Comparison of Volumetric Modulated Arc Therapy and Fixed-Field Intensity-Modulated Radiotherapy for Canine Prostatic...

Area of Science:

• Veterinary Radiation Oncology
• Comparative Planning Techniques
• Canine Carcinomas

Background:

• Hypofractionated radiotherapy protocols are becoming feasible for intrapelvic tumors in dogs due to advancements in radiation techniques.
• Intensity modulated radiation therapy (IMRT) and volumetric modulated arc therapy (VMAT) offer improved dose conformity and reduced toxicity.
• Canine prostatic carcinoma is a suitable candidate for advanced radiotherapy techniques.

Purpose of the Study:

• To determine the optimal radiotherapy planning technique for canine prostatic carcinoma.
• To compare the dosimetric outcomes of four techniques: 2-field full arcs (2FA), 2-field partial arcs (2PA), 9-field IMRT (9F), and 7-field IMRT (7F).
• To evaluate normal tissue complication probabilities (NTCPs) for critical organs at risk (OARs).

Main Methods:

• Retrospective analysis of computed tomography (CT) datasets from 22 dogs with prostatic carcinoma.
• Radiotherapy planning was performed using a protocol delivering 43 Gy in 10 fractions.
• Comparison of conformity index, homogeneity index, NTCPs, dose volume histograms (DVHs), maximum dose (Dmax), and mean dose (Dmean) for OARs including rectum, colon, small intestine, bladder, urethra, spinal cord, cauda equina, and femoral heads.

Main Results:

• IMRT demonstrated significantly lower homogeneity index, rectal NTCPs, Dmax, and V45 compared to VMAT.
• IMRT provided better sparing for the colon, small intestine, bladder, and urethra.
• While 2PA offered lower mean doses to some OARs, it resulted in higher femoral head toxicity; 2PA also provided superior sparing for the spinal cord and cauda equina.
• IMRT techniques, particularly 7F, required significantly more monitor units and beam-on time than VMAT.

Conclusions:

• Intensity modulated radiation therapy (IMRT) showed more favorable organ at risk (OAR) sparing and improved dose homogeneity than volumetric modulated arc therapy (VMAT) for canine prostatic carcinoma.
• The 7-field IMRT (7F) technique may be preferred over 9-field IMRT (9F) due to reduced treatment time and monitor units.
• Individualized treatment planning based on patient-specific dosimetric characteristics is recommended, as results may vary with different planning systems and optimization strategies.