- Email: [email protected]
benefit optimization in AVM radiosurgery in single or repeated sessions
$70
Thursday, 20 September 2001
Teaching Lectures 198
Risk/benefit optimization in AVM radiosurgery in single or repeated sessions B. Karlsson, I. Lax Departments of Neurosurgery (BK) and Hospital Physics (IL), Karolinska Hospital, Stockholm, Sweden The results following AVM radiosurgery is usually defined after the first treatment. It has been shown, however, that a second radiosurgical treatment should there be a small AVM remnant, still may be the optimal treatment for the patient. By using existing outcome prediction model, the probability for cure (Pobl= 35.69*ln(DmLn)-39.66; 0< Pobl <100) as well as the risk for adverse radiation effects (ARE=0,0688*Dave''') as well as the risk for AVM hemorrhage (7.53*exp (-0.00219*(Drain)2) in the latency time period following the treatment can be calculated. Thus, the dose dependent riskJbenefit relation can be calculated to optimize the prescription dose. However, by using the extended definitioin of radiosurgery suggested below, this analysis can be taken a step further. By utilizing the fact that almost all AVMs that do not completely obliterate following AVM radiosurgery significantly decrease in size, a potential second treatment can be taken into consideration before the optimal dose is decided. It will be shown that this makes radiosurgery a viable option also for the treatment of large AVMs with an acceptably rislVbenefit ratio, especially when compared to other treatment options as well as the natural course of the disease. A caveat is the yet unknown risk for long long term complications. In addition, before this can be scientifically validated, a relation between the treatment dose and the decrease of the >AVM volume in the patient AVMs following the first treatment needs to be substantiated, a work that has been initiated but yet not finalized. The present paper underlines that the definition of radiosurgery as a single session of radiation delivered to a small target volume may be questionable, it can be discussed if not too much importance is focused on the number of sessions rather than the importance of the highly conformal dose distributiion of radiation. Instead, maybe radiosurgery should be defined as a highly confrmal radiation delivery in a small number of sessions. This difference may sound as insignificant, but it may actually have an impact on the use of this treatment strategy, for instance for large AVMs. 199
Volume effects in plan evaluation A. Jackson Memorial Sloan-Kettering Cancer Ctr, Dept. of Medical Physics, New York, U.S.A. External beam radiotherapy for the treatment of cancer ideally seeks to locally eliminate tumor cells without causing complications in normal organs. Since tumors arise in the midst of normal tissues, in many disease sites radiation aimed at tumors must pass through normal organs and this ideal outcome cannot be achieved. Instead, proper treatment planning seeks to maximize local control while maintaining acceptable rates of normal tissue complications. To this end, we need to understand Tumor Control Probability (TCP) and Normal Tissue Complication Probability (NTCP) under conditions of inhomogeneous irradiation. In particular, beyond whole volume dose responses, we need to know how TCP deteriorates as the size and depth of cold-spots in the target increase, and how NTCP decreases as volume of a normal organ irradiated to significant doses decreases (volume effects). We will review models of volume effects devised to describe and predict the outcome of external beam radiotherapy for the treatment of cancer using dosevolume histograms (DV Hs). The Serial, Parallel, Relative Seriality, and Lyman models, which seek to describe the probability of specific complication endpoints in organs at risk after inhomogeneous irradiation, will be discussed. The differences and similarities of these models and their associated histogram reduction schemes will be described in terms of partial volume irradiation. TCP models based on Poisson cell kill statistics will be discussed, including the methods used to describe the relatively shallow dose response of tumors observed clinically. The relationship of TCP and NTCP models to the concept of Equivalent Uniform Dose (EUD) will be discussed. The limitations of the models wilt be outlined, stressing both the scarce data underlying the model parameters, and assumption implicit in the use of DVHs of DVH and outcome data in fitting volume effect models; the use of volume effect models in guiding dose-escalation, and the incorporation of more complex geometric dependencies than those allowed by DVHs.
