- Email: [email protected]
Evaluation of changes in the location and shape of the prostate and rectum during a seven week course of conformal radiotherapy
222
Radiation Oncology, Biology, Physics
Volume 27, Supplement 1
Results: The average translational deviation from the simulated isocenter in each dimension was less than 1 mm with a standard error of 3-3.5 mm. The results were similar for all three directions. The average rotational errors were less than 1 degree with a standard error of approximately 1 degree. The average undirected distance between the treatment and simulated isocenter was 8 mm with a standard error of 3 mm. Seven of the nine patients had mean translational shifts during treatment which differed significantly (p < 0.05) from the simulated isocenter. Conclusion: In a previous study of casted versus non-casted patients done using port films, variation in positioning of the magnitude observed above were seen in the non-casted patients and smaller variations were seen in the casted patie&. In this study, the use of the EPID was less intrusive and may have resulted in less additional attention being given each set-up. If this is the case, then the use of film in a study of set-up variation must be closely scrutinized for the possible introduction of measurement bias. Studies of set-up variations must precede the institution of conformal techniques so that the minimum margin may be added to the CTV to attain a PTV which is still large enough to ensure that all of the known and suspected tumor is treated in every teatment session. 1. Hunt et al., Int. J. Rad. One. Biol. Phys., accepted for publication. 2. Soffen et al, Int. J. Rad. One. Biol. Phys., Vol. 20, pp 141-146.
154 Evaluation of Changes in the Location aod Shape of the Prostate and Rectum During a Seven Week Course of Conformal Radiotherapy ID Forman, MD’. CF Mesina, MS’, T He MS’
, SB
Devi, MD,’ E Ben-Josef, MD’, C Pelixzari,* Vijayakumar MD2, GT Cheo PhD2
‘Department of Radiation Gncology, Wayne State University, Detroit, MI, *Department of Radiation Oncology, U of Chicago, Chicago, IL
Purpose: The purpose of this study was to sequeatially document the location aod shape of the prostate, semioal vesicles, bladder and rechuo throughout a course of external beam radiotherapy to determine the frequency, range sod dosimetric conseq-ces of chaoges in orgao location. Materials and Meulods: Patimts with localized carcinoma of the prostate had conventional simulation followed immediately by a treattoeot planning CT (TPCTJ. Once treatment was initiated, each patient had a weekly CT (TPCT,3 immediately before. or after treatmutt. Tbilty cc of intravenous contrast was administered prior to the CT to distinguish the prostate and bladder volumes. Contours of the external skin surface,bones, rectum. bladder, prostate sod seminal vesicles were interactively drawn on a computer workstation sod used in beam’s eye view planning of the block aperahres. The serial CT data sets were spatially registered with each other using image correlation software which brings the bony pelvis of the different scaos into congruence. The location of the prostate, seminal vesicles, rectum and bladder were on scans taken after external beam treatment was begun were compared to TPCT,. as well a with each other. Superimposing the dose distribution on the original TPCT onto the subsequent scans permitted quantification of the d&metric coosequeoces of organ motion. Results: Five of 10 patients have already completed 6-7 TPCT. An average of 175 images and up to six aoatomic structures were digitized per each image for each patient. Compared to TPCT movement of the prostate and seminal vesicles (PSV) was demonstrated in all patients (max. avg. 1.7 cm, range 3.5 cm). Excluding TPCT, movement of the PSV was also see” when inter-comparing TPCT,, (max. avg. 1.2 cm, range O-3.7 cm). Compared to TCPT,, aoterior move-t of the PSV was in 60% of studies and posterior movement io 40%. The dosimettic consequences of orgao motion varied inversely with margin sixe. Analysis of DVH’s bf the rectum showed volume chaoges of 10% or greater (at high dose) due to positional changes of the Rctum during the treatment course. In addition, to the same changes in PSV location (average dose range 78-10446) thao a standard 4 field conformal technique (average dose range 95-103 %).related totreatment technique. DVH analysis demoostrated that a non-axial 4-field cooformal technique was more seositive to the same changes inPSV location (average dose range 78-104%) than a standard 4 field technique (average dose range 95-103%). Conclusion: Chaoges in the location and shape of the hlmor volume sod normal tissues during a course of radiotherapy occur and have dosimetric consequences that may impact 011tumor control and normal tissue complication probabilities. Certain beam arrangements and margin size are more sensitive to this type of motion. Optimal cooformal radiotherapy for prostate caocer may require that the anatomic relationships at the time of treatment pbmoing remain relatively fixed throughout treatment.
