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Varying dose rate dynamic therapy with 3-D couch movement and with beam shaping
281
Proceedings of the 34th Annual ASTRO Meeting anterior centered
field centered on the symphysis pubis at mid-plane are simulated and marked.
and
a lateral
field
with
same
cranial-caudal
borders
and
A CT is taken in the cast,with the anterior and lateral midplanes marked with thinmetal wires.The distances the prostate extendsaway from the midplaneaxes,as marked by the wires,are measured.These values are then entered onto the first simulation films, thereby
Eight defining the target volume. These films are then used as the templates for the final simulation fields. patients had treatment plans generated by this method as well as standard multi-planar target planning using ROCS planning program. The isocenters and the target volumes were then compared.
a
The mean variation betweenthe isocenters on the anterior films was 0.3 cm (range 0.1 0.5 cm). The variation of the isocenters of the lateral fields was 0.2 cm (range0 - 0.75 cm). There was no cranial-caudal variation with thistechnique. The variation of the target volume was random, with an absolute mean of 0.25
RESULTS:
cm. The time to generate with the computer.
a plan
was approximately
45 minutes
without
using
the computer,
and 4 to 6 hours
A practical method for designing conformal prostate fields has been described. It has been CONCLUSIONS: shown lo be nearly equivalent in precision 10 multi-planar target planing. Use of this technique in the community will allow conformal field treatment of the prostate to gain wider acceptance, and thereby decrease treatment morbidity.
1070 FOUR, SIX OR EIGHT-FIELD TECHNIQUE (T) IN THE CONFORMAL RADIOTHERAPY (RT) IN PROSTATE CANCER (PC): A DOSE-VOLUME HISTOGRAM (DVH) ANALYSIS P. Chiru, S. Vijayakumar, L. Myrianthopoulos, D. Spelbring, H. Halpern, S. Rubin and G.T.Y. Chen University of Chicago Center for Radiotherapy, Department of Radiation and Cellular Oncology, University of Chicago, Chicago, IL. Puroose: It has been shown that Computerized Tomography (CT) based treatment planning is essential in the RT of PC. Conformal therapy also has been shown to have many advantages. However, the uncertainties associated with day-to-day set-up variations and possible mobility of the prostate with differences in rectal and/or bladder filling require allowing to give l-2 cm margin in defining the target volumes in the radical RT of PC. This practice raises the following questions: (a) How will the selection of a T (4 vs 6 vs 8 field [F]) be influenced by the margin used to define the target (TGT) volumes? (b) Will there be differences in T selection if one uses rectal DVH vis a vis bladder DVH? (c) Are there differences in inter-observer (OBS) selection if the same DVH data are provided to multiple experts? Materials & Methods: Planning CT was obtained in the treatment position, on a flat couch. Four different TGTs were defined: (a) prostate (P) + 1 cm (TGT-1); (b) P + 2 cm (TGT-2); (c) P + seminal vesicles (SV) + 1 cm (TGT-3); (d) P + SV + 2 cm (TGT-4). The TGTs were always covered by the 100% isodose line for three different Ts: 4, 6 and 8 F. Three physicians and one physicist independently selected an optimal T for each of 4 TGT volumes based on rectal or bladder DVH in 10 patients (pts). Results: (See Table)(l) The optimal Ts selected with rectal DVHs were often different from those selected from bladder DVHs. For instance, for TGT-1, 4 F was selected as optimal T by 80% from rectal DVH, whereas 6 F was selected in 65% from bladder DVHs. (2) Differences in margins sometimes lead to differences in selection of an optimal T. E.g., for TGT-1 and 2, from rectal DVHs, 4 F was selected in 80% and 85%, respectively. (3) There were inter-OBS differences. E.g., for TGT-4, 6 F was selected by 4 OBS in 70%, 30%, 30% and 70% (4) In general, 4 F was more often selected from rectal respectively, from bladder DVHs. DVHs; 6 F from bladder DVHs. Conclusion: (1) DVHs are very useful in the selection of optimal T in RT of PC. (2) DVHs should be used more routinely to customize T in individual pts. Routine use of 4 or 6 F in u pts with PC may have to be re-evaluated. (3) Differences in TGT definitions can lead to selection of different Ts as optimal. Further investigations to determine optimal margins in PC are urgent. (4) Objective methods of optimal T selection are needed to overcome subjective differences of interpretation of the same DVH data. FRC+! BLADDER 0"" FRCU RECTAL DVH TGT 1 06s 1 4-80X 085 2 4-100x OBS 3 4-80X OBS 4 4-50x )tote: eg: 4-80X
3 4 2 4-.30x 4-70x 4-60x 4-50x 4-90x 4-80X 4.90% 4-70x 4-90x 4.80% 4.60% means 4 field selected
4-80x
1 2 6-W% 6-90X 6-50.X 6.50% 6-50X 6-60X 6-70X 6-70X in 80% of patients
3 6-80X 6-60X 6-50X 6-50X
4 6-70X 6-30X 6-30X 6-70X
Proceedings of the 34th Annual ASTRO Meeting anterior centered
field centered on the symphysis pubis at mid-plane are simulated and marked.
