Accounting for center‐of‐mass target motion using convolution methods in Monte Carlo‐based dose calculations of the lung

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/134807/1/mp9083.pd

A novel flexible framework with automatic feature correspondence optimization for nonrigid registration in radiotherapy

Technical improvements in planning and dose delivery and in verification of patient positioning have substantially widened the therapeutic window for radiation treatment of cancer. However, changes in patient anatomy during the treatment limit the exploitation of these new techniques. To further improve radiation treatments, anatomical changes need to be modeled and accounted for. Non-rigid registration can be used for this purpose. This paper describes the design, the implementation and the validation of a new framework for non-rigid registration for radiotherapy applications. The core of this framework is an improved version of the Thin Plate Splines Robust Point Matching (TPS-RPM) algorithm. The TPS-RPM algorithm estimates a global correspondence and a transformation between the points that represent organs of interest belonging to two image sets. However, the algorithm does not allow for the inclusion of prior knowledge on the correspondence of subset of points and therefore, it can lead to inconsistent anatomical solutions. In this paper TPS-RPM was improved by employing a novel correspondence filter that supports simultaneous registration of multiple structures. The improved method allows for coherent organ registration and for the inclusion of user defined landmarks, lines and surfaces inside and outside of structures of interest. A procedure to generate control points form segmented organs is described. The framework parameters r and ?, which control the number of points and the non-rigidness of the transformation respectively, were optimized for three sites with different degrees of deformation: head and neck, prostate and cervix, using two cases per site. For the head and neck cases, the salivary glands were manually contoured on CT-scans, for the prostate cases the prostate and the vesicles, and for the cervix cases the cervix-uterus, the bladder and the rectum. The transformation error obtained using the best set of parameters was below 1 mm for all the studied cases. The length of the deformation vectors were on average (± 1 standard deviation) 5.8 ± 2.5 and 2.6 ± 1.1 mm for the head and neck cases, 7.2 ± 4.5 and 8.6 ± 1.9 mm for the prostate cases, and 19.0 ± 11.6 and 14.5 ± 9.3 mm for the cervix cases. Distinguishable anatomical features were identified for each case, and were used to validate the registration by calculating residual distances after transformation: 1.5 ± 0.8, 2.3 ± 1.0 and 6.3 ± 2.9 mm for the head and neck, prostate and cervix sites respectively. Finally, we demonstrated how the inclusion of these anatomical features in the registration process reduced the residual distances to 0.8 ± 0.5, 0.6 ± 0.5 and 1.3 ± 0.7 mm for the head and neck, prostate and cervix sites respectively. The inclusion of additional anatomical features produced more anatomically coherent transformations without compromising the transformation error. We concluded that the presented non-rigid registration framework is a powerful tool to simultaneously register multiple segmented organs with very different complexity

Decay Out of the Doubly Magic Superdeformed Band in the N=Z Nucleus 60Zn

The doubly magic superdeformed band in the N = Z nucleus Zn-60 has been identified. Linking transitions connecting this band to the yrast line provide the first spin, parity, and excitation energy measurements for superdeformed states in the A similar to 60 region. The stretched-E2 character and relatively large B(E2) values of these transitions suggest a nonstatistical decay-out process

Is hypofractionated whole pelvis radiotherapy (WPRT) as well tolerated as conventionally fractionated WPRT in prostate cancer patients? The HOPE trial

Background: Patients with high-risk prostate cancer are at increased risk of lymph node metastasis and are thought to benefit from whole pelvis radiotherapy (WPRT). There has been recent interest in the use of hypofractionated radiotherapy in treating prostate cancer. However, toxicity and cancer outcomes associated with hypofractionated WPRT are unclear at this time. This phase II study aims to investigate the impact in quality of life associated with hypofractionated WPRT compared to conventionally fractionated WPRT. Methods: Fifty-eight patients with unfavourable intermediate-, high- or very high-risk prostate cancer will be randomized in a 1:1 ratio between high-dose-rate brachytherapy (HDR-BT) + conventionally fractionated (45 Gy in 25 fractions) WPRT vs. HDR-BT + hypofractionated (25 Gy in 5 fractions) WPRT. Randomization will be performed with a permuted block design without stratification. The primary endpoint is late bowel toxicity and the secondary endpoints include acute and late urinary and sexual toxicity, acute bowel toxicity, biochemical failure-, androgen deprivation therapy-, metastasis- and prostate cancer-free survival of the hypofractionated arm compared to the conventionally fractionated arm. Discussion: To our knowledge, this is the first study to compare hypofractionated WPRT to conventionally fractionated WPRT with HDR-BT boost. Hypofractionated WPRT is a more attractive and convenient treatment approach, and may become the new standard of care if demonstrated to be well-tolerated and effective. Trial registration: This trial was prospectively registered in ClinicalTrials.gov as NCT04197141 on December 12, 2019

Impact of margin size on the predicted risk of radiogenic second cancers following proton arc therapy and volumetric modulated arc therapy for prostate cancer

We previously determined that the predicted risk of radiogenic second cancer in the bladder and rectum after proton arc therapy (PAT) was less than or equal to that after volumetric modulated arc therapy (VMAT) with photons, but we did not consider the impact of margin size on that risk. The current study was thus conducted to evaluate margin size’s effect on the predicted risks of second cancer for the two modalities and the relative risk between them. Seven treatment plans with margins ranging from 0 mm in all directions to 6 mm posteriorly and 8 mm in all other directions were considered for both modalities. We performed risk analyses using three risk models with varying amounts of cell sterilization and calculated ratios of risk for the corresponding PAT and VMAT plans. We found that the change in risk with margin size depended on the risk model but that the relative risk remained nearly constant with margin size, regardless of the amount of cell sterilization modeled. We conclude that while margin size influences the predicted risk of a second cancer for a given modality, it appears to affect both modalities in roughly equal proportions so that the relative risk between PAT and VMAT is approximately equivalent

Validation of deformable registration in head and neck cancer using analysis of variance

Deformable image registration (DIR) is often validated based on a distance-to-agreement (DTA) criterion of automatically propagated anatomical landmarks that were manually identified. Due to human observer variability, however, the performance of the registration method is diluted. The purpose of this study was to evaluate an analysis of variance (ANOVA) based validation to account for such observer variation. Weekly cone beam CTs (CBCTs) of ten head and neck cancer patients undergoing five weeks of radiotherapy were used. An expert identified 23 anatomical features (landmarks) on the planning CT. The landmarks were automatically propagated to the CBCT using multiregion-of-interest (mROI) registration. Additionally, two human observers independently localized these landmarks on the CBCTs. Subsequently, ANOVA was used to compute the variance of each observer on the pairwise distance (PWD). ANOVA based analysis demonstrated that a classical DTA approach underestimated the precision for the mROI due to human observer variation by about 25%. The systematic error (accuracy) of mROI ranged from 0.13 to 0.17 mm; the variability (1 SD) (precision) ranged from 1.3 to 1.5 mm demonstrating that its performance is dominated by the precision. The PWD-ANOVA method accounts for human observer variation allowing a better estimation of the of DIR error