Set-up errors in head and neck cancer treated with IMRT technique assessed by cone-beam computed tomography: a feasible protocol

PURPOSE: To investigate set-up errors, suggest the adequate planning target volume (PTV) margin and image-guided radiotherapy frequency in head and neck (H&N) cancer treated with intensity-modulated radiotherapy (IMRT) assessed by kV cone-beam computed tomography (CBCT). METHODS: We analyzed 360 CBCTs in 60 patients with H&N cancer treated with IMRT. The target delineation was contoured according to ICRU62. PTVs were generated by adding a 3–5 mm margin in all directions to the respective clinical target volumes. The kV CBCT images were obtained at first three days of irradiation and weekly thereafter. The overall mean displacement, range, systematic (∑) and random (σ) errors were calculated. Adequate PTV margins were calculated according to the van Herk formula (2.5∑ + 0.7r). RESULTS: The mean of set-up errors was less than 2 mm in any direction. The overall frequency of set-up displacements greater than 3 mm was 3.9% in medial-lateral (ML) direction, 8% in superior-inferior (SI) direction, and 15.5% in anterior-posterior (AP) direction. The range of translations shifts was 0–9 mm in ML direction, 0–5 mm in SI direction and 0–10 mm in AP direction, respectively. After systematic set-up errors correction, the adequate margin to overcome the problem of set-up errors was found to be less than 3 mm. CONCLUSION: Image-guided kV CBCT was effective for the evaluation of set-up accuracy in H&N cancer. The kV CBCT at first three fractions and followed-by weekly appears adequate for reducing significantly set-up errors in H&N cancer treated with IMRT technique. Finally, 3–5 mm PTV margins appear adequate and safe to overcome the problem of set-up errors.

Preliminary study of intensity modulation radiation therapy for patients with prostate carcinoma / 中国癌症杂志

Purpose: To study the clinical application of intensity modulation radiation therapy (IMRT) in patients with prostate cancer. Methods: From May 2000 to June 2001, 14 patients with prostate carcinoma were treated . 12 patients underwent orchiectomy before IMRT. All patients were treated by IMRT with PEACOCK-MIMiC system ( CORVUS 3. 0 NOMOS CORPORATION) and VARIAN 6MV-photons. The prescription dose-time- fraction was 2.5 to 3. 0 Gy per fraction, 5 times per week , the total was 25 to 30 fractions, the total IMRT dose was 72 to 77 Gy, 5 to 6 weeks. Results: 3 months after IMRT , PR: 10(71.4%), NC: 4 cases and 6 month after IMRT CR: 6,PR: 8 cases. The overall response( CR + PR) rate were 100% . No Grade Ⅲ ,Ⅳ gastrointestinal ( GI) and genitourinary ( GU) toxicity occurred in any of the patients. Conclusions: IMRT is an effective approach for patients with prostate carcinoma. The dose of 72 to 77 Gy was safe.