and
a lateral
field
with
same
cranial-caudal
borders
and
A CT is taken in the cast,with the anterior and lateral midplanes marked with thinmetal wires.The distances the prostate extendsaway from the midplaneaxes,as marked by the wires,are measured.These values are then entered onto the first simulation films, thereby
Eight defining the target volume. These films are then used as the templates for the final simulation fields. patients had treatment plans generated by this method as well as standard multi-planar target planning using ROCS planning program. The isocenters and the target volumes were then compared.
a
The mean variation betweenthe isocenters on the anterior films was 0.3 cm (range 0.1 0.5 cm). The variation of the isocenters of the lateral fields was 0.2 cm (range0 - 0.75 cm). There was no cranial-caudal variation with thistechnique. The variation of the target volume was random, with an absolute mean of 0.25
RESULTS:
cm. The time to generate with the computer.
a plan
was approximately
45 minutes
without
using
the computer,
and 4 to 6 hours
A practical method for designing conformal prostate fields has been described. It has been CONCLUSIONS: shown lo be nearly equivalent in precision 10 multi-planar target planing. Use of this technique in the community will allow conformal field treatment of the prostate to gain wider acceptance, and thereby decrease treatment morbidity.
1070 FOUR, SIX OR EIGHT-FIELD TECHNIQUE (T) IN THE CONFORMAL RADIOTHERAPY (RT) IN PROSTATE CANCER (PC): A DOSE-VOLUME HISTOGRAM (DVH) ANALYSIS P. Chiru, S. Vijayakumar, L. Myrianthopoulos, D. Spelbring, H. Halpern, S. Rubin and G.T.Y. Chen University of Chicago Center for Radiotherapy, Department of Radiation and Cellular Oncology, University of Chicago, Chicago, IL. Puroose: It has been shown that Computerized Tomography (CT) based treatment planning is essential in the RT of PC. Conformal therapy also has been shown to have many advantages. However, the uncertainties associated with day-to-day set-up variations and possible mobility of the prostate with differences in rectal and/or bladder filling require allowing to give l-2 cm margin in defining the target volumes in the radical RT of PC. This practice raises the following questions: (a) How will the selection of a T (4 vs 6 vs 8 field [F]) be influenced by the margin used to define the target (TGT) volumes? (b) Will there be differences in T selection if one uses rectal DVH vis a vis bladder DVH? (c) Are there differences in inter-observer (OBS) selection if the same DVH data are provided to multiple experts? Materials & Methods: Planning CT was obtained in the treatment position, on a flat couch. Four different TGTs were defined: (a) prostate (P) + 1 cm (TGT-1); (b) P + 2 cm (TGT-2); (c) P + seminal vesicles (SV) + 1 cm (TGT-3); (d) P + SV + 2 cm (TGT-4). The TGTs were always covered by the 100% isodose line for three different Ts: 4, 6 and 8 F. Three physicians and one physicist independently selected an optimal T for each of 4 TGT volumes based on rectal or bladder DVH in 10 patients (pts). Results: (See Table)(l) The optimal Ts selected with rectal DVHs were often different from those selected from bladder DVHs. For instance, for TGT-1, 4 F was selected as optimal T by 80% from rectal DVH, whereas 6 F was selected in 65% from bladder DVHs. (2) Differences in margins sometimes lead to differences in selection of an optimal T. E.g., for TGT-1 and 2, from rectal DVHs, 4 F was selected in 80% and 85%, respectively. (3) There were inter-OBS differences. E.g., for TGT-4, 6 F was selected by 4 OBS in 70%, 30%, 30% and 70% (4) In general, 4 F was more often selected from rectal respectively, from bladder DVHs. DVHs; 6 F from bladder DVHs. Conclusion: (1) DVHs are very useful in the selection of optimal T in RT of PC. (2) DVHs should be used more routinely to customize T in individual pts. Routine use of 4 or 6 F in u pts with PC may have to be re-evaluated. (3) Differences in TGT definitions can lead to selection of different Ts as optimal. Further investigations to determine optimal margins in PC are urgent. (4) Objective methods of optimal T selection are needed to overcome subjective differences of interpretation of the same DVH data. FRC+! BLADDER 0"" FRCU RECTAL DVH TGT 1 06s 1 4-80X 085 2 4-100x OBS 3 4-80X OBS 4 4-50x )tote: eg: 4-80X
3 4 2 4-.30x 4-70x 4-60x 4-50x 4-90x 4-80X 4.90% 4-70x 4-90x 4.80% 4.60% means 4 field selected
4-80x
1 2 6-W% 6-90X 6-50.X 6.50% 6-50X 6-60X 6-70X 6-70X in 80% of patients
3 6-80X 6-60X 6-50X 6-50X
4 6-70X 6-30X 6-30X 6-70X