- Email: [email protected]
187
S104
I. J. Radiation Oncology
● Biology ● Physics
Volume 66, Number 3, Supplement, 2006
Author Disclosure: D.P. Gierga, None; J.C. Turcotte, None; M. Riboldi, None; G.C. Sharp, None; S.B. Jiang, None; G.T.Y. Chen, None.
187
Cone-Beam CT Guidance for Daily Setup of Patients Receiving Accelerated Partial Breast Irradiation
E. A. White1, G. Lee1, H. Blackburn1, T. Nageeti1,2, C. McGibney1,2, K. A. Vallis1,2, J. Cho1,2, M. B. Sharpe1,2, D. A. Jaffray1,2 1 Princess Margaret Hospital, Toronto, ON, Canada, 2University of Toronto, Toronto, ON, Canada Purpose/Objective(s): To evaluate the role of cone-beam CT (CBCT) guidance for set-up error reduction and normal tissue visualization in accelerated partial breast irradiation (APBI). Materials/Methods: Ethics approval for the accrual of 20 patients for the delivery of radiation therapy using an APBI technique was obtained. Ten patients have completed treatment to date. The clinical target volume (CTV) is defined as the post-surgical seroma plus 1-2cm, with a further 1cm expansion for the planning target volume (PTV). A dose of 3850cGy was delivered in 10 fractions over 5 days (2 fractions per day). Initial set-up was performed using skin marks for alignment. CBCT datasets were acquired prior to delivery of each fraction and were assessed online. Manual registrations using the ipsilateral lung and external contours were performed. Table corrections were executed for translations exceeding 3mm in any cardinal direction. If a shift from the initial CBCT was implemented a second CBCT dataset was acquired and analyzed. The random and systematic errors associated with setup using skin marks and setup using CBCT guidance were calculated and compared. A margin formula was used to estimate the required PTV margins for each setup method. Results: CBCT datasets were successfully acquired for all fractions for the ten patients treated to date. Retrospective analysis showed that heart and lung could be visualized on all datasets. The CTV was visible on the CBCT images in 9 of the 10 patients. An adjustment to the isocentre was made for 52% of the fractions across all 10 patients. The largest shift applied was 15mm in the AP direction. The random errors for set-up using skin marks were 2.4, 2.3, and 3.3mm in the right-left (RL), anterior-posterior (AP), and superior-inferior (SI) directions respectively. These were reduced to 1.8, 1.8, and 1.7mm in the RL, AP, and SI directions when guidance using CBCT was performed. The systematic errors for set-up using skin marks were 2.4, 1.3, and 1.9mm in the RL, AP, and SI directions respectively. These were subsequently reduced to 0.7, 1.3, and 1.0mm when CBCT guidance was employed. Isotropic PTV margins were calculated to be 8.3mm for skin marks alone and 4.5mm for CBCT guidance. Conclusions: The use of skin marks for the set-up of APBI patients is sufficient for current PTV margins. Online CBCT guidance minimizes the occurrence of large random deviations, which may have a greater impact for accelerated fractionation schedules. CBCT guidance may also permit a reduction in PTV margins and provides additional benefits that include skin-line visualization and dosimetric evaluation of cardiac and lung volumes. Author Disclosure: E.A. White, None; G. Lee, None; H. Blackburn, None; T. Nageeti, None; C. McGibney, None; K.A. Vallis, None; J. Cho, None; M.B. Sharpe, None; D.A. Jaffray, None.
