Dataset Information

Prostate bed motion during intensity-modulated radiotherapy treatment.

ABSTRACT: Conformal radiation therapy in the postprostatectomy setting requires accurate setup and localization of the prostatic fossa. In this series, we report prostate bed localization and motion characteristics, using data collected from implanted radiofrequency transponders.The Calypso four-dimensional localization system uses three implanted radiofrequency transponders for daily target localization and real-time tracking throughout a course of radiation therapy. We reviewed the localization and tracking reports for 20 patients who received ultrasonography-guided placement of Calypso transponders within the prostate bed prior to a course of intensity-modulated radiation therapy at Fox Chase Cancer Center.At localization, prostate bed displacement relative to bony anatomy exceeded 5 mm in 9% of fractions in the anterior-posterior (A-P) direction and 21% of fractions in the superior-inferior (S-I) direction. The three-dimensional vector length from skin marks to Calypso alignment exceeded 1 cm in 24% of all 652 fractions with available setup data. During treatment, the target exceeded the 5-mm tracking limit for at least 30 sec in 11% of all fractions, generally in the A-P or S-I direction. In the A-P direction, target motion was twice as likely to move posteriorly, toward the rectum, than anteriorly. Fifteen percent of all treatments were interrupted for repositioning, and 70% of patients were repositioned at least once during their treatment course.Set-up errors and motion of the prostatic fossa during radiotherapy are nontrivial, leading to potential undertreatment of target and excess normal tissue toxicity if not taken into account during treatment planning. Localization and real-time tracking of the prostate bed via implanted Calypso transponders can be used to improve the accuracy of plan delivery.

SUBMITTER: Klayton T

PROVIDER: S-EPMC3285397 | biostudies-literature | 2012 Sep

REPOSITORIES: biostudies-literature

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Prostate bed motion during intensity-modulated radiotherapy treatment.

Klayton Tracy T Price Robert R Buyyounouski Mark K MK Sobczak Mark M Greenberg Richard R Li Jinsheng J Keller Lanea L Sopka Dennis D Kutikov Alexander A Horwitz Eric M EM

International journal of radiation oncology, biology, physics 20120211 1

<h4>Purpose</h4>Conformal radiation therapy in the postprostatectomy setting requires accurate setup and localization of the prostatic fossa. In this series, we report prostate bed localization and motion characteristics, using data collected from implanted radiofrequency transponders.<h4>Methods and materials</h4>The Calypso four-dimensional localization system uses three implanted radiofrequency transponders for daily target localization and real-time tracking throughout a course of radiation ...[more]

PMID: 22330987

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Project description:In this study, we present an intensity-modulated radiotherapy technique based on forward planning dose calculations to provide a concave dose distribution to the prostate and seminal vesicles by means of modified dynamic arc therapy (M-DAT). Dynamic arcs (350 degrees) conforming to the beam's eye view of the prostate and seminal vesicles while shielding the rectum, combined with two lateral oblique conformal fields (15 degrees with respect to laterals) fitting the prostate only,were applied to deliver doses of 78 Gy and 61.23 Gy in 39 fractions to the prostate and seminal vesicles respectively. Dynamic wedges (45 degrees of thick end, anteriorly oriented) were used with conformal beams to adjust the dose homogeneity to the prostate, although in some cases, hard wedges (30 degrees of thick part,inferiorly oriented) were used with arcs to adjust the dose coverage to the seminal vesicles. The M-DAT was applied to 10 patients in supine and 10 patients in prone positioning to determine the proper patient positioning for optimum protection of the rectum. The M-DAT was compared with the simplified intensity-modulated arc therapy (SIMAT) technique, composed of three phases of bilateral dynamic arcs. The mean rectal dose in M-DAT for prone patients was 22.5 +/- 5.1 Gy; in M-DAT and SIMAT for supine patients, it was 30.2 +/- 5.1 Gy and 39.4 +/- 6.0 Gy respectively. The doses to 15%, 25%, 35%, and 50% of the rectum volume in M-DAT for prone patients were 44.5 +/- 10.2 Gy, 33.0 +/- 8.2 Gy, 25.3 +/- 6.4 Gy, and 16.3 +/- 5.6 Gy respectively. These values were lower than those in M-DAT and in SIMAT for supine patients by 7.7%, 18.2%, 22.4%, and 28.5% and by 25.0%, 32.1%, 34.9%, and 41.9% of the prescribed dose (78 Gy) respectively. Ion chamber measurements showed good agreement of the calculated and measured isocentric dose (maximum deviation of 3.5%). Accuracy of the dose distribution calculation was evaluated by film dosimetry using a gamma index, allowing 3% dose variation and 4 mm distance to agreement as the individual acceptance criteria in prostate and seminal vesicle levels alike for all supine and prone patients. We found that fewer than 10% of the pixels in the dose distribution of the calculated area of10 x 10-cm failed the acceptance criteria. These pixels were observed mainly in the low-dose regions, particularly at the level of the seminal vesicles. In conclusion, the single-phase M-DAT technique with patients in the prone position was found to provide the intended coverage of the prescribed doses to the prostate and seminal vesicles with improved protection for the rectum. Accordingly, M-DAT has replaced non-modulated conformal radiotherapy or SIMAT as the standard treatment for prostate cancer in our department.

Dataset Information

Prostate bed motion during intensity-modulated radiotherapy treatment.

Publications

Prostate bed motion during intensity-modulated radiotherapy treatment.

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