Low Dose MV CBCT for Daily Pediatric Localization
1
Conclusions: Helical IMRT reduces the mean dose to the temporal lobes, chiasm and pituitary, but increases low doses to normal tissues. Whole ventricular irradiation for pediatric intracranial GCT using helical IMRT may reduce the likelihood of neurological sequelae, but may increase the risk of radioinduced secondary malignancies. Author Disclosure: S. Supiot, None; C. Munos, None; M. Mahe, None; A. Lisbona, None. 3131 Interclinician Variability in Making Nephroblastoma Dosimetric Decision: A Matter of Compromises L. Padovani 1 , A. Huchet 2 , V. Bernier 3 , P. Quetin 4 , M. Mahe 5 , P. Bondiau 6 , C. Kerr 7 , C. Carrie 8 , X. Muracciole 1 1 Ho ˆ pital de la Timone, Marseille, France, 2 Hopital St Andre ´, CHU, Bordeaux, France, 3 Centre Alexis Vautrin, Nancy, France, 4 Centre Paul Strauss, Strasbourg, France, 5 Centre Rene Gauducheau, Nantes, France, 6 Centre Antoine Lacassagne, Nice, France, 7 Centre Val d’Aurelle Paul Lamarque, Montpellier, France, 8 Centre Leon Berard, Lyon, France Purpose/Objective(s): To assess the inter clinician variability in delineating CT target volume (CTV), and in dosimetric planning for nephroblastoma (NB) treatment. Most patients with NB do meet the dose requirements of normal tissue and CTV. For the cat- egory of patients who don’t, we investigated different types of relaxation for planning goals for the most normal tissue constraining parameters (NTCP). Materials/Methods: Using the same case of high risk NB, 6 French pediatric radiation oncology teams outlined the post operative CTV (no macroscopic disease) on dosimetric CT scan, applying radiotherapy guidelines of NB SIOP protocol. On the same CTV and organ at risk (OAR) every clinician made dosimetric planning taking into account limited toxic doses to the OAR, and tumor control probability (TCP). The protocol guidelines recommendation was 25.2 Gy for CTV, a maximal dose of 20 Gy and 12 Gy for respectively 50% of liver’s and 15% of controlateral kidney’s volume, and homogenous dose to vertebral bodies (at least 95% re- ceiving 20 Gy). Quantitative volume analysis in 3 dimensions was carried out on the resulting CTVs and conformity index as well as an other analysis of treatment plans with different combinations of TCP and NTCP using Aquilab soft. Results: The defined CTV showed a large inter clinician variability. The dimension of the target volume had interclinician ranges of 80 to 92 mm cranio-caudal, 65 to 79 mm left-right, 50 to 74 mm antero-posterior. One team proposed an IMRT plan while the others proposed 3D-CRT plan. The correlation between target and normal structures showed no decreased dose to the CTV while relaxing the recommended liver doses in 4 cases : respectively more than 20 Gy at 74%, 75%, 78%, and 88% of the volume. The maximal over reference dose ratio for CTV ranged from 1.03 to 1.11 with an optimal ratio of 1.07. For controlateral kidney constraints, 4 plans reached the goal and 2 relaxed : 17.6% and 25% respectively with more than 12 Gy. For vertebral bodies, 1 plan respected the constraint, 5 resulted in relaxing it with 66.6%, 74%, 78.5%, 87.6%, and 90% of volume receiving a dose up to 20 Gy. Conclusions: This study reveals a large variability in CTV delineation of NB based on preoperative volume. Given this informa- tion one could suggest a reduction of the CTV to normal tissue surfaces in contact with preoperative tumor. It would result in reducing irradiated OAR significantly. This study also leads to the conclusion that in order to deliver the total dose to CTV and yet maintain an acceptable NTCP, different compromises reflecting differences of late effect risks have to be considered. It seems important to characterize tradeoffs among conflicting goals, relaxing those that provide the most benefit for each patient using a hierarchical optimization process. Author Disclosure: L. Padovani, None; A. Huchet, None; V. Bernier, None; P. Quetin, None; M. Mahe, None; P. Bondiau, None; C. Kerr, None; C. Carrie, None; X. Muracciole, None. 3132 Low Dose MV CBCT for Daily Pediatric Localization C. Beltran 1 , A. Bani-Hashemi 2 , B. Faddegon 3 , T. E. Merchant 1 1 St. Jude Children’s Research Hospital, Memphis, TN, 2 Siemens Medical, Concord, CA, 3 UCSF, San Francisco, CA Purpose/Objective(s): An IRB approved pediatric localization clinical protocol began accruing research participants in March 2008, in which CBCT is a central component. Because extraneous radiation is a major concern for pediatric patients, a modified version of the Siemens Mega Voltage CBCT (Siemens Medical USA, Concord, CA) was implemented to allow for