The use of radiochromic film (RCF) dosimetry in radiation therapy is extensive due to its high level of achievable accuracy for a wide range of dose values and its suitability under a variety of measurement conditions. However, since the publication of the 1998 AAPM Task Group 55, Report No. 63 on RCF dosimetry, the chemistry, composition, and readout systems for RCFs have evolved steadily. There are several challenges in using the new RCFs, readout systems and validation of the results depending on their applications. Accurate RCF dosimetry requires understanding of RCF selection, handling and calibration methods, calibration curves, dose conversion methods, correction methodologies as well as selection, operation and quality assurance (QA) programs of the readout systems. Acquiring this level of knowledge is not straight forward, even for some experienced users. This Task Group report addresses these issues and provides a basic understanding of available RCF models, dosimetric characteristics and properties, advantages and limitations, configurations, and overall elemental compositions of the RCFs that have changed over the past 20 yr. In addition, this report provides specific guidelines for data processing and analysis schemes and correction methodologies for clinical applications in radiation therapy.

Object Resected brain metastases have a high rate of local recurrence without adjuvant therapy. Adjuvant whole brain radiotherapy (WBRT) remains the standard of care with the rate of local control >90%. However, WBRT is delivered over 10–15 days, which can delay other therapy and is associated with acute and long-term toxicities. Intra-operative permanent Cesium-131 (Cs-131) implants can be performed at the time of surgery, thereby avoiding any additional therapy. We evaluate the safety, feasibility and efficacy of a novel treatment approach of brain metastases with a permanent intra-operative Cs-131 brachytherapy. Methods After IRB approval, 24 patients with a newly diagnosed metastasis to the brain (n=24) were accrued on a prospective protocol between 2010 and 2012. There were 10 frontal, 7 parietal, 4 cerebellar, 2 occipital, and 1 temporal metastases. Histology included lung (16), breast (2), kidney (2), melanoma (2), colon (1), and cervix (1). Cs-131 stranded seeds were placed as a permanent volume implant. Prescription dose was 80Gy at 5mm depth from the resection cavity surface. Distant metastases were treated with stereotactic radiosurgery (SRS) or WBRT, depending on the number of lesions. Primary end point was resection cavity freedom from progression (FFP). Secondary end points included distant metastases FFP, median survival, overall survival (OS), and toxicity. Results Median follow-up was 19.3 months (range, 12.89 – 29.57 months). Median age was 65 years (range, 45–84 years). Median volume of resected tumor was 10.31 cc (range, 1.77 - 87.11 cc). Median number of seeds employed was 12 (range, 4–35) with median activity per seed of 3.82 mCi (range, 3.31–4.83 mCi) and total activity of 46.91 mCi (range, 15.31–130.70 mCi). Local recurrence FFP was 100%. There was 1 adjacent leptomeningeal recurrence, resulting in a 1-year regional FFP of 93.8% (95% CI = 63.2%, 99.1%). Distant metastasis FFP was 48.4% (95% CI = 26.3%, 67.4%). Median OS was 9.9 months (95% CI = 4.8 months, upper limit not estimated) and 1-year OS was 50.0% (95% CI = 29.1%, 67.8%). Complications included cerebrospinal fluid leak (1), seizure (1), infection (1). There was no radiation necrosis. Conclusions Cs-131 post-resection permanent brachytherapy implants resulted in no local recurrences and no radiation necrosis. This treatment approach was safe, well tolerated, and convenient for patients, resulting in a short radiation treatment course, high response rates, and minimal toxicity. These results merit further study with a multicenter trial.

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