Neo-adjuvant chemo-radiation of rectal cancer with volumetric modulated arc therapy: summary of technical and dosimetric features and early clinical experience

Abstract

Background: To report about initial technical and clinical experience in preoperative radiation treatment of rectal cancer with volumetric modulated arcs with the RapidArc (RA) technology.

Methods: Twenty-five consecutive patients (pts) were treated with RA. All showed locally advanced rectal adenocarcinoma with stage T2-T4, N0-1. Dose prescription was 44 Gy in 22 fractions (or 45 Gy in 25 fractions). Delivery was performed with single arc with a 6 MV photon beam. Twenty patients were treated preoperatively, five did not receive surgery. Twenty-three patients received concomitant chemotherapy with oral capecitabine. A comparison with a cohort of twenty patients with similar characteristics treated with conformal therapy (3DC) is presented as well.

Results: From a dosimetric point of view, RA improved conformality of doses (CI95% = 1.1 vs. 1.4 for RA and 3DC), presented similar target coverage with lower maximum doses, significant sparing of femurs and significant reduction of integral and mean dose to healthy tissue. From the clinical point of view, surgical reports resulted in a down-staging in 41% of cases. Acute toxicity was limited to Grade 1-2 diarrhoea in 40% and Grade 3 in 8% of RA pts, 45% and 5% of 3DC pts, compatible with known effects of concomitant chemotherapy. RA treatments were performed with an average of 2.0 vs. 3.4 min of 3DC.

Conclusion: RA proved to be a safe, qualitatively advantageous treatment modality for rectal cancer, showing some improved results in dosimetric aspects.

Figure 1

Isodose distributions for two example patients for RA and 3DC treatments for an axial plane, sagittal and coronal views. Doses are shown in colorwash within the interval from 10 to 47 Gy. PTV, bladder and femurs are outlined.

Figure 2

Average Dose Volume Histograms for PTV for RA and 3DC plans. Dashed lines represent inter-patient variability at 1 standard deviation.

Figure 3

Average Dose Volume Histograms for Bladder, Bowel, Femurs and Healthy Tissue for RA and 3DC plans. Dashed lines represent inter-patient variability at 1 standard deviation.