low dose Mega Voltage CBCT (LD-MV CBCT) imaging. Data will be gathered to quantify the setup margin (SM) portion of the Planning Target Volume (PTV) margin for pediatric tumor sites according to age, localization technique, treatment position, and the use of general anesthesia. Materials/Methods: The research participants will be assigned a non-ionizing localization technique, such as optical tracking, ultrasound, or visual marks, based on disease site, treatment position, age, and use of anesthesia. After the non-ionizing localization technique, each patient will receive a LD-MV CBCT at the start of each fraction and the end of every other fraction. The pre-treat- ment LD-MV CBCT will be used to assess the accuracy of the localization technique, and the post-treatment LD-MV CBCT will quantify the rigidity of the immobilization schema used; thereby providing quantitative information about the inter- and intra-frac- tional motion of the target, which comprises the SM portion of the PTV. The basics of the LD-MV CBCT are as follows; the target is replaced with a low Z material, the flattening filter is removed and the beam energy is lowered by approximately 25%. Results: Per protocol, the LD-MV CBCT will deliver 1.0 cGy per scan at isocenter, with the mean dose of the imaged estimated to be 10-20 percent lower. In one week, the dose to the patient due to the CBCT will be approximately 7.5 cGy. Routine weekly localization/portal images will not be required. Localization/verification portal images on average deliver an additional 3.5 cGy at isocenter. At our institution, the verification ports are acquired on average twice a week. Therefore, the patient receives only 0.5 cGy a week extra when daily LD-MV CBCT is used compared to once a week port films. Conclusions: The LD-MV CBCT holds promise as an effective, accurate, and precise means of localizing pediatric patients on a daily basis whilst minimizing extraneous dose. Author Disclosure: C. Beltran, Beltran has a Grant from Siemens, B. Research Grant; A. Bani-Hashemi, Bani-Hashemi is employed by Siemens, A. Employment; B. Faddegon, Faddegon has a Grant from Siemens, B. Research Grant; T.E. Merchant, None. S678 I. J. Radiation Oncology d Biology d Physics Volume 72, Number 1, Supplement, 2008
Transcript of Low Dose MV CBCT for Daily Pediatric Localization
S678 I. J. Radiation Oncology d Biology d Physics Volume 72, Number 1, Supplement, 2008
Conclusions: Helical IMRT reduces the mean dose to the temporal lobes, chiasm and pituitary, but increases low doses to normaltissues. Whole ventricular irradiation for pediatric intracranial GCT using helical IMRT may reduce the likelihood of neurologicalsequelae, but may increase the risk of radioinduced secondary malignancies.
Author Disclosure: S. Supiot, None; C. Munos, None; M. Mahe, None; A. Lisbona, None.
3131 Interclinician Variability in Making Nephroblastoma Dosimetric Decision: A Matter of Compromises
L. Padovani1, A. Huchet2, V. Bernier3, P. Quetin4, M. Mahe5, P. Bondiau6, C. Kerr7, C. Carrie8, X. Muracciole1
1Hopital de la Timone, Marseille, France, 2Hopital St Andre, CHU, Bordeaux, France, 3Centre Alexis Vautrin, Nancy, France,4Centre Paul Strauss, Strasbourg, France, 5Centre Rene Gauducheau, Nantes, France, 6Centre Antoine Lacassagne, Nice,France, 7Centre Val d’Aurelle Paul Lamarque, Montpellier, France, 8Centre Leon Berard, Lyon, France
Purpose/Objective(s): To assess the inter clinician variability in delineating CT target volume (CTV), and in dosimetric planningfor nephroblastoma (NB) treatment. Most patients with NB do meet the dose requirements of normal tissue and CTV. For the cat-egory of patients who don’t, we investigated different types of relaxation for planning goals for the most normal tissue constrainingparameters (NTCP).
Materials/Methods: Using the same case of high risk NB, 6 French pediatric radiation oncology teams outlined the post operativeCTV (no macroscopic disease) on dosimetric CT scan, applying radiotherapy guidelines of NB SIOP protocol. On the same CTVand organ at risk (OAR) every clinician made dosimetric planning taking into account limited toxic doses to the OAR, and tumorcontrol probability (TCP). The protocol guidelines recommendation was 25.2 Gy for CTV, a maximal dose of 20 Gy and 12 Gy forrespectively 50% of liver’s and 15% of controlateral kidney’s volume, and homogenous dose to vertebral bodies (at least 95% re-ceiving 20 Gy). Quantitative volume analysis in 3 dimensions was carried out on the resulting CTVs and conformity index as wellas an other analysis of treatment plans with different combinations of TCP and NTCP using Aquilab soft.
