Physical and histopathological assessment of the effects of metallic stents on radiation therapy

Dosimetric characteristics of self-expandable metallic and plastic stents for transpapillary biliary decompression in external beam radiotherapy

There is little evidence regarding radiation dose perturbation caused by the self-expandable metallic stents (SEMSs) used for transpapillary biliary decompression. We aimed to compare SEMSs with plastic stents (PSs) and clarify their dosimetric characteristics. Fifteen SEMSs (10 braided and 5 lasercut type) and six PSs (diameter: 2.3-3.3 mm) were inserted into a water-equivalent solid phantom. In total, 13 SEMSs had radiopaque markers, whereas the other two did not. Using radiochromic films, the dose difference adjacent to the stents at locations proximal, distal, and arc delivery to the radiation source was evaluated based on comparison to measurement of the dose delivery in phantom without any stent in place. The median values of the dose difference for each stent were used to compare the SEMS and PS groups.Results: The dose difference (median (minimum/maximum)) was as follows: proximal, SEMSs + 2.1% (1.8 / 4.7) / PSs + 5.4% (4.1 / 6.3) (p < 0.001); distal, SEMSs -1.0% (-1.6 /-0.4) / PSs -8.9% (-11.7 / -7.4) (p < 0.001); arc delivery, SEMSs 1.2% (0.9 / 2.3) / PSs 2.2% (1.6 / 3.6) (p = 0.005). These results demonstrated that the dose differences of SEMSs were significantly smaller than those of PSs. On the other hand, the dose difference was large at surface of the radiopaque markers for SEMSs: proximal, 10.3% (7.2 / 20.9); distal, -8.4% (-16.3 / -4.2); arc delivery, 5.5% (4.2 / 9.2). SEMSs for biliary decompression can be safely used in patients undergoing radiotherapy, by focusing on the dose distribution around the stents and by paying attention to local changes in the dose distribution of radiopaque markers.

The impact of metal implants on the dose and clinical outcome of radiotherapy (Review)

Radiotherapy (RT) is one of the most widely used and effective cancer treatments. With the increasing need for organ reconstruction and advancements in material technology, an increasing number of patients with cancer have metallic implants. These implants can affect RT dosage and clinical outcomes, warranting careful consideration by oncologists. The present review discussed the mechanisms by which different types of metallic implants impact various stages of the RT process, examined methods to mitigate these effects during treatment, and discussed the clinical implications of metallic implants on RT outcomes. In summary, when metallic implants are present within the RT field, oncologists should carefully assess their impact on the treatment.

Long-term survival of airway silicone stents in patients with central airway stenosis or obstruction due to thoracic malignancy

OBJECTIVES

Silicone airway stents are used to manage central airway stenosis or obstruction, although their impact on long-term survival remains unknown in patients with central airway stenosis or obstruction due to thoracic malignancy. In this study, we retrospectively analyzed the impact of silicone stents on survival.

METHODS

We retrospectively analyzed clinical data of 106 patients with central airway stenosis or obstruction due to thoracic malignancy treated by stenting at Toho University Omori Medical Center between 1998 and 2018.

RESULTS

Patients treated with silicone stents had significantly higher survival rates than patients treated with metallic stents (p = 0.0173). Silicone stents patients also had significantly more additional treatments for thoracic malignancy after stenting than metallic stents patients (p = 0.0007). Notably, significantly more silicone stents patients underwent chemoradiotherapy or radiotherapy (p = 0.0268, p = 0.0300). During multivariate analyses, the additional treatment, including chemoradiotherapy or radiotherapy, was an independent optimal prognostic factor.

CONCLUSIONS

Silicone stents patients had significantly higher survival rates than metallic stents patients. Although stenting for airway stenosis or obstruction due to thoracic malignancy may be mainly palliative, additional treatments after stenting should be considered to improve the prognoses of patients with airway stenosis or obstruction due to thoracic malignancy.

Embolization for delayed arterial bleeding after percutaneous self-expandable metallic stent placement in patients with malignant biliary obstruction

OBJECTIVES

To retrospectively evaluate the safety and efficacy of transcatheter arterial embolization (TAE) for delayed arterial bleeding secondary to percutaneous self-expandable metallic stent (SEMS) placement in patients with malignant biliary obstruction (MBO).

METHODS

From January 1997 to September 2017, 1858 patients underwent percutaneous SEMS placement for MBO at a single tertiary referral center. Among them, 19 patients (mean age, 70.2 [range, 52-82] years; 13 men) presented with delayed SEMS-associated arterial bleeding and underwent TAE.

RESULTS

The incidence of delayed arterial bleeding was 1.0% (19/1858) after SEMS placement, with a median time interval of 225 days (range, 22-2296). Digital subtraction angiography (DSA) showed pseudoaneurysm alone close to the stent mesh (n = 10), pseudoaneurysm close to the stent mesh with contrast extravasation to the duodenum (n = 3), pseudoaneurysm close to the stent mesh with arteriobiliary fistula (n = 1), in-stent pseudoaneurysm alone (n = 4) and in-stent pseudoaneurysm with arteriobiliary fistula (n = 1). Bleeding was stopped after the embolization in all patients. Overall clinical success rate was 94.7% (18/19). One patient with recurrent bleeding was successfully treated with a second embolization. Overall 30-day mortality rate was 26.3% (5/19). A major procedure-related complication was acute hepatic failure in one hilar bile duct cancer patient (5.3%), which was associated with an obliterated portal vein.

CONCLUSION

TAE is safe and effective for the treatment of delayed arterial bleeding after percutaneous SEMS placement for MBO.

ADVANCES IN KNOWLEDGE

This study demonstrated TAE is safe and effective for arterial bleeding after SEMS placement after MBO through the largest case series so far.

