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438Breast treatment simulation: Evaluation of changes in dosification and irradiation volume due to arm position
Sl13 439
438 BPd~AsT TREATMENT SIMULATION: EVALUATION OF CHANGES IN DOSIFICATION AND IRRADIATION VOLUME DUE TO ARM
POSITION. '~krlH()Rb, hv, llloln)n',. ( 11~, ( *~tllllr\ Di~. S.*: Alg:is. A.R.: Fetter. C.: Fetter. E.: Dualdo. D : Gonzalez. A *Sen'. Radiofisica y PTOI.Radiol6giea. Sen'. Ra,'liolcrapia Hospital Clinic Universitari. Valencia. SPAIN \h,li,ll
CLINICAL IMPLEMENTATION OF COMPENSATORS FOR EXTERNAL TREATMENTS
DOSE BEAM
PL Roberson *#, M Ho *#, V N a r a y a n a #, P W M c L a u g h l i n *#, B A Fraass* *University of Michigan, Ann Arbor, Michigan. U S A #Providence Hospital, Southfield, Michigan, U S A
I
INTRODUCTION: Accurate irradiation of breast volumes requires a careful simulation of t~.am entrances and angles. Usually dose calculations are done with scanner images taken from either a conventional diagnostic scanner or from a simulator CT. The former providos a good image quality, while Ihc latter offers biggnsl reconstruction area. Breast treatment are often designed with the paUent lying on an inclined plane. When axilar-sopraclavicular volume is treated, the arm is positioned at 90°. In these situations, it is not possible to acqmre scanner images with the patient in treatment position because of the limited diameter of the diagnostic scanner tunnel. This forces Io extract patient contours manually, with incorrect information of internal structure geometD' and without the possibility of performing 3D calculations. As an alternative, images are taken arms up and with little or no inclination. This procedure provokes dosimetry errors which are evaluated in this work MATERIAL AND METHODS: Patients have been simulated with a SlXCially modified Scanner-CT so that its tunnel is extended up to 90 cm diameter. allowing tO extract patient contours ~ith arm abducted at 90 °. Contours have also been oblanied with patient positioned as in a conventional scanner 0.e. arms up). Dose distribution calculations have been made for both patient setup. Simulation of treatment calculated with data obtained with incorrect positioning and delivered in correct treatment position have been made. RESULTS: Signifieativc changes in patient contour are found depending on arm position. In patients which are calculated from incorrect data the irradiated lung volume is bigger than thai planned, l.-Simulation radiographs show position variations of internal structures from beam center in the sagital direction. 2.-Contour changes are evidenced from transversal slices when arm position is modified. 3.-Dose distributions differ from that planned. CONCLUSIONS: For a correct breast irradiation, is essential to simulate treatments acquiring anatomical data with patient set in treatment position. For this paq~se, a big scanner tunnel, like that o f a simulator-CT is nocessary. If this is not possible, manually extracted contours and 2D calculations are preferred. 3D calculations made from conventional scanner data induce more error than that of 2D calculations
441
440 T H E C H O I C E OF PTV: A C R U C I A L TREATMENT PLAN O P T I M I Z A T I O N
Background: U s e o f m i s s i n g tissue c o m p e n s a t o r s with 3D treatment planning w a s not optimal. Hurdles for implementation o f dose c o m p e n s a t o r s were: 1) presence of differential patient scatter due to n o n u n i f o r m irradiation; 2) c o m p e n s a t o r b e a m hardening; 3) target dose specification. Purpose: U s e o f c o m p e n s a t o r s with a 3D treatr, ,,.t planning s y s t e m ( U M P L A N ) with the s a m e calculation pret,~ton as noncompensated plans was desired. M a t e r i a l a n d M e t h o d s : C o m p e n s a t o r s were designed as a series of nested transmission blocks. Each block was constrained to c o v e r the area included within an isodose contour using a beam's-eye-view perspective. I s o d o s e c o n t o u r s w e r e d i s p l a y e d on a plane o f compensation. The transmission factor was chosen to be .95 to .98 (5% to 2 % per step). T h e compensator was cut from styrofoam and the c a v i t y filled with steel-loaded g y p s u m . T h e block scatter algorithm, fit to block data. provided corrections for differential patient scatter. B e a m h a r d e n i n g due to the p r e s e n c e o f the c o m p e n s a t o r w a s c o r r e c t e d by c h a n g i n g the t h i c k n e s s o f the compensator as a function o f off-axis position and local compensator thickness. D o s i m e t r y was verified with film m e a s u r e m e n t s in a flat phantom and with surface dose measurements. Results: Dose calculations in a flat phantom were verified to within a few percent. Measured data were more uniformly varying than the calculation. T h i s effect m a y be i m p r o v e d by an adjustment of the blocking algorithm. Conclusions: A s c h e m e for the i m p l e m e n t a t i o n o f d o s e c o m p e n s a t o r s w a s s a t i s f a c t o r y i m p l e m e n t e d for a 3D treatment planning system.
