A prospective study on the effect of tumor shrinkage on exit fluence gamma pass rate in high precision radiotherapy and influence of phantom setup error in patient-specific quality assurance.
J Cancer Res Ther
; 20(3): 935-942, 2024 Apr 01.
Article
in En
| MEDLINE
| ID: mdl-39023601
ABSTRACT
PURPOSE:
Objective parameters for decision on adaptive radiotherapy depend on patient, tumor and treatment related factors. Present study reports geometric uncertainties occurring during high precision radiotherapy, beam fluence analysis and serial exit dose measurement as a patient-specific tool for adaptive radiotherapy. MATERIALS ANDMETHODS:
Serial exit dose fluence of 24 patients (at baseline and mid-treatment) undergoing IMRT/VMAT treatment were measured. Baseline and midtreatment exit dose evaluation was done using gafchromic films in predefined region of interest. Difference of volume of GTV at baseline (from simulation CT scan) and midtreatment CBCT scan was calculated (ΔGTV).RESULTS:
Population based systematic errors (mm) were 4.15, 2.26, 0.88 and random errors (mm) were 2.56, 3.69, and 2.03 in mediolateral (ML), craniocaudal (CC) and anteroposterior (AP) directions respectively. Gamma pass rate reduced with incremental shift. For a 5 mm shift, maximum deviation was found in anteroposterior axis (22.16 ± 7.50) and lowest in mediolateral axis (12.85 ± 4.95). On serial measurement of exit dose fluence, tumor shrinkage significantly influenced gamma pass rate. The mean gamma pass rate was significantly different between groups with 50% shrinkage of tumor volume (86.36 vs 96.24, P = 0.008, on multivariate analysis P = 0.026).CONCLUSION:
Rapid fall of gamma pass rate was observed for set up error of ≥3 mm. Serial measurement of exit dose fluence by radiochromic film is a feasible method of exit dose comparison in IMRT/VMAT, where EPID dosimetry is not available with linear accelerator configuration. Our study suggests that there is a significant difference between gamma pass rates of baseline and mid treatment exit dose fluence with greater than 50% tumor shrinkage.
Full text:
1
Collection:
01-internacional
Database:
MEDLINE
Main subject:
Quality Assurance, Health Care
/
Radiotherapy Dosage
/
Radiotherapy Planning, Computer-Assisted
/
Phantoms, Imaging
/
Radiotherapy, Intensity-Modulated
Limits:
Humans
/
Male
Language:
En
Journal:
J Cancer Res Ther
/
J. cancer res. ther
/
Journal of cancer research and therapeutics
Journal subject:
NEOPLASIAS
/
TERAPEUTICA
Year:
2024
Document type:
Article
Affiliation country:
India
Country of publication:
India