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The objectives of this study were to evaluate dosimetric quality and acute toxicity of volumetric-modulated arc therapy (VMAT) and daily image guidance in high-risk prostate cancer patients. A total of 100 consecutive high-risk prostate cancer patients treated with definitive VMAT with prophylactic whole-pelvic radiotherapy (WPRT) were enrolled. All patients were treated with a double-arc VMAT plan delivering 52 Gy to the prostate planning target volume (PTV), while simultaneously delivering 46.8 Gy to the pelvic nodal PTV in 26 fractions, followed by a single-arc VMAT plan delivering 26 Gy to the prostate PTV in 13 fractions. Image-guided RT was performed with daily cone-beam computed tomography. Dose–volume parameters for the PTV and the organs at risk (OARs), total number of monitor units (MUs) and treatment time were evaluated. Acute toxicity was assessed using the Common Terminology Criteria for Adverse Events, version 4.0. All dosimetric parameters met the present plan acceptance criteria. Mean MU and treatment time were 471 and 146 s for double-arc VMAT, respectively, and were 520 and 76 s for single-arc VMAT, respectively. No Grade 3 or higher acute toxicity was reported. Acute Grade 2 proctitis, diarrhea, and genitourinary toxicity occurred in 12 patients (12%), 6 patients (6%) and 13 patients (13%), respectively. The present study demonstrated that VMAT for WPRT in prostate cancer results in favorable PTV coverage and OAR sparing with short treatment time and an acceptable rate of acute toxicity. These findings support the use of VMAT for delivering WPRT to high-risk prostate cancer patients.

Results: The mean rectal dose, the rectal volume receiving $30 Gy (V 30Gy ), rectal V 50Gy, the mean bladder dose, bladder V 30Gy and bladder V 50Gy were significantly increased in the WP group (p , 0.05 each); however, the rectal V 70Gy did not differ between groups (p 5 0.101), and the bladder V 70Gy was significantly lower in the WP group (p 5 0.029). The WP group experienced a significantly increased frequency of acute grade 2 diarrhoea relative to the PO group (5.9% vs 0%; p 5 0.015). No differences were seen between the WP and PO groups in terms of acute grade 2 proctitis (10.1% vs 6.7%; p 5 0.360) and genitourinary (GU) toxicity (12.6% vs 10.5%; p 5 0.620). Conclusion: Despite larger rectum and bladder volumes at low-and medium-dose levels, WP VMAT resulted in no significant increase in acute proctitis or GU toxicity when compared with PO VMAT. Advances in knowledge: This study demonstrates that whole-pelvic radiotherapy has comparable acute toxicity to those observed with prostate-only radiotherapy when VMAT with daily image guidance is used.

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