Small Field Dosimetry on Elekta Versa HD Comparative Evaluation of IBA CC01 and CC04 Chambers Against Golden Beam Data

Abstract

Author(s): Mohamed Ouali Alami*, El Mehdi Al Ibrahmi, Ouafae Chfik, El Mahjoub Chakir, Khalid El Ouardy, Yassine Herrassi, Yasser Raoui

Accurate small-field dosimetry is essential for precise stereotactic radiotherapy, but it remains challenging due to steep dose gradients and loss of charged-particle equilibrium. This study compares two ionization chambers with different sensitive volumes — the IBA CC01 (0.01 cm³) and CC04 (0.04 cm³) — for small-field measurements on an Elekta Versa HD linear accelerator. Percent depth-dose (PDD) curves, lateral profiles, and relative output factors were measured for 6 MV and 10 MV flattening-filter-free (FFF) photon beams, using field sizes from 1×1 cm² to 5×5 cm² (10×10 cm² as reference). Measurements were taken in water at 90 cm SSD and depths of 1.6, 3, 5, and 10 cm. Results were validated against Elekta’s Golden Beam Data (GBD) using a 2%/2 mm gamma analysis. Both chambers showed excellent agreement with the reference, achieving over 99% gamma pass rates and output factor differences within 2%. The CC01 and CC04 performed almost identically, with only minor differences due to volume averaging. The CC01 offered slightly better spatial resolution for the smallest fields, while the CC04 remained accurate for fields ≥1 cm under 2%/2 mm criteria. These results confirm that both CC01 and CC04 chambers provide reliable and precise small-field dosimetry for 6 MV FFF and 10 MV FFF beams. Their strong agreement with GBD data supports their use in commissioning and quality assurance of stereotactic treatments.

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