POINT
IN T H E
E. Celiai. G.P. Bitl, F. Banci Buonamici. M. Bueciolini, A. Compagnueci, C. Fallai, S.M. Magrini, P. OImi, F. Rossi, R. Santoni Clinical Physiopaihology Deparlmenl. University of Florence
ISOCENTRIC BREAST SIMULATION ANALYTICAL APPROACH
E.W. Lederer, S. Cosby, H. S c h w e n d e n e r Northeastern Ontario Regional Cancer Centre Department of Medical Physics Sudbury Canada : the s i m u l a t i o n o f tangential breast fields u s i n g an i s o c e n t r i c s e t - u p t e c h n i q u e is a l e n g t h y p r o c e s s i n v o l v i n g the placement of the isocentre and the determination o f the gantry angles and the selection lung shields, w h i c h in our centre is one o f six standard blocks. P u r p o s e : we s h o w that with a body contour taken through centralaxis, five m e a s u r e m e n t s and a calculator p r o g r a m , it is possible to significantly decrease the amount of time required to simulate a breast patient. M e t h o d s a n d m a t e r i a l s : we h a v e d e v e l o p e d a p r o g r a m for an H P 4 8 G X handheld calculator to d e t e r m i n e the g a n t r y angles, the isocentre, the field width, the standard angled block and the couch and c o l l i m a t o r rotation. T h e calculations are based on m e a s u r e m e n t s o f the field length, the horizontal d i s t a n c e b e t w e e n m i d l i n e a n d midaxillary line, and the vertical distances f r o m the midaxillary line to the inferior and superior b e a m border and central axis at midline. For the simulation process a j i g was developed that is inserted into the tray h o l d e r o f the s i m u l a t o r to s h o w the optical and the r a d i o l o g i c a l s h a d o w o f the calculated shielding along the patient's midline for clinical assessment during simulation and on the simulation film. The j i g also has a holder for an a l u m i n i u m w e d g e to i m p r o v e the i m a g e quality o f the simulation film. R e s u l t s a n d c o n c l u s i o n : the technique has been in use for two years and has resulted in time s a v i n g s of up to 30 percent per patient. It has p r o v e n to be an e a s y and accurate w a y o f s e t t i n g up i s o c e n t r i c treatments to the breast.
Background
The modern three-dimensional treatmenl planning are extremely useful equipments offering a series of options to help in the optimization of a treatment plan particularly as concerns the closer distribution to the target volume and sparing of the healthy tissues. The quantitative evaluation and comparison among rival plans for the same patient may he obtained by comparing dose-volume histograms. The volume(s) definition represent the first important step of all the process and it is probably the crucial point. Although the ICRU 50 recommendalions represent a good reference point for the radiation oncologists il is a common observation that different radiation oncologisls may define target volumes which differ considerably. Using our Scandiplan treatment planning system, which is a full 3-D system, based on an OCTREE-EDGE models, we decided to evaluate Ihe effects of the different choices made by five staff oncologists of the Department of Radiation Oneology of the University of Florence. The contoured primary treatment volumes (PTVs) and critical organs for four different patients, defined by five staff radiation oncologists, were obtained in a group of patients referred to our institution for irradialion of head and neck malignancies. These dose distributions, for each treatment plan and trealment technique, were compared. Quantitative differences in dose distributions for the different patients. PTVs and normal tissues are presented and their relevance is discussed.
