- Email: [email protected]
204 oral Transition from 2D breast-planning based on a conventional simulator to a 3D planning based on CT data
Proffered papers
Conclusion: A non-equispaced IMRT beam set-up results in a better planning and uses less number of beams compared with the equispaced beam set-up. Many beam set-ups have been proposed without extensive comparison. In the future, a new IMRT beam set-up technique should be proposed after examining several equispaced and non-equispaced, coplanar and non-coplanar beam set-ups in at least 5 patients. A detailed description of the chosen constraints should be reported too. 202 oral Robust treatment planning for intensity modulated radiotherapy (IMRT) treatment of prostate cancer based on coverage probabilities
C. Baum, M. Birkner, M. Alber, F. N(Jsslin Radioonkologische Universit#tsklinik, Abteilung f(Jr Medizinische Physik, TEIbingen, Germany introduction: Internal organ motion and patient setup cause geometrical uncertainty of the organ position in fractionated external beam radiotherapy which can be described by volume coverage probabilities. These coverage probabilities can be incorporated into the optimization of intensity modulated radiotherapy (IMRT) as an alternative to a volume margin. The robustness of resulting dose distributions with respect to setup error and organ motion was evaluated for both concepts. Material and Methods: For every point in the treatment room coordinate system, the probability of organ occupation during radiotherapy was computed from multiple pre-treatment CTs and the population distribution of systematic setup error. For a group of prostate patients, IMRT treatment planning was performed for the planning target volume (PTV) which comprises all voxels with a non-zero prostate coverage probability, and for the corresponding rectum volume (RPV). The coverage probability in each voxel is used as local weight in the costfunctions. Additionally, IMRT treatment plans were generated based on multiple contours of prostate and rectum plus margin. Dose distributions were optimized for 84 Gy equivalent uniform dose (EUD) in PTV and 65 Gy EUD in RPV for both concepts. Monte Carlo simulations of treatment courses were used to compute the probability distribution of prostate EUD and rectal wall EUD. Results: The overlap of PTV and RPV is the dominant conflict during the optimisation. The coverage probability as a local weight enables the optimisation algorithm to concentrate the rectum tolerance on regions of high rectum coverage probability and to increase the dose in regions of low rectum coverage probability and high prostate coverage probability. In contrast, the volume margin concept requires a dose sparing in the entire overlap to the same extent. Consequently, prostate and rectum EUD are more robust with respect to displacements and organ motion. The risk of geographic misses is diminished. The mean prostate EUD in the patient population is higher for similar or lower rectal toxicity. Conclusion: The inclusion of coverage probabilities as local weights allows dose escalation as well as improved rectal sparing and results in a safer IMRT treatment of prostate cancer.
Tuesday, October 26, 2004 $91
203 oral Conventional, conformal and IMRT treatment planning before and during external beam radiotherapy (EBRT) for cervical cancer; the impact of tumor regression
L. van de Bunt 1, U.A. van der Heide ~, G.A.P. de Kor~, M. Ketelaars 1, I.M. J#rgenliemk-Schulz ~ 1University Medical Center, Radiotherapy, Utrecht, the Netherlands 2University Medical Center, Radiology, Utrecht, the Netherlands Purpose: To investigate the impact of tumor regression on dose distributions within cervical tumors and critical surrounding organs, comparing conventional, conformal and IMRT planning and the need for repeated planning during external irradiation. Materials and methods: Fourteen patients with advanced cervical cancer underwent a CT scan and an MRI before radiotherapy. MR imaging was repeated after 30 Gy of a total of 45 Gy EBRT. Target volumes and critical organs were delineated on both MRIs. CT and MR images were registered for treatment planning. For all patients a pre-treatment conventional, a conformal and an IMRT plan were created. New conformal and IMRT plans were made based on the delineations of the second MR images. To evaluate the impact of tumor regression we calculated dose-volume histograms for the pre-treatment plans from the delineations of the second MRIs. The initial and new plans were compared with respect to critical organ doses and coverage of target volumes. Results: By planning with an IMRT or a conformal technique, the volumes of rectum and bladder receiving 45 Gy could be reduced to about 50% the amount of a conventional technique. Treated bowel volumes were even further reduced with IMRT. After 30 Gy EBRT the mean regression of the gross tumor volumes was 45%. This resulted in a mean regression of the planning target volumes of 9%. Although pre-treatment plans covered the clinical target volumes on the second MRIs with > 98 % of the prescribed dose, the volumes of rectum and bladder, receiving 45 Gy increased substantially. Newly created plans lowered the critical organ exposure, most prominently with IMRT planning. Compared to pre-treatment IMRT plans the in-field volumes of bowel, bladder and rectum in the new IMRT plans decreased with a mean of 25.1, 17.7 and 4.6 cc, respectively. Conclusion: After 30 Gy external irradiation IMRT treatment planning remains superior to conventional and conformal techniques in sparing of the critical surrounding organs, without deterioration of the tumor coverage. Repeated IMRT planning during EBRT can further improve this tendency.
