Implementation Science in Radiation Oncology: Case Study for Liver SBRT

PURPOSE/OBJECTIVE(S)

The translation of research into clinical practice is challenging and implementation science is becoming as important as the trial design and development. Implementation science methodologies have been shown to reduce research-to-practice gap in other clinical settings. This is especially true for the field of Radiation Oncology where modern hypofractionated techniques, like Stereotactic Ablative Body Radiotherapy for Liver are at a high risk of over enthusiastic implementation as well as underutilization. We present the results of a multicomponent implementation methodology utilized to develop our Liver SBRT program as a model to safely translate a complex technology into clinical practice.

MATERIALS/METHODS

After review of literature and market research a setup was created with focus on machine requirements, immobilization devices, motion management techniques and QA techniques. Clinical tools in the form of checklists were developed for patient selection, simulation along with image fusion, target delineation, planning (conformity indices, dose constraint criteria) and treatment delivery. All patients were treated on Truebeam® after Bodyfix® immobilization with plastic wrap. Planning was completed on Eclipse TPS with dose constraints and conformity guidelines defined per the RTOG 1112 and TG 101. Clinical outcomes including clinical and imaging follow-up for tumor control and toxicity were recorded. For this report, all patients treated were reviewed and compared to published data to assess the success of the implementation methodology.

RESULTS

A total of 64 consecutive Patients treated with liver SBRT at Dignity Health Cancer Institute (DHCI) were eligible for the study. 58 patients treated for primary liver malignancies were included in this analysis to assess outcomes including control of disease and toxicity to compare to the published literature. Median follow up for these patients 6.5 months (4-46mnths). Median GTV volume was 38.7cc (0.1cc-2056.1 cc), median PTV volume was 159.35 cc (21.5cc-2673.5cc). Median SBRT prescription dose was 50 Gy/5 fractions (35-50 Gy). Median Liver- GTV was 1595.8 cc(770.7cc-2983.0cc). Following toxicities were noted- Grade 1- 10.3%, Grade 2 - 1.72%, Grade 3- 3.44%. No Grade 4 toxicity was noted. 1 year LC rate was 96.6%. 8.6% showed out of field liver failure and 6.9% developed distant metastasis. These results were compared to the current published literature and are shown to be comparable.

CONCLUSION

Strong and well thought out Implementation methodologies can ensure reproducing results in clinical practice, comparable to the controlled environment of trials. These are crucial in translation of clinical trials utilizing advanced technologies to promote the culture of safety in clinical practice of Radiation Oncology. Regular assessment and tracking of clinical outcomes can be used as Quality markers for directing care and reimbursements for future.

SU-E-J-169: 4D-PET for Abdominal Tumor Target Volume Generation

PURPOSE

To examine the impact of 4D-PET on target volume delineation of upper-abdominal tumors, versus conventional un-gated PET.

METHODS

Four patients with upper-abdominal tumors underwent respiratory-correlated FDG PET/CT scanning (4D-PET) as part of a continuing IRB-approved research protocol. Internal target volumes of FDG-avid tumors were contoured on the 4D-PET and conventional un-gated PET by a radiation oncologist who is a specialist in gastro-intestinal tumors. To create the 4D-PET ITV, the end-inhale and end-exhale 4D-PET phases were used. The relative volumes and volumetric overlaps of the 4D and un-gated target volumes were examined. Additionally, 4D-PET was used to measure the motion of the tumors.

RESULTS

Of the four patients who were imaged, one showed minimal motion (〈 3 mm in any direction) and one showed minimal FDG avidity; these were removed from further analysis. Of the two tumors which showed significant motion and FDG uptake, 4D-PET volumes were 28% and 21% larger than un-gated PET volumes. The un-gated PET volumes were almost entirely contained within the 4D-PET volumes (95% and 93% for the two tumors). Tumors appeared to deform as well as translate with breathing, although this could be due to varying intra-gate motion rather than actual physiological deformation. The superior-inferior borders of the tumors exhibited the most motion, with displacements of 5.6 mm and 6.4 mm.

CONCLUSIONS

4D-PET can be used to estimate the motion of FDG-avid upper-abdominal tumors. Use of 4D-PET increases the size of target volumes compared to un-gated PET in a subset of upper-abdominal cancer patients. Direct measurement of tumor motion and deformation by 4D-PET imaging could allow the use of patient-specific margins rather than population-based margins, potentially leading to increased target coverage and reduced normal tissue irradiation.