188
True in-Vivo Dosimetry in Breast and Prostate Cancer Patients: Variance Between Predicted and Measured Dose
C. Scarantino1,2, B. Prestidge3, M. Anscher4, C. Ferree5, R. Black2, G. P. Beyer2 Rex Cancer Center, Raleigh, NC, 2Sicel Technologies Inc, Morrisville, NC, 3Texas Cancer Clinic, San Antonio, TX, 4Duke Univ Medical School, Durham, NC, 5Wake Forest School Medicine, Winston-Salem, NC
1
Purpose/Objective(s): Although IGRT allows for the identification of a target prior to radiation therapy and therefore more precise treatment, it cannot account for organ movement, tissue inhomogeneity changes, or errors during treatment. However, an implantable dosimeter can act as both: a fiducial marker for IGRT and a dosimeter for verification of dose delivered. Variance between predicted and measured dose, as previously reported1, would allow to adjust treatment plans and resulting dose delivery to minimize variation within and between patients. This study expands on earlier findings on the use of an implantable dosimeter for validating radiation dose delivered and the concept of integrating a dose verification system (DVS) with dose guided radiation therapy (DGRT). Materials/Methods: The implantable or in-vivo dosimeter is a product of Sicel Technologies, Inc2. In vitro testing has confirmed its accuracy3. The primary endpoints of this study were: a) determine the degree of movement and adverse events associated with the device; b) compare in vivo measured dose to calculated dose. Sixty patients (pts),- 30 breast and 30 prostate -were entered in an FDA approved pivotal trial. Insertion methods were previously described1. Following implantation of the dosimeters (49/60 pts received 2 dosimeters) a predicted dose point calculation was determined at the location of the dosimeter end of the device. CT scans were obtained every two weeks to determine device migration. Dose measurements were made following each treatment session. Results: To date 59 of the 60 patients have completed radiation therapy. There have been 3 cases of movement ⬎5mm (all device related) and no significant untoward adverse events associated with the device. The results of the dosimetric readings confirm the previously reported variance between predicted and measured dose. Greater than 1,600 dose measurements were available for evaluation. Of the breast pts, 40% had a variance ⬎5% and 21% had a variance of ⬎7%. For prostate pts., 36% had a variance ⬎5% and 22% of pts. had a variance ⬎7%. Also, 66% of pts had at least one sensor that registered variance ⱖ 5% during primary field treatment 25% of the time and 31% registered ⱖ7% variance 25% of the time. Analysis of dose measurement for individual patients helped define patterns of random (⬎3%-day to day deviation) and systematic (⬎5-7% persistent) variance. In addition, significant ⬎7%, variance was noted in the prostate pts treated with IGRT assistance. Conclusions: Significant variation between predicted and measured dose was observed in at least 33% of pts, with individual patterns able to identify random or systematic deviations. Although plan adjustment was not permitted in study protocol, in the future DVS may be utilized with planning and delivery tools to adjust the plan and mitigate set up errors . The variance noted
I. J. Radiation Oncology
● Biology ● Physics
Volume 66, Number 3, Supplement, 2006
Author Disclosure: D.P. Gierga, None; J.C. Turcotte, None; M. Riboldi, None; G.C. Sharp, None; S.B. Jiang, None; G.T.Y. Chen, None.
187
Cone-Beam CT Guidance for Daily Setup of Patients Receiving Accelerated Partial Breast Irradiation
E. A. White1, G. Lee1, H. Blackburn1, T. Nageeti1,2, C. McGibney1,2, K. A. Vallis1,2, J. Cho1,2, M. B. Sharpe1,2, D. A. Jaffray1,2 1 Princess Margaret Hospital, Toronto, ON, Canada, 2University of Toronto, Toronto, ON, Canada Purpose/Objective(s): To evaluate the role of cone-beam CT (CBCT) guidance for set-up error reduction and normal tissue visualization in accelerated partial breast irradiation (APBI). Materials/Methods: Ethics approval for the accrual of 20 patients for the delivery of radiation therapy using an APBI technique was obtained. Ten patients have completed treatment to date. The clinical target volume (CTV) is defined as the post-surgical seroma plus 1-2cm, with a further 1cm expansion for the planning target volume (PTV). A dose of 3850cGy was delivered in 10 fractions over 5 days (2 fractions per day). Initial set-up was performed using skin marks for alignment. CBCT datasets were acquired prior to delivery of each fraction and were assessed online. Manual registrations using the ipsilateral lung and external contours were performed. Table corrections were executed for translations exceeding 3mm in any cardinal direction. If a shift from the initial CBCT was implemented a second CBCT dataset was acquired and analyzed. The random and systematic errors associated with setup using skin marks and setup using CBCT guidance were calculated and