Results: The defined CTV showed a large inter clinician variability. The dimension of the target volume had interclinician rangesof 80 to 92 mm cranio-caudal, 65 to 79 mm left-right, 50 to 74 mm antero-posterior. One team proposed an IMRT plan while theothers proposed 3D-CRT plan. The correlation between target and normal structures showed no decreased dose to the CTV whilerelaxing the recommended liver doses in 4 cases : respectively more than 20 Gy at 74%, 75%, 78%, and 88% of the volume. Themaximal over reference dose ratio for CTV ranged from 1.03 to 1.11 with an optimal ratio of 1.07. For controlateral kidneyconstraints, 4 plans reached the goal and 2 relaxed : 17.6% and 25% respectively with more than 12 Gy. For vertebral bodies,1 plan respected the constraint, 5 resulted in relaxing it with 66.6%, 74%, 78.5%, 87.6%, and 90% of volume receiving a doseup to 20 Gy.
Conclusions: This study reveals a large variability in CTV delineation of NB based on preoperative volume. Given this informa-tion one could suggest a reduction of the CTV to normal tissue surfaces in contact with preoperative tumor. It would result inreducing irradiated OAR significantly. This study also leads to the conclusion that in order to deliver the total dose to CTV andyet maintain an acceptable NTCP, different compromises reflecting differences of late effect risks have to be considered. It seemsimportant to characterize tradeoffs among conflicting goals, relaxing those that provide the most benefit for each patient usinga hierarchical optimization process.
Author Disclosure: L. Padovani, None; A. Huchet, None; V. Bernier, None; P. Quetin, None; M. Mahe, None; P. Bondiau, None;C. Kerr, None; C. Carrie, None; X. Muracciole, None.
3132 Low Dose MV CBCT for Daily Pediatric Localization
C. Beltran1, A. Bani-Hashemi2, B. Faddegon3, T. E. Merchant1
1St. Jude Children’s Research Hospital, Memphis, TN, 2Siemens Medical, Concord, CA, 3UCSF, San Francisco, CA
Purpose/Objective(s): An IRB approved pediatric localization clinical protocol began accruing research participants in March2008, in which CBCT is a central component. Because extraneous radiation is a major concern for pediatric patients, a modifiedversion of the Siemens Mega Voltage CBCT (Siemens Medical USA, Concord, CA) was implemented to allow for low dose MegaVoltage CBCT (LD-MV CBCT) imaging. Data will be gathered to quantify the setup margin (SM) portion of the Planning TargetVolume (PTV) margin for pediatric tumor sites according to age, localization technique, treatment position, and the use of generalanesthesia.
Materials/Methods: The research participants will be assigned a non-ionizing localization technique, such as optical tracking,ultrasound, or visual marks, based on disease site, treatment position, age, and use of anesthesia. After the non-ionizing localizationtechnique, each patient will receive a LD-MV CBCT at the start of each fraction and the end of every other fraction. The pre-treat-ment LD-MV CBCT will be used to assess the accuracy of the localization technique, and the post-treatment LD-MV CBCT willquantify the rigidity of the immobilization schema used; thereby providing quantitative information about the inter- and intra-frac-tional motion of the target, which comprises the SM portion of the PTV.
The basics of the LD-MV CBCT are as follows; the target is replaced with a low Z material, the flattening filter is removed andthe beam energy is lowered by approximately 25%.
Results: Per protocol, the LD-MV CBCT will deliver 1.0 cGy per scan at isocenter, with the mean dose of the imaged estimated tobe 10-20 percent lower. In one week, the dose to the patient due to the CBCT will be approximately 7.5 cGy. Routine weeklylocalization/portal images will not be required. Localization/verification portal images on average deliver an additional 3.5 cGyat isocenter. At our institution, the verification ports are acquired on average twice a week. Therefore, the patient receives only0.5 cGy a week extra when daily LD-MV CBCT is used compared to once a week port films.
Conclusions: The LD-MV CBCT holds promise as an effective, accurate, and precise means of localizing pediatric patients ona daily basis whilst minimizing extraneous dose.
Author Disclosure: C. Beltran, Beltran has a Grant from Siemens, B. Research Grant; A. Bani-Hashemi, Bani-Hashemi is employedby Siemens, A. Employment; B. Faddegon, Faddegon has a Grant from Siemens, B. Research Grant; T.E. Merchant, None.
