Synthetic Megavoltage Cone Beam Computed Tomography Image Generation for Improved Contouring Accuracy of Cardiac Pacemakers

In this study, we aimed to enhance the contouring accuracy of cardiac pacemakers by improving their visualization using deep learning models to predict MV CBCT images based on kV CT or CBCT images. Ten pacemakers and four thorax phantoms were included, creating a total of 35 combinations. Each combination was imaged on a Varian Halcyon (kV/MV CBCT images) and Siemens SOMATOM CT scanner (kV CT images). Two generative adversarial network (GAN)-based models, cycleGAN and conditional GAN (cGAN), were trained to generate synthetic MV (sMV) CBCT images from kV CT/CBCT images using twenty-eight datasets (80%). The pacemakers in the sMV CBCT images and original MV CBCT images were manually delineated and reviewed by three users. The Dice similarity coefficient (DSC), 95% Hausdorff distance (HD95), and mean surface distance (MSD) were used to compare contour accuracy. Visual inspection showed the improved visualization of pacemakers on sMV CBCT images compared to original kV CT/CBCT images. Moreover, cGAN demonstrated superior performance in enhancing pacemaker visualization compared to cycleGAN. The mean DSC, HD95, and MSD for contours on sMV CBCT images generated from kV CT/CBCT images were 0.91 ± 0.02/0.92 ± 0.01, 1.38 ± 0.31 mm/1.18 ± 0.20 mm, and 0.42 ± 0.07 mm/0.36 ± 0.06 mm using the cGAN model. Deep learning-based methods, specifically cycleGAN and cGAN, can effectively enhance the visualization of pacemakers in thorax kV CT/CBCT images, therefore improving the contouring precision of these devices.

Bismuth Nanoparticle and Polyhydroxybutyrate Coatings Enhance the Radiopacity of Absorbable Inferior Vena Cava Filters for Fluoroscopy-Guided Placement and Longitudinal Computed Tomography Monitoring in Pigs

Inferior vena cava filters (IVCFs) constructed with poly-p-dioxanone (PPDO) are promising alternatives to metallic filters and their associated risks and complications. Incorporating high-Z nanoparticles (NPs) improves PPDO IVCFs' radiopacity without adversely affecting their safety or performance. However, increased radiopacity from these studies are insufficient for filter visualization during fluoroscopy-guided PPDO IVCF deployment. This study focuses on the use of bismuth nanoparticles (BiNPs) as radiopacifiers to render sufficient signal intensity for the fluoroscopy-guided deployment and long-term CT monitoring of PPDO IVCFs. The use of polyhydroxybutyate (PHB) as an additional layer to increase the surface adsorption of NPs resulted in a 2-fold increase in BiNP coating (BiNP-PPDO IVCFs, 3.8%; BiNP-PPDO + PHB IVCFs, 6.2%), enabling complete filter visualization during fluoroscopy-guided IVCF deployment and, 1 week later, clot deployment. The biocompatibility, clot-trapping efficacy, and mechanical strength of the control PPDO (load-at-break, 6.23 ± 0.13 kg), BiNP-PPDO (6.10 ± 0.09 kg), and BiNP-PPDO + PHB (6.15 ± 0.13 kg) IVCFs did not differ significantly over a 12-week monitoring period in pigs. These results indicate that BiNP-PPDO + PHB can increase the radiodensity of a novel absorbable IVCF without compromising device strength. Visualizing the device under conventional radiographic imaging is key to allow safe and effective clinical translation of the device.

Radiation Sciences Education in Africa: An Assessment of Current Training Practices and Evaluation of a High-Yield Course in Radiation Biology and Radiation Physics

PURPOSE

Formal education in the radiation sciences is critical for the safe and effective delivery of radiotherapy. Practices and patterns of radiation sciences education and trainee performance in the radiation sciences are poorly described. This study assesses the current state of radiation sciences education in Africa and evaluates a high-yield, on-site educational program in radiation biology and radiation physics for oncology and radiation therapy trainees in Africa.

