Role of in vivo dosimetry with radiochromic films for dose verification during cutaneous radiation therapy
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RESEARCH
Open Access
Role of in vivo dosimetry with radiochromic films for dose verification during cutaneous radiation therapy Hong-Wei Liu1,2,4*, James Gräfe3,4, Rao Khan3,4, Ivo Olivotto3,4 and J Eduardo Villarreal Barajas3,4
Abstract Purpose: To evaluate the role of in vivo dosimetry with radiochromic films for dose verification in cutaneous radiation therapy (RT). Methods: Five patients with 8 cutaneous or sub-cutaneous malignancies of the face, neck, trunk and extremity receiving RT were included. Orthovoltage, megavoltage photon therapies were applied based on anatomic location. The delivered dose for each target was measured with GAFCHROMIC EBT3TM film. The differences between the prescribed and measured doses in each target were analyzed based on the RT characteristics, target location and custom patient set up. The accuracy of EBT3TM film measurement was verified by measurements in a solid water phantom. Results: The mean measured dose was -3.2% (-9.6% to +2.3%, P=0.86) lower than prescribed over 23 measurements. A wide range of under dose was detected in orthovoltage therapy when a gap existed between skin and a closed-ended applicator surface. The magnitude of the under dosage was correlated with the degree of the gap (P=0.01). The phantom study confirmed the accuracy of GAFCHROMIC EBT3TM film measurement and found that the low measured dose in orthovoltage therapy was caused by the deviation from the inverse square law (ISL) of the beam output at extended source surface distance (SSD) for closed-ended applicators. Conclusions: A significantly low delivered dose for extended SSD orthovoltage therapy was demonstrated during cutaneous RT. The dose fall-off with distance is not completely compensated by the ISL standoff correction for orthovoltage therapy. GAFCHROMIC EBT3™ film is a useful and accurate tool for quality assurance of patients receiving a curative intended cutaneous RT. Keywords: GAFCHROMIC EBT3™ film, Extended source surface distance, Orthovoltage, Inverse square law, Quality assurance
Introduction Primary cutaneous malignancies mainly include basal cell carcinoma (BBC) and squamous cell carcinoma (SCC). BCC is usually slow growing, rarely metastasizes and may be cured with effective local therapy including surgical resection, radiation therapy (RT) or both [1-3]. RT for primary BCC has achieved local control rates of 80-100% [4-6]. RT is also commonly used for symptom relief in metastatic cutaneous malignancies. * Correspondence: [email protected] 1 Central Alberta Cancer Center, 3942-50a Ave, Red Deer, AB T4N 6R2, Canada 2 Department of Oncology, University of Alberta, Edmonton, AB, Canada Full list of author information is available at the end of the article
Orthovoltage X-rays or megavoltage (MV) energy electrons are the main cutaneous radiotherapy tools [3,7,8]. MV photon therapy is used for large, subcutaneous targets with deep tissue involvement. Commonly, cutaneous RT is delivered with an appositional field using a clinical set up and without 3D volumetric dos
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