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In Vivo Dosimetry of Stereotactic Radiation Therapy Using Integral Quality Monitor (IQM) System
E614
International Journal of Radiation Oncology Biology Physics
3539
this study is to compare the effective reduction in NTCP of swallowing and salivary structures using each approach. Materials/Methods: 14 patients with locally advanced HNC treated at our institution with bilateral neck RT were replanned using IMRT with identical cost functions to compare techniques for NTCP reduction. We compared three planning strategies: (1) standard dose of 70 Gy to CTV1 and 56 Gy to CTV2 with 3mm PTV margins (P70) (2) Standard dose to CTVs without PTV margins (assuming daily IGRT and frequent replanning) (C70) and (3) dose reduction to 60Gy to CTV1 and 50 Gy to CTV2 with 3mm PTV margins (P60). Clinical OAR mean dose constraints were attempted to the pharyngeal constrictors (PC, 50 Gy), parotid glands (PG, 24 Gy), and submandibular glands (SMG, 30 Gy). NTCP mean dose models for PC, glottis/supraglottic larynx (GSL), PG and SMG were based on published data. Toxicities for PC and GSL were severe dysphagia on modified barium-swallow videofluoroscopy (VF) and severe eating difficulty on the head and neck quality of life questionnaire eating domain at 12 months posttreatment. PG and SMG toxicity were <25% baseline salivary function (grade 4). For the purposes of this study, changes in NTCP > 5% were considered clinically meaningful. Results: The improvements (D) in NTCPs from P70 to either C70 or P60 are presented in the table below. Both C70 and P60 NTCPs were significantly lower than P70 in all
In Vivo Dosimetry of Stereotactic Radiation Therapy Using Integral Quality Monitor (IQM) System J. Qian,1 L. Lin,1 R. Gonzales,1 J. Keck,1 E.P. Armour,1 and J.W. Wong2; 1 Johns Hopkins University School of Medicine, Baltimore, MD, 2Johns Hopkins University, Baltimore, MD Purpose/Objective(s): Real-time dosimetry is a challenging problem for high-dose and highly precise stereotactic radiosurgery (SRS) or stereotactic body radiation therapy (SBRT). Integral quality monitor (IQM) is a new in vivo dose monitoring and interlocking system using on-line comparison of checksums calculated from geometric and dosimetric parameters of fields, jaws, MLC and ion chamber. The purpose of this work is to investigate the feasibility of using IQM for in vivo dosimetry of SRS/SBRT treatment. Materials/Methods: A beta-version IQM system was investigated on linear accelerator equipped with 160-MLC Agility head and later on a linear accelerator equipped with both Agility and high dose-rate flatteningfilter-free (FFF) energies. Prostate and head-and-neck (H&N) plans of conventional intensity modulated radiation therapy (IMRT) and volumetric modulated arc therapy (VMAT) were used to assess IQM constancy in stationary and rotational delivering modes, respectively. The IQM sensitivity of detecting dosimetric deviations caused by leaf errors in SBRT were evaluated with stationary and rotational 2000 MU picket fence (PF) plans with segment field size of 3x1 and 5x1 cm2, and IMRT/VMAT patient plans for brain SRS, lung, spine and pancreas SBRT with equivalent aperture size from 3x3 to 5x5 cm2. Single leaf offsets of 2 mm and 5 mm were intentionally introduced into these plans. Each plan was delivered three or five times for statistics and repeated for different energies including 6 MV, 6 MV FFF, 10 MV and 10 MV FFF. The accuracy of IQM detectability was verified with 2D measurement array measurements. Results: IQM constancy measurements across several days showed 0.10.2% average standard deviation for cumulative segment checksum comparison in prostate and H&N IMRT deliveries and 0.7-1.0% (excluding first three control points) in VMAT case. IQM detected systematic checksum deviations of 1.1-2.0% for 2 mm single leaf offset and 3.1-5.3% for 5 mm offset in deliveries of both stationary PF plans having different segment field sizes. The corresponding deviations (excluding first three control points) for rotational PF deliveries were 1.2-2.6% and 3.8-6.1%, respectively. IQM data of a 7-field lung SBRT delivery showed that average cumulative checksum deviations of 1.1% for 2 mm leaf offset and 2.4% for 5 mm leaf offset across all fields were consistently observed in three repeated measurements. Statistical analysis indicated that checksum differences observed in all these cases were significant (p < 0.05). Conclusion: IQM is a stable dosimetric system and sensitive to dosimetric deviations caused by single leaf errors of 2 mm or above in moderate-sized fields. Preliminary results suggest that IQM could afford an effective means for real-time dosimetric monitoring of stereotactic radiation therapy treatment. Author Disclosure: J. Qian: None. L. Lin: None. R. Gonzales: None. J. Keck: None. E.P. Armour: None. J.W. Wong: Research Grant; NCI, Toshiba Medical Inc.. Royalty; Elekta, Xstrahl. Co-Founder with spouse; JPLC Associates LLC.
