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INTERFRACTION VARIATION OF THE ANUS AND THE INGUINAL LYMPH NODE REGION DURING RT FOR ANAL CANCER
S 80
P OSTER
table of treatment is very common. The effects of attenuation of the carbon fiber are usually neglected and, in the most cases, this factor is not taken into account by planning systems. This may be of greater importance for IMRT due to multiple fields, segments and energy used. Materials: In this work it was investigated the attenuation of 6 treatment couches for 3 different linear accelerators: Elekta Precise, Elekta Synergy, Varian 2100 C/D and Siemens Oncor. There were several depth measurements for the Photon energies of 6 MV and 15 MV, for fields 5x5, 10x10 cm2 and for various angles of Gantry. For the measurements it was used an equivalent solid water phantom SP34 and a CC13 ionization chamber, both of Scanditronix. For the validation method it was used the treatment planning system XiO from CMS. Results: The results for perpendicular beams to the treatment couch vary between 5% for the photon energy of 6MV and 0.1% for photon energy of 15 MV beam. The photon energy of 6MV results at an increase in skin dose where the beam focuses on the treatment couch. Conclusions: This work had significant attenuation factors that may result in under-dosage estimation of the target volume when photon beams traverse the couch. This factor should be taken into account in planning systems to calculate the UM.
T UESDAY, S EPTEMBER 1, 2009
after registration on bony anatomy. Position and shape variation of the anus were determined in the upper-, middle- and lowest delineated slice. For the left-right (LR) and anterior-posterior (AP) position variation the centre of mass (CoM) positions were calculated. Since it was difficult to define the cranial border of the anus, only the caudal slice was used to determine cranio-caudal (CC) variation. Shape variation was determined by calculating the LR and AP diameter. For LR and AP position verification of the LNing region, the femoral artery was chosen as a surrogate reference structure. The artery was delineated at the level of the femoral head (high), os ischium (middle) and 5 cm below the minor trochanter (low). Its CoM position was calculated.The data of planCT and CBCT’s were compared. Results: For the anus, systematic (S) and random (s) position variation in AP and CC direction was in the order of 3 mm (Table 1a). In the LR direction the variation was negligible. Considerable variation in diameter was observed (S SD 2-3 mm for LR and 3-6 mm for AP).Position variation of the LNing region was highly dependent on the level. Close to the femoral head the variation was small (Table 1b), increasing towards the middle and lower level. The position variation of the femoral artery strongly correlated with a femur rotation around the AP-axis (R2 =0.93). At the low level, an AP-rotation of 6 dg corresponded with a displacement of roughly 1 cm.
219 oral USING CONE BEAM CT FOR ONE STOP SIMULATION AND TREATMENT IN PALLIATIVE SETTINGS M. Kamphuis1 , L. van Maurik1 , A. Bel1 , M. Hulshof1 1
ACADEMIC M EDICAL C ENTER , U NIVERSITY OF A MSTERDAM, Academic Radiation Oncology Department, Amsterdam, Netherlands
Purpose: CT-based simulation is a time demanding procedure, even in non complex treatment. The aim of this study was to design a fast procedure for simulation and treatment in one session using the cone beam CT in palliative settings. In addition, this new method was compared with our conventional CT-based procedure. Materials: A protocol was designed for simulation using the cone beam CT and consecutive treatment on the accelerator for palliative treatment. The protocol was first tested on an Alderson phantom and thereafter in a pilot study with patients. Feasibility and total simulation/treatment time were recorded and compared with a control group treated with the conventional CT-based method in the same period. The designed protocol includes indications for patient positioning on the treatment couch, followed by a cone beam CT-scan of the treatment area. Subsequently, field sizes and depth dose are determined by a radiotherapist on the acquired images. MU’s are calculated and treatment data entered in a database. An EPID-image is made for verification of the treatment field. If correct, the patient is being treated. During this period the patient remains in the same position on the treatment couch. Results: Until now, four patients were treated using the new protocol. Average simulation and treatment time was 33 minutes (range: 0.25-0.44 hours). CT-based control group consist of 15 patients, with an average treatment time of 2 hours and 25 minutes (range: 0:50-3:48 hours). Further advantages of the new protocol are a reduction of RTT’s working time and the fact that patients don’t have to change from simulator to treatment couch. Disadvantages of the new procedure include: the patient has to lie still for a longer time and the use of leaves and collimator rotations are not yet possible. The maximum length of the cone beam CT and thus treatment fields are restricted to about 25 cm. The quality of the images can not be used for diagnostic goals and might be poor in case of an obese patient. An update of our results with an increased number of patients will be presented at the ESTRO. Conclusions: The protocol for one stop simulation and treatment using the cone beam CT in palliative treatment is a faster and more patient friendly alternative for the conventional CT-based protocol. The indications for this procedure are limited, because of current machine and patient restrictions. 