METHODS

An anonymous survey was distributed to members of the African Organization for Research and Treatment in Cancer Training Interest Group to assess current attitudes and practices toward radiation sciences education. A 2-week, on-site educational course in radiation biology and radiation physics was conducted at the Cancer Diseases Hospital in Lusaka, Zambia. Pre- and postcourse assessments in both disciplines were administered to gauge the effectiveness of an intensive high-yield course in the radiation sciences.

RESULTS

Significant deficiencies were identified in radiation sciences education, especially in radiation biology. Lack of expert instructors in radiation biology was reported by half of all respondents and was the major contributing factor to deficient education in the radiation sciences. The educational course resulted in marked improvements in radiation biology assessment scores (median pre- and posttest scores, 27% and 55%, respectively; P < .0001) and radiation physics assessment scores (median pre- and posttest scores, 30% and 57.5%, respectively; P < .0001).

CONCLUSION

Radiation sciences education in African oncology training programs is inadequate. International collaboration between expert radiation biology and radiation physics instructors can address this educational deficiency and improve trainee competence in the foundational radiation sciences that is critical for the safe and effective delivery of radiotherapy.

In vivo performance of gold nanoparticle-loaded absorbable inferior vena cava filters in a swine model

Absorbable inferior vena cava filters (IVCFs) offer a promising alternative to metallic retrievable filters in providing protection against pulmonary embolism (PE) for patients contraindicated for anticoagulant therapy. However, because absorbable filters are not radiopaque, monitoring of the filter using conventional X-ray imaging modalities (e.g. plain film radiographs, computed tomography [CT] and fluoroscopy) during deployment and follow-up is not possible and represents a potential obstacle to widespread clinical integration of the device. Here, we demonstrate that gold nanoparticles (AuNPs) infused into biodegradable filters made up of poly-p-dioxanone (PPDO) may improve device radiopacity without untoward effects on device efficacy and safety, as assessed in swine models for 12 weeks. The absorbable AuNP-infused filters demonstrated significantly improved visualization using CT without affecting tensile strength, in vitro degradation, in vivo resorption, or thrombus-capturing efficacy, as compared to similar non-AuNPs infused resorbable IVCFs. This study presents a significant advancement to the development of imaging enhancers for absorbable IVCFs.

Radiation-induced lung toxicity in mice irradiated in a strong magnetic field

Strong magnetic fields affect radiation dose deposition in MRI-guided radiation therapy systems, particularly at interfaces between tissues of differing densities such as those in the thorax. In this study, we evaluated the impact of a 1.5 T magnetic field on radiation-induced lung damage in C57L/J mice. We irradiated 140 mice to the whole thorax with parallel-opposed Co-60 beams to doses of 0, 9.0, 10.0, 10.5, 11.0, 12.0, or 13.0 Gy (20 mice per dose group). Ten mice per dose group were irradiated while a 1.5 T magnetic field was applied transverse to the radiation beam and ten mice were irradiated with the magnetic field set to 0 T. We compared survival and noninvasive assays of radiation-induced lung damage, namely respiratory rate and metrics derived from thoracic cone-beam CTs, between the two sets of mice. We report two main results. First, the presence of a transverse 1.5 T field during irradiation had no impact on survival of C57L/J mice. Second, there was a small but statistically significant effect on noninvasive assays of radiation-induced lung damage. These results provide critical safety data for the clinical introduction of MRI-guided radiation therapy systems.