Dose perturbation by metallic biliary stent in external beam radiotherapy of pancreato-biliary cancers

This study aims to investigate dose perturbations caused by a metallic biliary stent (MBS) in patients undergoing external beam radiotherapy for cancers in the pancreato-biliary region. Four MBSs with nitinol mesh were examined in the EasyCube^® phantom including a custom stent holder fabricated by a 3D printer. For experimental models, three-dimensional conformal radiotherapy plans using a single anterior-posterior (AP) and four-field box (4FB) as well as volumetric modulated arc therapy (VMAT) plan were prepared to deliver the photon beam of 8 Gy to the stent holder. EBT3 film was used to measure dose distributions at four sides surrounding MBS. All MBSs in the AP beam demonstrated mean dose enhancements of 2.3-8.2% at the proximal, left, and right sides. Maximum dose enhancements of 12.3-19.5% appeared at regions surrounding the radiopaque markers. At the location distal to the source, there were mean dose reductions of - 3.6 to - 10.9% and minimum doses of - 11.1 to - 9.5%. The mean and maximum doses with the 4FB plan were in the ranges of - 0.1 to 3.6% and 6.7-14.9%, respectively. The VMAT produced mean doses of - 0.9 to 4.8% and maximum doses of 6.0-15.3%. Dose perturbations were observed with maximum and minimum spots near the stent surface. The use of multiple beams including parallel-opposed pairs reduced dose perturbations caused by the nitinol and radiopaque components within the stent. Special attention is required for patients in whom the radiopaque markers are closely located near critical structures or the target volume.

Effect of external beam radiotherapy on patency of uncovered metallic stents in patients with inoperable bile duct cancer

BACKGROUND

Although biliary decompression with metallic stenting is the preferred treatment for inoperable bile duct cancer (BDC), maintenance of patency is still unsatisfactory. We tried to assess the effectiveness and safety of external beam radiotherapy (EBRT) for prolonging stent patency in patients having uncovered metallic stents.

METHOD

We retrospectively reviewed 50 patients who received endoscopic stenting, of whom 18 received EBRT (RT group) and 32 did not (non-RT group).

RESULTS

No difference was found in baseline characteristics between the two groups. Although stent patency was longer in the RT group than that in the non-RT group (140.7+/-51.3 vs 136.4+/-34.9 days, P=0.94), the difference was not statistically significant. There were a lower rate of stent occlusion (27.8% vs 50.0% of patients, P=0.12) and a longer overall survival (420.1+/-73.2 vs 269.1+/-41.7 days, P=0.11) in the RT group than in the non-RT group, and the difference again was not statistically significant. The development of adverse reactions did not differ (55.6% vs 53.1% of patients, P=0.91). There was no serious adverse reaction in both groups (P=0.99).

CONCLUSIONS

EBRT did not significantly improve stent patency in patients with inoperable BDC having uncovered metallic stents. However, EBRT was safe. Future trials with refined protocols for better efficacy are expected.

The effect of metallic tracheal stents on radiation dose in the airway and surrounding tissues

BACKGROUND

Metallic airway stents are often used in the management of central airway malignancies. The presence of a metallic foreign body may affect radiation dose in tissue. We studied the effect of a metallic airway stent on radiation dose delivery in a phantom and an in vivo porcine model.

METHODS

A metallic tracheal stent was fitted onto a support in a water phantom. Point dosimeters were positioned in the phantom around the support and the stent. Irradiation was then performed on a linear accelerator with and without the stent. Metallic tracheal stents were deployed in the trachea of three pigs. Dosimeters were implanted in the tissues near (Group 1) and away (Group 2) from the stent. The pigs were then irradiated, and the dose perturbation factor was calculated by comparing the actual dose detected by the dosimeters versus the planned dose.

RESULTS

The difference in the dose detected by the dosimeters and the planned dose ranged from 1.8% to 6.1% for the phantom with the stent and 0%-5.3% for the phantom without the stent. These values were largely within the manufacturer's specified error of 5%. No significant difference was observed in the dose perturbation factor for Group 1 and Group 2 dosimeters (0.836 ± 0.058 versus 0.877 ± 0.088, P = 0.220) in all the three pigs.

CONCLUSIONS

Metallic airway stents do not significantly affect radiation dose in the airway and surrounding tissues in a phantom and porcine model. Radiation treatment planning systems can account for the presence of the stent. External beam radiation can be delivered without concern for significant dose perturbation.

Ureteric response to abdominal radiotherapy and metallic double-pigtail ureteric stents: a pig model

OBJECTIVE

To examine the safety and compatibility of full-length metal ureteric stents with abdominal radiotherapy.

MATERIALS AND METHODS

Four ureteric stents (Resonance(TM), Cook Urological, Ireland) (RS) and four RSs specially modified to contain thermocouples were placed unilaterally in eight pigs. The contralateral ureters of the same pigs served as their controls, and contained two polymeric ureteric catheters and two similar specially modified to contain thermocouples, while the remaining four control ureters remained intact. All pigs were exposed to abdominal radiotherapy. The dose rate was approximately 5.3 Gy/min and a total radiation dose of 10 Gy was administered. Throughout the treatment the temperature was monitored by the RSs and catheters containing the thermocouples. The pigs were killed at 1 day (four), 7 days (two) and 15 days (two) after treatment, and all ureters examined histologically.

RESULTS

There was no statistically significant increase in RS and catheter temperature throughout the treatment in any of the treated pigs (P > 0.05). All histological lesions reported were due to radiation treatment. There were no differences in histology between the ureters containing RSs and controls.

CONCLUSION

RS usage is unrelated to any increase in stent temperature during abdominal radiotherapy and does not cause any further deterioration in the histology of the ipsilateral ureter, additional to that caused by the initial treatment.