An evaluation of the use and efficacy of behavioural therapy when treating paediatric patients with radiation therapy.

INTRODUCTION: The paediatric radiation therapy group (PRTG) provided a multidisciplinary network to support patients accessing radiation therapy (RT). This study aims to evaluate the use and efficacy of behaviour therapy practices used by the PRTG. METHODS: A retrospective cross-sectional review of general anaesthetic (GA) utilisation for paediatric patients was completed between 1 January 2010 and 30 June 2014. The PRTG incorporated behavioural therapy techniques into all appointments but offered additional play appointments to children unable to comply with the requirements of RT. This aimed to increase their compliance and minimise GA use. RESULTS: Two-hundred and seventy-four patients had 5402 occasions of service, of which 1361 were delivered under GA (25.2%). Two-hundred and fifty-seven patients met the eligibility criteria. Patients under 8 years who required GA for their entire treatment reduced for each year of increase in age (odds ratio 0.37, 95% confidence interval 0.27-0.51, P < 0.001). Participants 3 years and younger were shown not as likely to change their GA requirements with the use of play appointments. Seventy-eight per cent (83/106) of 3-8-year-olds used no GA or ceased GA during treatment. CONCLUSIONS: Most paediatric patients <3 years will gain minimal benefit to reduce GA use from additional play appointments. Children older than nine were not likely to require play appointments to be compliant with RT. Encouragingly, 53.3% of 3-8-year-olds who were categorised as full GA after CT planning did not continue to a full course of GA due to the behavioural therapy interventions of the PRTG.

Effects of gas-filled temporary breast tissue expanders on radiation dose from modulated rotational photon beams.

Gas-filled temporary tissue expanders (TTEs), implanted to assist in post mastectomy breast reconstructions, are expected to produce increased dosimetric uncertainty in breast radiotherapy treatments, due to their containing both a substantial metallic component and a comparatively large volume of gas. This study therefore builds on previous investigations of the dosimetric effects of gas-filled TTEs in static photon and electron beams, by examining the effects of these implants on dose distributions from common modulated rotational treatment techniques; volumetric modulated arc therapy (VMAT) and helical tomotherapy (HT). Radiochromic film measurements were used to evaluate the accuracy of VMAT and HT dose calculations, for a humanoid phantom augmented with a sample Aeroform CO2-filled TTE (AirXpanders Inc, San Jose, USA) as well as purpose-designed and 3D printed "breast tissue." Results showed that the TomoTherapy Hi-Art VoLO convolution-superposition algorithm (Accuray Inc, Sunnyvale, USA) produced comparatively accurate calculations of treatment dose within this complex phantom, including immediately anterior and posterior to the TTE. The Varian Eclipse Acuros (AXB) algorithm generally showed better agreement with the film measurement than the Varian Eclipse AAA algorithm (Varian Medical Systems, Palo Alto, USA), although the film measurements showed regions of 5% to 10% disagreement with both AAA and AXB in the dosimetrically-challenging region on the anterior side of the implant. Although the Aeroform CO2-filled TTE has substantial and obvious effects on the downstream dose from a static photon beam, the results of this study showed how inverse-planning of modulated rotational radiotherapy treatments can produce modulated fluence distributions that compensate for the dramatic density heterogeneities in the implant. Despite some disagreements with the planned dose, all film measurements showed that the use of inverse-planned modulated rotational photon beams resulted in comparatively homogeneous coverage of the radiotherapy target, in the complex patient-like phantom with a gas-filled TTE. Due to the importance of matching each planned fluence distribution to the density distribution within each TTE, careful use of available 3D imaging techniques is advisable, when modulated rotational radiotherapy treatments are delivered to patients with gas-filled TTEs.

Evaluation of a deformable image registration quality assurance tool for head and neck cancer patients.

INTRODUCTION: A challenge in implementing deformable image registration (DIR) in radiation therapy planning is effectively communicating registration accuracy to the radiation oncologist. This study aimed to evaluate the MIM® quality assurance (QA) tool for rating DIR accuracy. METHODS: Retrospective DIR was performed on CT images for 35 head and neck cancer patients. The QA tool was used to rate DIR accuracy as good, fair or bad. Thirty registered patient images were assessed independently by three RTs and a further five patients assessed by five RTs. Ratings were evaluated by comparison of Hausdorff Distance (HD), Mean Distance to Agreement (MDA), Dice Similarity Coefficients (DSC) and Jacobian determinants for parotid and mandible subregions on the two CTs post-DIR. Inter-operator reliability was assessed using Krippendorff's alpha coefficient (KALPA). Rating time and volume measures for each rating were also calculated. RESULTS: Quantitative metrics calculated for most anatomical subregions reflected the expected trend by registration accuracy, with good obtaining the most ideal values on average (HD = 7.50 ± 3.18, MDA = 0.64 ± 0.47, DSC = 0.90 ± 0.07, Jacobian = 0.95 ± 0.06). Highest inter-operator reliability was observed for good ratings and within the parotids (KALPA 0.66-0.93), whilst ratings varied the most in regions of dental artefact. Overall, average rating time was 33 minutes and the least commonly applied rating by volume was fair. CONCLUSION: Results from qualitative and quantitative data, operator rating differences and rating time suggest highlighting only bad regions of DIR accuracy and implementing clinical guidelines and RT training for consistent and efficient use of the QA tool.

Impact of radiopacified bone cement on radiotherapy dose calculation.

BACKGROUND AND PURPOSE: Radiopacifiers are introduced to bone cements to provide the appearance of bone in kilovoltage (kV) radiographic images. For higher energy megavoltage (MV) radiotherapy treatment beams, however, these radiopacifiers do not cause a bone-like perturbation of dose. This study therefore aimed to determine the impact of the barium-contrasted plastic-based cement materials on radiotherapy dose calculations. MATERIALS AND METHODS: The radiological properties of a physical sample of bone cement were characterised by computed tomography (CT) imaging and transmission measurements. Monte Carlo simulations of percentage depth-dose profiles were performed to determine the possible dose error for MV treatment beams. Dose differences were then investigated for clinical volumetric modulated radiotherapy treatment plans, with and without density overrides applied. RESULTS: Differences of up to 7% were observed at the downstream interface of a 0.6 cm thick bone cement layer, compared to bone. Differences in planning target volume dose-volume metrics varied between -0.5% and 2.0%. CONCLUSION: Before planning radiotherapy treatments for patients who have undergone cranioplasty, every effort should be made to identify whether a radiopacified bone cement has been implanted. Density overrides should be applied to minimise dose calculation errors, whenever bone cement is used.