- Email: [email protected]
1279 poster SETUP VARIATIONS DURING RADICAL CONFORMAL RADIOTHERAPY FOR OESOPHAGEAL CANCER
IGRT: VOLUME DEFINITION , TREATMENT MARGINS AND GEOMETRIC UNCERTAINTIES
registered with the Preop-CT and the boost-CTV was delineated again on the Plan-CT (boost-CTV-2).To study the impact of the Preop-CT on the delineation of the boost-CTV, we calculated the delineated volume of both boostCTV-1 and boost-CTV-2. Subsequently, we calculated for each patient, for each observer pair and for both boost volumes, the conformity index (CI = (common volume) / (encompassing volume)) and the distance between the centres of mass (COMd). Finally, for each patient and both boost volumes, the standard deviation (sd) histogram of all delineations with respect to the median delineation was calculated. The volume, CI and COMd where compared between the datasets with and without a Preop-CT using Wilcoxon tests; the sd histograms using a Mann-Whitney test. Results: With a Preop-CT, the delineated volume decreased significantly, with the average decreasing 5.7cc (see table). The Mean CI did not change significantly, but the COMd showed a significant decrease with the average decreasing 1.5mm. For 46% of the patients the sd decreased significantly from on average 0.64mm to 0.49mm, whereas for 19% the sd increased significantly from on average 0.51mm to 0.70mm. See the figure for an example.While the observers mostly agreed on the GTV delineation, we observed a disagreement of the GTV for 3 patients. Since improved consensus is only expected if there is consensus on the GTV, the analysis has been repeated for the twenty-three patients for whom this was the case. For this subgroup there is a significant increase in CI and the improvement in COMd has increased to 2.2mm. The proportion of patients with a significant decrease in the sd increased slightly to 52%, while the proportion of patients with a significant increase in the sd decreased slightly to 17%.
S 477
ranged from 5 to 31cm3 . The PTVgating (ranging from 12 to 83cm3 ) was, on average, 45% smaller than PTVnogating (ranging from 18 to 135cm3 ). There was no significant difference in tumor coverage between the two plans. Mean lung dose was 6.6Gy and 4.0Gy, on average, respectively for the non gated and the gated plan; V20 was 10.0% (non gated plan) and 5.7% (gated plan), on average. Conclusions: In this sample of patients, with small mobile lung lesions, respiratory gating enabled a reduction in the margins necessary for the PTV, thus reducing the lung dose. 1279 poster SETUP VARIATIONS DURING RADICAL CONFORMAL RADIOTHERAPY FOR OESOPHAGEAL CANCER H. Ariyaratne1 1
R OYAL F REE H AMPSTEAD NHS T RUST, Academic Department of Radiation Oncology, London, United Kingdom Purpose: 1. To evaluate random and systematic setup errors during radical conformal radiotherapy for locally advanced oesophageal cancer. 2. To estimate the optimal target volume margin for planning of oesophageal volumes and compare with current guidelines.
