Interaction between CIEDs and modern radiotherapy techniques: Flattening filter free-VMAT, dose-rate effects, scatter radiation, and neutron-generating energies

Effect of simultaneous integrated boost concepts on photoneutron and distant out-of-field doses in VMAT for prostate cancer

BACKGROUND

A simultaneous integrated boost (SIB) may result in increased out-of-field (DOOF) and photoneutron (HPN) doses in volumetric modulated arc therapy (VMAT) for prostate cancer (PCA). This work therefore aimed to compare DOOF and HPN in flattened (FLAT) and flattening filter-free (FFF) 6‑MV and 10-MV VMAT treatment plans with and without SIB.

METHODS

Eight groups of 30 VMAT plans for PCA with 6 MV or 10 MV, with or without FF and with uniform (2 Gy) or SIB target dose (2.5/3.0 Gy) prescriptions (CONV, SIB), were generated. All 240 plans were delivered on a slab-phantom and compared with respect to measured DOOF and HPN in 61.8 cm distance from the isocenter. The 6‑ and 10-MV flattened VMAT plans with conventional fractionation (6- and 10-MV FLAT CONV) served as standard reference groups. Doses were analyzed as a function of delivered monitor units (MU) and weighted equivalent square field size Aeq. Pearson's correlation coefficients between the presented quantities were determined.

RESULTS

The SIB plans resulted in decreased HPN over an entire prostate RT treatment course (10-MV SIB vs. CONV -38.2%). Omission of the flattening filter yielded less HPN (10-MV CONV -17.2%; 10-MV SIB -22.5%). The SIB decreased DOOF likewise by 39% for all given scenarios, while the FFF mode reduced DOOF on average by 60%. A strong Pearson correlation was found between MU and HPN (r > 0.9) as well as DOOF (0.7 < r < 0.9).

CONCLUSION

For a complete treatment, SIB reduces both photoneutron and OOF doses to almost the same extent as FFF deliveries. It is recommended to apply moderately hypofractionated 6‑MV SIB FFF-VMAT when considering photoneutron or OOF doses.

Local dose rate effects in implantable cardioverter-defibrillators with flattening filter free and flattened photon radiation

Purpose

In the beam penumbra of stereotactic body radiotherapy volumes, dose rate effects in implantable cardioverter–defibrillators (ICDs) may be the predominant cause for failures in the absence of neutron-generating photon energies. We investigate such dose rate effects in ICDs and provide evidence for safe use of lung tumor stereotactic radioablation with flattening filter free (FFF) and flattened 6 Megavolt (MV) beams in ICD-bearing patients.

Methods

Sixty-two ICDs were subjected to scatter radiation in 1.0, 2.5, and 7.0 cm distance to 100 Gy within a 5 × 5 cm² radiation field. Radiation was applied with 6 MV FFF beams (constant dose rate of 1400 cGy/min) and flattened (FLAT) 6 MV beams (430 cGy/min). Local dose rates (LDR) at the position of all ICDs were measured. All ICDs were monitored continuously.

Results

With 6 MV FFF beams, ICD errors occurred at distances of 1.0 cm (LDR 46.8 cGy/min; maximum ICD dose 3.4 Gy) and 2.5 cm (LDR 15.6 cGy/min; 1.1 Gy). With 6 MV FLAT beams, ICD errors occurred only at 1 cm distance (LDR 16.8 cGy/min; 3.9 Gy). No errors occurred at an LDR below 7 cGy/min, translating to a safe distance of 2.5 cm (1.5 Gy) in flattened and 7 cm (0.4 Gy) in 6 MV FFF beams.

Conclusion

A LDR in ICDs larger than 7 cGy/min may cause ICD malfunction. At identical LDR, differences between 6 MV FFF and 6 MV FLAT beams do not yield different rates of malfunction. The dominant reason for ICD failures could be the LDR and not the total dose to the ICD. For most stereotactic treatments, it is recommended to generate a planning risk volume around the ICD in which LDR larger than 7 cGy/min are avoided.

Safety verification of carbon-ion radiotherapy for patients with cardiac implantable electronic devices (CIEDs)

According to guidelines, carbon-ion beam therapy is considered to carry a high safety risk for patients with cardiac implantable electronic devices (CIEDs), although the actual impacts remain unclear. In this study, we investigated the safety of carbon-ion beam therapy in patients with CIEDs. Patients with CIEDs who underwent carbon-ion therapy at Gunma University Heavy Ion Medical Center between June 2010 and December 2019 were identified and investigated for abnormalities in the operation of their CIEDs, such as oversensing and resetting during irradiation, and abnormalities in operation after treatment. In addition, the risk of irradiation from carbon-ion beam therapy was evaluated by model simulations. Twenty patients (22 sites) with CIEDs were identified, 19 with pacemakers and one with an implantable cardioverter-defibrillator (ICD). Treatments were completed without any problems, except for one case in which the treatment was discontinued because of worsening of the primary disease. Monte Carlo simulation indicated that the carbon beam irradiation produced neutrons at a constant and high level in the irradiation field. Nevertheless, with the distances between the CIEDs and the irradiation fields in the analyzed cases, the quantity of neutrons at the CIEDs was lower than that within the irradiation. Although carbon-ion beam therapy can be safely administered to patients with CIEDs, it is advisable to perform the therapy with sufficient preparation and backup devices because of the risks involved.