Breast cancer (RTT) 204 oral Transition from 2D breast-planning based on a conventional simulator to a 3D planning based on CT data
A. van Giersber.qen, C. van Vliet-Vroegindeweij, J.J.P. de Goede, K. De Jaeger The Netherlands'Cancer Institute, Radiotherapy, Amsterdam, The Netherlands Purpose: The purpose is to replace the current 2D conventional breast simulation by a more advanced 3D CT planning. The main arguments for introducing the 3D CT planning are the increase in geometrical information on the irradiated volume and a more accurate dose calculation. To enable much more sophisticated irradiation set-ups in the future, such as IMRT, high set-up accuracy is needed. Therefore, we also evaluated the set-up accuracy for these patients.
$92
Tuesday, October 26, 2004
Methods: The CT-based planning of breast tumours has been clinically introduced in three steps. First, the planning is based on CT, with conventional simulator as a control of the set-up. Field edges were drawn on the patients. Based on these field lines, patient set-up on the linac was performed for the treatment. Second, the planning was based on CT, and patient set-up on the linac was based on a reference cross on the sternum and a translation of the patient. Field set-up was controlled on the conventional simulator. Third, the control of the conventional simulator was omitted and patient set-up is controlled by electronic portal imaging device and an off-line verification protocol was introduced clinically. Results: 10 patients were entered in phase 1, 11 patients in phase 2, and up till now 70 patients were entered in phase 3. Compared with the 2D conventional simulation, no significant difference was found in table, gantry or collimator rotation or field size for the 3D virtual simulation. Preliminary results show a reduction in the maximum heart distance for the 3D CT planning compared with the 2D conventional simulation. A verification protocol based on different in-house protocols was adapted to accommodate breast tumours. Conclusions: The 3D CT planning has successfully been implemented together with an off-line verification protocol. The verification protocol opens the possibility for more sophisticated irradiation set-ups. Also, first analysis of the data shows a reduction in the maximum heart distance when the 3D CT information is used. 205 oral Treating the internal mammary nodes with the para mixed technique limits dose to the heart and other organs at risk
H.P. van der Laan, A.A. van 't Ve/d, H.P. Bij/, W. V. Do/sma Groningen University Hospital, Department of Radiation Oncology, Groningen, The Netherlands Purpose: A reduction in overall survival after irradiation of the internal mammary nodes is mainly due to heart damage. The Para Mixed Technique (PMT) is designed to minimise the radiation dose in the heart. The PMT dose-distributions in the heart and the other organs at risk are compared to those with three other commonly applied techniques. Methods and Materials: The Para Mixed Technique is a 3D Conformal, CT-based technique. Opposed beams are used to treat the supraclavicular region. To the inferior edges of these beams, three tangential beams are matched to treat the breast or chest wall in daily fractions of 2 Gy. One:of the two medial tangential beams is extended to include the internal mammary nodes and delivers0.75 Gy. A frontal electron beam is used to deliver the remaining 1.25 Gy to that region. CT-studies of sixteen patients (left/right, breast/chest wall, divided equally) were used to compare the PMT to the Partial Wide Tangents Technique (PWT) [IJROBP 29, 903], a modified Patched Technique (PT) [R&O 46, 83] and the Standard Technique (ST) [IJROBP 47, 1421]. Beam angles and beam shapes were optimised for all techniques to comply best with ICRU50 guidelines for dose homogeneity. Dose-distributions in heart, lungs, contralateral breast, skin and areas of beam overlap were evaluated for all techniques. Results: In left-sided irradiation, less dose is delivered to the heart with the PMT than with the PWT (V30:10.5 vs. 17.4%). In right-sided irradiation, the PMT delivers a comparable or slightly higher dose to the heart. PMT and PT have similar heart dose. The ST delivers the highest dose to the heart. Less dose is delivered to the lungs with the PMT than with the PWT (V20: 18.6 vs. 23.9%). The ST and PT deliverthe lowest dose to the lungs. A mean volume of 15.4% of the contralateral breast is irradiated with the PWT. This is avoided with the other techniques. A high dose is delivered to the skin with the PT
