Int J Radiat Oncol Biol Phys. 2023 Jul 9:S0360-3016(23)07628-9. doi: 10.1016/j.ijrobp.2023.07.002. Online ahead of print.
ABSTRACT
BACKGROUND: Rectal dose delivered during prostate radiotherapy is associated with gastrointestinal toxicity. Treatment plans are commonly optimised using rectal dose-volume constraints, often whole-rectum relative-volumes (%). We investigate whether improved rectal contouring, use of absolute-volumes (cc) or rectal truncation might improve toxicity prediction.
MATERIALS/METHODS: Patients from the XXXXXX trial (receiving 74Gy/37 fractions (Fr) vs 60Gy/20Fr vs 57Gy/19Fr) were included if radiotherapy plans were available (2350/3216 patients), plus toxicity data for relevant analyses (2170/3216 patients). Whole solid rectum relative-volumes (%) dose-volume-histogram (DVH), as submitted by treating centre (original contour), was assumed standard-of-care. Three investigational rectal DVHs were generated: i) reviewed contour per XXXXXX protocol; ii) original contour absolute volumes (cc); iii) truncated original contour (two versions; ±0 and ±2cm from planning target volume (PTV)). Dose levels of interest (V30,40,50,60,70,74Gy) in 74Gy arm were converted by equivalent-dose-in-2Gy-fractions (EQD2α/β=3Gy) for 60Gy/57Gy arms. Bootstrapped logistic models predicting late toxicities (frequency G1+/G2+, bleeding G1+/G2+, proctitis G1+/G2+, sphincter control G1+, stricture/ulcer G1+) were compared by area-under-curve (AUC) between standard-of-care and the three investigational rectal definitions.
RESULTS: The alternative dose/volume parameters were compared with the original relative-volume (%) DVH of the whole rectal contour, itself fitted as a weak predictor of toxicity (AUC range 0.57-0.65, across the 8 toxicity measures). There were no significant differences in toxicity prediction for: i) original vs reviewed rectal contours (AUCs 0.57-0.66, p-values 0.21-0.98); ii) relative- vs absolute-volumes (AUCs 0.56-0.63, p-values 0.07-0.91) iii) whole-rectum vs truncation at PTV±2cm (AUCs 0.57-0.65, p-values 0.05-0.99), nor PTV±0cm (AUCs 0.57-0.66, p-values 0.27-0.98).
CONCLUSIONS: We used whole-rectum relative-volume DVH, submitted by the treating centre, as the standard-of-care dosimetric predictor for rectal toxicity. There were no statistically significant differences in prediction performance when using central rectal contour review, use of absolute-volume dosimetry, nor rectal truncation relative to PTV. Whole-rectum relative-volumes were not improved upon for toxicity prediction and should remain standard-of-care.
PMID:37433374 | DOI:10.1016/j.ijrobp.2023.07.002
