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1323 poster ONCENTRA MASTERPLAN VMAT WITH SIMULTANEOUS INTEGRATED BOOST: PLANNING AND EVALUATION FOR DIFFERENT CANCER CASES
IMRT: R OTATIONAL THERAPIES Purpose: The study was performed to investigate how tumor shrinkage affects the dose given to head and neck patients’ spinal cord when treated with RapidArc. Materials: The study included 20 patients receiving radiotherapy for cancer in the head and neck area. All the patients were treated with arc-treatment (RapidArc, Varian). Cone-BeamCT scans (CBCT) were acquired daily with the On-Board Imager (Varian), and used for verifying the patient set-up and to correct the position before each daily treatment session. The contour for the spinal cord was transferred off-line from the planning CT to the CBCT scans. The original plan was thereafter recalculated on the CBCT scans, where monitor units and MLC movements were kept fixed. This was done to estimate the effect of the size of the patient’s tumor on the dose given to the spinal cord in each daily session. The maximum dose to the spinal cord (Dmax,spinal cord) was found on each of the CBCT scans, where Dmax,spinal cord was the maximum dose given to at least 2% of the contoured volume of the spinal cord. As a first approximation, was the size of the tumor indicated with the distance d defined in Fig 1, where d was taken as the largest measured distance from the tumor surface to the spinal cord. Results: Dmax,spinal cord and d were found for each patient on all the daily CBCT scans. The results for two of the patients are shown in Fig 1. The figure shows how Dmax,spinal cord is weakly dependent on the change in d (Δd) and therefore on the change in the size of the tumor. The results for the other patients show similar dependency on d. For different patients the planned Dmax,spinal cord will be different and thus give different fitted curves for each patient. If, on the other hand, the results for the patient group studied are normalized in that way that Dmax,spinal cord (0) =100% for all the patients, the results can be fitted with one linear curve, similar as can be seen in Fig 1. These results will be shown and discussed in further details, as well as threshold for Δd to keep Dmax,spinal cord below the allowed limit, will be presented.
Conclusions: The study shows that the dose given to the spinal cord in RapidArc treatments in the H&N area, are weakly dependent on the change in the distance from the tumor surface to the spinal cord. From this it can be concluded that in most cases it is probably not necessary to re-plan the patient due to the dose given to the spinal cord, when tumor shrinkage is seen, mainly in those cases when the dose planned to the spinal cord lies close to the limit for the dose used at our clinic (45 Gy). These results are the first step in a larger study, where the goal is to set-up simple strategies for when to re-plan the H&N patients receiving arc-treatment. 1322 poster IMPLEMENTATION OF VMAT FOR INTRA-CRANIAL TUMOURS: A PLANNING COMPARISON G. Lamb1 , S. Smith1 , A. James2 , M. Glegg1 1 T HE B EATSON W EST OF S COTLAND C ANCER C ENTRE, Department of Clinical Physics and Bio-Engineering, Glasgow, United Kingdom 2 T HE B EATSON W EST OF S COTLAND C ANCER C ENTRE, Department of Clinical Oncology, Glasgow, United Kingdom Purpose: The Varian VMAT solution, RapidArc was implemented for the treatment of intra-cranial tumours in August 2010. This planning study compared conventional RT with single, double and multiple non-coplanar arc VMAT treatment plans for intra-cranial sites that had planning target volumes (PTVs) overlapping organs at risk (OARs). Materials: 6 patients with intra-cranial PTVs were planned using conventional conformal RT, and using 3 different VMAT planning techniques. The first VMAT planning technique utilised a single complete arc, the second utilised two concentric coplanar arcs and the third technique utilised four non coplanar semi arcs, positioned to avoid entry through eyes. The PTV was separated into high and lower dose regions receiving 60Gy and 54Gy in 30
