Radiographic film dosimetry for IMRT fields in the near‐surface buildup region

Abstract

Radiographic film dosimetry provides fast, convenient 2‐D dose distributions, but is challenged by the dependence of film response on scatter conditions (i.e., energy dependence). Verification of delivered dose in the surface buildup region is important for intensity modulated radiation therapy (IMRT) when volumes of interest encroach on these regions (e.g., head/neck, breast). The current work demonstrates that film dosimetry can accurately predict the dose in the buildup region for IMRT, since 1) film dosimetry can be performed with sufficient accuracy for small fields and 2) IMRT is delivered by a series of “small” segments (step and shoot IMRT). This work evaluates the accuracy of X‐OMAT V (XV) and Extended Dose Range (EDR) film for measurements from 2 mm to 15 mm depths for small fields and clinical IMRT beams. Film measurements have been compared to single point measurements made with a stereotactic diode and parallel plate ionization chamber (P11) and thermoluminescent dosimeters (TLD) at various depths for square (diode, P11) and IMRT (diode, TLD) fields. Film calibration was performed using an 8‐field step exposure on a single film at 5 cm depth, which has been corrected to represent either small field or large field depth dependent film calibration techniques. Up to 10% correction for film response variation as a function of depth was required for measurements in the buildup region. A depth‐dependent calibration can sufficiently improve the accuracy for IMRT calculation verification (i.e., ≤5% uncertainty). A small field film calibration technique was most appropriate for IMRT field measurements. Improved buildup region dose measurements for clinical IMRT fields promotes improved dose estimation performance for (inverse) treatment planning and allows more quantitative treatment delivery validation.PACS numbers: 87.53.‐j, 87.53.Dq

Superficial dosimetry imaging of Čerenkov emission in electron beam radiotherapy of phantoms

“…Irregular surface profiles of the treatment region decrease the accuracy of superficial dose prediction and may result in under-dosing or overdosing in the delivered dose for specified treatment plans. Conventional surface dosimetry methods such as radiochromic film (Butson et al 2004, Chiu-Tsao and Chan 2009, Devic et al 2006, Klein et al 2003, Nakano et al 2012, Roberson et al 2008, ionization chamber (Apipunyasopon et al 2012, Chen et al 2010, Klein et al 2003, Wang et al 2012, metal-oxide semiconductor field-effect transistor (MOSFET)s (Gladstone and Chin 1995, Gladstone et al 1994, Qi et al 2009, Quach et al 2000, Xiang et al 2007 and thermoluminescent dosimeter (TLD)s (Kron et al 1993, Lin et al 2001, Nilsson and Sorcini 1989 have been proven to be able to measure superficial dose, however these techniques require clinical intervention and additional personnel time for use. Each are limited by small fixed region measurements and sensitivity is often a function of angular orientation of the detector with respect to the incident beam.…”

Superficial dosimetry imaging based on Čerenkov emission for external beam radiotherapy with megavoltage x‐ray beam

“…These factors, especially irregular surface profiles, internal heterogeneities, movement and deformation of the treatment region, decrease the accuracy of superficial dose prediction and may result in underdosing or overdosing in specified treatment plans. Several conventional dose measuring methods, such as radiochromic film, [16][17][18][19][20] ionization chamber, 21 MOSFETs, [22][23][24] and TLDs (Refs. [25][26][27], exist for superficial dose measurement; however, these techniques require clinical intervention to place detectors on the patient and additional personnel time for postprocessing.…”

Anatomy-corresponding method of IMRT verification

“…The gamma verification was executed for each therapeutic field and the portal dosimetry (Varian aS500) and films (Kodak X-Omat V) were applied for intensity fluence recording. 8,9 The traditional comprehension of therapeutic field border (50% of maximum dose in a total plane perpendicular to beam axis following 3D CRTs example) could entail the loss of information about part of the IMRT field, because of the intentional diversification of dose distribution. To have an undistorted view of plan delivery, the (D min ) criterion has to be reduced, however, it is difficult to define its correct value.…”