3540 Methods for Reducing Normal Tissue Complication Probabilities (NTCP) in Head and Neck Cancer (HNC): Dose Deescalation or PTV Elimination S. Samuels,1 K.A. Vineberg,1 C. Lee,1 M.M. Matuszak,1 R. K. Ten Haken,1 A. Eisbruch,1 and K.K. Brock2; 1University of Michigan, Ann Arbor, MI, 2Department of Radiation Oncology, University of Michigan, Ann Arbor, MI Purpose/Objective(s): Radiation treatment toxicity may be reduced by eliminating PTVs (by IGRT and replanning) or reducing dose in goodprognosis patients like HPV+ oropharyngeal cancer (OPC). The goal of
Poster Viewing Abstracts 3540; Table 1
D in median NTCP from treatment reduction strategies D P70-C70 D P70-P60
NTCP model
PC_VF swallow score PC_eating domain GSL_VF swallow score GSL_eating domain cPG_salivary flow iPG_salivary flow cSMG_salivary flow iSMG_salivary flow
3.4% 1.7% 2.3% 0.6% 1.8% 5.5% 6.7% 0.0%
4.9% 2.4% 4.6% 1.0% 1.9% 5.0% 5.8% 0.0%
iZ ipsilateral, cZcontralateral models (paired T-test P<0.01). However, only the NTCPs for the iPG and cSMG decreased by the predetermined 5% or more. Of these, the reduction in NTCP of the iPG between C70 and P60 plans was not significant (PZ0.89), however the reduction in NTCP of the cSMG by C70 was significantly better than by P60 (PZ0.036), i.e. lower NTCP by removing PTV than by dose reduction. Conclusion: Both eliminating the PTV and dose de-escalation were successful in lowering the NTCP in all evaluated organs, especially the ipsilateral parotid gland and contralateral submandibular gland whose reduction exceeded the target threshold of 5%. These data suggest that based on NTCP models, patients treated with dose de-escalation (HPV+ OPC) or IGRT with replanning to eliminate PTVs, are likely to have less xerostomia because of lower toxicity to salivary glands, but clinical improvements in dysphagia are less likely. Author Disclosure: S. Samuels: None. K.A. Vineberg: None. C. Lee: None. M.M. Matuszak: None. R.K. Ten Haken: None. A. Eisbruch: None. K.K. Brock: None.
3541 Isolating Texture Features of Gynecological Tumors With High Variability in the Context of an 18F-FDG PET Adaptive Protocol J. Nawrocki,1 J.P. Chino,2 and O.I. Craciunescu2; 1Duke University Medical Physics Graduate Program, Durham, NC, 2Duke University Medical Center, Durham, NC Purpose/Objective(s): This study of a gynecological FDG PET protocol identifies texture features that show statistically significant changes reflecting treatment during radiation therapy, independent of variable reconstruction parameters.