Proffered papers
because only electrons are used to irradiate the internal mammary region. The mean dose in an area of beam overlap is 23% higher with the PT and ST than with the PMT. Conclusion: The Para Mixed Technique yields the best overall results. In left-sided irradiation, the heart dose is less than with the PWT. PMT lung dose is always lower than with the PWT. The high skin dose with the PT is a disadvantage compared with the other techniques. There were no cases in which the ST proved to be the best technique. 206 oral Intraoperative radiotherapy (IORT) as partial treatment after surgery of early breast cancer
B. K(Jpper, U. Kraus-Tiefenbacher, F. Wenz University of Mannheim, Sektiion Strahlentherapie, Mannheim, Germany Purpose: Breast cancer is the most common malignant female tumour in Germany. Whereas in the past mastectomy was the method of choice, nowadays 70-80% of all patients can have breast conserving surgery followed by External Beam Radiation Therapy (EBRT). Studies pointed out: most of the local recurrences after 5 years occur in the same quadrant the primary tumour was located before. Therefore the tumour-bed itself seems to be the high-risk area for local recurrence and should be treated by a boost dose. There are different techniques to give this boost, one is the Intra Operative Radio Therapy (IORT) with a mobile miniature accelerator. Patients and methods: From February 2002 until March 2003 70 patients with breast carcinomas were treated by IORT after breast-conserving surgery. In 45 cases IORT was given as a tumour-bed boost and consecutive EBRT of the whole breast. Median age was 63 years. Definitive pathology results showed ductal-invasive histology in 20 patients, Iobular-invasive histology in 13 patients, mixed histology in 10 patients, medullar and mucinous in 1 patient each. IORT treatment time took 20 minutes. In most cases a spherical applicator with a diameter 0f4.5 cm was chosen. Intrabeam TM is producing low energy xrays, which can be applicated in an isotropic dose distribution to the tumor-bed. Therefore a single high-dose (20 Gy) can be applicated on the applicators surface up reaching the wrapped breast tissue up to a tissue depth of 1~5 cm. After woundhealing all IORT-patients were treated by external-beam radiotherapy with a total dose of 46 Gy. Results: Treatment was tolerated very well by all patients. No skin necroses were observed. Two patients showed skin erythemas °1-11 which disappeared without any delay. After a maximum follow-up of 22 months good cosmetic outcome were observed. One patient had to be treated by mastectomy a few days after BCS because of a previous not-diagnosed multifocality, one other patient developed cervical lymph node metastases. In both cases postoperative EBRT was omitted. One patient showed a multifocal relapse with several skin metastases 10 months after initial treatment. A secondary mastectomy was done, but the patient died 4 months later. Conclusions: IORT with the Intrabeam system is a comfortable effective method to deliver a single high-dose to the tumour-bed as a boost. The external beam course afterwards is shortened by 1.5 weeks. After tumour resection the tumour bed can ideally be adapted to the applicator surface and then be treated by low-distance x-rays. Through IORT a miss of the boost target volume as it is often in EBRT, can be avoided.
