Practical guidelines for routine intensity-modulated radiotherapy verification: pre-treatment verification with portal dosimetry and treatment verification with in vivo dosimetry.

The purpose of this work is to provide guidelines for the routine use of portal dosimetry and in vivo diode measurements to verify intensity-modulated radiotherapy (IMRT) treatments. To achieve tolerance levels that are sensitive enough to intercept problems, both the portal dosimetry and the in vivo procedure must be optimised. Portal dosimetry was improved by the introduction of an optimised two-dimensional (2D) profile correction, which also accounted for the effect of backscatter from the R-arm. The scaled score, indicating the fraction of points not meeting the desired gamma evaluation criteria within the field opening, was determined as the parameter of interest. Using gamma criteria of a 3% dose difference and 3 mm distance to agreement, a "scaled score" threshold value of 1.5% was chosen to indicate excessive tongue and groove and other problems. The pre-treatment portal dosimetry quality assurance (QA) does not encompass verification of the patient dose calculation or position, and so it is complemented by in vivo diode measurements. Diode positioning is crucial in IMRT, and so we describe a method for diode positioning at any suitable point. We achieved 95% of IMRT field measurements within ±5% and 99% within ±8%, with improved accuracy being achieved over time owing to better positioning. Although the careful preparation and setup of the diode measurements can be time-consuming, this is compensated for by the time efficiency of the optimised procedure. Both methods are now easily absorbed into the routine work of the department.

A multicentre timing study of intensity-modulated radiotherapy planning and delivery.

AIMS: The aim of the study was to measure how long the intensity-modulated radiotherapy (IMRT) process takes, both for planning and delivery, using several IMRT techniques and departments. MATERIALS AND METHODS: Timings were measured at three radiotherapy centres for each step of the process of outlining, planning and delivering IMRT for head and neck cancers. Times were measured for a total of 63 patients; 27 with helical tomotherapy, 37 with dynamic sliding window (26 in one centre, 11 in another) and nine with step-and-shoot. RESULTS: The mean time to outline a patient was 108 min, to produce and check the plan 7.9 h, to carry out and analyse patient-specific quality assurance 1.9 h. The mean treatment time (including on-treatment verification imaging where carried out), measured gate to gate, was 28 min 10 s for first fractions and 20 min 20 s for subsequent fractions. CONCLUSION: An analysis of subgroups showed some differences in times between techniques, and some differences between departments with the same techniques. For all four techniques, the median time from the end of outlining to the start of treatment was under 3 weeks.

High dose rate Microselectron moulds for Kaposi sarcoma of the palate.

PURPOSE: External beam radiotherapy for Kaposi sarcoma of the palate in HIV positive patients has often severe acute side-effects. As alternative treatment, a high dose Microselectron brachytherapy technique was developed. METHODS AND MATERIAL: A customised dental plate with afterloading tubes was made; from outlines, three dimensional coordinates of source positions and surface points were input to a Target 2 treatment planning computer. For the best dose-distribution on the mould surface, weighting of each source dwell position was adjusted, a plan produced, and a test run with TLD measurements performed. RESULTS: We planned and treated six patients and seven lesions with this technique. A median surface dose of 24 Gy (range 14-39.9 Gy) in 3 fractions over 3 to 10 days was prescribed. There was a complete response for all lesions with only mild mucositis. No relapse occurred in the treated areas. CONCLUSIONS: Kaposi sarcoma of the palate treated with a high dose rate Microselectron dental plate is convenient for the patient, achieves local control and has less acute toxicity compared with external beam radiotherapy.