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Dosimetric Consequences of Intrafraction Prostate Motion on Patients Enrolled on Multi-Institutional Hypofractionation Study

2007; Elsevier BV; Volume: 69; Issue: 3 Linguagem: Inglês

10.1016/j.ijrobp.2007.07.041

1879-355X

B. Pierburg, Parag J. Parikh, M. Roy, P. Kupelian, A. Mahadevan, G. Weinstein, C Enke, N. Flores, David Beyer, L. Levine,

Digital Radiography and Breast Imaging

Purpose/Objective(s)RTOG 0415 is a prospective, randomized study investigating hypofractionated radiation therapy for low risk prostate cancer. It mandates daily localization and recommends a minimal margin of 4 mm. The aim of this study was to determine the dosimetric effect of intrafraction prostate motion on patients planned on this study.Materials/MethodsThe Calypso® 4D Localization system was used to localize and continuously track the prostate isocenter (at a rate of 10 Hz) of 35 patients throughout the course of radiation therapy, representing 195 hours of tracking information captured in over 1228 separate tracking files. Probability distribution functions were generated from each tracking session by creating 5 × 5 × 5 matrices that represented the percent time spent in each of one-hundred and twenty-five 3 × 3 × 3mm bins, creating the largest population database of intrafraction prostate motion that we know of.Two patients from our institution who are enrolled on RTOG 0415 were randomly selected to have IMRT plans created with 3 mm, 4 mm and 5 mm uniform margins from the prostate to the PTV (Pinnacle 7.6, Philips Medical Systems). The control arm of the protocol specifies 73.8 Gy to the PTV, with >98% coverage of the PTV and 100% coverage of the prostate. One plan was a 5-field SMLC plan, and the other used 7 fields. The plans were exported to the Computation Environment for Radiation Research (CERR) where the dose distributions were individually convolved with each probability distribution function to generate motion-effected dose distributions (Matlab R2006b, Mathworks, MA). The number of fractions that resulted in a minimum dose to the prostate below 73.8 Gy was recorded.ResultsConvolution of each plan with the 1228 tracking sessions took 2 hours on a Pentium D 3.60 GHz machine with 3.5 Gb RAM. In both patients, plans with a uniform 5 mm margin resulted in less than 3% of the total fractions with prostate dose less than the prescription dose. In the patient with the 7-field SMLC plan, the 4 mm plan also resulted in 3% of the total fractions receiving less then prescription dose to the prostate. In the patient with the 5-field SMLC plan, the 4 mm plan resulted in 12% of the total fractions receiving less than the prescription dose to the prostate, with a range of 0–61% depending on which historical patient set of tracking data was used. The 3 mm plans resulted in 20% and 30% of the total fractions receiving less than the prescription dose to the prostate in the 7-field and 5-field plan, respectively.ConclusionsIntrafraction prostate motion may cause dosimetric consequences in patients who are enrolled on RTOG 0415, who have daily localization, and are planned with 4 mm margins. Plans with 5 mm margins do not show a dosimetric effect. It is unclear whether the different results between the two patients are a result of technique, anatomy or both. More work needs to be done to quantify the effects of rotation, deformation, MLC- prostate motion interplay, time from localization to therapy delivery, and duration of delivery on the dosimetric effects of intrafraction prostate motion on prostate and surrounding structures. Purpose/Objective(s)RTOG 0415 is a prospective, randomized study investigating hypofractionated radiation therapy for low risk prostate cancer. It mandates daily localization and recommends a minimal margin of 4 mm. The aim of this study was to determine the dosimetric effect of intrafraction prostate motion on patients planned on this study. RTOG 0415 is a prospective, randomized study investigating hypofractionated radiation therapy for low risk prostate cancer. It mandates daily localization and recommends a minimal margin of 4 mm. The aim of this study was to determine the dosimetric effect of intrafraction prostate motion on patients planned on this study. Materials/MethodsThe Calypso® 4D Localization system was used to localize and continuously track the prostate isocenter (at a rate of 10 Hz) of 35 patients throughout the course of radiation therapy, representing 195 hours of tracking information captured in over 1228 separate tracking files. Probability distribution functions were generated from each tracking session by creating 5 × 5 × 5 matrices that represented the percent time spent in each of one-hundred and twenty-five 3 × 3 × 3mm bins, creating the largest population database of intrafraction prostate motion that we know of.Two patients from our institution who are enrolled on RTOG 0415 were randomly selected