Conclusion: A non-equispaced IMRT beam set-up results in a better planning and uses less number of beams compared with the equispaced beam set-up. Many beam set-ups have been proposed without extensive comparison. In the future, a new IMRT beam set-up technique should be proposed after examining several equispaced and non-equispaced, coplanar and non-coplanar beam set-ups in at least 5 patients. A detailed description of the chosen constraints should be reported too. 202 oral Robust treatment planning for intensity modulated radiotherapy (IMRT) treatment of prostate cancer based on coverage probabilities
C. Baum, M. Birkner, M. Alber, F. N(Jsslin Radioonkologische Universit#tsklinik, Abteilung f(Jr Medizinische Physik, TEIbingen, Germany introduction: Internal organ motion and patient setup cause geometrical uncertainty of the organ position in fractionated external beam radiotherapy which can be described by volume coverage probabilities. These coverage probabilities can be incorporated into the optimization of intensity modulated radiotherapy (IMRT) as an alternative to a volume margin. The robustness of resulting dose distributions with respect to setup error and organ motion was evaluated for both concepts. Material and Methods: For every point in the treatment room coordinate system, the probability of organ occupation during radiotherapy was computed from multiple pre-treatment CTs and the population distribution of systematic setup error. For a group of prostate patients, IMRT treatment planning was performed for the planning target volume (PTV) which comprises all voxels with a non-zero prostate coverage probability, and for the corresponding rectum volume (RPV). The coverage probability in each voxel is used as local weight in the costfunctions. Additionally, IMRT treatment plans were generated based on multiple contours of prostate and rectum plus margin. Dose distributions were optimized for 84 Gy equivalent uniform dose (EUD) in PTV and 65 Gy EUD in RPV for both concepts. Monte Carlo simulations of treatment courses were used to compute the probability distribution of prostate EUD and rectal wall EUD. Results: The overlap of PTV and RPV is the dominant conflict during the optimisation. The coverage probability as a local weight enables the optimisation algorithm to concentrate the rectum tolerance on regions of high rectum coverage probability and to increase the dose in regions of low rectum coverage probability and high prostate coverage probability. In contrast, the volume margin concept requires a dose sparing in the entire overlap to the same extent. Consequently, prostate and rectum EUD are more robust with respect to displacements and organ motion. The risk of geographic misses is diminished. The mean prostate EUD in the patient population is higher for similar or lower rectal toxicity. Conclusion: The inclusion of coverage probabilities as local weights allows dose escalation as well as improved rectal sparing and results in a safer IMRT treatment of prostate cancer.
Tuesday, October 26, 2004 $91
203 oral Conventional, conformal and IMRT treatment planning before and during external beam radiotherapy (EBRT) for cervical cancer; the impact of tumor regression
L. van de Bunt 1, U.A. van der Heide ~, G.A.P. de Kor~, M. Ketelaars 1, I.M. J#rgenliemk-Schulz ~ 1University Medical Center, Radiotherapy, Utrecht, the Netherlands 2University Medical Center, Radiology, Utrecht, the Netherlands Purpose: To investigate the impact of tumor regression on dose distributions within cervical tumors and critical surrounding organs, comparing conventional, conformal and IMRT planning and the need for repeated planning during external irradiation. Materials and methods: Fourteen patients with advanced cervical cancer underwent a CT scan and an MRI before radiotherapy. MR imaging was repeated after 30 Gy of a total of 45 Gy EBRT. Target volumes and critical organs were delineated on both MRIs. CT and MR images were registered for treatment planning. For all patients a pre-treatment conventional, a conformal and an IMRT plan were created. New conformal and IMRT plans were made based on the delineations of the second MR images. To evaluate the impact of tumor regression we calculated dose-volume histograms for the pre-treatment plans from the delineations of the second MRIs. The initial and new plans were compared with respect to critical organ doses and coverage of target volumes. Results: By planning with an IMRT or a conformal technique, the volumes of rectum and bladder receiving 45 Gy could be reduced to about 50% the amount of a conventional technique. Treated bowel volumes were even further reduced with IMRT. After 30 Gy EBRT the mean regression of the gross tumor volumes was 45%. This resulted in a mean regression of the planning target volumes of 9%. Although pre-treatment plans covered the clinical target volumes on the second MRIs with > 98 % of the prescribed dose, the volumes of rectum and bladder, receiving 45 Gy increased substantially. Newly created plans lowered the critical organ exposure, most prominently with IMRT planning. Compared to pre-treatment IMRT plans the in-field volumes of bowel, bladder and rectum in the new IMRT plans decreased with a mean of 25.1, 17.7 and 4.6 cc, respectively. Conclusion: After 30 Gy external irradiation IMRT treatment planning remains superior to conventional and conformal techniques in sparing of the critical surrounding organs, without deterioration of the tumor coverage. Repeated IMRT planning during EBRT can further improve this tendency.