Thursday, 20 September 2001
Teaching Lectures 198
Risk/benefit optimization in AVM radiosurgery in single or repeated sessions B. Karlsson, I. Lax Departments of Neurosurgery (BK) and Hospital Physics (IL), Karolinska Hospital, Stockholm, Sweden The results following AVM radiosurgery is usually defined after the first treatment. It has been shown, however, that a second radiosurgical treatment should there be a small AVM remnant, still may be the optimal treatment for the patient. By using existing outcome prediction model, the probability for cure (Pobl= 35.69*ln(DmLn)-39.66; 0< Pobl <100) as well as the risk for adverse radiation effects (ARE=0,0688*Dave''') as well as the risk for AVM hemorrhage (7.53*exp (-0.00219*(Drain)2) in the latency time period following the treatment can be calculated. Thus, the dose dependent riskJbenefit relation can be calculated to optimize the prescription dose. However, by using the extended definitioin of radiosurgery suggested below, this analysis can be taken a step further. By utilizing the fact that almost all AVMs that do not completely obliterate following AVM radiosurgery significantly decrease in size, a potential second treatment can be taken into consideration before the optimal dose is decided. It will be shown that this makes radiosurgery a viable option also for the treatment of large AVMs with an acceptably rislVbenefit ratio, especially when compared to other treatment options as well as the natural course of the disease. A caveat is the yet unknown risk for long long term complications. In addition, before this can be scientifically validated, a relation between the treatment dose and the decrease of the >AVM volume in the patient AVMs following the first treatment needs to be substantiated, a work that has been initiated but yet not finalized. The present paper underlines that the definition of radiosurgery as a single session of radiation delivered to a small target volume may be questionable, it can be discussed if not too much importance is focused on the number of sessions rather than the importance of the highly conformal dose distributiion of radiation. Instead, maybe radiosurgery should be defined as a highly confrmal radiation delivery in a small number of sessions. This difference may sound as insignificant, but it may actually have an impact on the use of this treatment strategy, for instance for large AVMs. 199
Volume effects in plan evaluation A. Jackson Memorial Sloan-Kettering Cancer Ctr, Dept. of Medical Physics, New York, U.S.A. External beam radiotherapy for the treatment of cancer ideally seeks to locally eliminate tumor cells without causing complications in normal organs. Since tumors arise in the midst of normal tissues, in many disease sites radiation aimed at tumors must pass through normal organs and this ideal outcome cannot be achieved. Instead, proper treatment planning seeks to maximize local control while maintaining acceptable rates of normal tissue complications. To this end, we need to understand Tumor Control Probability (TCP) and Normal Tissue Complication Probability (NTCP) under conditions of inhomogeneous irradiation. In particular, beyond whole volume dose responses, we need to know how TCP deteriorates as the size and depth of cold-spots in the target increase, and how NTCP decreases as volume of a normal organ irradiated to significant doses decreases (volume effects). We will review models of volume effects devised to describe and predict the outcome of external beam radiotherapy for the treatment of cancer using dosevolume histograms (DV Hs). The Serial, Parallel, Relative Seriality, and Lyman models, which seek to describe the probability of specific complication endpoints in organs at risk after inhomogeneous irradiation, will be discussed. The differences and similarities of these models and their associated histogram reduction schemes will be described in terms of partial volume irradiation. TCP models based on Poisson cell kill statistics will be discussed, including the methods used to describe the relatively shallow dose response of tumors observed clinically. The relationship of TCP and NTCP models to the concept of Equivalent Uniform Dose (EUD) will be discussed. The limitations of the models wilt be outlined, stressing both the scarce data underlying the model parameters, and assumption implicit in the use of DVHs of DVH and outcome data in fitting volume effect models; the use of volume effect models in guiding dose-escalation, and the incorporation of more complex geometric dependencies than those allowed by DVHs.