Abstract 3722: Efficacy of irreversible electroporation in combination with liposome-nvp-bez235 for head and neck cancer

Introduction: Irreversible electroporation (IRE) is an emerging, minimally invasive ablation technique with the advantage of not being affected by heat sink effect and the ability of ablation in close vicinity of major blood vessels. One limitation is local recurrence at the original ablated site. We hypothesize that combining IRE with a chemotherapeutic drug could prevent recurrence. NVP-BEZ235 (BEZ) is a dual PI3K/mTOR inhibitor that has shown promise for treating advanced solid malignancies, including sensitizing head and neck squamous cell carcinoma to radiotherapy. However, clinical trials revealed low bioavailability and high toxicity due to high dose oral administration over a long period of time. Thus, we formulated a liposomal BEZ (L-BEZ) and studied its antitumor effect in combination with IRE and compared the results with orally delivered BEZ (oral-BEZ).

Methods: IRE was performed using ECM 830 (BTX Harvard Apparatus) at various field strengths. BEZ was loaded into liposome (L-BEZ) by hydration-sonication method. The in vitro and in vivo efficacy was tested against head and neck cancer cell line, HN5 cells and in nude mice bearing HN5 xenografts (n=4/group). Mice were divided into control (no treatment), IRE (2500 V/cm for 99 pulses), IRE + L-BEZ (IRE at 2500 V/cm for 99 pulses and 7 doses of L-BEZ) and IRE + oral-BEZ (IRE at 2500 V/cm for 99 pulses and 21 doses of oral-BEZ) groups. Tumor size was monitored for 60 days.

Results: The hydrodynamic volume of NVP-BEZ ranged from 100-500nm. Maximum drug loading was achieved at 2.7mg/mL of BEZ. Electroporation disrupted nanoparticle's integrity even at the lowest tested field strength (250 V/cm) and released BEZ. At the highest field strength (2500 V/cm), approximately 5% of cells survived with IRE, while cells electroporated at 500 V/cm increased cell viability (114%) as compared to the untreated group (100 %). Combination of electroporation and L-BEZ significantly decreased cell viability at 500 V/cm (p&lt;0.05). In vivo, IRE + L-BEZ suppressed tumor growth the longest, as compared with control (no treatment), IRE, and IRE + oral-BEZ. It was also the only group that resulted in no palpable tumor from day 30 to day 60. Survival studies show a significant difference between IRE + L-BEZ and the other groups. IRE + L-BEZ group had 100% animal survival on day 60. IRE + oral-BEZ had 50%, while IRE and control groups had 0% animal survival, on day 60. Also, the total administered BEZ amount in IRE + L-BEZ group was only 6.6% of that in IRE + oral-BEZ group.

Conclusion: Incomplete electroporation increases the viability of surviving cells both in vitro and in vivo. Co-delivery of L-BEZ enhances the antitumor efficacy of IRE alone. L-BEZ also decreases BEZ exposure compared to oral-BEZ. Thus, L-BEZ in combination with IRE potentially ensures complete eradication of surviving cells left after IRE.

Citation Format: Li Tian, Lucas Wang, Yang Qiao, Saisree Ravi, Ashley Chang, Thomas Alexander Rogers, Linfeng Lu, Adam D. Melancon, Marites Pasuelo Melancon. Efficacy of irreversible electroporation in combination with liposome-nvp-bez235 for head and neck cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 3722.

Technical Note: A Monte Carlo study of magnetic-field-induced radiation dose effects in mice

PURPOSE

Magnetic fields are known to alter radiation dose deposition. Before patients receive treatment using an MRI-linear accelerator (MRI-Linac), preclinical studies are needed to understand the biological consequences of magnetic-field-induced dose effects. In the present study, the authors sought to identify a beam energy and magnetic field strength combination suitable for preclinical murine experiments.

METHODS

Magnetic field dose effects were simulated in a mouse lung phantom using various beam energies (225 kVp, 350 kVp, 662 keV [Cs-137], 2 MV, and 1.25 MeV [Co-60]) and magnetic field strengths (0.75, 1.5, and 3 T). The resulting dose distributions were compared with those in a simulated human lung phantom irradiated with a 6 or 8 MV beam and orthogonal 1.5 T magnetic field.