- A NEW
438 BPd~AsT TREATMENT SIMULATION: EVALUATION OF CHANGES IN DOSIFICATION AND IRRADIATION VOLUME DUE TO ARM
POSITION. '~krlH()Rb, hv, llloln)n',. ( 11~, ( *~tllllr\ Di~. S.*: Alg:is. A.R.: Fetter. C.: Fetter. E.: Dualdo. D : Gonzalez. A *Sen'. Radiofisica y PTOI.Radiol6giea. Sen'. Ra,'liolcrapia Hospital Clinic Universitari. Valencia. SPAIN \h,li,ll
CLINICAL IMPLEMENTATION OF COMPENSATORS FOR EXTERNAL TREATMENTS
DOSE BEAM
PL Roberson *#, M Ho *#, V N a r a y a n a #, P W M c L a u g h l i n *#, B A Fraass* *University of Michigan, Ann Arbor, Michigan. U S A #Providence Hospital, Southfield, Michigan, U S A
I
INTRODUCTION: Accurate irradiation of breast volumes requires a careful simulation of t~.am entrances and angles. Usually dose calculations are done with scanner images taken from either a conventional diagnostic scanner or from a simulator CT. The former providos a good image quality, while Ihc latter offers biggnsl reconstruction area. Breast treatment are often designed with the paUent lying on an inclined plane. When axilar-sopraclavicular volume is treated, the arm is positioned at 90°. In these situations, it is not possible to acqmre scanner images with the patient in treatment position because of the limited diameter of the diagnostic scanner tunnel. This forces Io extract patient contours manually, with incorrect information of internal structure geometD' and without the possibility of performing 3D calculations. As an alternative, images are taken arms up and with little or no inclination. This procedure provokes dosimetry errors which are evaluated in this work MATERIAL AND METHODS: Patients have been simulated with a SlXCially modified Scanner-CT so that its tunnel is extended up to 90 cm diameter. allowing tO extract patient contours ~ith arm abducted at 90 °. Contours have also been oblanied with patient positioned as in a conventional scanner 0.e. arms up). Dose distribution calculations have been made for both patient setup. Simulation of treatment calculated with data obtained with incorrect positioning and delivered in correct treatment position have been made. RESULTS: Signifieativc changes in patient contour are found depending on arm position. In patients which are calculated from incorrect data the irradiated lung volume is bigger than thai planned, l.-Simulation radiographs show position variations of internal structures from beam center in the sagital direction. 2.-Contour changes are evidenced from transversal slices when arm position is modified. 3.-Dose distributions differ from that planned. CONCLUSIONS: For a correct breast irradiation, is essential to simulate treatments acquiring anatomical data with patient set in treatment position. For this paq~se, a big scanner tunnel, like that o f a simulator-CT is nocessary. If this is not possible, manually extracted contours and 2D calculations are preferred. 3D calculations made from conventional scanner data induce more error than that of 2D calculations
441
440 T H E C H O I C E OF PTV: A C R U C I A L TREATMENT PLAN O P T I M I Z A T I O N
Background: U s e o f m i s s i n g tissue c o m p e n s a t o r s with 3D treatment planning w a s not optimal. Hurdles for implementation o f dose c o m p e n s a t o r s were: 1) presence of differential patient scatter due to n o n u n i f o r m irradiation; 2) c o m p e n s a t o r b e a m hardening; 3) target dose specification. Purpose: U s e o f c o m p e n s a t o r s with a 3D treatr, ,,.t planning s y s t e m ( U M P L A N ) with the s a m e calculation pret,~ton as noncompensated plans was desired. M a t e r i a l a n d M e t h o d s : C o m p e n s a t o r s were designed as a series of nested transmission blocks. Each block was constrained to c o v e r the area included within an isodose contour using a beam's-eye-view perspective. I s o d o s e c o n t o u r s w e r e d i s p l a y e d on a plane o f compensation. The transmission factor was chosen to be .95 to .98 (5% to 2 % per step). T h e compensator was cut from styrofoam and the c a v i t y filled with steel-loaded g y p s u m . T h e block scatter algorithm, fit to block data. provided corrections for differential patient scatter. B e a m h a r d e n i n g due to the p r e s e n c e o f the c o m p e n s a t o r w a s c o r r e c t e d by c h a n g i n g the t h i c k n e s s o f the compensator as a function o f off-axis position and local compensator thickness. D o s i m e t r y was verified with film m e a s u r e m e n t s in a flat phantom and with surface dose measurements. Results: Dose calculations in a flat phantom were verified to within a few percent. Measured data were more uniformly varying than the calculation. T h i s effect m a y be i m p r o v e d by an adjustment of the blocking algorithm. Conclusions: A s c h e m e for the i m p l e m e n t a t i o n o f d o s e c o m p e n s a t o r s w a s s a t i s f a c t o r y i m p l e m e n t e d for a 3D treatment planning system.
