ESTRO 2024 - Abstract Book

S3468

Physics - Dose prediction, optimisation and applications of photon and electron planning

ESTRO 2024

Mathieu Gaudreault 1,2 , Nicholas Hardcastle 1,2,3 , Price Jackson 1,2 , Lachlan McIntosh 1 , Braden Higgs 4,5 , David Pryor 6 , Mark Sidhom 7 , Rachael Dykyj 8 , Alisha Moore 8 , Tomas Kron 1,2,3 , Shankar Siva 9,2 1 Peter MacCallum Cancer Centre, Physical Sciences, Melbourne, Australia. 2 the University of Melbourne, Sir Peter MacCallum Department of Oncology, Melbourne, Australia. 3 University of Wollongong, Centre for Medical Radiation Physics, Wollongong, Australia. 4 Royal Adelaide Hospital, Radiation Oncology, Adelaide, Australia. 5 John Hunter Hospital, Radiation Oncology, New Lambton Heights, Australia. 6 Princess Alexandra Hospital, Radiation Oncology, Woolloongabba, Australia. 7 Liverpool Hospital, Radiation Oncology, Liverpool, Australia. 8 Trans Tasman Radiation Oncology Group, Radiation Oncology, Waratah, Australia. 9 Peter MacCallum Cancer Centre, Radiation Oncology, Melbourne, Australia

Purpose/Objective:

Stereotactic body ablative radiotherapy (SABR) is a novel treatment option for inoperable renal cell carcinoma (RCC). As opposed to ablative techniques, kidney SABR is not limited to tumour size or location. However, the ipsilateral kidney may receive radiation dose; intermediate (50%) dose level in healthy kidney has been shown to be associated with kidney function decline [1]. This study investigated the dose-effect relationship post-SABR treatment in inoperable RCC patients.

Material/Methods:

This study was a predefined secondary endpoint of the FASTRACK II clinical trial (NCT02313819). In this prospective multicentre trial, patients were prescribed either 26 Gy in one fraction (SF) if the tumour size was less or equal to 4 cm or 42 Gy in three fractions (MF) if the tumour size was greater than 4 cm. Patients underwent 99mTc-DMSA SPECT/CT scans at baseline, 12-, and 24-months post-treatment, from which the split renal function was derived. The global renal function was estimated from serum creatinine measurements at each time point to calculate the glomerular filtration rate (GFR) by using the Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) equation. The resulting GFR distributions were compared with the Wilcoxon signed-rank test. SPECT imaging datasets were rigidly registered to the planning CT where the ipsilateral kidney structure excluding the internal target volume (ITV) was segmented [Fig. 1]. The Pearson correlation and its associated p-value between the ratio of ipsilateral kidney V50% / total volume (Vtotal) and the relative change in GFR from baseline were evaluated. Planned dose was projected on the registered imaging datasets and the dose-response curve (DRC) per patient was determined. The population DRC was obtained from the average of all DRCs weighted by the number of voxels considered in each dose bin. The renal function loss in the decreasing region of the population DRC was quantified from the average and standard deviation of the slopes obtained by varying the interval used in the linear regression. To compare the population DRCs between the two fractionations, the local dose was converted to biological equivalent dose (BED) with α/β = 3. Exponential [a×exp(-b BED)+c] and logistic [a/[1+exp(b BED)]+c]