Contact X-Ray Therapy

Abstract

Contact X-ray therapy (CXRT) with a 50 kV beam was first designed in Germany in 1933 (Siemens company). Between 1960 and 1990, Papillon in France popularized this technique for rectal cancer using a Philips RT50 device. Since then, CXRT has been used in Europe and North America. It was the first technique that was able to cure adenocarcinoma of the rectum, which till the 1970s was considered a radioresistant tumor, with radiotherapy alone. CXRT is a unique approach for rectal cancer because it allows very high doses of radiation to be accurately delivered to the tumor under direct visualization. CXRT alone can control the disease in 90% of cases of T1 N0 rectal adenocarcinoma with doses of 90–100 Gy delivered in three or four fractions over 4–5 weeks. Similarly, CXRT can be used after local excision for pT1 disease to increase tumor bed local control (45–50 Gy in three fractions in 3–4 weeks). CXRT with external beam radiotherapy (EBRT) can also be used with curative intent in inoperable elderly patients to treat T2–3 tumors measuring <5 cm in diameter, with local control achievable in 80% of T2 and 50% of T3 tumors. The Lyon R96.02 randomized trial has demonstrated that for T2 and small T3 tumors of the distal rectum, dose escalation (90 Gy/three fractions) with CXRT, in addition to preoperative EBRT, was able to increase the rate of sphincter preserving surgery (44–73%) and was compatible with transanal local excision (TLE) in patients achieving excellent response. A new CXRT machine,Papillon 50®, has been designed and will be commercialized in 2009. Its primary physical characteristics include a (1) beam energy of 50 kV, (2) dose rate of 20 Gy/min (computer controlled), (3) tube/applicator diameter of 2.5 cm, (4) real-time image control of the tumor during treatment (by fiberoscopy), (5) source-to-skin (mucosal) distance of 2–5 cm, and (6) surface treatment area of 3–12 cm². The use of Papillon 50® machine will be performed within the frame of the CONTEM trial in three clinical situations: (1) preoperative CXRT after local excision for pT1N0 disease, (2) neoadjuvant treatment of T2N0 not exceeding 4 cm (using CXRT with EBRT and concurrent chemotherapy followed by local excision following good tumor response), and (3) inoperable elderly patients treated with curative intent for T2–3 N0(1) with various combinations of CXRT and EBRT ± chemotherapy, brachytherapy, or local excision.