compared. A margin formula was used to estimate the required PTV margins for each setup method. Results: CBCT datasets were successfully acquired for all fractions for the ten patients treated to date. Retrospective analysis showed that heart and lung could be visualized on all datasets. The CTV was visible on the CBCT images in 9 of the 10 patients. An adjustment to the isocentre was made for 52% of the fractions across all 10 patients. The largest shift applied was 15mm in the AP direction. The random errors for set-up using skin marks were 2.4, 2.3, and 3.3mm in the right-left (RL), anterior-posterior (AP), and superior-inferior (SI) directions respectively. These were reduced to 1.8, 1.8, and 1.7mm in the RL, AP, and SI directions when guidance using CBCT was performed. The systematic errors for set-up using skin marks were 2.4, 1.3, and 1.9mm in the RL, AP, and SI directions respectively. These were subsequently reduced to 0.7, 1.3, and 1.0mm when CBCT guidance was employed. Isotropic PTV margins were calculated to be 8.3mm for skin marks alone and 4.5mm for CBCT guidance. Conclusions: The use of skin marks for the set-up of APBI patients is sufficient for current PTV margins. Online CBCT guidance minimizes the occurrence of large random deviations, which may have a greater impact for accelerated fractionation schedules. CBCT guidance may also permit a reduction in PTV margins and provides additional benefits that include skin-line visualization and dosimetric evaluation of cardiac and lung volumes. Author Disclosure: E.A. White, None; G. Lee, None; H. Blackburn, None; T. Nageeti, None; C. McGibney, None; K.A. Vallis, None; J. Cho, None; M.B. Sharpe, None; D.A. Jaffray, None.
188
True in-Vivo Dosimetry in Breast and Prostate Cancer Patients: Variance Between Predicted and Measured Dose
C. Scarantino1,2, B. Prestidge3, M. Anscher4, C. Ferree5, R. Black2, G. P. Beyer2 Rex Cancer Center, Raleigh, NC, 2Sicel Technologies Inc, Morrisville, NC, 3Texas Cancer Clinic, San Antonio, TX, 4Duke Univ Medical School, Durham, NC, 5Wake Forest School Medicine, Winston-Salem, NC
1
Purpose/Objective(s): Although IGRT allows for the identification of a target prior to radiation therapy and therefore more precise treatment, it cannot account for organ movement, tissue inhomogeneity changes, or errors during treatment. However, an implantable dosimeter can act as both: a fiducial marker for IGRT and a dosimeter for verification of dose delivered. Variance between predicted and measured dose, as previously reported1, would allow to adjust treatment plans and resulting dose delivery to minimize variation within and between patients. This study expands on earlier findings on the use of an implantable dosimeter for validating radiation dose delivered and the concept of integrating a dose verification system (DVS) with dose guided radiation therapy (DGRT). Materials/Methods: The implantable or in-vivo dosimeter is a product of Sicel Technologies, Inc2. In vitro testing has confirmed its accuracy3. The primary endpoints of this study were: a) determine the degree of movement and adverse events associated with the device; b) compare in vivo measured dose to calculated dose. Sixty patients (pts),- 30 breast and 30 prostate -were entered in an FDA approved pivotal trial. Insertion methods were previously described1. Following implantation of the dosimeters (49/60 pts received 2 dosimeters) a predicted dose point calculation was determined at the location of the dosimeter end of the device. CT scans were obtained every two weeks to determine device migration. Dose measurements were made following each treatment session. Results: To date 59 of the 60 patients have completed radiation therapy. There have been 3 cases of movement ⬎5mm (all device related) and no significant untoward adverse events associated with the device. The results of the dosimetric readings confirm the previously reported variance between predicted and measured dose. Greater than 1,600 dose measurements were available for evaluation. Of the breast pts, 40% had a variance ⬎5% and 21% had a variance of ⬎7%. For prostate pts., 36% had a variance ⬎5% and 22% of pts. had a variance ⬎7%. Also, 66% of pts had at least one sensor that registered variance ⱖ 5% during primary field treatment 25% of the time and 31% registered ⱖ7% variance 25% of the time. Analysis of dose measurement for individual patients helped define patterns of random (⬎3%-day to day deviation) and systematic (⬎5-7% persistent) variance. In addition, significant ⬎7%, variance was noted in the prostate pts treated with IGRT assistance. Conclusions: Significant variation between predicted and measured dose was observed in at least 33% of pts, with individual patterns able to identify random or systematic deviations. Although plan adjustment was not permitted in study protocol, in the future DVS may be utilized with planning and delivery tools to adjust the plan and mitigate set up errors . The variance noted