The purpose of the study is to measure anatomical and dosimetric changes experienced by patients with head and neck cancer undergoing intensity-modulated radiation therapy and evaluate the need for adaptive radiotherapy using predefined relative thresholds as benchmarks.

This study involved 31 consecutive patients. Two computed tomography (CT) scans were utilized for initial treatment planning and a midpoint assessment. The study employed rigid registration and contour transfer techniques to apply primary dose calculation to midpoint CT, generating a hybrid plan, and an adaptive plan was generated on the midpoint CT.

The results revealed statistically significant volume reductions mainly in PTV70, PTV60 and PTV54 volumes. The volume of the parotid glands exhibited volumetric reductions in most of the patients. Hybrid plans demonstrated inferior dose coverage of the tumour regions, and comparisons between hybrid and adaptive plans showed significant variations in the maximum doses.

Anatomical deviations necessitating a repeat CT scan, along with the application of a new immobilization mask, emerged as a primary rationale for replanning. Indicators that could potentially encompass a breach of 95% dose coverage for 95% of the tumour volume, maximum doses surpassing 50 Gy in the spinal cord and 59 Gy in the brainstem<>, as well as lateral neck displacement exceeding 1cm from the initial position act as benchmarks before implementing a replan.

This is a prospective study to evaluate the dosimetric benefits of treatment plan adaptation for patients who had undergone repeat computed tomography (ReCT)and re-planning due to treatment-induced anatomical changes during radiotherapy.

This study involved five head and neck cancer patients who had their treatment plan modified, based on weekly thrice imaging protocol. Impact of mid-course imaging was assessed in patients using ReCT and cone beam computed tomography (CBCT)-based dose verification. Patients were imaged, apart from their initial CT, during the course of their radiation therapy with a ReCT and on board imager CBCT (Varian Medical Systems Inc., Palo Alto, CA, USA). Each CBCT/CT series was rigidly registered to the initial CT in the treatment planning system Eclipse (Varian Medical Systems Inc.) using bony landmarks. The structures were copied to the current CBCT/CT series and, where needed, manually edited slicewise. The dose distribution from the treatment plan was viewed as of the current anatomy by applying the treatment plan the CBCT/CT series, and studying the corresponding dose–volume histograms for organs at risk doses.

The reduction of parotid volumes due to weight loss was observed in all patients, which means an increase in predicted mean doses of parotid when initial CT plan was re-calculated on ReCT and CBCT (Table 1). This explains the necessity of adaptive planning. The predicted mean dose of parotid glands was increased and constraints to spinal cord and skin were exceeded, so re-planning was performed.

The CBCT is a useful tool to view anatomic changes in patients and get an estimate of their impact on dose distribution. Re-planning based on imaging in head and neck patients during the course of radiotherapy is mandatory to reduce side effects.

The purpose of this study was to audit positioning errors during bladder image-guided radiotherapy (IGRT) and quantify survival outcomes.

We carried out a retrospective review of 141 patients treated between March 2007 and July 2010 with three-dimensional conformal radiotherapy. An offline imaging protocol using kV cone beam computed tomography (CBCT) was used. Positioning errors, clinical interventions and re-planning rates were quantified. Cancer outcomes and survival were collected by review of patient notes and a registry search.

Among all, 43% of the patients required no intervention. Isocentre corrections were used for systematic bony set-up error in 13% and to improve bladder coverage in 28%. Clinical interventions to improve bladder coverage were required in 16% of the patients and repeat computed tomography planning in a further 16%. Overall, 44% of the patients demonstrated some form of organ deformation that would have resulted in inadequate dose to the bladder or significant overdose to an organ at risk if not corrected for. Post-treatment check cystoscopy was undertaken in 107 patients (76%) with 72 noted to have a complete response. Overall survival was 47·8% at 3 years.

Organ deformation during radiotherapy for bladder cancer is a significant problem for over 40% of patients. Strategies to compensate are essential to ensure optimal plan delivery.

To use cone-beam computed tomography (CBCT) images for treatment planning, the Hounsfield unit (HU)-electron density (ED) calibration table for CBCT should be stable. The purpose of this study was to verify the stability of the HU values for the CBCT system over 1 year and to evaluate the effects of variation in HU-ED calibration curves on dose calculation.

A tissue characterisation phantom was scanned with the field of view (FOV) of size S (FOV-S) and FOV of size M (FOV-M) using the CBCT system once a month for 1 year. A single field treatment plan was constructed on digital phantom images to validate the dose distribution using mean HU-ED calibration curves and possible variations.

HU values for each material rod over the observation period varied with trend. The HU value of the cortical bone rod decreased by about 100 HU for the FOV-S and by about 300 HU for the FOV-M. Possible variation in the HU-ED calibration curves produced a ≤17·9% dose difference in the dose maximum in the treatment plan.

The CBCT system should be calibrated periodically for consistent dose calculation.

It is common for head and neck patients to be affected by time trend errors as a result of weight loss during a course of radiation treatment. The objective of this planning study was to investigate the impact of weight loss on volumetric modulated arc therapy (VMAT) as well as intensity modulated radiation therapy (IMRT) for locally advanced head and neck cancer using automatic co-registration of the cone beam computed tomography.

A retrospective analysis of previously treated IMRT plans for ten patients with locally advanced head and neck cancer was done. A VMAT plan was also produced for all patients. We calculated the dose–volume histograms (DVH) indices for spinal cord planning at risk volumes (PRVs), the brainstem PRVs (SC+0·5 cm and BS+0·5 cm, respectively) as well as mean dose to the parotid glands.

The results show that the mean difference in dose to the SC+0·5 cm was 1·03% and 1·27% for the IMRT and VMAT plans, respectively. As for dose to the BS+0·5, the percentage difference was 0·63% for the IMRT plans and 0·61% for the VMAT plans. The analysis of the parotid gland doses shows that the percentage change in mean dose to left parotid was −8·0% whereas that of the right parotid was −6·4% for the IMRT treatment plans. In the VMAT plans, the percentages change for the left and the right parotid glands were −6·6 and −6·7% respectively.

This study shows a clinically significant impact of weight loss on DVH indices analysed in head and neck organs at risk. It highlights the importance of adaptive radiotherapy in head and neck patients if organ at risk sparing is to be maintained.