to have IMRT plans created with 3 mm, 4 mm and 5 mm uniform margins from the prostate to the PTV (Pinnacle 7.6, Philips Medical Systems). The control arm of the protocol specifies 73.8 Gy to the PTV, with >98% coverage of the PTV and 100% coverage of the prostate. One plan was a 5-field SMLC plan, and the other used 7 fields. The plans were exported to the Computation Environment for Radiation Research (CERR) where the dose distributions were individually convolved with each probability distribution function to generate motion-effected dose distributions (Matlab R2006b, Mathworks, MA). The number of fractions that resulted in a minimum dose to the prostate below 73.8 Gy was recorded. The Calypso® 4D Localization system was used to localize and continuously track the prostate isocenter (at a rate of 10 Hz) of 35 patients throughout the course of radiation therapy, representing 195 hours of tracking information captured in over 1228 separate tracking files. Probability distribution functions were generated from each tracking session by creating 5 × 5 × 5 matrices that represented the percent time spent in each of one-hundred and twenty-five 3 × 3 × 3mm bins, creating the largest population database of intrafraction prostate motion that we know of. Two patients from our institution who are enrolled on RTOG 0415 were randomly selected to have IMRT plans created with 3 mm, 4 mm and 5 mm uniform margins from the prostate to the PTV (Pinnacle 7.6, Philips Medical Systems). The control arm of the protocol specifies 73.8 Gy to the PTV, with >98% coverage of the PTV and 100% coverage of the prostate. One plan was a 5-field SMLC plan, and the other used 7 fields. The plans were exported to the Computation Environment for Radiation Research (CERR) where the dose distributions were individually convolved with each probability distribution function to generate motion-effected dose distributions (Matlab R2006b, Mathworks, MA). The number of fractions that resulted in a minimum dose to the prostate below 73.8 Gy was recorded. ResultsConvolution of each plan with the 1228 tracking sessions took 2 hours on a Pentium D 3.60 GHz machine with 3.5 Gb RAM. In both patients, plans with a uniform 5 mm margin resulted in less than 3% of the total fractions with prostate dose less than the prescription dose. In the patient with the 7-field SMLC plan, the 4 mm plan also resulted in 3% of the total fractions receiving less then prescription dose to the prostate. In the patient with the 5-field SMLC plan, the 4 mm plan resulted in 12% of the total fractions receiving less than the prescription dose to the prostate, with a range of 0–61% depending on which historical patient set of tracking data was used. The 3 mm plans resulted in 20% and 30% of the total fractions receiving less than the prescription dose to the prostate in the 7-field and 5-field plan, respectively. Convolution of each plan with the 1228 tracking sessions took 2 hours on a Pentium D 3.60 GHz machine with 3.5 Gb RAM. In both patients, plans with a uniform 5 mm margin resulted in less than 3% of the total fractions with prostate dose less than the prescription dose. In the patient with the 7-field SMLC plan, the 4 mm plan also resulted in 3% of the total fractions receiving less then prescription dose to the prostate. In the patient with the 5-field SMLC plan, the 4 mm plan resulted in 12% of the total fractions receiving less than the prescription dose to the prostate, with a range of 0–61% depending on which historical patient set of tracking data was used. The 3 mm plans resulted in 20% and 30% of the total fractions receiving less than the prescription dose to the prostate in the 7-field and 5-field plan, respectively. ConclusionsIntrafraction prostate motion may cause dosimetric consequences in patients who are enrolled on RTOG 0415, who have daily localization, and are planned with 4 mm margins. Plans with 5 mm margins do not show a dosimetric effect. It is unclear whether the different results between the two patients are a result of technique, anatomy or both. More work needs to be done to quantify the effects of rotation, deformation, MLC- prostate motion interplay, time from localization to therapy delivery, and duration of delivery on the dosimetric effects of intrafraction prostate motion on prostate and surrounding structures. Intrafraction prostate motion may cause dosimetric consequences in patients who are enrolled on RTOG 0415, who have daily localization, and are planned with 4 mm margins. Plans with 5 mm margins do not show a dosimetric effect. It is unclear whether the different results between the two patients are a result of technique, anatomy or both. More work needs to be done to quantify the effects of rotation, deformation, MLC- prostate motion interplay, time from localization to therapy delivery, and duration of delivery on the dosimetric effects of intrafraction prostate motion on prostate and surrounding structures.