Dose-volume analysis of locoregional recurrences in head and neck IMRT, as determined by deformable registration: a prospective multi-institutional trial.

BACKGROUND AND PURPOSE: Although IMRT for head and neck cancer is widely accepted, the implications of sparing normal tissue immediately adjacent to target volumes are not well known. MATERIALS AND METHODS: Between 2002 and 2007, 124 patients with head and neck cancer were treated with surgery and postoperative IMRT (n=79) or definitive RT (n=45). Locoregional recurrences were analyzed for location relative to target volumes, and dosimetry. RESULTS: With a median follow-up of 26.1months, a total of 16 locoregional recurrences were observed. The five-year actuarial locoregional disease-free survival was 82% [95% CI, 72-90%]. Analysis of 18 distinct sites of locoregional failure revealed that five of these failures were within the high dose clinical target volume (CTV), nine failures were at the margin of the CTV, and four recurrences were outside the CTV. The mean dose delivered to these recurrent volumes was 63.1 Gy [range: 57-68 Gy], while the mean dose to the coolest 1cc within each recurrence was 60.0 Gy [range: 51-67 Gy]. There were two periparotid recurrences observed. CONCLUSIONS: We observed excellent locoregional control rates overall. The majority of recurrences occur within high dose regions of the neck and not near the spared parotid glands.

Planning target volume margins for prostate radiotherapy using daily electronic portal imaging and implanted fiducial markers.

BACKGROUND: Fiducial markers and daily electronic portal imaging (EPI) can reduce the risk of geographic miss in prostate cancer radiotherapy. The purpose of this study was to estimate CTV to PTV margin requirements, without and with the use of this image guidance strategy. METHODS: 46 patients underwent placement of 3 radio-opaque fiducial markers prior to prostate RT. Daily pre-treatment EPIs were taken, and isocenter placement errors were corrected if they were > or = 3 mm along the left-right or superior-inferior axes, and/or > or = 2 mm along the anterior-posterior axis. During-treatment EPIs were then obtained to estimate intra-fraction motion. RESULTS: Without image guidance, margins of 0.57 cm, 0.79 cm and 0.77 cm, along the left-right, superior-inferior and anterior-posterior axes respectively, are required to give 95% probability of complete CTV coverage each day. With the above image guidance strategy, these margins can be reduced to 0.36 cm, 0.37 cm and 0.37 cm respectively. Correction of all isocenter placement errors, regardless of size, would permit minimal additional reduction in margins. CONCLUSIONS: Image guidance, using implanted fiducial markers and daily EPI, permits the use of narrower PTV margins without compromising coverage of the target, in the radiotherapy of prostate cancer.

An investigation of beam parameters for Co-60 tomotherapy.

The effect of various physical beam parameters for Co-60 tomotherapy is examined, including: Cylindrical source size, source-to-collimator distance (SCD) and collimator leaf width. In general, beam profile effects are seen with larger Co-60 sources that are not seen with conventional linacs and multileaf collimators that are used for IMRT, including a broadening of the profile width as the source width increases. A treatment planning study was conducted to evaluate the effect of various beam parameter combinations with planning regions of interest typical of a simultaneous boost head and neck treatment. Combinations of SCD and source FWHM that produce an 80%-20% profile distance less than approximately 0.85 cm at 0.5 cm depth produced a Co-60 tomotherapy plan with better DVH results than a conventional 7-field linac plan for a 1 cm leaf width. Further improvement may be achieved by reducing the leaf width. In general it may be concluded that commercially available cylindrical Co-60 sources of 1.5-2.0 cm diameter may be appropriate for tomotherapy if the proper combination of beam parameters is chosen.