International Journal of Radiation Oncology Biology Physics
3539
this study is to compare the effective reduction in NTCP of swallowing and salivary structures using each approach. Materials/Methods: 14 patients with locally advanced HNC treated at our institution with bilateral neck RT were replanned using IMRT with identical cost functions to compare techniques for NTCP reduction. We compared three planning strategies: (1) standard dose of 70 Gy to CTV1 and 56 Gy to CTV2 with 3mm PTV margins (P70) (2) Standard dose to CTVs without PTV margins (assuming daily IGRT and frequent replanning) (C70) and (3) dose reduction to 60Gy to CTV1 and 50 Gy to CTV2 with 3mm PTV margins (P60). Clinical OAR mean dose constraints were attempted to the pharyngeal constrictors (PC, 50 Gy), parotid glands (PG, 24 Gy), and submandibular glands (SMG, 30 Gy). NTCP mean dose models for PC, glottis/supraglottic larynx (GSL), PG and SMG were based on published data. Toxicities for PC and GSL were severe dysphagia on modified barium-swallow videofluoroscopy (VF) and severe eating difficulty on the head and neck quality of life questionnaire eating domain at 12 months posttreatment. PG and SMG toxicity were <25% baseline salivary function (grade 4). For the purposes of this study, changes in NTCP > 5% were considered clinically meaningful. Results: The improvements (D) in NTCPs from P70 to either C70 or P60 are presented in the table below. Both C70 and P60 NTCPs were significantly lower than P70 in all
In Vivo Dosimetry of Stereotactic Radiation Therapy Using Integral Quality Monitor (IQM) System J. Qian,1 L. Lin,1 R. Gonzales,1 J. Keck,1 E.P. Armour,1 and J.W. Wong2; 1 Johns Hopkins University School of Medicine, Baltimore, MD, 2Johns Hopkins University, Baltimore, MD Purpose/Objective(s): Real-time dosimetry is a challenging problem for high-dose and highly precise stereotactic radiosurgery (SRS) or stereotactic body radiation therapy (SBRT). Integral quality monitor (IQM) is a new in vivo dose monitoring and interlocking system using on-line comparison of checksums calculated from geometric and dosimetric parameters of fields, jaws, MLC and ion chamber. The purpose of this work is to investigate the feasibility of using IQM for in vivo dosimetry of SRS/SBRT treatment. Materials/Methods: A beta-version IQM system was investigated on linear accelerator equipped with 160-MLC Agility head and later on a linear accelerator equipped with both Agility and high dose-rate flatteningfilter-free (FFF) energies. Prostate and head-and-neck (H&N) plans of conventional intensity modulated radiation therapy (IMRT) and volumetric modulated arc therapy (VMAT) were used to assess IQM constancy in stationary and rotational delivering modes, respectively. The IQM sensitivity of detecting dosimetric deviations caused by leaf errors in SBRT were evaluated with stationary and rotational 2000 MU picket fence (PF) plans with segment field size of 3x1 and 5x1 cm2, and IMRT/VMAT patient plans for brain SRS, lung, spine and pancreas SBRT with equivalent aperture size from 3x3 to 5x5 cm2. Single leaf offsets of 2 mm and 5 mm were intentionally introduced into these plans. Each plan was delivered three or five times for statistics and repeated for different energies including 6 MV, 6 MV FFF, 10 MV and 10 MV FFF. The accuracy of IQM detectability was verified with 2D measurement array measurements. Results: IQM constancy measurements across several days showed 0.10.2% average standard deviation for cumulative segment checksum comparison in prostate and H&N IMRT deliveries and 0.7-1.0% (excluding first three control points) in VMAT case. IQM detected systematic checksum deviations of 1.1-2.0% for 2 mm single leaf offset and 3.1-5.3% for 5 mm offset in deliveries of both stationary PF plans having different segment field sizes. The corresponding deviations (excluding first three control points) for rotational PF deliveries were 1.2-2.6% and 3.8-6.1%, respectively. IQM data of a 7-field lung SBRT delivery showed that average cumulative checksum deviations of 1.1% for 2 mm leaf offset and 2.4% for 5 mm leaf offset across all fields were consistently observed in three repeated measurements. Statistical analysis indicated that checksum differences observed in all these cases were significant (p < 0.05). Conclusion: IQM is a stable dosimetric system and sensitive to dosimetric deviations caused by single leaf errors of 2 mm or above in moderate-sized fields. Preliminary results suggest that IQM could afford an effective means for real-time dosimetric monitoring of stereotactic radiation therapy treatment. Author Disclosure: J. Qian: None. L. Lin: None. R. Gonzales: None. J. Keck: None. E.P. Armour: None. J.W. Wong: Research Grant; NCI, Toshiba Medical Inc.. Royalty; Elekta, Xstrahl. Co-Founder with spouse; JPLC Associates LLC.
