Effect Of Cavity On Nasopharyngeal Carcinoma Dose Calculation

Nasopharyngeal carcinoma(NPC) is common in China, the main therapy for NPC is Radiotherapy, the 5 years overall survival can be 59.0%~76.1%, but the main failure of NPC radiotherapy is local region recurrent, many are only located at nasopharyngeal.there are many reasons may cause NPC recurrence a fter first time radiotherapy, sensitivity of tumor stem cells, clinical stage, target definition, radiotherapy technique, and the dose to the tumor. It’s hard to treat the recorrent NPC, many people are found too late. It has the value for clinical to explore the reason of NPC reccurence, to prevent it happens.This paper discuss the dose reason of NPC reccurence, due to computer technique, dose calculation algorithm used in clinical many are based on physics model, this method has some limits, especially for inhomogeneous tissue, lack of transient electronic disequilibrium, there are errors of dose calculation. Nasopharyngeal has complex anatomy, it has bone support, air cavity, it is hard to calculate NPC dose accurately. 10 NPC cases are selected for study, IMRT plans are created in Xi O treatment planning system(TPS), then send to Monaco TPS with CT images, structures and dose. in Monaco TPS, the dose was recalculated using Monte Carlo algorithm XVMC, then compared to the dose from Xi O, to analyse the dose difference of GTV, cavity and muscosa located at GTV-cavity interface.Results: for the dose comparision of Superposition algorithm and XVMC algorithm, ① 95% volume of GTV dose, GTV minimum dose, muscosa minimum dose, the value calculated by Superposition is bigger than XVMC, and the difference has statistical meaning, p<<0.05; ② for cavity maximum dose, the value calculated by Superposition is less than X VMC, and the difference has statistical meaning, p<<0.05; ③ both for Superposition and XVMC, the maximum dose of cavity is bigger than minimum dose of muscosa, correlation between maximum dose of cavity and minimum dose of muscosa is positive, maximum dose of cavity increase, then minimum dose of muscosa also increase. to enhance cavity dose is useful for tumor dose.