220 oral INTERFRACTION VARIATION OF THE ANUS AND THE INGUINAL LYMPH NODE REGION DURING RT FOR ANAL CANCER P. de Ruiter1 , J. Nijkamp1 , L. Dewit1 , C. Rasch1 1 N ETHERLANDS C ANCER I NSTITUTE - A NTONI VAN L EEUWENHOEK H OSPITAL, Radiation Oncology, Amsterdam, Netherlands
Purpose: In our department patients with anal cancer stage T2-4N0/TxN1-3 are treated with an IMRT technique, in 33 fractions of 1.8 Gy to the primary tumor and macroscopically involved lymph nodes and 33 times 1.5 Gy to the elective lymph node regions. The PTV consists of the CTV_anus and the iliac, presacral- and inguinal lymph nodes (LNing), with a 10 mm margin. Patients are treated in supine position with no knee support and the legs spread with a distance of roughly 30 cm between the heels to reduce skin reaction in the inguinal region. The purpose of this study was to validate the used 10 mm CTV-PTV margin by quantifying the possible variation in position and shape of the anus and the position of the inguinal lymph node regions. Materials: For 11 patients (6 male, 5 female) the anus and the LNing region were delineated on planning CT and on weekly cone-beam CT (CBCT) scans
Conclusions: For the anus, the variation in position and shape in LR and CC direction is covered by the 10 mm margin. The AP margin needs to be reviewed.For the lower LNing region the position variation is insufficiently covered by the 10 mm PTV margin. The effect of a new feet fixation to improve the set up is under investigation.
P OSTER
table of treatment is very common. The effects of attenuation of the carbon fiber are usually neglected and, in the most cases, this factor is not taken into account by planning systems. This may be of greater importance for IMRT due to multiple fields, segments and energy used. Materials: In this work it was investigated the attenuation of 6 treatment couches for 3 different linear accelerators: Elekta Precise, Elekta Synergy, Varian 2100 C/D and Siemens Oncor. There were several depth measurements for the Photon energies of 6 MV and 15 MV, for fields 5x5, 10x10 cm2 and for various angles of Gantry. For the measurements it was used an equivalent solid water phantom SP34 and a CC13 ionization chamber, both of Scanditronix. For the validation method it was used the treatment planning system XiO from CMS. Results: The results for perpendicular beams to the treatment couch vary between 5% for the photon energy of 6MV and 0.1% for photon energy of 15 MV beam. The photon energy of 6MV results at an increase in skin dose where the beam focuses on the treatment couch. Conclusions: This work had significant attenuation factors that may result in under-dosage estimation of the target volume when photon beams traverse the couch. This factor should be taken into account in planning systems to calculate the UM.
T UESDAY, S EPTEMBER 1, 2009
after registration on bony anatomy. Position and shape variation of the anus were determined in the upper-, middle- and lowest delineated slice. For the left-right (LR) and anterior-posterior (AP) position variation the centre of mass (CoM) positions were calculated. Since it was difficult to define the cranial border of the anus, only the caudal slice was used to determine cranio-caudal (CC) variation. Shape variation was determined by calculating the LR and AP diameter. For LR and AP position verification of the LNing region, the femoral artery was chosen as a surrogate reference structure. The artery was delineated at the level of the femoral head (high), os ischium (middle) and 5 cm below the minor trochanter (low). Its CoM position was calculated.The data of planCT and CBCT’s were compared. Results: For the anus, systematic (S) and random (s) position variation in AP and CC direction was in the order of 3 mm (Table 1a). In the LR direction the variation was negligible. Considerable variation in diameter was observed (S SD 2-3 mm for LR and 3-6 mm for AP).Position variation of the LNing region was highly dependent on the level. Close to the femoral head the variation was small (Table 1b), increasing towards the middle and lower level. The position variation of the femoral artery strongly correlated with a femur rotation around the AP-axis (R2 =0.93). At the low level, an AP-rotation of 6 dg corresponded with a displacement of roughly 1 cm.
