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Beam Arrangement as a Method to Reduce Dose to An Implanted Cardiac Device for Cranial Stereotactic Radiotherapy Patients

A Licon*, K Rasmussen, N Kirby, S Stathakis, N Papanikolaou, P Myers, R Crownover, D Saenz, Mays Cancer Center - MD Anderson Cancer Center, San Antonio, TX

Presentations

(Sunday, 7/12/2020)   [Eastern Time (GMT-4)]

Room: AAPM ePoster Library

Purpose: determine the dose to an ICD (implanted cardiac device) during stereotactic radiotherapy and if beam arrangement is a viable method to reduce the dose.


Methods: treatment plan was created for a stereotactic radiotherapy patient with an ICD for a meningioma in the posterior parasagittal region of the brain. The beams were strategically placed to avoid the left side of the patient’s body in order to spare dose to the ICD. The arcs were set with the following table angles, 180°, 250°, 220°. The manufacturer recommended keeping the total dose to the device below 500 cGy and to limit the dose rate to <1 cGy/min to avoid oversensing. The plan was then delivered to an anthropomorphic phantom (Rando) with optically stimulated luminescent dosimeters (OSLD) in the place of the ICD. To determine the degree of dose reduction with beam arrangement, OSLDs were also placed on the opposite side to determine the amount of sparing. Four OSLDs were placed on each side and the time taken to deliver the treatment was recorded. The positioning of the OSLDs relative to the ICD was verified with AP and lateral radiographs.


Results: OSLDs on the side of the ICD showed a maximum point dose of 0.65 cGy or 3.25 cGy for all five fractions. The treatment time was 98 seconds (total of 490 seconds) of exposure and therefore the instantaneous dose rate was <0.4 cGy/min. The contralateral OSLDs however showed a maximum point dose of 3.62 cGy or 18.1 cGy for all five fractions resulting in an instantaneous dose of 2.2 cGy/min.


Conclusion: beam arrangement led to an allowable dose rate for the ICD. The contralateral however showed a dose rate higher than the manufacturer recommended. Therefore, beam arrangement can be used to spare an ICD in terms of dose and dose rate.

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