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Dose-volume Comparison of Proton Radiotherapy and Stereotactic Body Radiotherapy for Non-small Cell Lung Cancer
Proceedings of the 52nd Annual ASTRO Meeting position of the inhomogeneity. Margins for range uncertainties due the CT number variations were not considered in this study so as to focus only on the range changes caused by the displacement of inhomogeneity. An expanded or contracted contour of the high density or low density object was created by adding or subtracting 3 mm margin, respectively to the actual contours of the inhomogeneities (blurred image set). A single field optimization plan was created both in the original and blurred image sets for SSPBT. The robustness of these three plans for distal target coverage for up to 3 mm changes in the inhomogeneity position were studied. Results: The treatment plans for the SSPBT using the blurred image set showed similar robustness as the PSPBT plan with compensator smearing for dose coverage of the distal edge of the target. On the other hand, the distal target coverage in the treatment plan for the SSPBT, that used the image set without inhomogeneity blurring, was reduced when the location of the beam isocenter was changed, making the plan less robust compared to the PSPBT plan. Conclusions: The use of an expanded or contracted margin around high or low density objects in the images, respectively for SSPBT planning appears to be equivalent to the compensator smearing effect in PSPBT planning. Results of application of the proposed approach for designing treatment plans for SSPBT for prostate and targets in brain will be presented. Author Disclosure: N. Sahoo, Varian Medical Systems, C. Other Research Support; X. Song, None; X.R. Zhu, Varian Medical Systems, C. Other Research Support; M.T. Gillin, Varian Medical Systems, C. Other Research Support.
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Dose-volume Comparison of Proton Radiotherapy and Stereotactic Body Radiotherapy for Non-small Cell Lung Cancer
N. Kadoya1, T. Kato1, M. Suzuki1, M. Kagiya1, T. Saito1, T. Nakamura1, T. Tomoda1, A. Takada1, N. Fuwa1, Y. Obata2 1
Southern Tohoku Proton Therapy Center, Koriyama, Japan, 2Nagoya University Graduate School of Medicine, Nagoya, Japan
Purpose/Objective(s): We analyzed the dosimetric difference proton therapy (PT) and stereotactic body radiotherapy (SBRT) in treating primary peripheral early-stage non-small-cell lung cancer (NSCLC) using the dose-volume histograms (DVHs) to explain clearly the differences in the dose distributions between PT and SBRT. Materials/Methods: Twenty-one patients with NSCLC (15 with Stage IA and 6 with Stage IB) were studied. They were treated by hypofractionated PT in the Southern Tohoku Proton Therapy Center (STPTC). All tumors were located in the peripheral lung. A total dose was 66 GyE (6.6 GyE/fraction). The PT system in STPTC (Mitsubishi Electric, Kobe, Japan) used a synchrotron that could accelerate protons up to 235 MeV. This system employed a passive scattering method. A treatment planning system (Xio-M; CMS Japan, Tokyo Japan and Mitsubishi Electric) was used to calculate dose distributions for both PT and SBRT. For treatment planning, the beam incidence for proton beam technique was restricted to 2-3 directions for PT, and 7 or 8 noncoplanar beams were manually selected for SBRT to achieve optimal planning target volume (PTV) coverage and minimal organ at risk dose. Results: No significant difference in Dmin, Dmax, HI or CI of the PTV between PT and SBRT were seen. Regarding lung tissues, mean dose, V5, V10, V13, V15 and V20 were 4.6 Gy, 13,2%, 11.4%, 10.6%, 10.1% and 9.1%, respectively, for PT (p \ 0.05), whereas those were 7.8 Gy, 32.0%, 21.8%, 17.4%, 15.3% and 11.4%, respectively, for SBRT(p \ 0.05) with a prescribed dose of 66 Gy. We found that differences between PT and SBRT were small with the received dose of the total lung and almost no difference was seen in V20. Pearson product moment correlation coefficients between PTV and the dose-volume parameters of V5, V10 V15 and V20 were 0.45, 0.52, 0.58 and 0.63, respectively, for PT, compared to 0.52, 0.45, 0.71 and 0.74, respectively, for SBRT. These correlations were significant (p \ 0.05). Conclusions: We analyzed dose distributions in PT and SBRT using the DVHs. Our results showed no significant difference in dosimetric parameters of the PTV between PT and SBRT. However, while small differences in parameters of the lung receiving a dose .10 Gy were visible, large differences were seen in that receiving #10 Gy. Correlations between dose volume parameters of the lung and the PTV were observed. In addition, PT appears more advantageous than SBRT when treating tumors with a relatively large PTV or several tumors. Author Disclosure: N. Kadoya, None; T. Kato, None; M. Suzuki, None; M. Kagiya, None; T. Saito, None; T. Nakamura, None; T. Tomoda, None; A. Takada, None; N. Fuwa, None; Y. Obata, None.
