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Clinical Application of Isorad and QED In Vivo Semiconductor Diodes for IMRT and Total Skin Electron Therapy: Feasibility Study
Proceedings of the 51st Annual ASTRO Meeting
3076
Clinical Application of Isorad and QED In Vivo Semiconductor Diodes for IMRT and Total Skin Electron Therapy: Feasibility Study
R. A. Kinhikar1, S. Chaudhary1, R. Upreti1, P. Kumar1, C. Tambe1, D. Dhote2, D. Deshpande1 1
Tata Memorial Hospital, Mumbai, India, 2Brijlal Biyani Science College, Amravati, India
Purpose/Objective(s): Semiconductor detectors are widely used for patient dosimetry for photon and electron beams due to high sensitivity and spatial resolution compared to the air filled ionization chamber with the same volume. The objective of this study was to validate the new in vivo semiconductor diodes Isorad (yellow) and QEDTM electron (Silver) for intensity modulated radiotherapy (IMRT) and total skin electron therapy (TSET) respectively. Materials/Methods: The Isorad photon (yellow) and QED electron (silver) diode (both from Sun Nuclear Corporation, Fl, USA) were used for 6 MV photon beam from a Clinac 6EX linear accelerator (LINAC) and 6 MeV electron energy from dual energy Clinac 2100CD LINAC (Both Varian Medical Systems, Palo Alto, USA) respectively. Isorad was first calibrated for 6 MV photon beam with 10 cm x 10 cm field size at target to axis distance (TAD) of 100 cm with solid water (SW) slabs as full scatter medium. Later, the diode was characterized for its reproducibility, monitor unit (MU) linearity (25 to 800), dependence on field size, dose rate, source to surface distance (SSD), beam incidence and axial orientation. Further, the response of the diode was also investigated for IMRT dosimetry by placing the diode in SW slabs at 5.4 cm depth. QEDTM was calibrated for TSET by irradiating it with 36 cm x 36 cm field size at 493 cm TAD at Dmax (8 mm). Diode was irradiated for 740 and 1060 gantry angle (+ 140 from gantry lateral) for a total dose of 2 Gy. Later the diode was used for a patient dosimetry to measure the dose delivered at the isocenter level (umbilicus). The diode was directly taped on the skin of the patient for the entire treatment. The thermolunescent dosimeters Lif:Mg:Ti (TLD 100 in powder form) was used subsequently along with the diode in the same setup. Results: The Isorad showed an excellent reproducibility (+ 0.5%). MU linearity was in agreement within (+ 2%). Maximum variation of 4% was observed for the measured dose with the largest field size (40 cm x 40 cm). The dose rate and SSD has no effect on the response of the diode. The diode showed an angular dependence of (+ 1.5%). The IMRT measured dose with diode was in well agreement (\ 2%) with the planned dose. The dose measured with QEDTM and TLD for TSET patient at the isocenter was in well agreement (\ 1%). The variation between measured (QEDTM) and planned dose was 8%. Conclusions: The semiconductor diodes used in this study were validated for advanced and special radiotherapy treatments like IMRT and TSET. The diodes are feasible, handy and exhibited a reasonable reproducibility, dosimetric stability and reliability. These diodes have proven to be useful quality assurance tool in the assessment of the in vivo dose in this kind of treatment. Author Disclosure: R.A. Kinhikar, None; S. Chaudhary, None; R. Upreti, None; P. Kumar, None; C. Tambe, None; D. Dhote, None; D. Deshpande, None.