Radiation Oncology, Biology, Physics
Volume 27, Supplement 1
Results: The average translational deviation from the simulated isocenter in each dimension was less than 1 mm with a standard error of 3-3.5 mm. The results were similar for all three directions. The average rotational errors were less than 1 degree with a standard error of approximately 1 degree. The average undirected distance between the treatment and simulated isocenter was 8 mm with a standard error of 3 mm. Seven of the nine patients had mean translational shifts during treatment which differed significantly (p < 0.05) from the simulated isocenter. Conclusion: In a previous study of casted versus non-casted patients done using port films, variation in positioning of the magnitude observed above were seen in the non-casted patients and smaller variations were seen in the casted patie&. In this study, the use of the EPID was less intrusive and may have resulted in less additional attention being given each set-up. If this is the case, then the use of film in a study of set-up variation must be closely scrutinized for the possible introduction of measurement bias. Studies of set-up variations must precede the institution of conformal techniques so that the minimum margin may be added to the CTV to attain a PTV which is still large enough to ensure that all of the known and suspected tumor is treated in every teatment session. 1. Hunt et al., Int. J. Rad. One. Biol. Phys., accepted for publication. 2. Soffen et al, Int. J. Rad. One. Biol. Phys., Vol. 20, pp 141-146.
154 Evaluation of Changes in the Location aod Shape of the Prostate and Rectum During a Seven Week Course of Conformal Radiotherapy ID Forman, MD’. CF Mesina, MS’, T He MS’
, SB
Devi, MD,’ E Ben-Josef, MD’, C Pelixzari,* Vijayakumar MD2, GT Cheo PhD2
‘Department of Radiation Gncology, Wayne State University, Detroit, MI, *Department of Radiation Oncology, U of Chicago, Chicago, IL
Purpose: The purpose of this study was to sequeatially document the location aod shape of the prostate, semioal vesicles, bladder and rechuo throughout a course of external beam radiotherapy to determine the frequency, range sod dosimetric conseq-ces of chaoges in orgao location. Materials and Meulods: Patimts with localized carcinoma of the prostate had conventional simulation followed immediately by a treattoeot planning CT (TPCTJ. Once treatment was initiated, each patient had a weekly CT (TPCT,3 immediately before. or after treatmutt. Tbilty cc of intravenous contrast was administered prior to the CT to distinguish the prostate and bladder volumes. Contours of the external skin surface,bones, rectum. bladder, prostate sod seminal vesicles were interactively drawn on a computer workstation sod used in beam’s eye view planning of the block aperahres. The serial CT data sets were spatially registered with each other using image correlation software which brings the bony pelvis of the different scaos into congruence. The location of the prostate, seminal vesicles, rectum and bladder were on scans taken after external beam treatment was begun were compared to TPCT,. as well a with each other. Superimposing the dose distribution on the original TPCT onto the subsequent scans permitted quantification of the d&metric coosequeoces of organ motion. Results: Five of 10 patients have already completed 6-7 TPCT. An average of 175 images and up to six aoatomic structures were digitized per each image for each patient. Compared to TPCT movement of the prostate and seminal vesicles (PSV) was demonstrated in all patients (max. avg. 1.7 cm, range 3.5 cm). Excluding TPCT, movement of the PSV was also see” when inter-comparing TPCT,, (max. avg. 1.2 cm, range O-3.7 cm). Compared to TCPT,, aoterior move-t of the PSV was in 60% of studies and posterior movement io 40%. The dosimettic consequences of orgao motion varied inversely with margin sixe. Analysis of DVH’s bf the rectum showed volume chaoges of 10% or greater (at high dose) due to positional changes of the Rctum during the treatment course. In addition, to the same changes in PSV location (average dose range 78-10446) thao a standard 4 field conformal technique (average dose range 95-103 %).related totreatment technique. DVH analysis demoostrated that a non-axial 4-field cooformal technique was more seositive to the same changes inPSV location (average dose range 78-104%) than a standard 4 field technique (average dose range 95-103%). Conclusion: Chaoges in the location and shape of the hlmor volume sod normal tissues during a course of radiotherapy occur and have dosimetric consequences that may impact 011tumor control and normal tissue complication probabilities. Certain beam arrangements and margin size are more sensitive to this type of motion. Optimal cooformal radiotherapy for prostate caocer may require that the anatomic relationships at the time of treatment pbmoing remain relatively fixed throughout treatment.