Assessment of PTV for Whole Stomach Irradiation Using Daily Megavoltage CT
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within 12 months of ASCT and warrant further study with respect selection for transplant, salvage regime and use of consolidative and adjuvant treatments. Longer term follow-up is planned. Author Disclosure: C.L. Hann, None; J. Sussman, None. 2783 Assessment of PTV for Whole Stomach Irradiation Using Daily Megavoltage CT M. E. Johnson 1 , G. C. Pereira 2 , I. M. El Naqa 2 , S. M. Goddu 2 , R. Al-Lozi 2 , A. Apte 2 , D. B. Mansur 2 1 University of Missouri, Columbia, MO, 2 Washington University, Saint Louis, MO Purpose/Objective(s): Appropriate PTV margins for the stomach have not been clearly elucidated, and interfractional variation of the stomach may be significant due to irregularities in shape, volume, and mobility. We investigated the daily variation in gastric position by examining daily megavoltage CT scans in comparison to CT simulation images. Materials/Methods: Images from three patients treated with Tomotherapy for gastric lymphoma were evaluated retrospec- tively for this study. Patients were simulated with 80 or 100 cc of oral contrast after a 6 hour fast. During therapy, gastric volume was controlled similarly with a 6 hour fast and administration of 80 or 100 cc of water prior to treatment. The stomach volumes were identified and contoured on each daily megavoltage scan, for a total of 41 scans. Each contour was examined by two observers. To determine organ motion variation, daily megavoltage scans were registered to the CT simulation image set and the margins in the r/l, sup/inf, ant/post directions that covered 95% of the daily image motion were computed using a sim- ple grid search with a discrete set of margins ranging from 0 to 2.4 cm in increments of 0.6 cm. In addition, the setup variation was calculated based on the daily shifts using the margin recipe published by van Herk et al., IJROBP, 2000. To estimate total variation for patients not receiving daily image guidance, overall margins were determined by adding organ motion and daily setup variation. Results: The maximum margin to the right, left, posterior, anterior, superior, and inferior axes for the line encompassing 95% of daily volume is 0.88cm, 1.75cm, 0.88cm, 1.75cm, 1.75cm, and 0.5cm, respectively. The maximum calculated setup var- iation is 0.85cm, 0.13cm, 0.05cm, 0.57cm, 0.15cm, and 0.36cm, respectively. Therefore, the overall margin required to cover 95% of the stomach in a patient not receiving daily image guidance is 1.72cm, 1.88cm, 0.92cm, 2.32cm, 1.90cm, and 0.86cm, respectively. Conclusions: This study demonstrates considerable daily variability in stomach localization. The necessary expansion of the GTV for 95% coverage is direction-dependent and ranges from 0.5cm to 1.75cm with daily image guidance and 0.86cm to 2.32cm with- out image guidance. While the data suggest margins can be reduced by using image guidance, the required margins are still rel- atively large. These data should be confirmed with additional patient numbers, but provides guidance for those patients currently undergoing treatment planning for gastric irradiation. Author Disclosure: M.E. Johnson, None; G.C. Pereira, None; I.M. El Naqa, None; S.M. Goddu, None; R. Al-Lozi, None; A. Apte, None; D.B. Mansur, None. 2784 Contribution of Three-dimensional Conformational Radiotherapy with Modulation of Intensity (IMRT) for Women Affected by Stage II Supradiaphragmatic Hodgkin’s Disease: A Dosimetric Study Comparing IMRT by Tomotherapy and a Three-dimensional Conformational Radiotherapy (3D-CRT) D. N. Antoni 1 , P. Meyer 1 , S. Ame 2 , C. Niederst 1 , K. Bourahla 3 , D. Karamanoukian 1 , G. Noel 1 1 CLCC Paul Strauss Service de Radiothe ´rapie, Strasbourg, France, 2 Service d’Onco-He ´matologie CHU Strasbourg, Strasbourg, France, 3 CLCC Paul Strauss Service de Me ´decine Nucle ´aire, Strasbourg, France Purpose/Objective(s): Long-term survival rate has reached more than 80% for patients with Hodgkin’s disease. An increased in- cidence of second cancers led by the chemotherapy and radiation treatments has been observed. For women, age at irradiation and a higher dose delivered in breast are the most incriminated in appearance of breast cancers. IMRT could decrease the dose