3540 Methods for Reducing Normal Tissue Complication Probabilities (NTCP) in Head and Neck Cancer (HNC): Dose Deescalation or PTV Elimination S. Samuels,1 K.A. Vineberg,1 C. Lee,1 M.M. Matuszak,1 R. K. Ten Haken,1 A. Eisbruch,1 and K.K. Brock2; 1University of Michigan, Ann Arbor, MI, 2Department of Radiation Oncology, University of Michigan, Ann Arbor, MI Purpose/Objective(s): Radiation treatment toxicity may be reduced by eliminating PTVs (by IGRT and replanning) or reducing dose in goodprognosis patients like HPV+ oropharyngeal cancer (OPC). The goal of
Poster Viewing Abstracts 3540; Table 1
D in median NTCP from treatment reduction strategies D P70-C70 D P70-P60
NTCP model
PC_VF swallow score PC_eating domain GSL_VF swallow score GSL_eating domain cPG_salivary flow iPG_salivary flow cSMG_salivary flow iSMG_salivary flow
3.4% 1.7% 2.3% 0.6% 1.8% 5.5% 6.7% 0.0%
4.9% 2.4% 4.6% 1.0% 1.9% 5.0% 5.8% 0.0%
iZ ipsilateral, cZcontralateral models (paired T-test P<0.01). However, only the NTCPs for the iPG and cSMG decreased by the predetermined 5% or more. Of these, the reduction in NTCP of the iPG between C70 and P60 plans was not significant (PZ0.89), however the reduction in NTCP of the cSMG by C70 was significantly better than by P60 (PZ0.036), i.e. lower NTCP by removing PTV than by dose reduction. Conclusion: Both eliminating the PTV and dose de-escalation were successful in lowering the NTCP in all evaluated organs, especially the ipsilateral parotid gland and contralateral submandibular gland whose reduction exceeded the target threshold of 5%. These data suggest that based on NTCP models, patients treated with dose de-escalation (HPV+ OPC) or IGRT with replanning to eliminate PTVs, are likely to have less xerostomia because of lower toxicity to salivary glands, but clinical improvements in dysphagia are less likely. Author Disclosure: S. Samuels: None. K.A. Vineberg: None. C. Lee: None. M.M. Matuszak: None. R.K. Ten Haken: None. A. Eisbruch: None. K.K. Brock: None.
3541 Isolating Texture Features of Gynecological Tumors With High Variability in the Context of an 18F-FDG PET Adaptive Protocol J. Nawrocki,1 J.P. Chino,2 and O.I. Craciunescu2; 1Duke University Medical Physics Graduate Program, Durham, NC, 2Duke University Medical Center, Durham, NC Purpose/Objective(s): This study of a gynecological FDG PET protocol identifies texture features that show statistically significant changes reflecting treatment during radiation therapy, independent of variable reconstruction parameters.