S 495
fractions respectively. The lower dose region encompassed overlapping critical OARs. The objectives were to cover 95% of the PTVs to 95% of the dose (CI95) and 99% of the PTVs to 90% of the dose(CI90) , without violating OAR constraints. Dose volume histograms for PTVs and OARs were compared. Results: Semi arc treatment plans achieved all CI90 and CI95 PTV and OAR dose constraints for all patients. In contrast, the double arc technique achieved all the constraints for only 1 out of 6 patients while the single arc plans did not achieve all constraints for any patient. Double and single arc plans were able to achieve the mean brain dose constraint for only 1 patient, however other OAR constraints were met. Conventional RT plans did not achieve the PTV or brain dose constraints for any patient. Normal tissue conformity index (NI CI 95%) was comparable for all VMAT treatment plans (0.97 -0.99) and significantly reduced for conventional treatments (0.65 -0.75). Conclusions: VMAT achieved better PTV coverage when compared with conventional RT. Similar OAR doses were achieved, except for normal brain tissue, where the dose was greater with conventional RT, single and double arc VMAT plans. Semi arc non-coplanar treatment plans produced better PTV coverage than single or double arc VMAT plans while achieving OAR dose constraints. Semi arc non-coplanar treatment plans will now be used as a class solution when planning intra-cranial tumours that have PTVs overlapping OARs. 1323 poster ONCENTRA MASTERPLAN VMAT WITH SIMULTANEOUS INTEGRATED BOOST: PLANNING AND EVALUATION FOR DIFFERENT CANCER CASES S. Cilla1 , F. Deodato2 , G. Macchia2 , C. Digesù2 , D. Sabatino1 , M. Massaccesi2 , V. Picardi2 , M. Ferro2 , P. Bonomo2 , L. Caravatta2 , A. Fidanzio3 , A. Piermattei3 , A. G. Morganti2 1 C ATHOLIC U NIVERSITY - C ENTER FOR H IGH T ECNOLOGY R ESEARCH AND E DUCATION IN B IOM, Medical Physics Unit, Campobasso, Italy 2 C ATHOLIC U NIVERSITY - C ENTER FOR H IGH T ECNOLOGY R ESEARCH AND E DUCATION IN B IOM, Radiotherapy Unit, Campobasso, Italy 3 C ATHOLIC U NIVERSITY, Physics Unit, Rome, Italy Purpose: At our Institution, the transition from fixed field IMRT to Volumetric Modulated Arc Therapy (VMAT) technique stems from the need to significantly reduce the treatment time while maintaining the dosimetric plan accuracy. The objective of this study was to evaluate the dosimetric quality and the delivery efficiency of VMAT plans with Simultaneous Integrated Boost (SIBVMAT) for complex-shaped target volumes. Four different cancer settings (head and neck, prostate, rectum and pancreas) were selected. Materials: Twenty patients treated with SIB-VMAT in clinical protocols using Elekta Precise linacs were selected. They included five head-and-neck, five prostate, five rectal, and five pancreatic cancer cases. SIB-VMAT plans were compared with fixed field SIB-IMRT plans, assumed as benchmark. All plans were generated with Oncentra Masterplan TPS, with VMAT plans optimized in dual arc modality. For head and neck cancer cases, three targets were simultaneously irradiated over 30 daily fractions. Doses of 67.5, 60.0 Gy and 55.5 Gy were prescribed to primary tumor, high-risk lymph nodal regions and low-risk nodal region, respectively. For prostate, rectal and pancreatic cancer cases, two target volumes were defined for each patient and simultaneously irradiated over 25 daily fractions (prostate cases: 65 Gy to prostate plus seminal vesicles and 45 Gy to pelvic lymph nodes; rectal cases: 57.5 Gy to GTV and 45 Gy to lymph nodal region; pancreatic cases: 55 Gy to primary tumor and 45 Gy to pancreas and primary lymphatic drainage). Plan evaluation statistics included various dosimetric endpoints for the target volumes and normal organs. MUs number and treatment times were analyzed to score the treatment efficiency. Results: Dual arc VMAT showed similar target coverage as SIB-IMRT plans, with slightly better conformity indices in all cancer cases. All dosimetric endpoints were fulfilled with no significant differences in OARs sparing, with