Posters $471

brought the new concept and related schedules into operation for all 27 Radiotherapy processes at once.

Results : Zero measurement Jan + Feb 2003 Intervention measurement May + June + July 2003

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Zero Intervention p* measurement measurement

"FIZZ i~°a~iia~io~°session i i - - , ~ / /

i<= 14 days from consultationi~ . . . . ~, o, . . . . . . ~, ~ r,~4 L U L [ U U ,3) o ~ ~ / t u ) ~ u u u | iRadtatton oncologlst ' ' '

iMultidiscipl.peer review bef°re 123 (37,6%) 386 (76,3°/0) <0,001 istart RT.

iMore than 2 technologists in~{195~58,4% ~ J 132(26,0%) < 0 0 0 1 prepary phase

Conclusions:

a. The new production concept has been a success, because it reduces waiting time for patients. It improves Quality and Safety due to the various disciplines involved in radiotherapy collaborate intensively in a small team. It is a more pleasant way of working and all activities are done in a natural sequence.

b. The project did not achieve the goals completely. We would like to reduce even more the number of technicians involved and the time component. We are convinced that we are on the right track and assume it will take a further year of improvements to realise the objectives.

1125 poster

MVI in stereotactic Radiotherapy of the liver

M. van Os, R. Brandwijk, A. Mendez Romero, J. Nuyttens, W. Wunderink, B. Heijmen, P. Levendag

ErasmusMC - Daniel den Hoed Cancer Centre, Radiotherapy, Rotterdam, The Netherlands

Introduction: In Rotterdam patients with liver lesions are treated with Stereotactic Radiotherapy with a hypofractionation scheme which requires high precision dose delivery. Each fraction a pretreatment-CT is made and the coordinates of the isocentre are adjusted to the actual position of the PTV. The patient is then transported to the treatment machine where the position of the PTV is reassured by means of MVI. On these images only the bony structures of the vertebrae are visible. Furthermore, the reference image is the old DRR of the planning-CT, while we want to spare time by not processing new DRR's.

We developed a procedure to check the position of the PTV on MVI in relation to the vertebrae on the planning-CT.

Material & methods: 14 Patients are treated in the Stereotactic Body Frame, for 3 fractions each. On the pretreatment-CT the translation of both PTV and vertebrae in relation to the planning-CT is calculated. These results are inserted in an Excel datasheet which calculates the sum of these two translations, yielding the expected position of the vertebrae on MVI after having set up the adjusted isocentre.

On the treatment machine online MVI is performed, matching the vertebrae with the DRR of the planning-CT. In the Excel datasheet this measured translation of the vertebrae is

compared with the expected position and has a tolerance of 5 mm.

Results: In 3 patients the difference between measured and expected translation was over 5 mm. In 2 cases the difference could be explained and corrected. For 1 patient no explanation other than patient movement could be found, so his treatment was postponed.

Discussion: It is a roundabout method but adequate while waiting for implanted markers.

1126 poster

Time bandits in radiotherapy

L. Lukassen 1, J. Carl, V. Karlsen ~, M. Schimka~, R. Villadsen ~

~Aalborg Sygehus, Radiotherapy, Department of Oncology, DK-9100 Aalborg, Denmark 2Aalborg Sygehus, Department of Medical Physics, Department of Oncology, DK-9100 Aalborg, Denmark

In the recent years the accelerators and relevant software has undergone a revolutionary renewal. In the radiotherapy department of Aalborg Sygehus, Denmark multi leave collimators (MLC) and electronic portal vision (EPID) were implemented on all four accelerators within a short time period of a few months.

Patients were previously scheduled for treatments according to a relative simple formula, predicting basic treatment equivalent (bte) in multiples of ten minute slots. Ten minute slots were allocated at the accelerator for each additional two fields in the treatment plan.

With the new technology this rude bte - assessment were no longer considered appropriate. No longer using blocks or x- ray films, we found that most treatments were done faster.

To fully exploit the benefits of new technology a registration of actual spent time for treatments was started. The registration was done over a six months period, running from November 2003 to may 2004.

The registration included various parameters such as positioning, patient performance status, use of hard wedge, ICDN code, number of fields in the actual treatment and fields involving EPID. For each accelerator time measurements were registered for a whole day every third week. The day of the week was also permuted each time. This resulted in ten measurements at each accelerator distributed evenly on all weekdays.

The complete database will be used for statistical analysis of treatment logistics. The aim of the analysis is to provide a model for optimal allocation of treatment time at the four linacs in the radiotherapy department.

An interim analysis of the preliminary results after finishing half of the measurements has demonstrated a significant influence on treatment time from a number of parameters.

The final result of the analysis will be presented at ESTRO conference in October 2004 for a full discussion.

1127 poster

Stage I non-small cell lung cancer: treatment planning for extracranial stereotactic radiotherapy

K. de Vries, G.B. Simons, B.J. Slotman, S. Senan, J.P. Cuijpers, F.J. Lagerwaard

VU University medical center, Radiation Oncology, Amsterdam, The Netherlands

Extracraniat stereotactic radiotherapy offers an alternative for patients with medically inoperable stage I non-small cell lung