Stability of metabolic tumor volume may enable radiotherapy dose painting in anal cancer

Phys Med. 2023 Oct:114:103151. doi: 10.1016/j.ejmp.2023.103151. Epub 2023 Oct 7.


Purpose: To evaluate the variability of the 18F-FDG-PET/CT-based metabolic tumor volume (MTV) in anal cancers during fractionated chemoradiotherapy (CRT), and assess the impact of this variability on dosimetric accuracy in MTV-targeted dose painting.

Methods: Eleven patients with anal squamous cell carcinoma who received fractionated chemoradiotherapy with curative intent were included. 18F-FDG PET/CT images were acquired at pre- and mid-treatment. Target volumes and organs at risk (OARs) were contoured manually on both image series. The MTV was generated from the PET images by thresholding. Treatment plans were retrospectively optimized for both image series using volumetric modulated arc therapy (VMAT). Standard plans prescribed 48.6 Gy, 54 Gy and 57.5 Gy in 27 fractions to elective regions, lymph node metastases and primary tumor, respectively. Dose painting plans included an extra dose level of 65 Gy to the MTV. Pre-treatment plans were transferred and re-calculated at mid-treatment basis.

Results: MTV decreased from pre- to mid-treatment in 10 of the 11 patients. On average, 71 % of MTVmid overlapped with MTVpre. The median and mean doses to the MTV were robust against anatomical changes, but the transferred dose painting plans had lower D98% values than the original and re-optimized plans. No major differences were found between standard and dose painting plans for OARs.

Conclusions: Despite volumetric changes in the MTV, adequate dose coverage was observed in most dose painting plans. The findings indicate little or no need for adaptive dose painting at mid-treatment. Dose painting appears to be a safe treatment alternative with similar dose sparing of OARs.

Keywords: Anal cancer; Dose painting; Metabolic tumor volume; Positron emission tomography; Radiotherapy.

MeSH terms

  • Anus Neoplasms* / diagnostic imaging
  • Anus Neoplasms* / radiotherapy
  • Fluorodeoxyglucose F18
  • Humans
  • Organs at Risk
  • Positron Emission Tomography Computed Tomography / methods
  • Radiotherapy Dosage
  • Radiotherapy Planning, Computer-Assisted / methods
  • Radiotherapy, Intensity-Modulated* / methods
  • Retrospective Studies
  • Tumor Burden


  • Fluorodeoxyglucose F18