delivered in breast. This dosimetric study aims at comparing 3D-CRT with IMRT. Materials/Methods: Twelve patients of median age of 25.4 years in the diagnosis (17-38 years) have been treated for a supradiaph- ragmatic Hodgkin’s disease. The adjuvant radiation treatment delivered a dose of 30 Gy in sites initially invaded with a complement of 6 Gy on those suspect of not sterilization observed on CT-scan simulation. The delineation of target volumes has been achieved on a CT-scan simulation made after chemotherapy using the fusion images with a first CT-scan simulation and fluorodeoxyglucose- positron emission tomography (PET) performed in treatment position at the diagnosis. The clinical target volume (CTV) corre- sponded to the initially invaded node areas, whereas the planning target volume (PTV) was defined as the CTV with adding a mar- gin of 1 cm. Results: PTV coverage: The median volume of target receiving at least 95% of prescription dose (V95%) was 97.5% for IMRT ([94.6%-99.4%], mean: 96.8%) and 94.6% for 3D-CRT ([76.8%-98.8%], mean: 93.0%). Normal tissue: Median maximal dose of right breast was lower for IMRT than for 3D-CRT, respectively: 31.4 Gy ([18.4 -38.2 Gy], mean: 29.7 Gy) and 36.5 Gy ([30.5 -39.0 Gy], mean: 34.9 Gy). For left breast, the difference was also observed: 29.9 Gy ([10.2 -39.3 Gy], mean: 28.6 Gy) for IMRT vs. 36.2 Gy ([3.5 -39.1 Gy], mean 29.4 Gy) for 3D-CRT. Median and mean doses were different for heart, lung and esophagus between IMRT and 3D-CRT, respectively 8.4 and 10.80 Gy vs. 9.1 and 12.24 Gy, 8.1 and 9.36 Gy vs. 9.7 and 11.4 Gy, 18.6 and 19.6 Gy vs. 20.7 and 22.1 Gy; and were not different for breast and thyroid. As expected, the volumes receiving the highest dose were lower with IMRT. For breast doses, we observed a crossing of mean HDV at 20 and 14 Gy respectively for right and left breast. For heart, thyroid, lung and esophagus doses, crossing of mean HDV were observed respectively for 9, 19, 10 and 7 Gy. Conformal indexes: The conformity index (CI) was better for IMRT than for 3D-CRT, respectively 1.24 and 2.53. S554 I. J. Radiation Oncology d Biology d Physics Volume 78, Number 3, Supplement, 2010
Transcript of Assessment of PTV for Whole Stomach Irradiation Using Daily Megavoltage CT
S554 I. J. Radiation Oncology d Biology d Physics Volume 78, Number 3, Supplement, 2010
within 12 months of ASCT and warrant further study with respect selection for transplant, salvage regime and use of consolidativeand adjuvant treatments. Longer term follow-up is planned.
Author Disclosure: C.L. Hann, None; J. Sussman, None.
2783 Assessment of PTV for Whole Stomach Irradiation Using Daily Megavoltage CT
M. E. Johnson1, G. C. Pereira2, I. M. El Naqa2, S. M. Goddu2, R. Al-Lozi2, A. Apte2, D. B. Mansur2
1University of Missouri, Columbia, MO, 2Washington University, Saint Louis, MO
Purpose/Objective(s): Appropriate PTV margins for the stomach have not been clearly elucidated, and interfractional variation ofthe stomach may be significant due to irregularities in shape, volume, and mobility. We investigated the daily variation in gastricposition by examining daily megavoltage CT scans in comparison to CT simulation images.
Materials/Methods: Images from three patients treated with Tomotherapy for gastric lymphoma were evaluated retrospec-tively for this study. Patients were simulated with 80 or 100 cc of oral contrast after a 6 hour fast. During therapy, gastricvolume was controlled similarly with a 6 hour fast and administration of 80 or 100 cc of water prior to treatment. The stomachvolumes were identified and contoured on each daily megavoltage scan, for a total of 41 scans. Each contour was examined bytwo observers. To determine organ motion variation, daily megavoltage scans were registered to the CT simulation image setand the margins in the r/l, sup/inf, ant/post directions that covered 95% of the daily image motion were computed using a sim-ple grid search with a discrete set of margins ranging from 0 to 2.4 cm in increments of 0.6 cm. In addition, the setup variationwas calculated based on the daily shifts using the margin recipe published by van Herk et al., IJROBP, 2000. To estimate totalvariation for patients not receiving daily image guidance, overall margins were determined by adding organ motion and dailysetup variation.
