Rebecca Owen

Intra-fraction prostate displacement in radiotherapy estimated from pre- and post-treatment imaging of patients with implanted fiducial markers

PURPOSE To determine intra-fraction displacement of the prostate gland from imaging pre- and post-radiotherapy delivery of prostate cancer patients with three implanted fiducial markers. METHODS AND MATERIALS Data were collected from 184 patients who had two orthogonal X-rays pre- and post-delivery on at least 20 occasions using a Varian On Board kV Imaging system. A total of 5778 image pairs covering time intervals between 3 and 30 min between pre- and post-imaging were evaluated for intra-fraction prostate displacement. RESULTS The mean three dimensional vector shift between images was 1.7 mm ranging from 0 to 25 mm. No preferential direction of displacement was found; however, there was an increase of prostate displacement with time between images. There was a large variation in typical shifts between patients (range 1 +/- 1 to 6 +/- 2 mm) with no apparent trends throughout the treatment course. Images acquired in the first five fractions of treatment could be used to predict displacement patterns for individual patients. CONCLUSION Intra-fraction motion of the prostate gland appears to be a limiting factor when considering margins for radiotherapy. Given the variation between patients, a uniform set of margins for all patients may not be satisfactory when high target doses are to be delivered.

Predicting the need for adaptive radiotherapy in head and neck cancer.

BACKGROUND AND PURPOSE Adaptive radiotherapy (ART) can account for the dosimetric impact of anatomical change in head and neck cancer patients; however it can be resource intensive. Consequently, it is imperative that patients likely to require ART are identified. The purpose of this study was to find predictive factors that identify oropharyngeal squamous cell carcinoma (OPC) and nasopharyngeal carcinoma (NPC) patients more likely to need ART. MATERIALS AND METHODS One hundred and ten patients with OPC or NPC were analysed. Patient demographics and tumour characteristics were compared between patients who were replanned and those that were not. Factors found to be significant were included in logistic regression models. Risk profiles were developed from these models. A dosimetric analysis was performed. RESULTS Nodal disease stage, pre-treatment largest involved node size, diagnosis and initial weight (categorised in 2 groups) were identified as significant for inclusion in the model. Two models were found to be significant (p=0.001), correctly classifying 98.2% and 96.1% of patients respectively. Three ART risk profiles were developed. CONCLUSION Predictive factors identifying OPC or NPC patients more likely to require ART were reported. A risk profile approach could facilitate the effective implementation of ART into radiotherapy departments through forward planning and appropriate resource allocation.

Assessment of cone beam CT registration for prostate radiation therapy: fiducial marker and soft tissue methods

This investigation aimed to assess the consistency and accuracy of radiation therapists (RTs) performing cone beam computed tomography (CBCT) alignment to fiducial markers (FMs) (CBCTFM) and the soft tissue prostate (CBCTST).

Interobserver variability of radiation therapists aligning to fiducial markers for prostate radiation therapy.

As the use of fiducial markers (FMs) for the localisation of the prostate during external beam radiation therapy (EBRT) has become part of routine practice, radiation therapists (RTs) have become increasingly responsible for online image interpretation. The aim of this investigation was to quantify the limits of agreement (LoA) between RTs when localising to FMs with orthogonal kilovoltage (kV) imaging.

The effect of beam arrangements and the impact of non‐coplanar beams on the treatment planning of stereotactic ablative radiation therapy for early stage lung cancer

The aim of this study was to compare various coplanar and non‐coplanar 3‐dimensional conformal radiation therapy (3DCRT) beam arrangements for the delivery of stereotactic ablative radiation therapy (SABR) to patients with early stage lung cancer, based on the dosimetric criteria from the Radiation Therapy Oncology Group (RTOG) 1021 protocol.

Head and neck adaptive radiotherapy: predicting the time to replan

Head and neck (H&N) cancer patients can undergo anatomical change throughout radiotherapy treatment. Adaptive radiotherapy (ART) is effective in addressing the impact of this change on the planned dose distribution. The aim of this study was to identify pretreatment factors that influence the need for and timing of replanning for patients receiving chemoradiotherapy for node‐positive nasopharyngeal (NPC) and oropharyngeal carcinoma (OPC).

A prone technique for treatment of the breast, supraclavicular and axillary nodes

Radiation therapy to women with large pendulous breasts presents dosimetric challenges when the whole breast (WB) and supraclavicular and axillary (SCF + AX) nodes need to be encompassed. The aim of this case study was to demonstrate the feasibility of planning and treating a pendulous breasted patient in the prone position. Computerised tomography (CT) images were acquired of the patient in both the prone and supine positions. A Perspex plate was added to the CDR Systems Inc. (Calgary, Canada) prone breastboard to minimize SCF + AX contour variations. Dosimetry was performed on both CT scans and the resultant treatment plans were evaluated for conformity, homogeneity, dose to the lung and maximum doses to the spinal cord (SC) and irradiated volume. The daily set‐up in the prone position was monitored for stability and reproducibility. The patient completed her treatment course in the prone position. Minimal daily interventions were required to ensure the position was reproduced. Grade 3 skin toxicity was recorded in the SCF + AX region where the Perspex plate was added to the prone positioning device. There was minimal difference in dosimetry between prone and supine plans in the SCF + AX region. The prone WB plan showed improved homogeneity (prone 0.15; supine 0.22) and conformity (prone 0.90; supine 0.77). A simple addition to the breastboard has enabled a pendulous breasted woman with SC + AX involvement to be treated in the prone position. Set‐up of this technique is achievable on a daily basis with minimal impact on workflow. It is a feasible alternative to supine treatment for this patient group.

Evaluating the dosimetric effect of treatment‐induced changes in virally mediated head and neck cancer patients

Patients with virally mediated head and neck cancer (VMHNC) often present with advanced nodal disease that is highly radioresponsive as demonstrated by tumour and nodal regression during treatment. The resultant changes may impact on the planned dose distribution and so adversely affect the therapeutic ratio. The aim of this study was to evaluate the dosimetric effect of treatment‐induced anatomical changes in VMHNC patients who had undergone a replan.