289
A Comparison of Neutron Activities Produced in Brass and Tungsten MLC: A Monte Carlo Study
V. P. Moskvin1, C. Cheng2, D. Nichihporov3, I. Das1 1
Indiana University, Indianapolis, IN, 2Indiana University, Bloomington, IN, 3Indiana University, IUCF, Bloomington, IN
Purpose/Objective(s): A major advantage of a multi-leaf collimator (MLC) is its readiness to provide field shaping, eliminating the need to fabricate aperture, which is time consuming and expensive. However, a potential drawback compared to a patient specific aperture is the generation of neutrons in the MLC and the buildup of activities in an extended period of time. Two most commonly material used for MLC is brass and tungsten (W). In this study, we used Monte Carlo simulation (FLUKA) to investigate the buildup and decay of neutron activities in brass (C3600) and W, respectively to investigate their potential neutron hazard when used in the construction of an MLC. Materials/Methods: In the Monte Carlo simulation, a proton beam of 200 MeV covering an area of 10 cm diameter circle is assumed. An initial simulation is performed with the proton beam consisting of 2x107 particles/sec incident, respectively on a brass and a W metal block of dimension 6.5 cm thick and 15 cm diameter circle for one min. The decay of the block is followed for several time intervals: 1 hour, 1 day and 40 days. The second simulation uses a detailed irradiation schema to simulate a treatment day, in which every 2 min. irradiation is followed by 15 min. break continuously for 8.25 hours. The proton beam at a rate of 1.5x109 protons/sec is incident on the same two metal blocks, resulting in 180 c Gy absorbed dose at the Bragg peak in 2 min. The neutrons are sampled at the entire surface of the block. The simulation is carried out for several time intervals (1 day, 1 week and 40 days) to compare the activity buildup and decay between brass and W. In the 40-day simulation, the metal block is allowed to cool off on the weekends.
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288
Dose-volume Comparison of Proton Radiotherapy and Stereotactic Body Radiotherapy for Non-small Cell Lung Cancer
N. Kadoya1, T. Kato1, M. Suzuki1, M. Kagiya1, T. Saito1, T. Nakamura1, T. Tomoda1, A. Takada1, N. Fuwa1, Y. Obata2 1
Southern Tohoku Proton Therapy Center, Koriyama, Japan, 2Nagoya University Graduate School of Medicine, Nagoya, Japan
Purpose/Objective(s): We analyzed the dosimetric difference proton therapy (PT) and stereotactic body radiotherapy (SBRT) in treating primary peripheral early-stage non-small-cell lung cancer (NSCLC) using the dose-volume histograms (DVHs) to explain clearly the differences in the dose distributions between PT and SBRT. Materials/Methods: Twenty-one patients with NSCLC (15 with Stage IA and 6 with Stage IB) were studied. They were treated by hypofractionated PT in the Southern Tohoku Proton Therapy Center (STPTC). All tumors were located in the peripheral lung. A total dose was 66 GyE (6.6 GyE/fraction). The PT system in STPTC (Mitsubishi Electric, Kobe, Japan) used a synchrotron that could accelerate protons up to 235 MeV. This system employed a passive scattering method. A treatment planning system (Xio-M; CMS Japan, Tokyo Japan and Mitsubishi Electric) was used to calculate dose distributions for both PT and SBRT. For treatment planning, the beam incidence for proton beam technique was restricted to 2-3 directions for PT, and 7 or 8 noncoplanar beams were manually selected for SBRT to achieve optimal planning target volume (PTV) coverage and minimal organ at risk dose. Results: No significant difference in Dmin, Dmax, HI or CI of the PTV between PT and SBRT were seen. Regarding lung tissues, mean dose, V5, V10, V13, V15 and V20 were 4.6 Gy, 13,2%, 11.4%, 10.6%, 10.1% and 9.1%, respectively, for PT (p \ 0.05), whereas those were 7.8 Gy, 32.0%, 21.8%, 17.4%, 15.3% and 11.4%, respectively, for SBRT(p \ 0.05) with a prescribed dose of 66 Gy. We found that differences between PT and SBRT were small with the received dose of the total lung and almost no difference was seen in V20. Pearson product moment correlation coefficients between PTV and the dose-volume parameters of V5, V10 V15 and V20 were 0.45, 0.52, 0.58 and 0.63, respectively, for PT, compared to 0.52, 0.45, 0.71 and 0.74, respectively, for SBRT. These correlations were significant (p \ 0.05). Conclusions: We analyzed dose distributions in PT and SBRT using the DVHs. Our results showed no significant difference in dosimetric parameters of the PTV between PT and SBRT. However, while small differences in parameters of the lung receiving a dose .10 Gy were visible, large differences were seen in that receiving #10 Gy. Correlations between dose volume parameters of the lung and the PTV were observed. In addition, PT appears more advantageous than SBRT when treating tumors with a relatively large PTV or several tumors. Author Disclosure: N. Kadoya, None; T. Kato, None; M. Suzuki, None; M. Kagiya, None; T. Saito, None; T. Nakamura, None; T. Tomoda, None; A. Takada, None; N. Fuwa, None; Y. Obata, None.
289
A Comparison of Neutron Activities Produced in Brass and Tungsten MLC: A Monte Carlo Study
V. P. Moskvin1, C. Cheng2, D. Nichihporov3, I. Das1 1
Indiana University, Indianapolis, IN, 2Indiana University, Bloomington, IN, 3Indiana University, IUCF, Bloomington, IN
Purpose/Objective(s): A major advantage of a multi-leaf collimator (MLC) is its readiness to provide field shaping, eliminating the need to fabricate aperture, which is time consuming and expensive. However, a potential drawback compared to a patient specific aperture is the generation of neutrons in the MLC and the buildup of activities in an extended period of time. Two most commonly material used for MLC is brass and tungsten (W). In this study, we used Monte Carlo simulation (FLUKA) to investigate the buildup and decay of neutron activities in brass (C3600) and W, respectively to investigate their potential neutron hazard when used in the construction of an MLC. Materials/Methods: In the Monte Carlo simulation, a proton beam of 200 MeV covering an area of 10 cm diameter circle is assumed. An initial simulation is performed with the proton beam consisting of 2x107 particles/sec incident, respectively on a brass and a W metal block of dimension 6.5 cm thick and 15 cm diameter circle for one min. The decay of the block is followed for several time intervals: 1 hour, 1 day and 40 days. The second simulation uses a detailed irradiation schema to simulate a treatment day, in which every 2 min. irradiation is followed by 15 min. break continuously for 8.25 hours. The proton beam at a rate of 1.5x109 protons/sec is incident on the same two metal blocks, resulting in 180 c Gy absorbed dose at the Bragg peak in 2 min. The neutrons are sampled at the entire surface of the block. The simulation is carried out for several time intervals (1 day, 1 week and 40 days) to compare the activity buildup and decay between brass and W. In the 40-day simulation, the metal block is allowed to cool off on the weekends.
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