slightly improvement observed in the head-neck cases. In all cancer cases MUs were reduced by 20-30%. Treatment times (excluding patient set-up and imaging procedure) were reduced from 14-20 minutes (according to the type of treatment) to less than 5 minutes for all patients, regardless of cancer site. Conclusions: Oncentra Masterplan produced SIB-VMAT plans with high conformal dose distribution, similar target coverage and similar or even better OARs sparing compared to benchmark SIB-IMRT plans. However, VMAT was able to provide approximately a 50-70% reduction in treatment time, with all patients treated within 5 minutes. Patient compliance to treatment has been significantly increased and the risk of intra-fractional motion potentially reduced. SIB-VMAT is currently our standard approach for IMRT technique. 1324 poster RAPID DOUBLE ARC REPLACES DYNAMIC IMRT IN PROSTATE BED AND STOMACH RADIATION THERAPY G. Zeng1 , J. Murphy1 , Q. Zhan1 , Y. Wang1 , Y. Wang1 , J. R. Tsao1 , T. S. McGowan1 , M. MacPherson1 C REDIT VALLEY H OSPITAL, Department of Radiation Oncology, Mississauga, Ontario, Canada
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Conclusions: The study shows that the dose given to the spinal cord in RapidArc treatments in the H&N area, are weakly dependent on the change in the distance from the tumor surface to the spinal cord. From this it can be concluded that in most cases it is probably not necessary to re-plan the patient due to the dose given to the spinal cord, when tumor shrinkage is seen, mainly in those cases when the dose planned to the spinal cord lies close to the limit for the dose used at our clinic (45 Gy). These results are the first step in a larger study, where the goal is to set-up simple strategies for when to re-plan the H&N patients receiving arc-treatment. 1322 poster IMPLEMENTATION OF VMAT FOR INTRA-CRANIAL TUMOURS: A PLANNING COMPARISON G. Lamb1 , S. Smith1 , A. James2 , M. Glegg1 1 T HE B EATSON W EST OF S COTLAND C ANCER C ENTRE, Department of Clinical Physics and Bio-Engineering, Glasgow, United Kingdom 2 T HE B EATSON W EST OF S COTLAND C ANCER C ENTRE, Department of Clinical Oncology, Glasgow, United Kingdom Purpose: The Varian VMAT solution, RapidArc was implemented for the treatment of intra-cranial tumours in August 2010. This planning study compared conventional RT with single, double and multiple non-coplanar arc VMAT treatment plans for intra-cranial sites that had planning target volumes (PTVs) overlapping organs at risk (OARs). Materials: 6 patients with intra-cranial PTVs were planned using conventional conformal RT, and using 3 different VMAT planning techniques. The first VMAT planning technique utilised a single complete arc, the second utilised two concentric coplanar arcs and the third technique utilised four non coplanar semi arcs, positioned to avoid entry through eyes. The PTV was separated into high and lower dose regions receiving 60Gy and 54Gy in 30
S 495
fractions respectively. The lower dose region encompassed overlapping critical OARs. The objectives were to cover 95% of the PTVs to 95% of the dose (CI95) and 99% of the PTVs to 90% of the dose(CI90) , without violating OAR constraints. Dose volume histograms for PTVs and OARs were compared. Results: Semi arc treatment plans achieved all CI90 and CI95 PTV and OAR dose constraints for all patients. In contrast, the double arc technique achieved all the constraints for only 1 out of 6 patients while the single arc plans did not achieve all constraints for any patient. Double and single arc plans were able to achieve the mean brain dose constraint for only 1 patient, however other OAR constraints were met. Conventional RT plans did not achieve the PTV or brain dose constraints for any patient. Normal tissue conformity index (NI CI 95%) was comparable for all VMAT treatment plans (0.97 -0.99) and significantly reduced for conventional treatments (0.65 -0.75). Conclusions: VMAT achieved better PTV coverage when compared with conventional RT. Similar OAR doses were achieved, except for normal brain tissue, where the dose