What question did this study set out to answer?

The study seeks to identify factors predicting tumor volumetric response in patients undergoing the 0-7-21 palliative radiation regimen.

May 24, 2026Open Access

Adaptive Radiotherapy in the 0-7-21 Regimen: A Retrospective Study of Tumor Volumetric Response

RCRevadhi ChelvarajahUniversity Health Network DBDana D BartolucciUniversity Health Network JJJoanna JavorUniversity Health Network

Key Points

The study seeks to identify factors predicting tumor volumetric response in patients undergoing the 0-7-21 palliative radiation regimen.
Retrospective review of patients treated with 0-7-21 regimen from February 2017 to June 2022.
Gross tumor volumes were measured at Day 0 and Day 21 using cone beam CT, and percent volume change was analyzed.
Univariate and multivariable linear regression models identified predictive factors for tumor volume changes.
105 patients with 193 lesions were analyzed, revealing a mean percent volume change of -9.9%.
Merkel cell histology was significantly associated with tumor volume reduction (mean change -24.24%, p=0.03).
A smoking history was associated with tumor growth (OR=6.10, p=0.047).

Abstract

Purpose: A hypofractionated palliative radiation regimen referred as "0-7-21," which involves 1500-2400cGy prescribed in 3 fractions delivered over 3 weeks (i.e Day 0, 7 and 21) has been well documented in literature as an effective way to alleviate symptoms in solid malignancies with minimal toxicity and logistics.Given its time between fractions, this study aims to identify predictive factors of on-treatment tumor response in patients treated with 0-7-21 regime to help select palliative patients who may benefit from adaptive therapy. Methods: This single-institution retrospective review of patients treated with 0-7-21 from February 2017 to June 2022.Gross tumor volumes (GTV) from cone beam CT (CBCT) at Day 0 and Day 21 were collected.Calculated percent change in lesion volume were grouped into quartiles.Groups showing greatest reduction (25th percentile) versus the greatest growth or least reduction (75th percentile) were analyzed.Univariate and multivariable linear regression models identified factors associated with percent change in tumor volume.Results: A total of 105 patients with 193 lesions were included.mean age was 77, majority male (n=57, 54.3%) and non-smokers (n=42, 40%).Head and neck primaries (n=125, 64.8%), head and neck anatomic sites (n=160, 82.9%), and squamous cell carcinoma (n=148, 76.7%) were the most common.Nine lesions (4.7%) were treated during concurrent systemic therapy.From Day 0 to 21, mean percent volume change was -9.9% (SD: 19.94).On multivariable analysis, Merkel cell histology (-24.24%95%CI -45.4 --3.06, p=0.03) and smoking history (6.10 95%CI -0.22-10.84),p=0.047) were associated with tumor volume reduction and growth respectively.Merkel cell histology was the only factor associated with the group with the largest volume reduction (25th percentile) on multivariable analysis (odds ratio: 15.34 [95%CI 1.52-154.41,p=0.02). Conclusions:Online adaptive radiation therapy may benefit selected 0-7-21 palliative regimen patients with Merkel cell histology and a smoking history, warranting consideration in future studies and resource allocation.

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