Paediatric radiotherapy in the United Kingdom: an evolving subspecialty and a paradigm for integrated teamworking in oncology.

Many different malignancies occur in children, but overall, cancer in childhood is rare. Survival rates have improved appreciably and are higher compared with most adult tumour types. Treatment schedules evolve as a result of clinical trials and are typically complex and multi-modality, with radiotherapy an integral component of many. Risk stratification in paediatric oncology is increasingly refined, resulting in a more personalized use of radiation. Every available modality of radiation delivery: simple and advanced photon techniques, proton beam therapy, molecular radiotherapy, and brachytherapy, have their place in the treatment of children's cancers. Radiotherapy is rarely the sole treatment. As local therapy, it is often given before or after surgery, so the involvement of the surgeon is critically important, particularly when brachytherapy is used. Systemic treatment is the standard of care for most paediatric tumour types, concomitant administration of chemotherapy is typical, and immunotherapy has an increasing role. Delivery of radiotherapy is not done by clinical or radiation oncologists alone; play specialists and anaesthetists are required, together with mould room staff, to ensure compliance and immobilization. The support of clinical radiologists is needed to ensure the correct interpretation of imaging for target volume delineation. Physicists and dosimetrists ensure the optimal dose distribution, minimizing exposure of organs at risk. Paediatric oncology doctors, nurses, and a range of allied health professionals are needed for the holistic wrap-around care of the child and family. Radiographers are essential at every step of the way. With increasing complexity comes a need for greater centralization of services.

Ureter dose optimization during image guided brachytherapy for cervical cancer.

PURPOSE: In the era of image guided radiotherapy and interstitial needle use, radiation dose to ureters can cause toxicity. METHODS: A retrospective analysis of 106 patients with cervical cancer was performed to investigate ureter dose in brachytherapy patients. Re-optimization of brachytherapy treatment plans in 20 MRI planned patients was performed to reduce ureter dose whilst maintaining HRCTV D90 and OAR dose constraints. RESULTS: A total of 212 ureters were contoured and dose recorded. The crude incidence of ureteric stenosis was 6.6%. Ureter dose for all patients was 75.8 Gy and 74.4 Gy on the right and left respectively. A cohort of 20 MRI planned patients were reoptimized to reduce dose to ureters. Ureter dose was reduced from 91.1 Gy to 84.4 Gy and 73.9 Gy to 67.8 Gy on the right and left side respectively. A subgroup of patients with HRCTV D90 ≥84.3 Gy prior to reoptimisation saw a greater reduction in ureter dose of 13.3%. These were smaller tumours with better HRCTV coverage at the outset. Larger tumours with poorer HRCTV coverage (<84.3 Gy) saw a smaller reduction in ureter dose of 6.4%. Organ at risk dose to rectum, sigmoid and bladder were also significantly reduced. CONCLUSIONS: Patients treated with MRI guided brachytherapy and interstitial needles are at risk of ureteric stenosis. Contouring ureters and setting dose constraints should be considered to reduce ureteric dose while tracking HRCTV coverage.

Using multi-centre data to train and validate a knowledge-based model for planning radiotherapy of the head and neck.

Background and purpose: Knowledge-based radiotherapy planning models have been shown to reduce healthy tissue dose and optimisation times, with larger training databases delivering greater robustness. We propose a method of combining knowledge-based models from multiple centres to create a 'super-model' using their collective patient libraries, thereby increasing the breadth of training knowledge. Materials and methods: A head and neck super-model containing 207 patient datasets was created by merging the data libraries of three centres. Validation was performed on 30 independent datasets during which optimiser parameters were tuned to deliver the optimal set of model template objectives. The super-model was tested on a further 40 unseen patients from four radiotherapy centres, including one centre external to the training process. The generated plans were assessed using established plan evaluation criteria. Results: The super-model generated plans that surpassed the dose objectives for all patients with single optimisations in an average time of 10 min. Healthy tissue sparing was significantly improved over manual planning, with dose reductions to parotid of 4.7 ± 2.1 Gy, spinal cord of 3.3 ± 0.9 Gy and brainstem of 2.9 ± 1.7 Gy. Target coverage met the established constraints but was marginally reduced compared with clinical plans. Conclusions: Three centres successfully merged patient libraries to create a super-model capable of generating plans that met plan evaluation criteria for head and neck patients with improvements in healthy tissue sparing. The findings indicate that the super-model could improve head and neck planning quality, efficiency and consistency across radiotherapy centres.

Feasibility of ureter delineation and dose recording in the assessment of ureteric stenosis during brachytherapy for cervical cancer.

INTRODUCTION: Ureteric stenosis is the commonest complication to affect the ureter after radiotherapy for cervical cancer; despite this ureters are not contoured as organs at risk and limited dosimetric data exist for them. METHODS/MATERIALS: Bilateral ureters were retrospectively delineated on brachytherapy planning imaging for patients treated for cervical cancer between 2014 and 2019. Ureteric stenosis toxicity data and D2cc, D1cc, D0.1cc of the right and left ureter were collated. Ureter V80, V100, V120, and V150 were also analyzed. Univariate analysis was performed to identify predictors of high ureter dose and ureteric stenosis. RESULTS: 95 patients were identified and 190 ureters contoured on brachytherapy planning imaging, with a median follow-up duration of 24 months (IQR23.7). 4.2% (4) of patients had grade 3/4 ureteric stenosis. Mean ureter D0.1cc, D1.0cc and D2.0cc on the right were 80.4Gy (±28.9), 56.2Gy (±7.2) and 52.8Gy (±7.6), and on the left were 75.6Gy (±14.6), 54.3Gy (±5.5) and 52.7Gy (±5.5) respectively. Significantly higher ureter doses were present in patients with baseline hydronephrosis (p < 0.002) and interstitial needle use (p = 0.047). Ureters affected by ureteric stenosis received D0.1cc doses between 60-98Gy. 10-14% received point doses in excess of 150% of the prescribed dose (7Gy) with no resulting ureteric stenosis. No significant difference in D0.1cc was found in patients with or without ureteric stenosis. CONCLUSIONS: It is feasible to accurately contour ureters on brachytherapy planning imaging. Baseline hydronephrosis and interstitial needle use contribute to higher ureter doses. No association between dose and ureteric stenosis was found.