ESTRO 37 Abstract book

ESTRO 37

S561

2 Academic Medical Center, Radiation Oncology, Amsterdam, The Netherlands 3 Catharina Hospital Eindhoven, Radiation Oncology, Eindhoven, The Netherlands 4 Radiotherapygroup - treatment location Deventer, Radiation Oncology, Deventer, The Netherlands Purpose or Objective To obtain optimal radiotherapy treatment within the Netherlands, patients should be treated with plans of equal high quality independent of the institute they are being treated at. The aim of the current pilot study was to gain insight in the different plan evaluation criteria used in 4 Dutch radiotherapy institutes. An earlier survey showed that a wide variation is present in radiation treatment techniques for breast cancer between radiation oncology departments in the Netherlands. To decide on which technique may be the optimal one, consensus is needed on plan evaluation criteria. Material and Methods The 4 participating institutes represent a mixture of characteristic hospitals within the Netherlands (academic, general and specialized radiotherapy hospitals). Each institute provided data of 10 to 15 patients for 3 different treatments: left breast radiotherapy without boost, left breast radiotherapy with integrated boost and left breast radiotherapy including lymph node levels I-IV. For all patients, deep-inspiration breathhold was used. Treatment technique, delineation and DVH parameters were assessed. The following DVH parameters were evaluated: PTV V95%, Dmean, D2%, D98%, Paddick CI, MHD, Heart V5Gy, Heart V30Gy, MLD, Lungs V5Gy and V20Gy. Results All institutes used a tangential IMRT technique and added IMRT and/or VMAT beams in case of a boost or lymph node irradiation. Delineation varied a lot: two centers delineated the CTV according to the ESTRO atlas, whereas two centers based the CTV mainly on markers put in place before CT-scanning and also included some non-breast tissue. Consequently, DVH parameters with respect to target coverage also varied. Our data showed that for all treatment groups, PTV V95% as well as Dmean differed on average by < 2.5 % (p-values 0.001-0.6) between the institutes. MHD and MLD fluctuated typically by about 1 Gy (p values 0.001-0.9) and < 1.5 Gy (p-values 0.001-0.8), respectively. For almost all patients, MHD < 3 Gy and MLD < 4/5/7 Gy for group 1, 2, 3 respectively. CI ranged between 0.67 and 0.74 for breast and breast with integrated boost (p-values 0.001-0.03). For breast plus lymph node levels I-IV, CI varied between 0.41 and 0.69 (p-values 0.00-0.03). Although the differences are relatively small for most cases, some were statistically significant and may also be clinically relevant. Conclusion Based on the results of this 4-institute study, it can be concluded that the differences in radiation technique do not seem to lead to large variations in target volume coverage and specified doses to heart and lung. However, quite some large variation was seen in CI, suggesting that the institutes take different considerations into account when evaluating target dose conformity versus more dose in the OAR. The next step will be to organize a workshop with different institutes to discuss the observed differences, aiming to reach consensus on the tissues to be spared and on accepted dose-volume levels.

contoured using automatic tools to assure consistency among the different sets of contours. We then performed DIR among the nine CT series using the version of ANACONDA implemented in RaySt ation v5. This is a hybrid algorithm in which information from both the voxel values and the distance between homologous designated landmarks (ROI/POI) may be used. As a measure of image similarity the correlation coefficient is employed. We have analyzed the three different methods of DIR provided by the algorithm: first using only image information, second using only ROI, and third the full method using both types of information. To assess the accuracy of each DIR, we used the Dice similarity coefficient (DSC) of the rectal ballo on, as well as the target registration error (TRE) of the markers. To evaluate the invertibility, we doubly deformed the rectal balloon and markers, from one imageset to the other and then back to the original imageset, and measured again the DSC and TRE, and the change of volume of the balloon.

Results

The most important results of our study are summarized in the attached table: a) the reduction in the distance between homologous markers, with a TRE of 2-3 mm if ROI information is used; b) a DSC of at least 0.98 is obtained when ROI information is used, obtaining bad results only when no ROI are used and the contrast between the balloon and the medium is low. The displacements applied on the markers by the algorithm are invertible, within an uncertainty of 2 mm, if ROI information is used as input for the algorithm. Conclusion ANACONDA achieves good accuracy and invertibility for the kind and amplitude of the deformations present in our phantom, especially when good and consistent ROI information is used. In this case, the accuracy and invertibility are within 2-3 mm. It is inadequate to use image information only, but in the highest contrast cases. Moreover, the deformation field around the balloon does not affect the shape of nearby structures, such as the bone inserts, which preserved their shape and volume after the registration. PO-1005 Towards Dutch consensus on treatment planning for breast cancer, current variation across institutes C. Van Beveren 1 , N. Bijker 2 , L.J. Boersma 1 , K.F. Crama 2 , C.W. Hurkmans 3 , T.T. Nuver 4 , M.J.C. Van der Sangen 3 1 MAASTRO Clinic, Radiation Oncology, Maastricht, The Netherlands