POINT
IN T H E
E. Celiai. G.P. Bitl, F. Banci Buonamici. M. Bueciolini, A. Compagnueci, C. Fallai, S.M. Magrini, P. OImi, F. Rossi, R. Santoni Clinical Physiopaihology Deparlmenl. University of Florence
ISOCENTRIC BREAST SIMULATION ANALYTICAL APPROACH
E.W. Lederer, S. Cosby, H. S c h w e n d e n e r Northeastern Ontario Regional Cancer Centre Department of Medical Physics Sudbury Canada : the s i m u l a t i o n o f tangential breast fields u s i n g an i s o c e n t r i c s e t - u p t e c h n i q u e is a l e n g t h y p r o c e s s i n v o l v i n g the placement of the isocentre and the determination o f the gantry angles and the selection lung shields, w h i c h in our centre is one o f six standard blocks. P u r p o s e : we s h o w that with a body contour taken through centralaxis, five m e a s u r e m e n t s and a calculator p r o g r a m , it is possible to significantly decrease the amount of time required to simulate a breast patient. M e t h o d s a n d m a t e r i a l s : we h a v e d e v e l o p e d a p r o g r a m for an H P 4 8 G X handheld calculator to d e t e r m i n e the g a n t r y angles, the isocentre, the field width, the standard angled block and the couch and c o l l i m a t o r rotation. T h e calculations are based on m e a s u r e m e n t s o f the field length, the horizontal d i s t a n c e b e t w e e n m i d l i n e a n d midaxillary line, and the vertical distances f r o m the midaxillary line to the inferior and superior b e a m border and central axis at midline. For the simulation process a j i g was developed that is inserted into the tray h o l d e r o f the s i m u l a t o r to s h o w the optical and the r a d i o l o g i c a l s h a d o w o f the calculated shielding along the patient's midline for clinical assessment during simulation and on the simulation film. The j i g also has a holder for an a l u m i n i u m w e d g e to i m p r o v e the i m a g e quality o f the simulation film. R e s u l t s a n d c o n c l u s i o n : the technique has been in use for two years and has resulted in time s a v i n g s of up to 30 percent per patient. It has p r o v e n to be an e a s y and accurate w a y o f s e t t i n g up i s o c e n t r i c treatments to the breast.
Background
The modern three-dimensional treatmenl planning are extremely useful equipments offering a series of options to help in the optimization of a treatment plan particularly as concerns the closer distribution to the target volume and sparing of the healthy tissues. The quantitative evaluation and comparison among rival plans for the same patient may he obtained by comparing dose-volume histograms. The volume(s) definition represent the first important step of all the process and it is probably the crucial point. Although the ICRU 50 recommendalions represent a good reference point for the radiation oncologists il is a common observation that different radiation oncologisls may define target volumes which differ considerably. Using our Scandiplan treatment planning system, which is a full 3-D system, based on an OCTREE-EDGE models, we decided to evaluate Ihe effects of the different choices made by five staff oncologists of the Department of Radiation Oneology of the University of Florence. The contoured primary treatment volumes (PTVs) and critical organs for four different patients, defined by five staff radiation oncologists, were obtained in a group of patients referred to our institution for irradialion of head and neck malignancies. These dose distributions, for each treatment plan and trealment technique, were compared. Quantitative differences in dose distributions for the different patients. PTVs and normal tissues are presented and their relevance is discussed.
- A NEW