Status report Q2 1999

Status report Q2 1999


Info-Tag @ GSI

Status report as of January '99

After a machine shut down of six months, two therapy blocks of 4 weeks each were available in 1998, from August 12 to September 12 and from October 23 to November 23, respectively. In each therapy block 9 patients have been treated, suffering from chordomas, chondrosarcomas and adenocystic carcinomas. Half of the patients recieved all fractions with carbon beam only, the other half had a carbon boost of at least 5 fractions combined with precision photon treatment. The tumors were mostly located in the base of the skull. Target volumes up to 300 ccm were dissected into range layers of 2 mm thickness resulting in up to 120 isoenergy slices and up to 20.000 treatment pixels.
Major problems at the beginning of each patient treatment period resulted from the many changes in the accelerator system and the beam line reconstruction. It took always a few days to obtain a stable beam having less than 1mm dislocation at the target point for all 250 energies between 88 and 430 MeV/u and the different intensity steps and beam diameters. When the stability conditions were fulfilled the irradiation could be performed without major problems over the complete time course. For the second patient treatment period there were only a few hours of interruption mainly caused by defects in the oldest part of the accelerator system, the Alvarez tanks. In such cases of longer interruptions the patients were released from their fixation mask and realigned after the problems were fixed. The treatment started at the same pixel at the same range layer and lateral position as it was stopped before.
The intensity and the spatial limits for each pixel were very narrow: in lateral position an error of 50 % of the half width and +/- 50 % in calculated intensity were allowed for a single pixel. Only a few interrupts occurred during irradiation mostly because of intensity fluctuations rather than because of lateral errors. The total agreement between planning volume and irradiated volume could be also tested using the positron emitting nuclides mainly 11C and 10C. The decay of these isotopes was monitored online by means of a PET camera. The comparison of planning contours and PET reconstruction were very useful and agreement within 2-3 mm was found which is the spatial resolution of the PET camera.
However in some cases the PET image was influenced by biological effects as for instance the fast wash out of C isotopes from soft tissue. For bones these wash out effects were not observed. This yields a biologically weighted PET image depending on time after irradiation. Another difference was found in measured and planned particle ranges when "mixed" tissues are traversed by the beam: Volume elements consisting of bones and soft tissues showed Hounsfield numbers that represent an average of both tissues but do not reflect the local tissue density that is responsible for the energy loss of the beam, because range correction are based on CT images. Therefore calibration-experiments with fresh animals tissues have been carried out and animal experiments are in preparation.
During treatment these inaccurancies of the range correction were not expected to cause problems, because entrance channels were selected in such a way that possible range overshoots would not be directed towards critical organs. For treatment planning the Voxelplan programm was used in combination with TRIP that takes into account particle fragmentation as well as local variations in RBE. The physical dose distribution (absorbed dose) could be verified in phantom irradiations and the distal fall off by PET analysis. For the RBE verifications the response of tumors and healthy tissue has to be waited for. Up to now no effects in the patients treated with carbon alone have been observed. Analysis of the first two patients treated in December 1997 yielded an unexpected fast tumor regression although these patients received a boost of 5 fractions with carbon ions only.
As a general conclusion it can be stated that the treatment of the first twenty patients with the intensity controlled rasterscan system went extremely well concerning the reliability of the accelerator, the precision of the dose distribution and online PET verification and also in the interplay of the four institutions at Darmstadt, Heidelberg and Dresden. This success supports the desire for a dedicated therapy machine, where carbon beams for treatment are available every day throughout the year.
A proposal of a heavy ion treatment facility to be installed at Heidelberg has been completed and handed over to the minister for science and technology at an inauguration ceremony of the Heavy Ion Therapy at GSI at September 16 that was held in the connection with PTCOG meeting at Heidelberg. (This proposal written in English is available on request.) For 1999, three patient treatment periods are scheduled between February and end of September.
Uwe Bechthold

Status report as of March '99


Including the beam time block in March '99 a total of 32 patients has been treated from 12/97 through 3/99. 12 patients received 20 fractions with carbon ions, 3 Gye each (mostly chordoma/chondrosarcoma). 20 patients received carbon ion boosts (6 x 3 Gye) in addition to conventional photon therapy (25 x 2 Gy), mostly adenoidcystic carcinoma.
Tumour Total number primary rec.
Chordoma (skull base) 10 7 3
Chordoma (sacral) 3 2 1
Chondrosarcoma 5 5 0
ACCa 8 5 3
Squamous cell ca. 1 0 1
mal. Schwannoma 2 1 1
atyp. Meningeoma 1 0 1
Transitional cell ca. 1 1 0
Myoblastoma 1 0 1

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Last update: January 29th 2003, M.Kraemer@gsi.de, Design: Marcus Winter, M.Winter@gsi.de