Radiotherapy for patient with cardiac implantable electronic device, consensus from French radiation oncology society

Radiotherapy in patients with cardiac implantable electronic device such as pacemakers or defibrillators, is a clinical situation that is becoming increasingly common. There is a risk of interaction between the magnetic field induced by accelerators and the cardiac implantable electronic device, but also a risk of device dysfunction due to direct and/or indirect irradiation if the cardiac implantable electronic device is in the field of treatment. The risk can be dose-dependent, but it is most often independent of the total dose and occurs randomly in case of neutron production (stochastic effect). The presence of this type of device is therefore described as a contraindication for radiotherapy by the French national agency for the safety of medicines and health products (Agence nationale de sécurité du médicament et des produits de santé, ANSM). Nevertheless, since radiotherapy is often possible, it is advisable to respect the recommendations of good practice, in particular the eligibility criteria, the monitoring modalities before, during and after irradiation according to the type of treatment, the dose and the characteristics of the cardiac implantable electronic device. It is sometimes necessary to discuss repositioning the device and/or modifying the treatment plan to minimize the risk of cardiac implantable electronic device dysfunction. We present the update of the recommendations of the French society of oncological radiotherapy on in patients with cardiac implantable electronic device.

Study of feasible and safe condition for total body irradiation using cardiac implantable electronic devices

Cardiac implantable electronic devices (CIEDs) were believed to have a tolerance dose and that direct irradiation has to be avoided. Thus, no clinical guidelines have mentioned the feasibility of total body irradiation (TBI) with a CIED directly. The purpose of this work was to study a feasible and safe condition for TBI using a CIED. Eighteen CIEDs were directly irradiated by a 6-MV X-ray beam, where a non-neutron producible beam was employed for the removal of any neutron contribution to CIED malfunction. Irradiation up to 10 Gy in accumulated dose was conducted with a 100-cGy/min dose rate, followed by up to 20 Gy at 200 cGy/min. An irradiation test of whether inappropriate ventricular shock therapy was triggered or not was also performed by using a 6-MV beam of 5, 10, 20 and 40 cGy/min to two CIEDs. No malfunction was observed during irradiation up to 20 Gy at 100 and 200 cGy/min without activation of shock therapy. These results were compared with typical TBI, suggesting that a CIED in TBI will not encounter malfunction because the prescribed dose and the dose rate required for TBI are much safer than those used in this experiment. Several inappropriate shock therapies were, however, observed even at 10 cGy/min if activated. The present result suggested that TBI was feasible and safe if a non-neutron producible beam was employed at low dose-rate without activation of shock therapy, where it was not inconsistent with clinical and non-clinical data in the literature. The feasibility of TBI while using a CIED was discussed for the first time.

Photoneutron-induced damage reduction for cardiac implantable electronic devices using neutron-shielding sheets in high-energy X-ray radiotherapy: A phantom study

PURPOSE

To evaluate damage reduction in cardiac implantable electronic devices (CIEDs) caused by photoneutrons in high-energy X-ray radiotherapy using a neutron-shielding sheet (NSS).

METHODS

The NSS consists of a bolus with a thickness of 1 or 2 cm (Bls1 or Bls2) as a moderator and several absorbers (20%, 50%, or 80% B₄C silicone sheet [B₄C20, B₄C50, or B₄C80] or a 40% LiF silicone sheet [LiF40]). First, a linear accelerator (LINAC) with a water-equivalent phantom was modeled in the simulation and measured experimentally. Several NSSs were placed on the phantom, a Eu:LiCaAlF₆ scintillator was placed between the phantom and the NSS, and X-rays were irradiated. The relative counts (Cr = counts when placing the NSS or Bls2) were compared between the experiment and simulation. Second, CIED damage was evaluated in the simulation. The relative damage (Dr = damage when placing or not placing the NSS) was compared among all the NSSs. In addition, the γ-ray and leaking X-ray dose from B₄C was measured using a dosimetric film. After determining the optimal NSS combination, Dr value analysis was performed by changing the length of one side and the thickness.

RESULTS

The Cr values of the simulation and experiment agreed within a 30% percentage difference, except for Bare or LiF40-only. The Dr value was reduced by 43% when Bls2 + B₄C80 was applied. The photon dose was less than 5 cGy/1500 MU. The Dr values were smaller for the smaller lengths of one side of B₄C80 and decreased as the M-layer thickness increased.

