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Lung Cancer Positioning Accuracy Evaluated by CBCT
I. J. Radiation Oncology d Biology d Physics
S574
2875
Volume 75, Number 3, Supplement, 2009
Lung Cancer Positioning Accuracy Evaluated by CBCT
F. Xu, J. Wang, S. Bai, Y. Lu, R. Zhong Department of Radiation Oncology West China Hospital, Sichuan University, Chengdu Sichuan, China, China Purpose/Objective(s): To evaluate the positioning accuracy of four different immobilizations using cone-beam CT (CBCT) guidance for radiotherapy of non-small cell lung cancer (NSCLC). Materials/Methods: Sixty-seven patients with NSCLC were treated with radiotherapy, 30 were immobilized with thermoplastic frame and normal breathing (TF), 16 with thermoplastic frame and active breathing control (TF-ABC), 7 with stereotactic body frame and normal breathing (SBF), 14 with stereotactic body frame and ABC (SBF-ABC). CBCT was scanned at initial setup and after correction, registered to planning CT, the errors of isocenter position on the left-to-right (LR), superior-inferior (SI) and anterior-posterior (AP) directions were analyzed. Results: Before correction, the mean errors were \1mm for normal breathing (NB), there is no significant difference between TF and SBF (p.0.05). The pre-correction mean errors ranged -0.5 to -2.0 mm for ABC. The initial error of TF-ABC in the LR direction was significantly larger than that of TF (p\0.05). The initial error of SBF-ABC in the AP direction was significantly larger than that of SBF (p\0.05). After correction, the errors were reduced in all directions for the four immobilizations; the PTV margin was reduced for a magnitude of 9 -10 mm in NB and 5 -10 mm in ABC. Using ABC reduced ITV with a magnitude of 4.1 mm. Conclusions: CBCT online correction improved the positioning accuracy of NSCLC patients. The positioning accuracy of stereotactic body frame and thermoplastic frame were similar. ABC increased positioning error but reduced internal margin. Author Disclosure: F. Xu, None; J. Wang, None; S. Bai, None; Y. Lu, None; R. Zhong, None.
2876
Novel Internal Markers for 4DCT
J. E. McGary1 E. B. Butler2 1
Baylor College of Medicine, Houston, TX, 2Methodist Hospital, Houston, TX
Purpose/Objective(s): Real-time internal markers are needed for 4DCT to acquire real-time tumor positioning for gated therapy. Currently, there is no real-time localization system due to CT environmental noise factors and geometric constraints. We have developed a scaled-up prototype transponder system that is capable of producing a detectable signal within a CT system for real-time tumor positioning to help solve this problem. This transponder is designed to work with our existing SQUID (superconducting quantum interference) detection system designed for 4DCT. Materials/Methods: The energizer component of the system is composed of an antenna, signal source (Tektronix 2024B), and resonant circuit capable of amplitude modulation at frequencies greater than 30 MHz. The transponder consists of a tank circuit in parallel with a low forward voltage diode where the circuit is scaled for an implant scale of less than 1 mm diameter by 7 mm length, where a novel thin film inductor (5 mH) is to be used for inductive coupling to the antenna magnetic field. Systems with operating frequencies of 20, 150, 300, and 550 kHz were designed and tested to determine the optimal configuration. Search coils and current probes were used to measure the transponder signal. Measurements were made at source to transponder distances from 1-30 cm along the center axis as well as off-axis points. Circuit models of the system were made using PSPICE and MATLAB/SIMULINK in combination with analytic solutions using Mathematica. Results: The transponder creates a carrier frequency component and two side bands at twice the carrier frequency at 2/3 the amplitude of the carrier amplitude as predicted in the models. Experimental results compare well with the model calculations for frequencies less than 1 MHz; at higher frequencies, the agreement is within 25% due to power losses in the solenoid component. At distances greater than 20 cm, the side bands are not present due to low forward voltages resulting from coupling losses from the antenna. At higher frequencies, power losses reduce the signal-source distance, while at lower frequencies, 300-500 kHz, the distance is limited by maximum antenna field strengths defined by FCC. Conclusions: The advantage of this system is the ability to select an arbitrary frequency and remove the signal from the noise or reduce the frequency to within the bandwidth of the detection system, which is important for high gain detection systems. Furthermore, the amplitude modulation increases the signal to noise by a factor greater than 10, which improves localization accuracy. The disadvantage of this design is the forward voltage needed to operate the diode, which decreases the source-transponder distance. This will require an antenna design composing or multiple current loops with active selection due to couch motion. Author Disclosure: J.E. McGary, None; E.B. Butler, None.
2877
On-board SPECT Imaging: Improved Target Localization via Spatial Resolution Compensation
J. R. Roper, J. E. Bowsher, F. Yin Duke University, Durham, NC Purpose/Objective(s): Single photon emission computed tomography (SPECT) is being investigated for imaging on-board radiation therapy machines to localize biological targets. SPECT spatial resolution degrades as distance increases between the detector and radiotracer, an effect of collimation which results in spatially-varying, asymmetric blurring. Here we assess localization accuracy in noisy images that were reconstructed with and without spatial resolution compensation. Materials/Methods: Uptake of 99mTc-Sestamibi was simulated in a female NCAT phantom. Twenty, 1.4-cm-diameter biological targets were simulated in the torso. Target activity ratios were 3:1 and 6:1 relative to a background concentration of 0.25 mCi/ml.
