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Rectal and bladder motion during conformal radiotherapy after radical prostatectomy
Claudio Fiorino1, Franca Foppiano, Paola Franzone
1Servizio di Fisica Sanitaria, IRCCS H. S. Raffaele, Via Olgettina 60, 20132 Milano, Italy.
Summary
Rectal motion significantly impacts radiotherapy after prostatectomy, increasing rectal dose and uncertainty. Anterior rectal shifts were observed, affecting treatment accuracy and requiring careful consideration in planning.
Area of Science:
- Radiation Oncology
- Medical Physics
- Urologic Oncology
Background:
- Adjuvant radiotherapy after radical prostatectomy (RP) aims to eradicate residual cancer.
- Understanding organ motion, particularly rectum and bladder, is crucial for precise radiation delivery.
Purpose of the Study:
- To quantify rectum and bladder motion during adjuvant 3DCRT post-RP.
- To assess the impact of this motion on radiation dose distribution and treatment uncertainty.
Main Methods:
- Nine patients undergoing adjuvant 3DCRT post-RP were studied.
- Weekly CT scans were acquired and registered to planning CT.
- Rectum and bladder contours were analyzed for volume, position shifts, and dose-volume histograms (DVHs).
Main Results:
- Bladder volume showed significant variation due to filling, tending to be smaller during treatment.
- Rectal DVHs were worse in 6/9 patients, with dose increases up to 10-20%.
- A systematic anterior shift of the cranial rectum was observed in 6/9 patients, impacting CTV margins.
Conclusions:
- Rectal motion introduces significant uncertainty in adjuvant 3DCRT post-RP.
- Anterior rectal migration may be linked to post-surgical changes or irradiation effects.
- Cranial rectal motion was more pronounced, necessitating careful CTV margin adjustments.