3077
Dose Grid Effects in Adaptive Planning of Helical Tomotherapy for Hypofractionated Treatments
C. Yang, N. Sheth, S. Murphy, M. Weiss, S. Sim Monmouth Medical Center, Long Branch, NJ Purpose/Objective(s): To evaluate potential dosimetry discrepancies generated by varying the dose grid resolution in adaptive planning of TomoTherapy for hypofractionated treatments. Materials/Methods: Twelve patients with intracranial lesions treated with image guided helical TomoTherapy under a hypofractionated protocol are reviewed. Due to the short course and high dose per fraction, we use the adaptive planning tool to obtain the delivered dose distribution. The associated pretreatment MVCT and planning kVCT images are fused and the treatment doses are calculated comparing the fine dose grid (1.51x1.51x2mm3) and the normal grid (3.02x3.02x2mm3) settings. The summative dosimetry of the targets is analyzed to identify the effects of dose grid size on adaptive planning. Results: The mean difference in coverage of the GTVs by the prescription dose, calculated with fine versus normal dose grid, over all patients is 2.6% ± 10.5. When segregated by size the mean difference and standard deviation in GTV coverage for small lesions (\2.5cc) is 3.1% ± 12.2. It improved for medium (2.5-7.5cc) and large (.7.5cc) lesions at 0.6% ± 0.6 and 1.4% ± 2.5, respectively. For all the patients the mean variation between the fine and normal grids in the calculated coverage of the PTVs by the prescription dose is 16.3% ± 17.4. For small PTVs alone (\5cc) the mean difference in coverage is 19.5%±19.4. The variation improved again at 9.1% ± 1.1 for medium PTVs (5-15cc) and 7.3% ± 1.9 for large PTVs (.15cc). Conclusions: While performing critical adaptive planning evaluation for intracranial patients treated with TomoTherapy, influence of the dose grid on the summation dosimetry must be considered. In our study, there is an appreciable difference in calculated target coverage amongst different dose grid resolutions, especially for small targets treated under hypofractionated protocols. Consequently, the use of fine dose grid is necessary if adaptive planning is performed for assessing positioning errors. Author Disclosure: C. Yang, None; N. Sheth, None; S. Murphy, None; M. Weiss, None; S. Sim, None.
3078
Dose Correction Strategies for Inter-fraction Motion in Prostate IGRT
A. Plypoo, A. Sethi, S. Alsager, R. Garza Loyola University Medical Center, Maywood, IL Purpose/Objective(s): To quantify the impact of inter-fraction prostate motion on target and normal structure dose in prostate IGRT and develop effective dose correction strategies. Materials/Methods: Organ motion data were obtained for four consecutive prostate patients over the course of IGRT (156 daily fractions). Two Visicoil fiducial markers (2cm long) were implanted in the prostate one-week prior to CT simulation. Planning target volume, PTV(prostate + 0.7 cm in all directions except 0.5cm posterior), organs at risk (OAR), and fiducial markers were contoured on planning CT. Patients were treated with a 5-field IMRT plan to 78Gy PTV dose in 39 daily fractions. Pre-treatment patient setup was based on kilo-voltage X-ray bony fusion, followed by marker match. Differences between bony fusion and
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3076
Clinical Application of Isorad and QED In Vivo Semiconductor Diodes for IMRT and Total Skin Electron Therapy: Feasibility Study
R. A. Kinhikar1, S. Chaudhary1, R. Upreti1, P. Kumar1, C. Tambe1, D. Dhote2, D. Deshpande1 1
Tata Memorial Hospital, Mumbai, India, 2Brijlal Biyani Science College, Amravati, India
Purpose/Objective(s): Semiconductor detectors are widely used for patient dosimetry for photon and electron beams due to high sensitivity and spatial resolution compared to the air filled ionization chamber with the same volume. The objective of this study was to validate the new in vivo semiconductor diodes Isorad (yellow) and QEDTM electron (Silver) for intensity modulated radiotherapy (IMRT) and total skin electron therapy (TSET) respectively. Materials/Methods: The Isorad photon (yellow) and QED electron (silver) diode (both from Sun Nuclear Corporation, Fl, USA) were used for 6 MV photon beam from a Clinac 6EX linear accelerator (LINAC) and 6 MeV electron energy from dual energy Clinac 2100CD LINAC (Both Varian Medical Systems, Palo Alto, USA) respectively. Isorad was first calibrated for 6 MV photon beam with 10 cm x 10 cm field size at target to axis distance (TAD) of 100 cm with solid water (SW) slabs as full scatter medium. Later, the diode was characterized for its reproducibility, monitor unit (MU) linearity (25 to 800), dependence on field size, dose rate, source to surface distance (SSD), beam incidence and axial orientation. Further, the response of the diode was also investigated for IMRT dosimetry by placing the diode in SW slabs at 5.4 cm depth. QEDTM was calibrated for TSET by irradiating it with 36 cm x 36 cm field size at 493 cm TAD at Dmax (8 mm). Diode was irradiated for 740 and 1060 gantry angle (+ 140 from gantry lateral) for a total dose of 2 Gy. Later the diode was used for a patient dosimetry to measure the dose delivered at the isocenter level (umbilicus). The diode was directly taped on the skin of the patient for the entire treatment. The thermolunescent dosimeters Lif:Mg:Ti (TLD 100 in powder form) was used subsequently along with the diode in the same setup. Results: The Isorad showed an excellent reproducibility (+ 0.5%). MU linearity was in agreement within (+ 2%). Maximum variation of 4% was observed for the measured dose with the largest field size (40 cm x 40 cm). The dose rate and SSD has no effect on the response of the diode. The diode showed an angular dependence of (+ 1.5%). The IMRT measured dose with diode was in well agreement (\ 2%) with the planned dose. The dose measured with QEDTM and TLD for TSET patient at the isocenter was in well agreement (\ 1%). The variation between measured (QEDTM) and planned dose was 8%. Conclusions: The semiconductor diodes used in this study were validated for advanced and special radiotherapy treatments like IMRT and TSET. The diodes are feasible, handy and exhibited a reasonable reproducibility, dosimetric stability and reliability. These diodes have proven to be useful quality assurance tool in the assessment of the in vivo dose in this kind of treatment. Author Disclosure: R.A. Kinhikar, None; S. Chaudhary, None; R. Upreti, None; P. Kumar, None; C. Tambe, None; D. Dhote, None; D. Deshpande, None.
