Anthony Kavanagh

Feasibility of the use of the Active Breathing Co ordinator™ (ABC) in patients receiving radical radiotherapy for non-small cell lung cancer (NSCLC)

INTRODUCTION One method to overcome the problem of lung tumour movement in patients treated with radiotherapy is to restrict tumour motion with an active breathing control (ABC) device. This study evaluated the feasibility of using ABC in patients receiving radical radiotherapy for non-small cell lung cancer. METHODS Eighteen patients, median (range) age of 66 (44-82) years, consented to the study. A training session was conducted to establish the patients breath hold level and breath hold time. Three planning scans were acquired using the ABC device. Reproducibility of breath hold was assessed by comparing lung volumes measured from the planning scans and the volume recorded by ABC. Patients were treated with a 3-field coplanar beam arrangement and treatment time (patient on and off the bed) and number of breath holds recorded. The tolerability of the device was assessed by weekly questionnaire. Quality assurance was performed on the two ABC devices used. RESULTS 17/18 patients completed 32 fractions of radiotherapy using ABC. All patients tolerated a maximum breath hold time >15s. The mean (SD) patient training time was 13.8 (4.8)min and no patient found the ABC very uncomfortable. Six to thirteen breath holds of 10-14 s were required per session. The mean treatment time was 15.8 min (5.8 min). The breath hold volumes were reproducible during treatment and also between the two ABC devices. CONCLUSION The use of ABC in patients receiving radical radiotherapy for NSCLC is feasible. It was not possible to predict a patients ability to hold breath. A minimum tolerated breath hold time of 15 s is recommended prior to commencing treatment.

A novel respiratory motion compensation strategy combining gated beam delivery and mean target position concept – A compromise between small safety margins and long duty cycles

PURPOSE To evaluate a novel respiratory motion compensation strategy combining gated beam delivery with the mean target position (MTP) concept for pulmonary stereotactic body radiotherapy (SBRT). MATERIALS AND METHODS Four motion compensation strategies were compared for 10 targets with motion amplitudes between 6mm and 31mm: the internal target volume concept (plan(ITV)); the MTP concept where safety margins were adapted based on 4D dose accumulation (plan(MTP)); gated beam delivery without margins for motion compensation (plan(gated)); a novel approach combining gating and the MTP concept (plan(gated&MTP)). RESULTS For 5/10 targets with an average motion amplitude of 9mm, the differences in the mean lung dose (MLD) between plan(gated) and plan(MTP) were <10%. For the other 5/10 targets with an average motion amplitude of 19mm, gating with duty cycles between 87.5% and 75% reduced the residual target motion to 12mm on average and 2mm safety margins were sufficient for dosimetric compensation of this residual motion in plan(gated&MTP). Despite significantly shorter duty cycles, plan(gated) reduced the MLD by <10% compared to plan(gated&MTP). The MLD was increased by 18% in plan(MTP) compared to that of plan(gated&MTP). CONCLUSIONS For pulmonary targets with motion amplitudes >10-15mm, the combination of gating and the MTP concept allowed small safety margins with simultaneous long duty cycles.

Dosimetric consequences of inter-fraction breathing-pattern variation on radiotherapy with personalized motion-assessed margins.

The data from eight patients who had undergone stereotactic body radiotherapy were selected due to their 4D-CT planning scans showing that their tumours had respiratory induced motion trajectories of large amplitude (greater than 9 mm in cranio-caudal direction). Radiotherapy plans with personalized motion-assessed margins were generated for these eight patients. The margins were generated by inverse 4D planning on an eight-bin phase-sorted 4D-CT scan. The planning was done on an in-house software system with a non-rigid registration stage being completed using freely available software. The resultant plans were then recalculated on a 4D-CT scan taken later during the course of treatment. Simulated image-guided patient set-up was used to align the geometric centres of the tumour region and minimize any misalignment between the two reconstructions. In general, the variation in the patient breathing patterns was found to be very small. Consequently, the degradation of the mean dose to the tumour region was found to be around a few percent (<3%) and hence was not a large effect.

Fluoroscopy as a surrogate for lung tumour motion

OBJECTIVES The aim of this article was to test a simple approach of using pixel density values from fluoroscopy images to enable gated radiotherapy. METHODS Anterior and lateral (LAT) from images were acquired from 18 patients referred for radical radiotherapy for non-small cell lung cancer for a period of 30-45 s. The amplitude of movement and the number of breathing cycles were determined in the right-left (RL) and superoinferior (SI) directions on the anterior images and the anteroposterior (AP) and SI directions on the lateral images. The breathing pattern was created by analysing the variation in a summation of pixel values within a defined area. The greatest and lowest 30% of pixel values were set as the duty cycle to represent inhale and exhale amplitude-based gating. RESULTS A median of eight breathing cycles was captured for each patient with a duration of 2.2-11.8 s per cycle. The mean (range) motion was 4.7 mm (2.4-5.8 mm), 7.2 mm (2.3-17.6 mm), 6.2 mm (1.9-13.8 mm) and 4.8 mm (2.4-11.3 mm) in the RL, SI (AP), SI (LAT) and AP directions, respectively. A total of 10/14 anterior videos and 7/11 LAT videos had correlations between motion and breathing of >0.6. Margins of 5.5 mm, 6.8 mm and 6.6 mm in the RL, SI and AP directions, respectively, were determined to gate in exhale. The benefit of gating was greater when motion was >5 mm. CONCLUSION The simple approach of using pixel density values from fluoroscopy images to distinguish inhale from exhale and enable gating was successfully applied in all patients. This technique may potentially provide an accurate surrogate for tumour position.

Injection of metallic elements into an electron-beam ion trap using a Knudsen cell

A method of injecting metallic elements into an electron-beam ion trap (EBIT) is described. The method is advantageous over the conventional coaxial and pulsed injection methods in two ways: (a) complicated switching of injection and extraction beams can be avoided when extracting beams of highly charged ions from the EBIT and (b) a beam of stable intensity can be achieved. This method may be applicable to any metallic elements or metallic compounds that have vapor pressures of ∼0.1Pa at a temperature lower than 1900°C. We have employed this method for the extraction of highly charged ions of Bi, Er, Fe, and Ho.

Injection of refractory metals into EBIT using a Knudsen cell

A new method for injection of metallic elements into an electron-beam ion trap (EBIT) is described. Injection of metallic elements into an EBIT has so far been mainly achieved by MEVVA (metal vapor vacuum arc) ion sources. However, continuous injection, as is the case of rare gases, is sometimes desirable, especially for stable extraction of highly charged ions. In the course of DR (dielectronic recombination) study, we have developed a method of such a stable injection of metallic elements. This method is applicable to any metallic elements or metallic compounds that have vapor pressures of ~0.1 Pa at a temperature lower than 1900°C. We have employed this method for the extraction of highly charged ions of Bi, Er, Fe, Ho and W.

Relativistic effects on resonant interactions between electrons and highly charged ions

We report measurements of resonant processes in electron collisions with very highly charged heavy ions made using an electron beam ion trap. By measuring the ion abundance ratio in the trap at the equilibrium condition as a function of electron energy, we have observed resonant processes such as dielectronic recombination and resonant excitation double autoionization very clearly. Remarkable relativistic effects due to the generalized Breit interaction have been clearly shown in dielectronic recombination for highly charged heavy ions.

Recent activities at the Tokyo EBIT 2006

The electron beam ion trap (EBIT) in Tokyo was constructed about 10 years after the first EBIT at Lawrence Livermore National Laboratory was built, and has been being stably operated since then. In this paper, we present recent experimental activities at the Tokyo EBIT. In particular, experiments utilizing slow, very highly charged ion beams extracted from the EBIT are reported. PACS Nos.: 39.10.+j, 32.30.Rj, 34.50.Dy, 34.80.Kw

Radiation from K-shell filling in highly charged ions: a driver for resonant combination cancer therapy?

The possibility of using x-radiation from bare and hydrogen-like highly charged ions as a driver for a proposed form of cancer therapy is discussed. This proposed form of therapy, called resonant combination therapy, benefits from a very high contrast ratio between dose to the tumour and dose to the surrounding healthy tissue as is illustrated by some simple model calculations of isodose/ion distributions. The need for further radiobiological measurements and ion source developments in order to make this form of therapy feasible are highlighted.

Resonant electron processes with open-shell highly charged ion targets

Recent activities at the Tokyo electron beam ion trap related to observations of resonant processes in the collisions of electrons with open-shell highly charged ions are reported. Extracted ion observations and high resolution x-ray spectroscopic observations have been applied to resolve the contribution from different charge states. In particular, dielectronic recombination (DR) of a H-like ion have been observed by high resolution x-ray spectroscopy for the first time. The DR satellite spectra obtained in the present experiment are compared with theoretical spectra.