Conclusions: We showed that inter-observer variation in the delineation of the boost-CTV for breast conserving therapy can be substantially decreased using a Preop-CT, with a significant average decrease in COMd of 1.5mm. In particular in those cases where there was consensus on the GTV, we saw a marked improvement. We also found that the delineated boost-CTV was smaller when the Preop-CT was available. 1278 poster RESPIRATORY GATED RADIATION THERAPY: A DOSIMETRIC ANALYSIS R. Righetto1 , M. Valenti1 , G. Mantello2 , M. Cardinali2 , S. Maggi1
Materials: The study sample population consisted of 12 patients treated with radical courses of radiotherapy with concomitant chemotherapy for locally advanced carcinoma of the oesophagus between April 2007 and April 2010. All patients were treated on an Elekta radiotherapy unit using a conformal technique after CT planning. Standard positioning and immobilization techniques were used. Kilovoltage verification images were obtained using the onboard imager during the first 3 fractions of treatment and weekly thereafter, as a minimum requirement. A total of 114 KV verification images were available for analysis. The Pinnacle system was used for fusion and comparison of images with the digitally reconstructed radiographs from the planning images, and appropriate correction was applied if setup was outside predetermined tolerances.. Results: The population random inter-fraction error was 5.5 mm in the supero-inferior (SI), 2.7 mm in the left-right (LR) and 2.2 mm in the anteroposterior (AP) direction. The systematic setup error (weighted by number of images) was 3.3 mm in the SI, 1.4 mm in the LR and 1.4 mm in the AP direction. The Van Herk formula: Margin = (2.5 x systematic error) + (0.7 x random error) was used to calculate the clinical target volume (CTV)-planning target volume (PTV) margin. Using this formula, margins of 12.1 mm in the SI, 5.4 mm in the LR, and 5.1 mm in the AP direction were obtained. Conclusions: There is significant setup variation in the superior-inferior direction during radiotherapy of oesophageal cancer. This would require a CTVPTV margin in the vertical direction larger than is recommended in contemporary radiotherapy trials. Individual radiotherapy centres should audit their setup errors to ensure that adequate margins are used during radiotherapy of the oesophagus. 1280 poster THE DAILY ANALYSIS OF PROSTATE ROTATION D. Grabec1 , B. Kragelj2 1 I NSTITUTE OF O NCOLOGY L JUBLJANA, Radiophysics Unit, Ljubljana, Slovenia 2 I NSTITUTE OF O NCOLOGY L JUBLJANA, Radiotherapy, Ljubljana, Slovenia
1
A ZIENDA O SPEDALIERO U NIVERSITARIA O SPEDALI R IUNITI U MBERTO I G. M. L ANCISI - G. S ALESI, Department of Medical Physics and Radiation Safety, Ancona, Italy 2 A ZIENDA O SPEDALIERO U NIVERSITARIA O SPEDALI R IUNITI U MBERTO I G. M. L ANCISI - G. S ALESI, Department of Radiation Oncology, Ancona, Italy
Purpose: This study aims to evaluate the effectiveness of respiratory gated radiation therapy (RGRT) in reducing the planning target volume (PTV) and in minimizing organ at risk dose. Materials: Two different three-dimensional conformal radiation therapy(3DCRT) plans were generated for 8 pre-selected patients with non-smallcell lung cancer or lung metastases. Two different PTVs were considered (a) PTVnogating derived from an internal target volume (ITV) encompassing all 3D tumor mobility and (b) PTVgating derived from an ITV incorporating tumor mobility observed in a gating window centered at end of inspiration. For the purpose of this study 60Gy were prescribed to the isocenter placed at the center of gross target volume (GTV). Results: The average free-breathing tumor motion was 16±9mm, 11±10mm and 6±2mm respectively in the superior-inferior (SI), anteriorposterior (AP) and latero-lateral (LL) directions. With respiratory gating the average tumor motion reduced to 6±1mm 5±1mm 5±1mm, respectively, along SI, AP and LL directions (duty cycles ranging from 20 to 35%). GTVs
