$462 Posters

right liver lobes were quite different each other. The motion of the tumor in the lower intra-thoracic esophagus was found to be larger than that in the left lobe of the liver. According to the correlation coefficients obtained (Table 1), the orbit of the motions for tumors in the lung was oval-shaped (hysteresis loop) whereas that for tumors in the liver was linear. The orbit for tumors in the midd le intra-thoracic esophagus was similar to that in the upper lobe of the lung. T he orbit for tumors in the lower intra-thoracic esophagus and that in the liver was similar on the z-y plane but different on the x-y plane.

Conclusion: Tumor motion is quite complicated, and differs for each organ and direction. Therefore the margin to compensate for the respiratory motion should be added to CTV, not uniformly, but using parameters suitable to each organ and direction. This information is essential to subdivide the uncertainty factor of the internal margin for each organ in treatment planning of respiratory gated irradiation.

1101 poster

Assuring the quality of nursing in a department of radiotherapy - Ensuring the consistency and the development in nursing care

I. Schultz~ I. Habeek, S. Kehler, A. Jepsen

Odense University Hospital, Department of Oncology and Radiotherapy, Odense, Denmark Background: The background for our work is that The Danish Medicines Agency announced a notice coming into apply May 1 st 2000. This notice includes demands on nursing care and treatment of patients receiving high-volt radiotherapy.

Aim: The aim of the work has been to create a tool and a reference book useful to both experienced personnel and new appointees in the department. A tool to secure that the quality of the nursing care is optimum, and that all patients receive a consistent nursing and treatment care. Further we would like to secure development of nursing care in our department.

Method: First we elucidated the existing nursing care partly by elaborating different graphs showing the nursing care of all the diagnoses that are being treated in the department, and partly by registration of the guidance's and instructions that already exists in the department.

Second we outlined the optimum nursing care of patients in a department of radiotherapy. We made different courses/graphs, procedures and instructions of all possible nursing functions that can appear when you are treating patients with radiotherapy. When we elaborated the procedures and instructions, we made use of knowledge and

experience from our colleagues who each have certain knowledge about different areas.

Results: Working with elaboration of the tool has now been fulfilled. What we have left now is implementation of the tool in the department. It is planned to install the result in the department's computer system in order to make it accessible to all personnel and to make it useful in the training of new appointees and useful as a reference book for more experienced personnel.

1102 poster

A comparison of 3 different techniques for mediastinal irradiation in malignant lymphoma

M. Klessens, L. van Rijen, R. Reijenga, S. Hol, P. Poortmans

Dr Bernard Verbeeten Instituut, Radiotherapy, Tilburg, The Netherlands Purpose: To evaluate the coverage of the target volume and the dose to the lungs and the heart, we compared the DVH for conventional mediastinal radiotherapy with CT-based volume delineated and with 3-D conformal radiotherapy.

Materials and Methods: Field delineation and treatment planning for mediastinal irradiation was done for 7 consecutive patients in 3 different ways:

1. conventional anterior-posterior field set-up and calculation, using a DRR and conventional shielding of the lungs;

2. conventional anterior-posterior field set-up and calculation, using CT-based target volume delineation with individualised shielding;

3. 3-D conformal field set-up and calculation, using CT-based target volume delineation with individualised shielding.

Complete treatment planning including DVH for target volume, lungs and heart was done for comparison of the 3 techniques.

Results: The coverage of the target volume was insufficient for all treatment plans using conventional shielding, mostly for the PTV but in 3 patients also for the CTV, namely at the level of the lung hill. The dose distribution was more homogeneous for the 3-D technique compared to both anterior-posterior techniques. The mean V20 for the lungs was 45%, 47% and 50% for the 3 techniques respectively for a prescribed dose of 36 Gy. For all but 3 patients, the V20 was the highest with technique 3. The dose to the heart was highest with technique 1 and lowest with technique 3 for all but one patient where the DVH of the heart was similar for all 3 techniques.

Conclusion: To optimise the coverage of the target volume in mediastinal radiotherapy for lymphoma patients, CT-based target volume delineation is necessary. The technique using a conformal 3-D field set-up offers a more homogeneous dose distribution to the target volume and a lower dose to the heart at the cost of a slight increase in the dose to the lungs for some patients. Therefore, we advice now to use CT- based target volume delineation with individualised shielding and to choose for the field set-up based on DVH comparison for heart and lungs.