was greater with conventional RT, single and double arc VMAT plans. Semi arc non-coplanar treatment plans produced better PTV coverage than single or double arc VMAT plans while achieving OAR dose constraints. Semi arc non-coplanar treatment plans will now be used as a class solution when planning intra-cranial tumours that have PTVs overlapping OARs. 1323 poster ONCENTRA MASTERPLAN VMAT WITH SIMULTANEOUS INTEGRATED BOOST: PLANNING AND EVALUATION FOR DIFFERENT CANCER CASES S. Cilla1 , F. Deodato2 , G. Macchia2 , C. Digesù2 , D. Sabatino1 , M. Massaccesi2 , V. Picardi2 , M. Ferro2 , P. Bonomo2 , L. Caravatta2 , A. Fidanzio3 , A. Piermattei3 , A. G. Morganti2 1 C ATHOLIC U NIVERSITY - C ENTER FOR H IGH T ECNOLOGY R ESEARCH AND E DUCATION IN B IOM, Medical Physics Unit, Campobasso, Italy 2 C ATHOLIC U NIVERSITY - C ENTER FOR H IGH T ECNOLOGY R ESEARCH AND E DUCATION IN B IOM, Radiotherapy Unit, Campobasso, Italy 3 C ATHOLIC U NIVERSITY, Physics Unit, Rome, Italy Purpose: At our Institution, the transition from fixed field IMRT to Volumetric Modulated Arc Therapy (VMAT) technique stems from the need to significantly reduce the treatment time while maintaining the dosimetric plan accuracy. The objective of this study was to evaluate the dosimetric quality and the delivery efficiency of VMAT plans with Simultaneous Integrated Boost (SIBVMAT) for complex-shaped target volumes. Four different cancer settings (head and neck, prostate, rectum and pancreas) were selected. Materials: Twenty patients treated with SIB-VMAT in clinical protocols using Elekta Precise linacs were selected. They included five head-and-neck, five prostate, five rectal, and five pancreatic cancer cases. SIB-VMAT plans were compared with fixed field SIB-IMRT plans, assumed as benchmark. All plans were generated with Oncentra Masterplan TPS, with VMAT plans optimized in dual arc modality. For head and neck cancer cases, three targets were simultaneously irradiated over 30 daily fractions. Doses of 67.5, 60.0 Gy and 55.5 Gy were prescribed to primary tumor, high-risk lymph nodal regions and low-risk nodal region, respectively. For prostate, rectal and pancreatic cancer cases, two target volumes were defined for each patient and simultaneously irradiated over 25 daily fractions (prostate cases: 65 Gy to prostate plus seminal vesicles and 45 Gy to pelvic lymph nodes; rectal cases: 57.5 Gy to GTV and 45 Gy to lymph nodal region; pancreatic cases: 55 Gy to primary tumor and 45 Gy to pancreas and primary lymphatic drainage). Plan evaluation statistics included various dosimetric endpoints for the target volumes and normal organs. MUs number and treatment times were analyzed to score the treatment efficiency. Results: Dual arc VMAT showed similar target coverage as SIB-IMRT plans, with slightly better conformity indices in all cancer cases. All dosimetric endpoints were fulfilled with no significant differences in OARs sparing, with slightly improvement observed in the head-neck cases. In all cancer cases MUs were reduced by 20-30%. Treatment times (excluding patient set-up and imaging procedure) were reduced from 14-20 minutes (according to the type of treatment) to less than 5 minutes for all patients, regardless of cancer site. Conclusions: Oncentra Masterplan produced SIB-VMAT plans with high conformal dose distribution, similar target coverage and similar or even better OARs sparing compared to benchmark SIB-IMRT plans. However, VMAT was able to provide approximately a 50-70% reduction in treatment time, with all patients treated within 5 minutes. Patient compliance to treatment has been significantly increased and the risk of intra-fractional motion potentially reduced. SIB-VMAT is currently our standard approach for IMRT technique. 1324 poster RAPID DOUBLE ARC REPLACES DYNAMIC IMRT IN PROSTATE BED AND STOMACH RADIATION THERAPY G. Zeng1 , J. Murphy1 , Q. Zhan1 , Y. Wang1 , Y. Wang1 , J. R. Tsao1 , T. S. McGowan1 , M. MacPherson1 C REDIT VALLEY H OSPITAL, Department of Radiation Oncology, Mississauga, Ontario, Canada
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