Purpose: In radiotherapy of prostate cancer the precise definition of safety margin around prostate is very important, since it allows optimal OAR sparing at desired dose to the PTV. The safety margin due to the day by day prostate motion is reduced with the usage of the golden markers. After the prostate translation is subtracted, the prostate rotation is still present. We are presenting the day by day prostate rotation analysis during the radiotherapy course, and the corresponding estimation of the safety margins around the prostate. When necessary, the rotation analysis can lead to the adaptive prostate planning. Materials: Prior to the CT acquisition for the treatment planning three golden markers are implanted in the patient’s prostate to assure the precise daily prostate position. During the planning procedure one of the markers is chosen to be the in the isocentre (IC). The marker in the IC is named O. The daily treatment patient position is corrected so the marker O is positioned in the IC, also with help of the other two markers (A and B). The positioning of O in the IC is done with the finite precision that leads to the translational safety margins. The vector analysis OA and OB shows that the plane defined with the three markers (AOB) rotates and deforms only slightly or not at all. Therefore also the rotational safety margins should be considered. The measure of rotation is the direction of the cross product OA B = n, while the measure of deformation is the norm of n. The reference condition is defined with planning CT (O0, A0, B0, n0). The positions (O, A, B) of the markers at each irradiation
registered with the Preop-CT and the boost-CTV was delineated again on the Plan-CT (boost-CTV-2).To study the impact of the Preop-CT on the delineation of the boost-CTV, we calculated the delineated volume of both boostCTV-1 and boost-CTV-2. Subsequently, we calculated for each patient, for each observer pair and for both boost volumes, the conformity index (CI = (common volume) / (encompassing volume)) and the distance between the centres of mass (COMd). Finally, for each patient and both boost volumes, the standard deviation (sd) histogram of all delineations with respect to the median delineation was calculated. The volume, CI and COMd where compared between the datasets with and without a Preop-CT using Wilcoxon tests; the sd histograms using a Mann-Whitney test. Results: With a Preop-CT, the delineated volume decreased significantly, with the average decreasing 5.7cc (see table). The Mean CI did not change significantly, but the COMd showed a significant decrease with the average decreasing 1.5mm. For 46% of the patients the sd decreased significantly from on average 0.64mm to 0.49mm, whereas for 19% the sd increased significantly from on average 0.51mm to 0.70mm. See the figure for an example.While the observers mostly agreed on the GTV delineation, we observed a disagreement of the GTV for 3 patients. Since improved consensus is only expected if there is consensus on the GTV, the analysis has been repeated for the twenty-three patients for whom this was the case. For this subgroup there is a significant increase in CI and the improvement in COMd has increased to 2.2mm. The proportion of patients with a significant decrease in the sd increased slightly to 52%, while the proportion of patients with a significant increase in the sd decreased slightly to 17%.
S 477
ranged from 5 to 31cm3 . The PTVgating (ranging from 12 to 83cm3 ) was, on average, 45% smaller than PTVnogating (ranging from 18 to 135cm3 ). There was no significant difference in tumor coverage between the two plans. Mean lung dose was 6.6Gy and 4.0Gy, on average, respectively for the non gated and the gated plan; V20 was 10.0% (non gated plan) and 5.7% (gated plan), on average. Conclusions: In this sample of patients, with small mobile lung lesions, respiratory gating enabled a reduction in the margins necessary for the PTV, thus reducing the lung dose. 1279 poster SETUP VARIATIONS DURING RADICAL CONFORMAL RADIOTHERAPY FOR OESOPHAGEAL CANCER H. Ariyaratne1 1
R OYAL F REE H AMPSTEAD NHS T RUST, Academic Department of Radiation Oncology, London, United Kingdom Purpose: 1. To evaluate random and systematic setup errors during radical conformal radiotherapy for locally advanced oesophageal cancer. 2. To estimate the optimal target volume margin for planning of oesophageal volumes and compare with current guidelines.
Conclusions: We showed that inter-observer variation in the delineation of the boost-CTV for breast conserving therapy can be substantially decreased using a Preop-CT, with a significant average decrease in COMd of 1.5mm. In particular in those cases where there was consensus on the GTV, we saw a marked improvement. We also found that the delineated boost-CTV was smaller when the Preop-CT was available. 1278 poster RESPIRATORY GATED RADIATION THERAPY: A DOSIMETRIC ANALYSIS R. Righetto1 , M. Valenti1 , G. Mantello2 , M. Cardinali2 , S. Maggi1