Results: The maximum margin to the right, left, posterior, anterior, superior, and inferior axes for the line encompassing 95%of daily volume is 0.88cm, 1.75cm, 0.88cm, 1.75cm, 1.75cm, and 0.5cm, respectively. The maximum calculated setup var-iation is 0.85cm, 0.13cm, 0.05cm, 0.57cm, 0.15cm, and 0.36cm, respectively. Therefore, the overall margin required to cover95% of the stomach in a patient not receiving daily image guidance is 1.72cm, 1.88cm, 0.92cm, 2.32cm, 1.90cm, and 0.86cm,respectively.
Conclusions: This study demonstrates considerable daily variability in stomach localization. The necessary expansion of the GTVfor 95% coverage is direction-dependent and ranges from 0.5cm to 1.75cm with daily image guidance and 0.86cm to 2.32cm with-out image guidance. While the data suggest margins can be reduced by using image guidance, the required margins are still rel-atively large. These data should be confirmed with additional patient numbers, but provides guidance for those patientscurrently undergoing treatment planning for gastric irradiation.
Author Disclosure: M.E. Johnson, None; G.C. Pereira, None; I.M. El Naqa, None; S.M. Goddu, None; R. Al-Lozi, None; A. Apte,None; D.B. Mansur, None.
2784 Contribution of Three-dimensional Conformational Radiotherapy with Modulation of Intensity (IMRT)
for Women Affected by Stage II Supradiaphragmatic Hodgkin’s Disease: A Dosimetric Study ComparingIMRT by Tomotherapy and a Three-dimensional Conformational Radiotherapy (3D-CRT)D. N. Antoni1, P. Meyer1, S. Ame2, C. Niederst1, K. Bourahla3, D. Karamanoukian1, G. Noel1
1CLCC Paul Strauss Service de Radiotherapie, Strasbourg, France, 2Service d’Onco-Hematologie CHU Strasbourg,Strasbourg, France, 3CLCC Paul Strauss Service de Medecine Nucleaire, Strasbourg, France
Purpose/Objective(s): Long-term survival rate has reached more than 80% for patients with Hodgkin’s disease. An increased in-cidence of second cancers led by the chemotherapy and radiation treatments has been observed. For women, age at irradiation anda higher dose delivered in breast are the most incriminated in appearance of breast cancers. IMRT could decrease the dose deliveredin breast. This dosimetric study aims at comparing 3D-CRT with IMRT.
Materials/Methods: Twelve patients of median age of 25.4 years in the diagnosis (17-38 years) have been treated for a supradiaph-ragmatic Hodgkin’s disease. The adjuvant radiation treatment delivered a dose of 30 Gy in sites initially invaded with a complementof 6 Gy on those suspect of not sterilization observed on CT-scan simulation. The delineation of target volumes has been achievedon a CT-scan simulation made after chemotherapy using the fusion images with a first CT-scan simulation and fluorodeoxyglucose-positron emission tomography (PET) performed in treatment position at the diagnosis. The clinical target volume (CTV) corre-sponded to the initially invaded node areas, whereas the planning target volume (PTV) was defined as the CTV with adding a mar-gin of 1 cm.
Results: PTV coverage: The median volume of target receiving at least 95% of prescription dose (V95%) was 97.5% for IMRT([94.6%-99.4%], mean: 96.8%) and 94.6% for 3D-CRT ([76.8%-98.8%], mean: 93.0%). Normal tissue: Median maximal doseof right breast was lower for IMRT than for 3D-CRT, respectively: 31.4 Gy ([18.4 -38.2 Gy], mean: 29.7 Gy) and 36.5 Gy([30.5 -39.0 Gy], mean: 34.9 Gy). For left breast, the difference was also observed: 29.9 Gy ([10.2 -39.3 Gy], mean: 28.6 Gy)for IMRT vs. 36.2 Gy ([3.5 -39.1 Gy], mean 29.4 Gy) for 3D-CRT. Median and mean doses were different for heart, lung andesophagus between IMRT and 3D-CRT, respectively 8.4 and 10.80 Gy vs. 9.1 and 12.24 Gy, 8.1 and 9.36 Gy vs. 9.7 and 11.4Gy, 18.6 and 19.6 Gy vs. 20.7 and 22.1 Gy; and were not different for breast and thyroid. As expected, the volumes receivingthe highest dose were lower with IMRT. For breast doses, we observed a crossing of mean HDV at 20 and 14 Gy respectivelyfor right and left breast. For heart, thyroid, lung and esophagus doses, crossing of mean HDV were observed respectively for9, 19, 10 and 7 Gy. Conformal indexes: The conformity index (CI) was better for IMRT than for 3D-CRT, respectively 1.24and 2.53.
