ESTRO 38 Abstract book

S606 ESTRO 38

were corrected online using cone-beam CT. Interfraction and intrafraction clipbox translations and rotations were assessed. Linear mixed models were used to calculate differences between cohorts. Results A total of 1,605 matches were performed derived from 827 cone-beam CT’s in 413 fractions. Interfraction mean translation vectors of the clipbox were <1.5 mm for all cohorts. These vectors were significantly lower for IHS-6 compared to SHS-3 (0.8±0.3 vs. 1.4±0.7 mm, P =0.001). Interfraction translation vectors of ≥2 mm were seen in 22%, 7%, and 5% of fractions for SHS-3, SHS-6 and IHS-6, respectively (Figure A). Interfraction rotation angles of ≥1 degree were seen in 71% of all fractions for SHS-3, as opposed to <8% of all fractions in the other cohorts (Figure B). Intrafraction clipbox translations and rotations did not differ between cohorts.

The data was taped, transcribed and analyzed within the 5 topics. Results Through the analysis of the interviews it was clear that most of the patients, despite the information provided, had a misconception about how the organs are placed inside the small pelvic – including the prostate. The patients claimed that they understood the protocol presented to them, but most of them were not able to explain why it was important to follow. Some patients had formed their own alternative understanding of why the protocol was important to make sense of it. Almost all patients pointed out that beside side effects from the treatment itself, external factors such as finding a parking lot and different time of treatment appointments, had a negative impact on their ability to follow the protocol. All the patients, who were shown the two images, pointed out that the animated image helped them to a better understanding of the bowel/bladder protocol. The three patients who were shown the animated movie all preferred the movie and the animated image as a combination. All the patients felt that the use of multimedia as an information tool had a great impact on their understanding of the protocol and why it is important The use of multimedia assisted information to patients undergoing curatively intended radiotherapy treatment for prostate cancer can support and improve the understanding of the importance of complying with the bladder/bowel protocol - as well as the understanding of organs anatomical placement in the treatment area. The results of this study are going to be used for further investigation of patient ability, and an animated movie is created as well as animated images are implemented in the department. Even though this study only focuses on patients with prostate cancer, we presume that data can be applied to similar diagnostic groups, that also need to follow a bowel/bladder protocol. PO-1092 The influence of a 6D couch and an individual head support on positioning in head-and- neck cancer M. RodrigueS 1 , S. Veen 1 , J. Van Egmond 2 , M. Van Hameren 1 , T. Van Oorschot 1 , S. De Vet 1 , J. Van Santvoort 2 , R. Wiggenraad 1 , M. Mast 1 1 Haaglanden Medical Center, Radiation Oncology, Leidschendam, The Netherlands ; 2 Haaglanden Medical Center, Medical Physics, Leidschendam, The Netherlands Purpose or Objective Accurate patient positioning in head and neck radiotherapy is of utmost importance because of the enhanced risk of overdosage to radiation-sensitive tissues. A six degrees of freedom couch permits optimization of set-up by enabling correction of rotational errors. Improved patient immobilization can be achieved by adding an individual head support to the immobilization system. No previous study has compared different treatment couches and head supports in combination with online cone-beam CT-based position verification in head and neck radiotherapy. Therefore, the aim of this comparative study was to evaluate the benefit of a six degrees of freedom couch and an individual head support using online cone-beam CT position verification and correction in head-and-neck cancer patients. Material and Methods This prospective study analysed 30 patients in three cohorts. Patients were either treated with a standard head support and conventional three degrees of freedom couch (SHS-3), a standard head support and six degrees of freedom couch (SHS-6), or an individual head support and six degrees of freedom couch (IHS-6). All set-up errors to comply. Conclusion

Conclusion A six degrees of freedom couch and an individual head support in head and neck radiotherapy yields less interfraction clipbox translations and rotations. The use of these tools could be of importance in reducing radiation- related toxicity of organs at risk in head-and-neck cancer patients. PO-1093 Comparison of conventional dark tattoo ink versus invisible tattoo ink for breast radiotherapy L.H. Lim 1 , P.P.E. Pang 1 , F.Y. Wong 1 1 National Cancer Centre Singapore, Division of Radiation Oncology, Singapore, Singapore Purpose or Objective Reproducibility is critical in radiotherapy (RT). In addition to immobilization, patients are usually tattooed. Occasionally, female breast cancer patients have refused permanent tattoos due to cosmetic reasons and a wish not to be reminded of their disease. Henna was used as a non- permanent alternative. Sometimes, these markings are