf collimator and a computer controlled radiotherapy system

Conventional radiosurgery techniques require multiple isocenters for complex target geometries, leading to increased treatment time and complexity, as well as significant target dose inhomogeneity. Segmental conformal radiotherapy techniques under computer control offer the potential for improved target dose distributions, reduced treatment time, and greater assurance of the precision of treatment delivery for complex Radiosurgery treatments. The purpose of this study is to demonstrate the clinical feasibility of Radiosurgery using a multileaf collimator (MLC) and a computer controlled radiotherapy system (CCRS), and to summarize current clinical experiences using this system.