CONCLUSIONS

The CIED damage induced by photoneutrons generated by a LINAC was effectively reduced by applying the optimal NSS.

Implantable cardiac pacemaker failure by cumulative dose effects of flattening filter free beams

Cumulative dose effects, which are one of the main causes of errors that occur when an implantable cardiac pacemaker (ICP) is irradiated with ionizing radiation, induce permanent failure in ICPs. Although flattening filter free (FFF) beams, which are often used in stereotactic radiotherapy, are known to have different characteristics from conventional (with flattening filter [WFF]) beams, the cumulative dose effects on ICPs with FFF beams have been under-investigated. This study investigates ICP failure induced by cumulative dose effects of FFF beams. When the ICP placed in the center of the irradiation field was irradiated with 10 MV-FFF at 24 Gy/min, the cumulative dose at which failure occurred was evaluated on the basis of the failure criteria associated with high cumulative dose as described in the American Association of Physicists in Medicine Task Group 203. The ICP failures such as a mild battery depletion at a cumulative dose of 10 Gy, pacing-output voltage change >25% at a cumulative dose of 122 Gy, and the loss of telemetry capability at cumulative dose 134 Gy were induced by cumulative dose effects. The cumulative doses by which the cumulative dose effects of FFF beams induced ICP failure were not very different from those reported in previous studies with WFF beams. Therefore, radiotherapy with FFF beams (and WFF beams) for patients with ICP requires appropriate management for minimizing the cumulative dose effects.

Impact of different radiation techniques and doses on cardiac implantable electronic devices

BACKGROUND AND OBJECTIVE

Purpose of this investigation was to get deeper insight into the impact of different radiation techniques and doses on cardiac implantable electric devices (CIEDs). We aimed to mimic a worst-case scenario with very high doses and external radiation being applied directly on the devices.

METHODS

Radiation was applied on 21 CIEDs as photon or electron therapy with maximum dose of 150Gy in fractions of 2 -20Gy. CIEDS were put directly into the beam. Brachytherapy was applied with doses of 6Gy to a maximum of 42Gy. Check-ups took place after every fraction and one week after radiation. We calculated the estimated potential risk for the health and survival of patients as well as the risk for CIEDs' loss of function.

RESULTS

28 life- or health-threatening errors occurred during photon therapy, 3/7 devices showed complete loss of function. During electron therapy, 31 potentially patient-threatening errors and 2 losses of function were detected. During brachytherapy, none of the devices showed loss of function but 8 patient-threatening errors occurred. Inadequate shock releases were mostly seen after photon and brachytherapy, random noises occurred more often during electron therapy. The earliest potentially serious error occurred during after 2Gy photon radiation and 6Gy brachytherapy. Losses of function occurred earliest at 80Gy.

CONCLUSION

The results underline the warning for precaution concerning CIED patients derived from recommendations in the literature. Our study offers new information especially about the impact of electron radiation and brachytherapy on CIEDs. Risk for the devices to for loss of telemetry or battery capacity might be negligible with normafractionated therapy.

Safety of lung stereotactic ablative radiotherapy for the functioning of cardiac implantable electronic devices

BACKGROUND AND PURPOSE

The prevalence of patients with a cardiac implantable device (CIED) developing cancer and requiring a course of radiotherapy (RT) is increasing remarkably. Previously published reports agree that standard and conventionally fractionated RT is usually safe for CIEDs, but no "in-vivo" reports are available on the potential effects of thoracic stereotactic ablative radiotherapy (SABR) regimens to CIEDs functioning. The purpose of our study is therefore to evaluate the effects of SABR on CIEDs (pacemakers [PM] or implantable cardiac defibrillators [ICD]) in a cohort of patients affected by primary or metastatic lung lesions.

MATERIALS AND METHODS

We retrospectively collected all CIED-bearing patients undergoing SABR between 2007 and 2019 at our Institution. All CIEDs were interrogated before and after the SABR course to check for any malfunction. Prescription dose, beam energy and maximum dose (Dmax) to CIEDs were retrieved for each patient. Electrical records of the CIEDs were reviewed by the medical records.

RESULTS

Thirty-four consecutive patients (24 with a PM and 10 with an ICD), who underwent 38 separate SABR courses, were included in the study. Eight patients (24%) were PM-dependent. Prescription dose of SABR ranged 26-60 Gy in 1-8 fractions, with a photon energy ranging 6-to-10 MV (76.3% and 23.7%, respectively) and a median Dmax to CIEDs of 0.17 Gy (range 0.04-1.97 Gy). Electrical parameters were stable in post-treatment device programming visits and no transient or persistent alteration of the CIED function was recorded in any patient. No inappropriate interventions were recorded in the 10 ICD-bearing patients during the treatment fractions.

CONCLUSIONS

Thoracic SABR proved to be safe for CIEDs when the dose is kept <2 Gy and the beam energy is ≤10 MV, irrespective of the pacing-dependency and of the CIED type.