219 oral USING CONE BEAM CT FOR ONE STOP SIMULATION AND TREATMENT IN PALLIATIVE SETTINGS M. Kamphuis1 , L. van Maurik1 , A. Bel1 , M. Hulshof1 1
ACADEMIC M EDICAL C ENTER , U NIVERSITY OF A MSTERDAM, Academic Radiation Oncology Department, Amsterdam, Netherlands
Purpose: CT-based simulation is a time demanding procedure, even in non complex treatment. The aim of this study was to design a fast procedure for simulation and treatment in one session using the cone beam CT in palliative settings. In addition, this new method was compared with our conventional CT-based procedure. Materials: A protocol was designed for simulation using the cone beam CT and consecutive treatment on the accelerator for palliative treatment. The protocol was first tested on an Alderson phantom and thereafter in a pilot study with patients. Feasibility and total simulation/treatment time were recorded and compared with a control group treated with the conventional CT-based method in the same period. The designed protocol includes indications for patient positioning on the treatment couch, followed by a cone beam CT-scan of the treatment area. Subsequently, field sizes and depth dose are determined by a radiotherapist on the acquired images. MU’s are calculated and treatment data entered in a database. An EPID-image is made for verification of the treatment field. If correct, the patient is being treated. During this period the patient remains in the same position on the treatment couch. Results: Until now, four patients were treated using the new protocol. Average simulation and treatment time was 33 minutes (range: 0.25-0.44 hours). CT-based control group consist of 15 patients, with an average treatment time of 2 hours and 25 minutes (range: 0:50-3:48 hours). Further advantages of the new protocol are a reduction of RTT’s working time and the fact that patients don’t have to change from simulator to treatment couch. Disadvantages of the new procedure include: the patient has to lie still for a longer time and the use of leaves and collimator rotations are not yet possible. The maximum length of the cone beam CT and thus treatment fields are restricted to about 25 cm. The quality of the images can not be used for diagnostic goals and might be poor in case of an obese patient. An update of our results with an increased number of patients will be presented at the ESTRO. Conclusions: The protocol for one stop simulation and treatment using the cone beam CT in palliative treatment is a faster and more patient friendly alternative for the conventional CT-based protocol. The indications for this procedure are limited, because of current machine and patient restrictions. 220 oral INTERFRACTION VARIATION OF THE ANUS AND THE INGUINAL LYMPH NODE REGION DURING RT FOR ANAL CANCER P. de Ruiter1 , J. Nijkamp1 , L. Dewit1 , C. Rasch1 1 N ETHERLANDS C ANCER I NSTITUTE - A NTONI VAN L EEUWENHOEK H OSPITAL, Radiation Oncology, Amsterdam, Netherlands
Purpose: In our department patients with anal cancer stage T2-4N0/TxN1-3 are treated with an IMRT technique, in 33 fractions of 1.8 Gy to the primary tumor and macroscopically involved lymph nodes and 33 times 1.5 Gy to the elective lymph node regions. The PTV consists of the CTV_anus and the iliac, presacral- and inguinal lymph nodes (LNing), with a 10 mm margin. Patients are treated in supine position with no knee support and the legs spread with a distance of roughly 30 cm between the heels to reduce skin reaction in the inguinal region. The purpose of this study was to validate the used 10 mm CTV-PTV margin by quantifying the possible variation in position and shape of the anus and the position of the inguinal lymph node regions. Materials: For 11 patients (6 male, 5 female) the anus and the LNing region were delineated on planning CT and on weekly cone-beam CT (CBCT) scans
Conclusions: For the anus, the variation in position and shape in LR and CC direction is covered by the 10 mm margin. The AP margin needs to be reviewed.For the lower LNing region the position variation is insufficiently covered by the 10 mm PTV margin. The effect of a new feet fixation to improve the set up is under investigation.