A margin from the clinic target volume to the planning target volume for esophagus carcinoma / 实用医学杂志

ABSTRACT

Objective To measure the setup errors and organ movements of patients with esophagus carcinoma during radiotherapy and find a reasonable margin from the clinic target volume (CTV) to the planning target volume (PTV). Methods (1) Set-up veri cation Forty-two cases of untreated esophageal cancer were enrolled into this study. The physicist firstly made the planning according to the doctor requests and ensured the best distribution at the target. Thereafter, the 0° and 90° digitally reconstructed radiograph (DRR) was transmitted to the iView GT workshop. Meanwhile, two copies of cross-cut electronic portal image (EPI) were required before radiotherapy. Two doctors confirmed the variance of the osteal mark from the EPI and DRR,and output a 3D direction (left to right, superior to inferior, anterior to posterior) of the setup errors through the iView GT software. (2)Breathing motionTen cases of untreated esophageal cancer were enrolled into this study.Three distinct breathing levels were deflned FB (free breathing), EBH (expiration with breath-held) and IBH (inspiration with breath-held). We gave the treatment planning in FB, then by moving the isocenter to EBH and IBH, we recalculated the dose distribution without changing the field angle, shape and weighing (Mus). Displacements were analyzed at four points (anterior, posterior, right lateral and left lateral) and five levels of target (upper, quarter, isocenter, three-quarter and lower). Results (1) The systematic setup errors were -0.23 cm, -0.02 cm and -0.06 cm, and the random errors were 0.44 cm, 0.45 cm and 0.44 cm at the direction of left to right(LR), superior to inferior (SI), anterior to posterior(AP), respectively. (2) The organ movements were 0.3 cm, 0.6cm and 0.3cm at the LR, SI, AP, respectively. Conclusions As an alternative, the root-sum-of-squares of set-up error and organ motion are suggested by σtot=√ (σITV2+σSM2). The CTV to PTV margins are 0.8cm left to right, 0.78cm superior to inferior, 0.5cm anterior to posterior.