64 speaker: LDR Brachytherapy Techniques and Results for Base of Tongue Cancer

S 22

S YMPOSIUM

S ATURDAY, M AY 16, 2009

Saturday, May 16, 2009

Symposium

Teaching lecture

Brachytherapy of base of tongue cancer

63 speaker RADIOBIOLOGY FOR THE BRACHYTHERAPY EXPERT? E. Van Limbergen1 1 U NIVERSITY H OSPITAL G ASTHUISBERG, Department of Radiotherapy, Leuven, Belgium

The radiobiological effects of external beam radiotherapy( EBRT) and brachytherapy (BT) depend both on the total dose, the fraction size and total treatment time. However, the treated volumes and the dose distribution within the target are substantially different. In EBRT dose is prescribed at a normalization part within the target allowing for dose inhomogeneities being smaller than +7% and -5%.In brachytherapy the dose is prescribed to a peripheral Minimal Target Isodose , while closer to the applied sources exponentially increasing doses are delivered, leading to significant V150 and even V200 volumes within the treated area resulting in an increased integral dose delivered to the target . The increased biological effects of these dose inhomogeneities within the target can be modeled and mathematically calculated and expressed by EUD values. Such high doses could never be tolerated by normal tissues, except for radio-resistant organs as the uterine cervix and the prostate However the absolute volumes to which BT is delivered are usually small as compared to external beam treated volumes. These small treated volumes have to do as well with selection of patients for BT as with the fact that in BT usually no pTV margins for organ movement on daily set-up are needed.Another difference with external radiotherapy in the radiobiology is the dose rate. BT can be delivered at very low dose rate by low energy permanent seed implants, at continuous Low Dose Rate (LDR), Medium Dose rate(MDR), High Dose Rate (HDR) or by Pulsed Dose Rate(PDR).The RBE of these dose rates is very different. Permanent seed implants deliver the dose at a very low dose rate over several weeks, while repair and repopulation which interfere with the ultimate cytotoxic effects.Also during LDR (< -200 cGy/hr) repair is taking place and cells with a high repair capacity ( low α/β ratio ) and a fast half time of repair will show increased survival. The effect of HDR (> 200 cGy/min) is strongly fraction-size dependent, while the dose rate itself is not determinant for the effects. In MDR (> 200 cGy/hr- < 200cGy/ min) the cell killing effect is rapidly increasing and dose rate corrections for organs at risk have to be taken into account.Pulsed Dose Rate is mimicking the biological effects of Low Dose Rate, using pulses with intervals allowing only for incomplete repair. Pulse sizes and interval times as well as repair capacity (α/β ratio) as well as repair kinetics ( Half time of repair) determine the effects. Small pulse sizes and short interval times allow for equivalent effects as compared to continuous LDR.

64 speaker LDR BRACHYTHERAPY TECHNIQUES AND RESULTS FOR BASE OF TONGUE CANCER D. Peiffert1 1 CRAN - C ENTRE A. VAUTRIN, Radiation Oncology, Vandoeuvre-Les Nancy, France Base of tongue tumours usually present at a loco regional advanced stage. Combination of surgery and irradiation ± chemotherapy is a standard but with poor functional results for speech and eating. A high dose of irradiation can improve the local control and avoid surgery in good responders. Brachytherapy is an elegant technique of boost of the primary in this mobile and deep infiltrative area, while external beam irradiation ± chemotherapy is well designed for the treatment of the regional disease.The technique of implantation is described for LDR brachytherapy, in a patient under general anaesthesia with nasal intubation, in a supine position. The loop technique is well indicated and is tailored depending on the size and the infiltration of the tumour. The homolateral or bilateral base is implanted, with the possibility to extend the treated volume to the mobile tongue, or the glossotonsillar sulcus, or the junction zone. The infiltration of the vallecula is a relative contraindication. Usually, loops are implanted with a distance between the tubes of 12 mm. An adapted technique is developed for HDR and PDR treatments to avoid narrow loops and the risk of kinking of the tubes.The dose delivered by the brachytherapy boost is usually 25-30 Gy on the reference isodose of the Paris System, or its equivalent, when 50 Gy were delivered by external beam irradiation (in 5 weeks) on the primary and the neck.The 5-year local control ranges between 70% to 88% depending on the stage and the dose of brachytherapy.No randomised trial could prove the benefit of a brachytherapy boost compared to an EBI boost, but it was described by historical mono institutional reports.The functional results are described with a benefit for brachytherapy. 65 speaker TECHNIQUE OF CURVED PLASTIC TUBES TO TREAT BASE OF TONGUE CARCINOMAS WITH HDR BRACHYTHERAPY J. L. Guinot1 , M. I. Tortajada1 , M. Carrascosa1 , L. Arribas1 1 I NSTITUTO VALENCIANO O NCOLOGIA, Radiation Oncology, Valencia, Spain Purpose: Base of tongue carcinomas have been treated with low dose rate (LDR) brachytherapy (BT) with the traditional "loop technique". The wide spread of high dose rate (HDR) BT units has supposed the abandonment of this indication, because the HDR source cannot curve so much as to pass through a loop. We present a technique to solve that conflict and to show that HDR advantages are useful for these tumours. Material and methods: We review 18 cases of carcinomas involving base of tongue, 2 woman and 16 men, treated from March 2003 until January 2009. Seven cases were T3, three T2 and eight cases had received previous irradiation by another primary head and neck cancer. Three out of eight received exclusive BT. All the other cases received a combination of external beam radiotherapy (EBRT) 40-60 Gy and BT. The dose per fraction was 3 Gy. Four Gy were used in two cases of exclusive BT. The treatment was given twice a day separated at least 6 hours between them. Total dose was calculated to arrive to an equivalent with LDR to 75-80 Gy and to 70Gy in previously irradiated patients (60 in exclusive BT). Chemotherapy was given to 72% of patients. The technique of BT consists in using curved needles and bending the plastic tubes used in BT. Several boucles were inserted, as in LDR techniques, going from the back to the front of the tongue. A curved needle was led through the base, as high as possible to exit near the lingual V. A straight needle was placed in the posterior third of the tongue, and a boucle was made with a plastic tube and a button in the middle. The tube was bent close to the button carefully, in order to maintain the posterior leg in a curved shape, resembling the anatomy of the base of the tongue, and keeping the anterior leg in a straight shape (Fig 1,2). Every leg was treated as an independent tube. Another single was inserted between both legs. Results: Acute complications were mucositis during 4-6 weeks. Two patients had severe bleeding during the withdrawal of the tubes. Slight bleeding was controlled by pressing with the finger on the hole left by the tube, but these two cases required to apply a bandage inside the mouth to stop the bleeding up. One of them aspirated blood inside the lungs and died after one month due to a respiratory distress. Late complications were minimal, no necrosis has been reported. With a median follow up of 24 months (1-71) two patients have died by local tumour progression, two by a new primary neoplasm, and one by nodal involvement. Local failures and new carcinomas were all in cases of previous irradiation. No local failure has happened in the 10 cases treated with a radical aim. Conclusions: HDR BT is useful to treat base of tongue carcinomas, by means of a technique that avoid the curvature of the plastic tubes. A careful handling and a general anaesthesia is recommended during the withdrawal,