A Hybrid Electron and Photon IMRT Planning Technique in Vulvar Cancer

Abstract

IMRT is increasingly used instead of 3DCRT in vulvar cancer. Critical structures around the target volumes can be spared with IMRT technique, but normal tissue integral dose (NTID) may increase due to increased number of beams. In this study we aimed to produce homogeneous dose distribution in target volumes while decreasing the NTID and critical organ doses in the vicinity. The 3DCRT, IMRT, and hybrid electron-IMRT treatment plans of seven patients with the diagnosis of vulvar cancer were performed using the Eclipse 8.9 TPS. The dose DVHs of techniques were compared for target volume and critical structures. Also, NTID was calculated for each treatment plan. The prescribed dose was 5040 cGy in 28 fractions. When hybrid plan was performed 70% of dose was given with electron beams and 30% with IMRT. Female Alderson rando phantom, TLD, and Gafchromic EBT3 film calculations were used for dosimetric analyses. Treatment plan comparisons were made by using D95%, Dmax, Dmean, and D5% of PTV (Table 1). Both IMRT plans were resulted in a significantly higher D95% compared to 3DCRT technique; however, there was no difference between IMRT and hybrid electron-IMRT techniques. Dmean and D5% were significantly improved with hybrid electron-IMRT techniques compared to sole IMRT techniques. For the 3DCRT, IMRT, and hybrid electron-IMRT techniques, the volume received ≥40 Gy (V40) for bladder were 95%, 39.4%, and 34.4%; V40 for rectum were 54.8%, 32.8%, and 28.4%; V35 for bowel were 42.2%, 41.8%, and 36%; V50 for femoral head were 3%, 3.1%, and 2.5%, respectively. NTID was compared based on the body-PTV Dmean and were calculated as 1221 cGy, 1404 cGy, and 1288 cGy for 3DCRT, IMRT and hybrid electron-IMRT technique, respectively (p = 0.018). The percent difference between TPS and TLD calculations were between 0.9%-13%. For EBT3 film measurements, this ratio is between 0.2%-4.2%. Hybrid electron-IMRT technique produced the lowest doses in the critical organs. Additionally, NTID values were significantly lower with hybrid electron-IMRT technique than the IMRT technique. All these values were confirmed dosimetrically. We think that hybrid electron-IMRT technique should be the preferred technique for patients with vulvar cancer.Abstract 3588; Table 1D95%, Dmax, Dmean, D5% and p values of PTV for 3DCRT, IMRT, and hybrid electron-IMRT techniquesTechniqueD95%DmaxDmeanD5%3DCRT4713.15459.45066.85295IMRT4936.55496.75094.55212.4p value0.0280.2370.3980.0283DCRT4713.15459.45066.85295Hybrid electron-IMRT4914.755935145.55329.5p value0.0180.0180.0910.398IMRT4936.55496.75094.55212.4Hybrid electron-IMRT4914.755935145.55329.5p value0.6120.0910.0280.018 Open table in a new tab