Statistical motion modelling for robust evaluation of clinically delivered accumulated dose distributions after curative radiotherapy of locally advanced prostate cancer.

BACKGROUND AND PURPOSE: Planned doses are used as surrogate for the actually delivered dose in radiotherapy. We have estimated the delivered dose in a dose-escalation trial of locally advanced prostate cancer by statistical dose-accumulation and by DVH-summation, and compared to planned dose. MATERIALS AND METHOD: Prescribed dose-escalation to the prostate was 67.5 Gy/25fr., corresponding to 81GyEQD2 assuming α/ß = 1.5. The 21 patients had three targets (i.e. CTV67.5 + 2 mm, CTV60 + 5 mm, CTV50 + 10 mm) irradiated by a simultaneous-integrated-boost technique. Analysis was based on 213 CT scans and 5-years of follow-up. For statistical dose-accumulation, we modelled 10000 possible treatment courses based on planned dose and deformation-vector-fields from contour-based registration. For DVH-summation we recalculated dose on repeat-CTs and estimated median D98%/EUD. Groups with/without disease recurrence were compared. RESULTS: Discrepancies between planned and accumulated dose were mostly seen for CTV67.5, where under-dosage was found at different locations in the prostate in 12/21 patients. Delivered dose-escalation (D98%) was on average 73.9GyEQD2 (range: 68.3-78.7GyEQD2). No significant difference in accumulated-D98% was found in patients with (n = 8) and without (n = 13) recurrence (p > 0.05). Average D98%/EUD with statistical dose-accumulation vs DVH-summation was significantly different in CTV60, CTV50, rectum and bladder but not in CTV67.5. CONCLUSION: The planned dose escalation was not received by more than half-of-the patients. Robustness of the prostate target (CTV67.5) should therefore be better prioritized in these patients given the low toxicity profile. Estimates of delivered dose were less conservative for dose-accumulation due to interaction of random organ motion with the dose matrix.

Assessment of late urinary, bowel and sexual function after dose escalation from 70 to 76 Gy using image-guided radiotherapy in curative treatment of prostate cancer.

OBJECTIVE: The aim of this study was to evaluate the late urinary, bowel and sexual function among men with localized or locally advanced prostate cancer treated with curative radiotherapy after the introduction of image-guided radiotherapy to 76 Gy using the Swedish BeamCath® technique. MATERIAL AND METHODS: All patients treated with curative radiotherapy during 2003-2006 were invited to participate in this retrospective study. In total, 87% (158/181) participated in the study. The median observation time was 35 months. Comparisons were made between the standard 70 Gy (n = 73) and the 76 Gy (n = 85) treatment groups. Assessments of late urinary, bowel and sexual function were questionnaire based, and included function items in the Expanded Prostate Cancer Index Composite. RESULTS: Most late urinary and bowel symptoms were reported to occur seldom or never in the majority of men, while late sexual toxicity was reported in a large proportion (66%) of men. Seven men (4%) used diapers. Only 25% (n = 40) reported having an erection firm enough for intercourse. None of the reported urinary or sexual function symptoms differed between the treatment groups. Rectal urgency at least once daily was a more frequent symptom in the 70 Gy group than the 76 Gy group (28% vs 9%, p = 0.006). Painful bowel movements were a more common symptom in the 70 Gy group (11% vs 1%, p = 0.01). CONCLUSION: Dose escalation up to 76 Gy using the BeamCath technique was not associated with more late toxicities than the standard 70 Gy dose.