Selection of motion management in liver stereotactic body radiotherapy and its impact on treatment time.

Background and purpose: Reduction of respiratory tumour motion is important in liver stereotactic body radiation therapy (SBRT) to reduce side effects and improve tumour control probability. We have assessed the distribution of use of voluntary exhale breath hold (EBH), abdominal compression (AC), free breathing gating (gating) and free breathing (FB), and the impact of these on treatment time. Materials and Methods: We assessed all patients treated in a single institution with liver SBRT between September 2017 and September 2021. Data from pre-simulation motion management assessment using fluoroscopic assessment of liver dome position in repeat breath holds, and motion with and without AC, was reviewed to determine liver dome position consistency in EBH and the impact of AC on motion. Treatment time was assessed for all fractions as time from first image acquisition to last treatment beam off. Results: Of 136 patients treated with 145 courses of liver SBRT, 68 % were treated in EBH, 20 % with AC, 7 % in gating and 5 % in FB. AC resulted in motion reduction < 1 mm in 9/26 patients assessed. Median treatment time was higher using EBH (39 min) or gating (42 min) compared with AC (30 min) or FB (24 min) treatments. Conclusions: Motion management in liver SBRT needs to be assessed per-patient to ensure appropriate techniques are applied. Motion management significantly impacts treatment time therefore patient comfort must also be taken into account when selecting the technique for each patient.

Development of a multicentre automated model to reduce planning variability in radiotherapy of prostate cancer.

BACKGROUND AND PURPOSE: Inter-institutional studies highlighted correlation between consistent radiotherapy quality and improved overall patient survival. In treatment planning automation has the potential to address differences due to user-experience and training, promoting standardisation. The aim of this study was to evaluate implementation and clinical effect of a multicentre collaboratively-developed automated planning model for Intensity-Modulated Radiation Therapy/Volumetric-Modulated Arc Therapy of prostate. The model was built using a variety of public institutions' clinical plans, incorporating different contouring and dose protocols, aiming at minimising their variation. METHODS AND MATERIALS: A model using 110 clinically approved and treated prostate plans provided by different radiotherapy centres was built with RapidPlan (RP), for use on intact and post-prostatectomy prostate cases. The model was validated, distributed and introduced into clinical practice in all institutions. To investigate its impact a total of 126 patients, originally manually inverse planned (OP), were replanned using RP without additional planner manual intervention. Target and organ-at-risk (OAR) metrics were statistically compared between original and automated plans. RESULTS: For all centres combined and individually, RP provided plans comparable or superior to OP for all dose metrics. Statistically significant reductions with RP were found in bladder (V40Gy) and rectal (V50Gy) low doses (within 2.3% and 3.4% for combined and 4% and 10% individually). No clinically significant changes were seen for the PTV, independently of seminal vesicle inclusion. CONCLUSION: This project showed it is feasible to develop, share and implement RP models created with plans from different institutions treated with a variety of techniques and dose protocols, with the potential of improving treatment planning results and/or efficiency despite the original variability.

Comparison of four 3D conformal treatment techniques to optimise radiotherapy treatment for anal cancer.

INTRODUCTION: Chemoradiotherapy is the standard of care for anal cancer. Sizeable target volume leads to significant toxicity. We compared four different 3D conformal radiotherapy (3DCRT) techniques with the aim of finding the best technique to achieve the lowest dose to the organs at risk (OAR) without compromising the planning target volume (PTV) coverage. METHODS: Fifteen computed tomography (CT) data sets from previously treated anal cancer patients (five male and 10 female) were re-contoured according to the Australasian Gastrointestinal Trials Group (AGITG) anal cancer contouring guidelines for N3 disease. Four different 3DCRT plans for each CT data set (standard, V-shape, diamond shape and alternate diamond shape) were generated. Comparisons of the radiation dose to non-rectal bowel (NRB), urinary bladder, genitalia, and femurs were performed. RESULTS: V-shape technique achieved significantly lower NRB V40 (mean = 59.6% SD = 11%) than diamond (63.8% SD = 13%), standard (63.8% SD = 11%) and alternate diamond (63.6% SD = 12%) techniques. V-shape technique achieved the lowest mean bladder dose (mean = 45.3 Gy SD = 1.4 Gy). Diamond technique achieved the lowest femur V40 (mean = 32.4%) P < 0.001 for all comparisons between diamond and all other techniques. For genitalia V40, diamond technique (mean = 26.4% SD = 20%) and alternate diamond technique (mean = 27.6% SD = 20%) achieved significantly lower dose than V-shape technique (mean = 43.2% SD = 26%) and standard technique (mean = 76.1% SD = 16%) P < 0.001 for all comparisons. CONCLUSIONS: Sophisticated 3DCRT techniques are superior to conventional techniques. Different 3DCRT techniques provide varying levels of dose reduction to OAR, with none of the four techniques investigated capable of reducing dose to all OAR. A combination of techniques may provide the best solution. Further refinement of these techniques should be explored.