S574
2875
Volume 75, Number 3, Supplement, 2009
Lung Cancer Positioning Accuracy Evaluated by CBCT
F. Xu, J. Wang, S. Bai, Y. Lu, R. Zhong Department of Radiation Oncology West China Hospital, Sichuan University, Chengdu Sichuan, China, China Purpose/Objective(s): To evaluate the positioning accuracy of four different immobilizations using cone-beam CT (CBCT) guidance for radiotherapy of non-small cell lung cancer (NSCLC). Materials/Methods: Sixty-seven patients with NSCLC were treated with radiotherapy, 30 were immobilized with thermoplastic frame and normal breathing (TF), 16 with thermoplastic frame and active breathing control (TF-ABC), 7 with stereotactic body frame and normal breathing (SBF), 14 with stereotactic body frame and ABC (SBF-ABC). CBCT was scanned at initial setup and after correction, registered to planning CT, the errors of isocenter position on the left-to-right (LR), superior-inferior (SI) and anterior-posterior (AP) directions were analyzed. Results: Before correction, the mean errors were \1mm for normal breathing (NB), there is no significant difference between TF and SBF (p.0.05). The pre-correction mean errors ranged -0.5 to -2.0 mm for ABC. The initial error of TF-ABC in the LR direction was significantly larger than that of TF (p\0.05). The initial error of SBF-ABC in the AP direction was significantly larger than that of SBF (p\0.05). After correction, the errors were reduced in all directions for the four immobilizations; the PTV margin was reduced for a magnitude of 9 -10 mm in NB and 5 -10 mm in ABC. Using ABC reduced ITV with a magnitude of 4.1 mm. Conclusions: CBCT online correction improved the positioning accuracy of NSCLC patients. The positioning accuracy of stereotactic body frame and thermoplastic frame were similar. ABC increased positioning error but reduced internal margin. Author Disclosure: F. Xu, None; J. Wang, None; S. Bai, None; Y. Lu, None; R. Zhong, None.
2876
Novel Internal Markers for 4DCT
J. E. McGary1 E. B. Butler2 1
Baylor College of Medicine, Houston, TX, 2Methodist Hospital, Houston, TX
Purpose/Objective(s): Real-time internal markers are needed for 4DCT to acquire real-time tumor positioning for gated therapy. Currently, there is no real-time localization system due to CT environmental noise factors and geometric constraints. We have developed a scaled-up prototype transponder system that is capable of producing a detectable signal within a CT system for real-time tumor positioning to help solve this problem. This transponder is designed to work with our existing SQUID (superconducting quantum interference) detection system designed for 4DCT. Materials/Methods: The energizer component of the system is composed of an antenna, signal source (Tektronix 2024B), and resonant circuit capable of amplitude modulation at frequencies greater than 30 MHz. The transponder consists of a tank circuit in parallel with a low forward voltage diode where the circuit is scaled for an implant scale of less than 1 mm diameter by 7 mm length, where a novel thin film inductor (5 mH) is to be used for inductive coupling to the antenna magnetic field. Systems with operating frequencies of 20, 150, 300, and 550 kHz were designed and tested to determine the optimal configuration. Search coils and current probes were used to measure the transponder signal. Measurements were made at source to transponder distances from 1-30 cm along the center axis as well as off-axis points. Circuit models of the system were made using PSPICE and MATLAB/SIMULINK in combination with analytic solutions using Mathematica. Results: The transponder creates a carrier frequency component and two side bands at twice the carrier frequency at 2/3 the amplitude of the carrier amplitude as predicted in the models. Experimental results compare well with the model calculations for frequencies less than 1 MHz; at higher frequencies, the agreement is within 25% due to power losses in the solenoid component. At distances greater than 20 cm, the side bands are not present due to low forward voltages resulting from coupling losses from the antenna. At higher frequencies, power losses reduce the signal-source distance, while at lower frequencies, 300-500 kHz, the distance is limited by maximum antenna field strengths defined by FCC. Conclusions: The advantage of this system is the ability to select an arbitrary frequency and remove the signal from the noise or reduce the frequency to within the bandwidth of the detection system, which is important for high gain detection systems. Furthermore, the amplitude modulation increases the signal to noise by a factor greater than 10, which improves localization accuracy. The disadvantage of this design is the forward voltage needed to operate the diode, which decreases the source-transponder distance. This will require an antenna design composing or multiple current loops with active selection due to couch motion. Author Disclosure: J.E. McGary, None; E.B. Butler, None.
2877
On-board SPECT Imaging: Improved Target Localization via Spatial Resolution Compensation
J. R. Roper, J. E. Bowsher, F. Yin Duke University, Durham, NC Purpose/Objective(s): Single photon emission computed tomography (SPECT) is being investigated for imaging on-board radiation therapy machines to localize biological targets. SPECT spatial resolution degrades as distance increases between the detector and radiotracer, an effect of collimation which results in spatially-varying, asymmetric blurring. Here we assess localization accuracy in noisy images that were reconstructed with and without spatial resolution compensation. Materials/Methods: Uptake of 99mTc-Sestamibi was simulated in a female NCAT phantom. Twenty, 1.4-cm-diameter biological targets were simulated in the torso. Target activity ratios were 3:1 and 6:1 relative to a background concentration of 0.25 mCi/ml.