Dosimetry challenges and opportunities in modern radiation therapy

Modern radiation therapy (RT) includes conformal therapy, intensity modulated radiation therapy, proton therapy, image-guided radiation therapy, adaptive radiation therapy (ART), and recently magnetic-resonance guided radiation therapy and, upcoming, 4 pi radiation therapy. These techniques show the continual increase in complexity of radiation therapy techniques which, coupled with a stagnant medical physics workforce, means that the amount and complexity of work per physicist has increased and is likely to increase in the foreseeable future. Three distinct challenges can be identified that need to be addressed. First, is the recent commercial development of automated multi-metastases stereotactic radiosurgery (SRS) techniques. These techniques plan and irradiate a number (up to approximately 20) brain lesions in one treatment session, typically employing one isocenter. The spatial accuracy specifications for SRS imply that attention to the angular accuracy is more critical for these treatments than conventional SRS or other treatment methods. In parallel, our and other groups are developing 4 pi techniques, which is a proposed method for optimizing both beam angles and intensity fluence to provide x-ray based dose distributions with unparalleled compactness and conformality. One cost to deliver these dose distributions is the added requirement to not only rotate the couch but also shift the couch to increase the number of available beam angles. These two techniques will require efficient and quantitative dose distribution measurements of relatively large volumes for, at least, end to end testing of multi-metastases and 4 pi treatments. Finally, magnetic resonance guided radiation therapy has led to a resurgence in the development of on-table ART, which requires that the medical physicist compare two calculated treatment plans and efficiently and effectively determine if differences between those treatment plans are clinically significant. Modifying and improving existing tools will be critical to the safe and effective on-table ART.