RESULTS

In the human lung phantom, the authors observed a dose increase of 45% and 54% at the soft-tissue-to-lung interface and a dose decrease of 41% and 48% at the lung-to-soft-tissue interface for the 6 and 8 MV beams, respectively. In the mouse simulations, the magnetic fields had no measurable effect on the 225 or 350 kVp dose distribution. The dose increases with the Cs-137 beam for the 0.75, 1.5, and 3 T magnetic fields were 9%, 29%, and 42%, respectively. The dose decreases were 9%, 21%, and 37%. For the 2 MV beam, the dose increases were 16%, 33%, and 31% and the dose decreases were 9%, 19%, and 30%. For the Co-60 beam, the dose increases were 19%, 54%, and 44%, and the dose decreases were 19%, 42%, and 40%.

CONCLUSIONS

The magnetic field dose effects in the mouse phantom using a Cs-137, 3 T combination or a Co-60, 1.5 or 3 T combination most closely resemble those in simulated human treatments with a 6 MV, 1.5 T MRI-Linac. The effects with a Co-60, 1.5 T combination most closely resemble those in simulated human treatments with an 8 MV, 1.5 T MRI-Linac.

Anatomic variation and dosimetric consequences of neoadjuvant hormone therapy before radiation therapy for prostate cancer

PURPOSE

To characterize anatomic variation during neoadjuvant androgen deprivation (NAD) and determine a treatment planning strategy to maintain acceptable normal tissue dose while treating potential microscopic disease in the original (pre-NAD) tumor bed.

METHODS AND MATERIALS

We retrospectively examined the effects of treating the post-NAD anatomy with plans derived before and after NAD in a group of 44 patients enrolled in an institutional review board-approved protocol. An 8-field intensity modulated radiation therapy (IMRT) treatment plan was generated on anatomy both before and after NAD for the first 35 patients. The pre-NAD treatment plan was applied to the post-NAD anatomy to evaluate the effect of complete pre-NAD tumor bed treatment on normal tissue sparing, and the post-NAD treatment plan was applied to the pre-NAD anatomy to investigate whether microscopic disease might go untreated in the location of the pre-NAD tumor bed.

RESULTS

The prostate decreased in volume by an average of about 14 cm(3) (24.3%) and was correlated with NAD duration (P = .002). The prostate center of volume systematically shifted in the inferior direction (mean = 1.4 mm, P = .005) and inferior shift was correlated with absolute volume reduction of the prostate (P = .044) in a multivariate model containing rectal and bladder volume change and initial prostate volume. Pre-NAD treatment planning resulted in a significant increase in the bladder volume (P < .01) but little increase in the rectal volume treated to all dose levels. Post-NAD treatment planning resulted in decreased treatment of the prostate and seminal vesicles (on the pre-NAD anatomy) at the prescribed and 95% isodose levels (prostate: P = .033 and 0.025; seminal vesicles: P < .001).

CONCLUSIONS

Anisotropic volume reduction of the prostate was found during NAD and correlated with NAD duration. Post-NAD based treatment planning can minimize excess bladder and rectal dose.

A beam-specific planning target volume (PTV) design for proton therapy to account for setup and range uncertainties

PURPOSE

To report a method for explicitly designing a planning target volume (PTV) for treatment planning and evaluation in heterogeneous media for passively scattered proton therapy and scanning beam proton therapy using single-field optimization (SFO).

METHODS AND MATERIALS

A beam-specific PTV (bsPTV) for proton beams was derived by ray-tracing and shifting ray lines to account for tissue misalignment in the presence of setup error or organ motion. Range uncertainties resulting from inaccuracies in computed tomography-based range estimation were calculated for proximal and distal surfaces of the target in the beam direction. The bsPTV was then constructed based on local heterogeneity. The bsPTV thus can be used directly as a planning target as if it were in photon therapy. To test the robustness of the bsPTV, we generated a single-field proton plan in a virtual phantom. Intentional setup and range errors were introduced. Dose coverage to the clinical target volume (CTV) under various simulation conditions was compared between plans designed based on the bsPTV and a conventional PTV.

