## 1 Introduction  
Nowadays, all physics and technical problems related to the dosimetry of small radiotherapy photon beams and unconventional fields are prominently indicated in the literature [1]. These dosimetric problems are dependent on the size of the field. In the present work, a small field is understood to be one that has one or more of the following characteristics: lack of lateral equilibrium of the charged particle, partial occlusion of the primary source, and beam quality (spectral changes), and when considering the detector, its dimensions compared to the size of the beam. An unconventional field refers to a field in which Bragg Gray conditions can be established, field size of which differs from the standard field size of 10 cm \(\times\) 10 cm. The above definitions are in line with those established in TRS-483 [2]. The code of practice refers to these unconventional fields as machine-specific reference fields, or \"msr.\"  
There are well-established dosimetry protocols for conventional fields, such as IAEA-TRS-398 [3] and the AAPM-TG-51 [4]. Both protocols are based on standards of dose absorbed to water under reference conditions. It is crucial to consider that the codes of practice used in conventional fields cannot be applied in unconventional fields. The limitations of conventional codes of practice rely on the reference conditions regarding field size and irradiation geometry. Moreover, the relative dosimetry of small static fields is challenging, because the sensitive volumes of the detectors dedicated to these fields are tiny (about 15% relative to the field size); their correct spatial location is essential for achieving correct relative dosimetry. Therefore, the TRS 483 [2] code of practice provides adequate guidelines for reference dosimetry and relative dosimetry in unconventional fields and small static fields, respectively.  
The challenges and dosimetric problems related to unconventional and small static fields must be considered in order to be able to perform correct dosimetry. Furthermore, as part of good clinical practice, implementing a new code of practice implies the development of a dosimetry audit program to guarantee that the beam output is within tolerance limits. Therefore, a pilot study of a clinical audit in these fields is necessary and suggested in this article. A clinical audit must be carried out by an expert external to the service to be evaluated. The objective of a comprehensive audit is to review and evaluate the quality of all of the components related to the practice of radiotherapy at an institution, including multidisciplinary professional competence; therefore, a significant part of the audit is patient-oriented (diagnosis, decision to treat, treatment prescription, planning treatment preparation, and delivery and finally follow-up process) [5]. Considering this, it is essential to consider that quality audits can be of various types and levels, ranging from partial processes (reviewing specific critical parts of the radiotherapy process) to comprehensive audits (assessing the whole process) [5; 6; 7; 8; 9; 10; 11; 12]  
This work focuses on a partial audit, specifically regarding clinical dosimetric analysis, aiming to measure the absorbed dose in water using thermoluminescent dosimeters (TLD) for a small photon beam in a linear accelerator commissioned following the recommendation of [PERSON] et al. [13]. TLDs have been widely used for postal audits in conventional fields [14; 15; 16; 17]. Unlike other micro dosimeters such as micro-diamond, TLDs are passive detectors that do not require an electrometer when irradiated; they are cheap and can be deployed in large quantities.