Principles of Treatment Planning

In treatment planning three aspects can be considered in general: tumor localization, treatment strategy, and treatment simulation. In tumor localization the exact location of the tumor is defined in relation to critical organs and patient coordinates. All information about available equipment and equipment behavior in relation to tumor location defines the treatment strategy. Finally, the complete treatment has to be simulated on the planning computer; furthermore, when using radiotherapy a treatment simulator is often employed, and when using hyperthermia “dry runs” with the actual heating equipment are sometimes conducted to complete the simulation procedure (MYERSON et al. 1991). In radiotherapy, patient treatment position verification using the laser alignment system, the light field, and the optical distance indicator in relation to skin markers and megavolt imaging (MEERTENS et al. 1990; VISSER et al. 1990) completes the treatment planning and guarantees an overall accuracy of about 5% (BRAHME et al. 1988). In hyperthermia, because of the influence of physiology where 80%–90% of all heat transfer is directly related to blood flow (LAGENDIJK et al. 1988), it is impossible to predict the final temperature distribution with reasonable accuracy. It is an absolute necessity to have a feedback system during the actual treatment. ROEMER and CETAS (1984) called this concurrent dosimetry; it entails the use of (invasive) thermometry and E-field probes to measure the temperature, the absorbed power (SAR) distributions, tissue cooling rates (ROEMER 1990; DE LEEUW et al. 1993), and effective thermal conductivities (CREZEE and LAGENDIJK 1990). After treatment all these treatment data can be used to optimize the treatment planning computations. ROEMER and CETAS (1984) called this retrospective thermal dosimetry, i.e., the use of all treatment data to calculate the final temperature/thermal dose distribution given. However, in must be stated that, except for simple temperature control feedback, no clinical (treatment planning) systems have been described in the literature which use these concurrent and retrospective thermal dosimetry aspects systematically to optimize treatment. As a first step, in vivo SAR measurements for optimizing regional RF hyperthermia are entering clinical use (DE LEEUW et al. 1993; WUST et al. 1992).