RESULTS

The simulated treatment using the bsPTV design performed significantly better than the plan using the conventional PTV in maintaining dose coverage to the CTV. With conventional PTV plans, the minimum coverage to the CTV dropped from 99% to 67% in the presence of setup error, internal motion, and range uncertainty. However, plans using the bsPTV showed minimal drop of target coverage from 99% to 94%.

CONCLUSIONS

The conventional geometry-based PTV concept used in photon therapy does not work well for proton therapy. We investigated and validated a beam-specific PTV method for designing and evaluating proton plans.

Is a 3-mm intrafractional margin sufficient for daily image-guided intensity-modulated radiation therapy of prostate cancer?

PURPOSE

To determine whether a 3-mm isotropic target margin adequately covers the prostate and seminal vesicles (SVs) during administration of an intensity-modulated radiation therapy (IMRT) treatment fraction, assuming that daily image-guided setup is performed just before each fraction.

MATERIALS AND METHODS

In-room computed tomographic (CT) scans were acquired immediately before and after a daily treatment fraction in 46 patients with prostate cancer. An eight-field IMRT plan was designed using the pre-fraction CT with a 3-mm margin and subsequently recalculated on the post-fraction CT. For convenience of comparison, dose plans were scaled to full course of treatment (75.6 Gy). Dose coverage was assessed on the post-treatment CT image set.

RESULTS

During one treatment fraction (21.4+/-5.5 min), there were reductions in the volumes of the prostate and SVs receiving the prescribed dose (median reduction 0.1% and 1.0%, respectively, p<0.001) and in the minimum dose to 0.1 cm(3) of their volumes (median reduction 0.5 and 1.5 Gy, p<0.001). Of the 46 patients, three patients' prostates and eight patients' SVs did not maintain dose coverage above 70 Gy. Rectal filling correlated with decreased percentage-volume of SV receiving 75.6, 70, and 60 Gy (p<0.02).

CONCLUSIONS

The 3-mm intrafractional margin was adequate for prostate dose coverage. However, a significant subset of patients lost SV dose coverage. The rectal volume change significantly affected SV dose coverage. For advanced-stage prostate cancers, we recommend to use larger margins or improve organ immobilization (such as with a rectal balloon) to ensure SV coverage.

Changes in the Pelvic Anatomy After an IMRT Treatment Fraction of Prostate Cancer

PURPOSE

To quantify the three-dimensional variations of pelvic anatomy after a single treatment fraction.

METHODS AND MATERIALS

Forty-six prostate cancer patients underwent computed tomography (CT) scanning with an in-room CT-on-rail system, before and immediately after one intensity-modulated radiotherapy (IMRT) session. To study the soft-tissue anatomy changes, the pre- and post-treatment CT images were registered using the bony structure with an in-house image registration software system. The center of volume for both the prostate and seminal vesicles was used to assess the relative displacement of the same structure after the treatment fraction.

RESULTS

During one treatment fraction (21 +/- 4 min), both the prostate and seminal vesicles showed statistically significant systematic trends in the superior and anterior directions of the patient's anatomy. The net increase in bladder volume was huge (127 +/- 79 cm(3)), yet this change did not translate into large target displacements. Although the population mean displacements in either direction were 1.3 +/- 2.9 mm for the prostate and 1.2 +/- 4.1 mm for the seminal vesicles in the anterior direction, a few patients had displacements as large as 8.4 mm and 15.6 mm, respectively. These large displacements correlated strongly (p < 0.001) with large rectal volume increases caused by gaseous build-up in the rectum.

CONCLUSION

The observed intrafraction variations in anatomy during prostate IMRT sessions suggest that, for any given fraction, the organ motion and volume changes can potentially lead to compromised target coverage in about 15% of patients in whom the prostate position shifted >4 mm.