Margriet Kwint

Chapter 8 156 Part II Image Guided Radiotherapy Image guided radiotherapy and adaptive radiotherapy Nowadays, image guided radiotherapy (IGRT) using CBCT for position verification and dosimetric quality assurance, is widely adopted in radiotherapy departments around the world (36). Repeated CBCT’s made us aware of intra thoracic anatomical changes (ITAC) during the treatment course of lung cancer patients. In the Netherlands, CBCT’s are typically analyzed by radiation therapy technologists (RTTs); the radiation oncologist is informed only when a change is observed. It is important that the RTT knows how to act on these detected ITACs. Therefore, a practical decision support system: “the traffic-light protocol”, was developed in our institute to guide the RTT. Chapter 4 describes the quantity of ITACs during the course of a radical radiotherapy treatment for LA-NSCLC patients. The traffic-light protocol has three urgency levels: red (considerable impact on dose distribution), orange (moderate impact on dose distribution) and green (negligible impact on dose distribution). The traffic-light protocol was retrospectively applied to all CBCT-scans of 177 patients. In the majority of the patients (72%) ITAC’s were observed and 8% of the patients required a new planning CT-scan and an adapted treatment plan to account for anatomical changes. This study illustrated that ITACs indeed frequently occur and that it is important to have a practical decision support system in daily clinical practice to adequately react to these ITACs. Several studies reported on the dosimetric consequences of ITACs during treatment (37-39). A strategy to adjust for these ITACs is adaptive radiotherapy by performing a re-planning (40). Adaptive radiotherapy has the unique ability to prevent under dosing of the primary tumor or increased dose to the OARs when e.g. a tumor baseline shift or atelectasis occurs. Another advantage of adaptive radiotherapy is the possibility to reduce the dose to the OAR while maintaining the dose to the primary tumor after tumor regression is seen on a CBCT. This adaptive strategy raised the concern of local failure due to under dosing of microscopic disease in the new treatment plan. The LARTIA study (41) investigated the failure pattern of LA-NSCLC patients with an adaptive approach. A re-planning was performed in 50 out of 217 patients (23%). The decisionof re-planningwas basedon regression seenonweekly CT- scans during treatment, visualized by 2 radiation oncologist, without a predetermined classification criteria. A local failure rate of 30% was reported (median follow-up of 25.8 months) in this trial which is comparable to the 25%-40% local failure rate in published literature (4, 9, 42, 43). Local failures were in-field (20%), marginal (6%), and