Entrance dose measurement: a simple and reliable technique

Journal Article · Mon Jun 30 04:00:00 EDT 2003 · Medical Dosimetry

DOI:https://doi.org/10.1016/S0958-3947(02)00236-4· OSTI ID:20655440

Banjade, D P; Raj, T Aloysius; Ng, B S; Xavier, S; Tajuddin, A A; Shukri, A

Verification of tumor dose for patients undergoing external beam radiotherapy is an important part of quality assurance programs in radiation oncology. Among the various methods available, entrance dose in vivo is one reliable method used to verify the tumor dose delivered to a patient. In this work, entrance dose measurements using LiF:Mg;Ti and LiF:Mg;Cu;P thermoluminescent dosimeters (TLDs) without buildup cap was carried out. The TLDs were calibrated at the surface of a water equivalent phantom against the maximum dose, using 6- and 10-MV photon and 9-MeV electron beams. The calibration geometry was such that the TLDs were placed on the surface of the 'solid-water' phantom and a calibrated ionization chamber was positioned inside the phantom at calibration depth. The calibrated TLDs were then utilized to measure the entrance dose during the treatment of actual patients. Measurements were also carried out in the same phantom simultaneously to check the stability of the system. The dose measured in the phantom using the TLDs calibrated for entrance dose to 6-and 10-MV photon beams was found to be close to the dose determined by the treatment planning system (TPS) with discrepancies of not more than 4.1% (mean 1.3%). Consequently, the measured entrance dose during dose delivery to the actual patients with a prescribed geometry was found to be compatible with a maximum discrepancy of 5.7% (mean 2.2%) when comparison was made with the dose determined by the TPS. Likewise, the measured entrance dose for electron beams in the phantom and in actual patients using the calibrated TLDs were also found to be close, with maximum discrepancies of 3.2% (mean 2.0%) and 4.8% (mean 2.3%), respectively. Careful implementation of this technique provides vital information with an ability to confidently accept treatment algorithms derived by the TPS or to re-evaluate the parameters when necessary.

• OSTI ID: 20655440
• Journal Information: Medical Dosimetry, Journal Name: Medical Dosimetry Journal Issue: 2 Vol. 28; ISSN 0958-3947; ISSN MEDOEJ
• Country of Publication: United States
• Language: English

Related Subjects

62 RADIOLOGY AND NUCLEAR MEDICINE
ALGORITHMS
CALIBRATION
CARCINOMAS
DOSIMETRY
ELECTRON BEAMS
IN VIVO
IONIZATION CHAMBERS
LITHIUM FLUORIDES
MEV RANGE 01-10
PATIENTS
PHANTOMS
PHOTON BEAMS
PHOTONS
QUALITY ASSURANCE
RADIATION DOSES
RADIOTHERAPY
THERMOLUMINESCENT DOSEMETERS