Materials: The study sample population consisted of 12 patients treated with radical courses of radiotherapy with concomitant chemotherapy for locally advanced carcinoma of the oesophagus between April 2007 and April 2010. All patients were treated on an Elekta radiotherapy unit using a conformal technique after CT planning. Standard positioning and immobilization techniques were used. Kilovoltage verification images were obtained using the onboard imager during the first 3 fractions of treatment and weekly thereafter, as a minimum requirement. A total of 114 KV verification images were available for analysis. The Pinnacle system was used for fusion and comparison of images with the digitally reconstructed radiographs from the planning images, and appropriate correction was applied if setup was outside predetermined tolerances.. Results: The population random inter-fraction error was 5.5 mm in the supero-inferior (SI), 2.7 mm in the left-right (LR) and 2.2 mm in the anteroposterior (AP) direction. The systematic setup error (weighted by number of images) was 3.3 mm in the SI, 1.4 mm in the LR and 1.4 mm in the AP direction. The Van Herk formula: Margin = (2.5 x systematic error) + (0.7 x random error) was used to calculate the clinical target volume (CTV)-planning target volume (PTV) margin. Using this formula, margins of 12.1 mm in the SI, 5.4 mm in the LR, and 5.1 mm in the AP direction were obtained. Conclusions: There is significant setup variation in the superior-inferior direction during radiotherapy of oesophageal cancer. This would require a CTVPTV margin in the vertical direction larger than is recommended in contemporary radiotherapy trials. Individual radiotherapy centres should audit their setup errors to ensure that adequate margins are used during radiotherapy of the oesophagus. 1280 poster THE DAILY ANALYSIS OF PROSTATE ROTATION D. Grabec1 , B. Kragelj2 1 I NSTITUTE OF O NCOLOGY L JUBLJANA, Radiophysics Unit, Ljubljana, Slovenia 2 I NSTITUTE OF O NCOLOGY L JUBLJANA, Radiotherapy, Ljubljana, Slovenia
1
A ZIENDA O SPEDALIERO U NIVERSITARIA O SPEDALI R IUNITI U MBERTO I G. M. L ANCISI - G. S ALESI, Department of Medical Physics and Radiation Safety, Ancona, Italy 2 A ZIENDA O SPEDALIERO U NIVERSITARIA O SPEDALI R IUNITI U MBERTO I G. M. L ANCISI - G. S ALESI, Department of Radiation Oncology, Ancona, Italy
Purpose: This study aims to evaluate the effectiveness of respiratory gated radiation therapy (RGRT) in reducing the planning target volume (PTV) and in minimizing organ at risk dose. Materials: Two different three-dimensional conformal radiation therapy(3DCRT) plans were generated for 8 pre-selected patients with non-smallcell lung cancer or lung metastases. Two different PTVs were considered (a) PTVnogating derived from an internal target volume (ITV) encompassing all 3D tumor mobility and (b) PTVgating derived from an ITV incorporating tumor mobility observed in a gating window centered at end of inspiration. For the purpose of this study 60Gy were prescribed to the isocenter placed at the center of gross target volume (GTV). Results: The average free-breathing tumor motion was 16±9mm, 11±10mm and 6±2mm respectively in the superior-inferior (SI), anteriorposterior (AP) and latero-lateral (LL) directions. With respiratory gating the average tumor motion reduced to 6±1mm 5±1mm 5±1mm, respectively, along SI, AP and LL directions (duty cycles ranging from 20 to 35%). GTVs
Purpose: In radiotherapy of prostate cancer the precise definition of safety margin around prostate is very important, since it allows optimal OAR sparing at desired dose to the PTV. The safety margin due to the day by day prostate motion is reduced with the usage of the golden markers. After the prostate translation is subtracted, the prostate rotation is still present. We are presenting the day by day prostate rotation analysis during the radiotherapy course, and the corresponding estimation of the safety margins around the prostate. When necessary, the rotation analysis can lead to the adaptive prostate planning. Materials: Prior to the CT acquisition for the treatment planning three golden markers are implanted in the patient’s prostate to assure the precise daily prostate position. During the planning procedure one of the markers is chosen to be the in the isocentre (IC). The marker in the IC is named O. The daily treatment patient position is corrected so the marker O is positioned in the IC, also with help of the other two markers (A and B). The positioning of O in the IC is done with the finite precision that leads to the translational safety margins. The vector analysis OA and OB shows that the plane defined with the three markers (AOB) rotates and deforms only slightly or not at all. Therefore also the rotational safety margins should be considered. The measure of rotation is the direction of the cross product OA B = n, while the measure of deformation is the norm of n. The reference condition is defined with planning CT (O0, A0, B0, n0). The positions (O, A, B) of the markers at each irradiation