3077
Dose Grid Effects in Adaptive Planning of Helical Tomotherapy for Hypofractionated Treatments
C. Yang, N. Sheth, S. Murphy, M. Weiss, S. Sim Monmouth Medical Center, Long Branch, NJ Purpose/Objective(s): To evaluate potential dosimetry discrepancies generated by varying the dose grid resolution in adaptive planning of TomoTherapy for hypofractionated treatments. Materials/Methods: Twelve patients with intracranial lesions treated with image guided helical TomoTherapy under a hypofractionated protocol are reviewed. Due to the short course and high dose per fraction, we use the adaptive planning tool to obtain the delivered dose distribution. The associated pretreatment MVCT and planning kVCT images are fused and the treatment doses are calculated comparing the fine dose grid (1.51x1.51x2mm3) and the normal grid (3.02x3.02x2mm3) settings. The summative dosimetry of the targets is analyzed to identify the effects of dose grid size on adaptive planning. Results: The mean difference in coverage of the GTVs by the prescription dose, calculated with fine versus normal dose grid, over all patients is 2.6% ± 10.5. When segregated by size the mean difference and standard deviation in GTV coverage for small lesions (\2.5cc) is 3.1% ± 12.2. It improved for medium (2.5-7.5cc) and large (.7.5cc) lesions at 0.6% ± 0.6 and 1.4% ± 2.5, respectively. For all the patients the mean variation between the fine and normal grids in the calculated coverage of the PTVs by the prescription dose is 16.3% ± 17.4. For small PTVs alone (\5cc) the mean difference in coverage is 19.5%±19.4. The variation improved again at 9.1% ± 1.1 for medium PTVs (5-15cc) and 7.3% ± 1.9 for large PTVs (.15cc). Conclusions: While performing critical adaptive planning evaluation for intracranial patients treated with TomoTherapy, influence of the dose grid on the summation dosimetry must be considered. In our study, there is an appreciable difference in calculated target coverage amongst different dose grid resolutions, especially for small targets treated under hypofractionated protocols. Consequently, the use of fine dose grid is necessary if adaptive planning is performed for assessing positioning errors. Author Disclosure: C. Yang, None; N. Sheth, None; S. Murphy, None; M. Weiss, None; S. Sim, None.
3078
Dose Correction Strategies for Inter-fraction Motion in Prostate IGRT
A. Plypoo, A. Sethi, S. Alsager, R. Garza Loyola University Medical Center, Maywood, IL Purpose/Objective(s): To quantify the impact of inter-fraction prostate motion on target and normal structure dose in prostate IGRT and develop effective dose correction strategies. Materials/Methods: Organ motion data were obtained for four consecutive prostate patients over the course of IGRT (156 daily fractions). Two Visicoil fiducial markers (2cm long) were implanted in the prostate one-week prior to CT simulation. Planning target volume, PTV(prostate + 0.7 cm in all directions except 0.5cm posterior), organs at risk (OAR), and fiducial markers were contoured on planning CT. Patients were treated with a 5-field IMRT plan to 78Gy PTV dose in 39 daily fractions. Pre-treatment patient setup was based on kilo-voltage X-ray bony fusion, followed by marker match. Differences between bony fusion and
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