摘要
Purpose: To develop a new statistical index “percent CTV (clinical target vo-lume) coverage probability” (%CCP), defined as the probability that a specific percent (e.g., 95%) of the CTV can be reliably covered by the prescription dose, for evaluating the coverage loss of brain (fractionated) stereotactic radiosurgery (SRS/fSRS) when the PTV (planning target volume) margin is zero. Methods: The random variable Q for CTV percent coverage was derived using a previously developed model for CTV random motion that follows a three-dimensional (3D) independent normal distribution with a zero mean and a standard deviation of 𝜎<sub>𝑆</sub>(for translation) or 𝜎<sub>𝛿</sub>(for rotation). Assuming both CTV and PTV are spherical with the same diameter d<sub>CTV</sub>, the cumulative distribution function of Q could be obtained analytically using the relation of sphere-sphere intersection. The %CCP was then derived as the reliability function of Q and was used to quantify the coverage loss for selected d<sub>CTV</sub>. Results: The 95%-95% clinical goal (95% of the times, at least 95% of the CTV is covered) is not achievable with d<sub>CTV</sub> mm. For common CTVs (d<sub>CTV</sub> mm) encountered in SRS/fSRS, only 60%-90% of the CTV could be reliably covered by the prescription dose 95% of the time. For 𝜎𝑆</sub></sub>=0.5mm and 𝜎𝛿</sub></sub> =0.4˚, the 95% CCP was the highest when the distance between the CTV and the isocenter 𝑑𝐼⇔𝑇</sub><sub></sub>=0 and gradually decreased with the increasing 𝑑<sub>𝐼⇔𝑇</sub></sub>. Conclusions: The %CCP was successfully derived for evaluating the CTV coverage loss for brain SRS/fSRS. When the PTV margin is zero, the 95%-95% clinical goal cannot be achieved for most targets (d<sub>CTV</sub> mm).
Purpose: To develop a new statistical index “percent CTV (clinical target vo-lume) coverage probability” (%CCP), defined as the probability that a specific percent (e.g., 95%) of the CTV can be reliably covered by the prescription dose, for evaluating the coverage loss of brain (fractionated) stereotactic radiosurgery (SRS/fSRS) when the PTV (planning target volume) margin is zero. Methods: The random variable Q for CTV percent coverage was derived using a previously developed model for CTV random motion that follows a three-dimensional (3D) independent normal distribution with a zero mean and a standard deviation of 𝜎<sub>𝑆</sub>(for translation) or 𝜎<sub>𝛿</sub>(for rotation). Assuming both CTV and PTV are spherical with the same diameter d<sub>CTV</sub>, the cumulative distribution function of Q could be obtained analytically using the relation of sphere-sphere intersection. The %CCP was then derived as the reliability function of Q and was used to quantify the coverage loss for selected d<sub>CTV</sub>. Results: The 95%-95% clinical goal (95% of the times, at least 95% of the CTV is covered) is not achievable with d<sub>CTV</sub> mm. For common CTVs (d<sub>CTV</sub> mm) encountered in SRS/fSRS, only 60%-90% of the CTV could be reliably covered by the prescription dose 95% of the time. For 𝜎𝑆</sub></sub>=0.5mm and 𝜎𝛿</sub></sub> =0.4˚, the 95% CCP was the highest when the distance between the CTV and the isocenter 𝑑𝐼⇔𝑇</sub><sub></sub>=0 and gradually decreased with the increasing 𝑑<sub>𝐼⇔𝑇</sub></sub>. Conclusions: The %CCP was successfully derived for evaluating the CTV coverage loss for brain SRS/fSRS. When the PTV margin is zero, the 95%-95% clinical goal cannot be achieved for most targets (d<sub>CTV</sub> mm).
作者
Jenghwa Chang
Jenghwa Chang(Department of Radiation Medicine, Northwell Health and Donald and Barbara Zucker School of Medicine at Hofstra/Northwell, New York, USA;Department of Physics and Astronomy, Hofstra University, New York, USA)
