In-vitro effects of relevant clinical radiotherapy regimes on Cardiac Implanted Electrical Devices
Steve Manley,
United Kingdom
MO-0310
Abstract
In-vitro effects of relevant clinical radiotherapy regimes on Cardiac Implanted Electrical Devices
Authors: Steve Manley1,2, Amy Fenwick3, Megan Fraser3, Mark Lowrey3, Nick West2
1The James Cook University Hospital, Radiotherapy, Middlesbrough, United Kingdom; 2The Freeman Hospital, Northern Centre for Cancer Care, Newcastle-upon-Tyne, United Kingdom; 3The Freeman Hospital, Cardiac Rhythm Management, Newcastle-upon-Tyne, United Kingdom
Show Affiliations
Hide Affiliations
Purpose or Objective
Quantify the effects of clinically relevant (6X and 10FFF) radiotherapy to Cardiac Implanted Electrical Devices (CIEDs).
International guidelines for radiotherapy of patients with a CIED, have been developed over the past four decades, however, the current data set contains results from situations which may be less relevant with modern devices. Newer technology has improved electronic filtering which prevents both inappropriate pacing inhibition and increased current drain, preserving battery life. There is a lack of data for effects on modern devices from modern techniques such as hypofractionation and FFF beams. Data were sought on a clinically relevant change of >25% from the set pacing voltage, or inappropriate defibrillation shock. Current international guidelines advise limiting the energy to <10MV and the total treatment dose to no more than 5Gy to any CIED
Material and Methods
A total of 160 explanted CIEDs with remaining battery >1 - 15 years (median 8.5), were set to output a fixed, clinically relevant pacing signal. The devices were exposed to either 6, or 10MV radiotherapy beams from a Varian TrueBeam LINAC at our centre. CIEDs were irradiated in both normal operating conditions having set the sensitivity to a maximal uniform voltage of >1mV; and in MRI-conditional / Asynchronous mode, with pace sensing turned off. Devices were split by manufacturer, randomised, then exposed to either 6X or 10FFF regimes with pacing data recorded via PicoScope.
Results
| Beam | Regime
| Dose Rate | CIED Mode | Pacing voltage change >25%
| Pacing voltage reduction >10% <25%
| Other recorded errors
| No clinically relevant failures recorded
|
6X
| 48Gy/8#
| 6Gy/min
| Normal
| Not collected
| Not collected
| 1/45 (2%) Pacing inhibition
| 44/45 (98%)
|
10FFF
| 48Gy/1#
| 24Gy/min
| Normal
| Not collected
| Not collected
| 8/49 (16%) Pacing inhibition
1/49 (2%) Inappropriate shock
2/49 (4%)* Device reset * model subsequently recalled by manufacturer on safety notice
| 38/49 (78%)
|
6X
| 48Gy/8#
| 6Gy/min
| Asynchronous
| 0/19 (0%)
| Not collected
| Not collected
| 19/19 (100%)
|
10FFF
| 48Gy/1#
| 24Gy/min
| Asynchronous
| 2/21 (10%)* *Increase in pulse voltage | Not collected
| Not collected
| 19/21 (90%)
|
10FFF
| 60Gy/5#
| 12Gy/min
| Asynchronous
| 0/13 (0%)
| 2/13 (15%)
| Not collected
| 13/13 (100%)
|
10FFF
| 60Gy/5#
| 24Gy/min
| Asynchronous
| 0/13 (0%)
| 3/13 (23%)
| Not collected
| 13/13 (100%)
|
Conclusion
6X treatments of 6Gy/#, to a cumulative dose of 48Gy, far in excess of current guideline limits, were found to not affect CIED pacing output while in asynchronous mode. Inappropriate defibrillation or device reset were also not found under normal CIED operation modes.
These results suggest current dose limits using 6X could be significantly increased using these parameters, reducing constraints on choice of treatment plan and dose distributions.
10FFF deliveries to CIEDs in asynchronous mode found a clinically insignificant reduction 10%<20% of output voltage only after a total of 24Gy was delivered. However, more data is felt required to suggest any revision of guidelines with 10FFF beams.