Breast cancer (RTT) 204 oral Transition from 2D breast-planning based on a conventional simulator to a 3D planning based on CT data
A. van Giersber.qen, C. van Vliet-Vroegindeweij, J.J.P. de Goede, K. De Jaeger The Netherlands'Cancer Institute, Radiotherapy, Amsterdam, The Netherlands Purpose: The purpose is to replace the current 2D conventional breast simulation by a more advanced 3D CT planning. The main arguments for introducing the 3D CT planning are the increase in geometrical information on the irradiated volume and a more accurate dose calculation. To enable much more sophisticated irradiation set-ups in the future, such as IMRT, high set-up accuracy is needed. Therefore, we also evaluated the set-up accuracy for these patients.
$92
Tuesday, October 26, 2004
Methods: The CT-based planning of breast tumours has been clinically introduced in three steps. First, the planning is based on CT, with conventional simulator as a control of the set-up. Field edges were drawn on the patients. Based on these field lines, patient set-up on the linac was performed for the treatment. Second, the planning was based on CT, and patient set-up on the linac was based on a reference cross on the sternum and a translation of the patient. Field set-up was controlled on the conventional simulator. Third, the control of the conventional simulator was omitted and patient set-up is controlled by electronic portal imaging device and an off-line verification protocol was introduced clinically. Results: 10 patients were entered in phase 1, 11 patients in phase 2, and up till now 70 patients were entered in phase 3. Compared with the 2D conventional simulation, no significant difference was found in table, gantry or collimator rotation or field size for the 3D virtual simulation. Preliminary results show a reduction in the maximum heart distance for the 3D CT planning compared with the 2D conventional simulation. A verification protocol based on different in-house protocols was adapted to accommodate breast tumours. Conclusions: The 3D CT planning has successfully been implemented together with an off-line verification protocol. The verification protocol opens the possibility for more sophisticated irradiation set-ups. Also, first analysis of the data shows a reduction in the maximum heart distance when the 3D CT information is used. 205 oral Treating the internal mammary nodes with the para mixed technique limits dose to the heart and other organs at risk
H.P. van der Laan, A.A. van 't Ve/d, H.P. Bij/, W. V. Do/sma Groningen University Hospital, Department of Radiation Oncology, Groningen, The Netherlands Purpose: A reduction in overall survival after irradiation of the internal mammary nodes is mainly due to heart damage. The Para Mixed Technique (PMT) is designed to minimise the radiation dose in the heart. The PMT dose-distributions in the heart and the other organs at risk are compared to those with three other commonly applied techniques. Methods and Materials: The Para Mixed Technique is a 3D Conformal, CT-based technique. Opposed beams are used to treat the supraclavicular region. To the inferior edges of these beams, three tangential beams are matched to treat the breast or chest wall in daily fractions of 2 Gy. One:of the two medial tangential beams is extended to include the internal mammary nodes and delivers0.75 Gy. A frontal electron beam is used to deliver the remaining 1.25 Gy to that region. CT-studies of sixteen patients (left/right, breast/chest wall, divided equally) were used to compare the PMT to the Partial Wide Tangents Technique (PWT) [IJROBP 29, 903], a modified Patched Technique (PT) [R&O 46, 83] and the Standard Technique (ST) [IJROBP 47, 1421]. Beam angles and beam shapes were optimised for all techniques to comply best with ICRU50 guidelines for dose homogeneity. Dose-distributions in heart, lungs, contralateral breast, skin and areas of beam overlap were evaluated for all techniques. Results: In left-sided irradiation, less dose is delivered to the heart with the PMT than with the PWT (V30:10.5 vs. 17.4%). In right-sided irradiation, the PMT delivers a comparable or slightly higher dose to the heart. PMT and PT have similar heart dose. The ST delivers the highest dose to the heart. Less dose is delivered to the lungs with the PMT than with the PWT (V20: 18.6 vs. 23.9%). The ST and PT deliverthe lowest dose to the lungs. A mean volume of 15.4% of the contralateral breast is irradiated with the PWT. This is avoided with the other techniques. A high dose is delivered to the skin with the PT