Evaluation of sequentially crosslinked ultra-high molecular weight polyethylene

This study was undertaken to investigate the effect of crosslinking ultra-high molecular weight polyethylene (UHMWPE) in a sequential manner to the final desired dose and to compare the results to single-dose crosslinking. To verify these results, an explanted, commercially available, sequentially crosslinked component was characterized. Finally, additional tensile testing was conducted to determine if tensile-sample thickness has a significant effect on the mechanical properties of UHMWPE. Based upon this well-controlled study with the same starting material, there is no apparent benefit of sequential crosslinking over crosslinking by single dose in any of the mechanical, thermophysical, physical, or oxidative properties evaluated in this study. In contrast, the soak temperature of the postirradiation heat treatment was more influential and exhibited statistically significant effects on the stability, structure, and properties of the resultant material. Compared to virgin material, crosslinking always resulted in decreases in tensile strength, elongation, and impact strength. These results were confirmed by characterization of a retrieved, sequentially crosslinked (X3) cup. All of the metrics derived for the retrieved cup were virtually identical to the sequential- and single-dose-crosslinked materials produced in this study. Examination of the effect of tensile-sample thickness demonstrated that there are significant effects on the resultant properties. In particular, the ultimate tensile strength of UHMWPE can be elevated by conducting tensile tests with thin specimens.

Particle analysis for the determination of UHMWPE wear

Three types of ultrahigh molecular weight polyethylene (UHMWPE) acetabular liners were tested against cobalt-chrome (CoCr) femoral heads on a hip simulator to approximately 20 million cycles. The materials included (1) conventional, nonirradiated liners (C-PE); (2) 5 Mrad gamma-irradiated, remelted, and artificially aged liners (5-XPE); and (3) 10 Mrad gamma-irradiated, remelted, and artificially aged liners (10-XPE). Wear was quantified by gravimetric analysis and wear particle characterization. Particle number and morphology were quantified by scanning electron microscopy (SEM) and compared between groups. Atomic force microscopy (AFM) was used to measure particle height in an effort to improve the total wear volume estimation. The wear debris, as characterized by SEM, was predominantly submicron and round, with occasional fibrils documented in the C-PE material. AFM analysis showed that particle height was approximately one-third of the particle equivalent circular diameter for all three materials. This correlation was used to improve the estimation of volumetric wear rate through SEM particle analysis. This technique is particularly useful for high-dose crosslinked UHMWPE, such as 10-XPE, which show weight gain due to fluid absorption during wear testing. This study has shown that particle analysis provides additional particle morphology and quantity information that cannot be obtained through gravimetric analysis.

Relationship between gravimetric wear and particle generation in hip simulators: conventional compared with cross-linked polyethylene

Hip-simulator studies have shown reduced gravimetric wear rates for inert-gas gamma-irradiated ultra-high molecular weight polyethylene when compared with conventional ethylene-oxide-sterilized ultra-high molecular weight polyethylene. Analysis shows a greater number of particles generated from inert-gas gamma-irradiated ultra-high molecular weight polyethylene. This study was undertaken to examine particle-generation rates of polyethylene with different levels of cross-linking and to correlate them with gravimetric wear data. Particle-generation rates did not correlate with gravimetric wear rates. Particle analysis should be performed to predict the in vivo behavior of bearing surface materials. Cross-linked ultra-high molecular weight polyethylene subjected to 10 Mrad (100,000 Gy) of gamma irradiation generated significantly fewer particles than ethylene-oxide-sterilized ultra-high molecular weight polyethylene; it also demonstrated a 96% reduction in the volume of particles.

Comparison of three joint simulator wear debris isolation techniques: acid digestion, base digestion, and enzyme cleavage

