Risk of Cardiac Implantable Electronic Device Malfunctioning During Pencil Beam Proton Scanning in an In Vitro Setting.

PURPOSE: Cardiac implantable electronic devices (CIED) are sensitive to scattered secondary neutrons from proton beam irradiation. This experimental in vitro study investigated risk of CIED errors during pencil beam proton therapy. METHODS AND MATERIALS: We used 62 explanted CIEDs from 4 manufacturers; 49 CIEDs were subjected to a simulated clinical protocol with daily 2 Gy relative biological effectiveness fractions prescribed to the phantom. Devices were located at 3 different lateral distances from the spread-out Bragg peak to investigate the risk of permanent or temporary device errors. Additionally, 13 devices with leads connected were monitored live during consecutive irradiations to investigate the risk of noise, over- or undersense, pace inhibition, and inappropriate shock therapy. RESULTS: We detected 61 reset errors in 1728 fractions, and all except 1 CIED were reprogrammed to normal function. All, except 1 reset, occurred in devices from the same manufacturer. These were successfully reprogrammed to normal function. The 1 remaining CIED was locked in permanent safety mode. Secondary neutron dose, as estimated by Monte Carlo simulations, was found to significantly increase the odds of CIED resets by 55% per mSv. Clinically significant battery depletion was observed in 5 devices. We observed no noise, over- or undersense, pace inhibition, or inappropriate shock therapy during 362 fractions of live monitoring. CONCLUSIONS: Reprogrammable CIED reset was the most commonly observed malfunction during proton therapy, and reset risk depended on secondary neutron exposure. The benefits of proton therapy are expected to outweigh the risk of CIED malfunctioning for most patients.

Treatment planning for proton therapy: what is needed in the next 10 years?

Treatment planning is the process where the prescription of the radiation oncologist is translated into a deliverable treatment. With the complexity of contemporary radiotherapy, treatment planning cannot be performed without a computerized treatment planning system. Proton therapy (PT) enables highly conformal treatment plans with a minimum of dose to tissues outside the target volume, but to obtain the most optimal plan for the treatment, there are a multitude of parameters that need to be addressed. In this review areas of ongoing improvements and research in the field of PT treatment planning are identified and discussed. The main focus is on issues of immediate clinical and practical relevance to the PT community highlighting the needs for the near future but also in a longer perspective. We anticipate that the manual tasks performed by treatment planners in the future will involve a high degree of computational thinking, as many issues can be solved much better by e.g. scripting. More accurate and faster dose calculation algorithms are needed, automation for contouring and planning is required and practical tools to handle the variable biological efficiency in PT is urgently demanded just to mention a few of the expected improvements over the coming 10 years.