Proffered papers
because only electrons are used to irradiate the internal mammary region. The mean dose in an area of beam overlap is 23% higher with the PT and ST than with the PMT. Conclusion: The Para Mixed Technique yields the best overall results. In left-sided irradiation, the heart dose is less than with the PWT. PMT lung dose is always lower than with the PWT. The high skin dose with the PT is a disadvantage compared with the other techniques. There were no cases in which the ST proved to be the best technique. 206 oral Intraoperative radiotherapy (IORT) as partial treatment after surgery of early breast cancer
B. K(Jpper, U. Kraus-Tiefenbacher, F. Wenz University of Mannheim, Sektiion Strahlentherapie, Mannheim, Germany Purpose: Breast cancer is the most common malignant female tumour in Germany. Whereas in the past mastectomy was the method of choice, nowadays 70-80% of all patients can have breast conserving surgery followed by External Beam Radiation Therapy (EBRT). Studies pointed out: most of the local recurrences after 5 years occur in the same quadrant the primary tumour was located before. Therefore the tumour-bed itself seems to be the high-risk area for local recurrence and should be treated by a boost dose. There are different techniques to give this boost, one is the Intra Operative Radio Therapy (IORT) with a mobile miniature accelerator. Patients and methods: From February 2002 until March 2003 70 patients with breast carcinomas were treated by IORT after breast-conserving surgery. In 45 cases IORT was given as a tumour-bed boost and consecutive EBRT of the whole breast. Median age was 63 years. Definitive pathology results showed ductal-invasive histology in 20 patients, Iobular-invasive histology in 13 patients, mixed histology in 10 patients, medullar and mucinous in 1 patient each. IORT treatment time took 20 minutes. In most cases a spherical applicator with a diameter 0f4.5 cm was chosen. Intrabeam TM is producing low energy xrays, which can be applicated in an isotropic dose distribution to the tumor-bed. Therefore a single high-dose (20 Gy) can be applicated on the applicators surface up reaching the wrapped breast tissue up to a tissue depth of 1~5 cm. After woundhealing all IORT-patients were treated by external-beam radiotherapy with a total dose of 46 Gy. Results: Treatment was tolerated very well by all patients. No skin necroses were observed. Two patients showed skin erythemas °1-11 which disappeared without any delay. After a maximum follow-up of 22 months good cosmetic outcome were observed. One patient had to be treated by mastectomy a few days after BCS because of a previous not-diagnosed multifocality, one other patient developed cervical lymph node metastases. In both cases postoperative EBRT was omitted. One patient showed a multifocal relapse with several skin metastases 10 months after initial treatment. A secondary mastectomy was done, but the patient died 4 months later. Conclusions: IORT with the Intrabeam system is a comfortable effective method to deliver a single high-dose to the tumour-bed as a boost. The external beam course afterwards is shortened by 1.5 weeks. After tumour resection the tumour bed can ideally be adapted to the applicator surface and then be treated by low-distance x-rays. Through IORT a miss of the boost target volume as it is often in EBRT, can be avoided.