Quantification of ultrahigh molecular weight polyethylene (UHMWPE) wear debris remains a challenging task in orthopedic device analysis. Currently, the weight loss method is the only accepted practice for quantifying the amount of wear generated from a PE component. This technique utilizes loaded soak controls and weight differences to account for polymeric material lost through wear mechanisms. This method enables the determination of the amount of wear in the orthopedic device, but it provides no information about debris particulate size distribution. In order to shed light on wear mechanisms, information about the wear debris and its size distribution is necessary. To date, particulate isolation has been performed using the base digestion technique. The method uses a strong base, ultracentrifugation, and filtration to digest serum constituents and to isolate PE debris from sera. It should be noted that particulate isolation methods provide valuable information about particulate size distribution and may elucidate the mechanisms of wear associated with polymeric orthopedic implants; however, these techniques do not yet provide a direct measure of the amount of wear. The aim of this study is to present alternative approaches to wear particle isolation for analysis of polymer wear in total joint replacements without recourse to ultracentrifugation. Three polymer wear debris isolation techniques (the base method, an acid treatment, and an enzymatic digestion technique) are compared for effectiveness in simulator studies. A requirement of each technique is that the wear particulate must be completely devoid of serum proteins in order to effectively image and count these particles. In all methods the isolation is performed through filtration and chemical treatment. Subsequently, the isolated polymer particles are imaged using scanning electron microscopy and quantified with digital image analysis. The results from this study clearly show that isolation can be performed without the use of ultracentrifugation and that these methods provide a viable option for wear debris analysis.

Radiation therapy to inhibit restenosis: early clinical results

BACKGROUND

Although several early trials indicate that treatment of restenosis with radiation therapy is safe and effective, the long-term impact of this new technology has been questioned. The objective of this report is to document angiographic and clinical outcome 3 years after treatment of restenosis of stented coronary arteries with catheter-based iridium-192 (192Ir).

METHODS

A double-blind, randomized trial compared 192Ir with placebo sources in patients with previous restenosis after coronary angioplasty. Over a 9-month period, 55 patients were enrolled; 26 were randomized to 192Ir and 29 to placebo.

RESULTS

At 3-year follow-up, target-lesion revascularization was significantly lower in the 192Ir group (15.4% vs. 48.3%; p < 0.01). The dichotomous restenosis rate at 3-year follow-up was also significantly lower in 192Ir patients (33% vs. 64%; p < 0.05). In a subgroup of patients with 3-year angiographic follow-up not subjected to target-lesion revascularization by the 6-month angiogram, the mean minimal luminal diameter between 6 months and 3 years decreased from 2.49 +/- 0.81 mm to 2.12 +/- 0.73 mm in 192Ir patients, but was unchanged in placebo patients.

CONCLUSIONS

The early clinical benefits observed after treatment of coronary restenosis with 192Ir appear durable at late follow-up. Angiographic restenosis continues to be significantly reduced in 192Ir-treated patients, but a small amount of late loss was observed between the 6-month and 3-year follow-up time points. No events occurred in the 192Ir group to suggest major untoward effects of vascular radiotherapy. At 3-year follow-up, vascular radiotherapy continues to be a promising new treatment for restenosis.

Localized intracoronary gamma-radiation therapy to inhibit the recurrence of restenosis after stenting

BACKGROUND

Although the frequency of restenosis after coronary angioplasty is reduced by stenting, when restenosis develops within a stent, the risk of subsequent restenosis is greater than 50 percent. We report on a multicenter, double-blind, randomized trial of intracoronary radiation therapy for the treatment of in-stent restenosis.

METHODS

Of 252 eligible patients in whom in-stent restenosis had developed, 131 were randomly assigned to receive an indwelling intracoronary ribbon containing a sealed source of iridium-192, and 121 were assigned to receive a similar-appearing nonradioactive ribbon (placebo).

RESULTS

The primary end point, a composite of death, myocardial infarction, and the need for repeated revascularization of the target lesion during nine months of follow-up, occurred in 53 patients assigned to placebo (43.8 percent) and 37 patients assigned to iridium-192 (28.2 percent, P=0.02). However, the reduction in the incidence of major adverse cardiac events was determined solely by a diminished need for revascularization of the target lesion, not by reductions in the incidence of death or myocardial infarction. Late thrombosis occurred in 5.3 percent of the iridium-192 group, as compared with 0.8 percent of the placebo group (P=0.07), resulting in more late myocardial infarctions in the iridium-192 group (9.9 percent vs. 4.1 percent, P=0.09). Late thrombosis occurred in irradiated patients only after the discontinuation of oral antiplatelet therapy (with ticlopidine or clopidogrel) and only in patients who had received new stents at the time of radiation treatment.

CONCLUSIONS

Intracoronary irradiation with iridium-192 resulted in lower rates of clinical and angiographic restenosis, although it was also associated with a higher rate of late thrombosis, resulting in an increased risk of myocardial infarction. If the problem of late thrombosis within the stent can be overcome, intracoronary irradiation with iridium-192 may become a useful approach to the treatment of in-stent restenosis.