Dosimetric Comparison between Volumetric Modulated Arc Therapy and Helical Tomotherapy in Prostate Cancer Treatment Planning

Abstract

Background: Prostate cancer is common in Thai males. The two major radiation therapy advance techniques, volumetric modulated arc therapy (VMAT) and helical tomotherapy (HT), provide high-precision radiation dose to planning target volume (PTV) while sparing organs at risk (OARs) in prostate radiotherapy.

Objectives: To compare the dosimetric parameters and treatment efficiency between VMAT and HT treatment plan for prostate cancer.

Materials and Methods: This is a retrospective study of sixteen prostate cancer patients who were treated with Simultaneous integrated boost (SIB) technique using HT. The PTV includes the prostate (PTV-P) and pelvic lymph nodes (PTV-LN). The prescription doses for PTV-P and PTV-LN were 70 Gy and 50.4 Gy in 28 fractions, respectively. These patient images data were used to generated Single-arc (SA) and Double-arc (DA) VMAT plan by Monaco planning system. The same computed tomography images and structure contours data sets were used. Target volumes were constrained according to the criteria of the International Commission on Radiation Units and Measurements (ICRU) report no.83 and the OAR doses were evaluated by following the criteria of Radiation Therapy Oncology Group (RTOG) 0415 report and ICRU 83. The plan quality assessment indexes were the conformity number (CN) and the homogeneity index (HI). The OAR (bladder, rectum, femoral heads, penile bulb and bowels) doses were evaluated by following criteria of RTOG 0415 and ICRU 83 (D₅₀, D₁₀, Mean dose and D₂). The beam-on time was also compared for the treatment efficiency assessment.

Results: The SA and DA VMAT achieved clinically acceptable dosimetric goals. There was no statistically significant difference (p>0.05) between these plans and the previous HT plan. CN showed no statistically significant difference between these plans. HT provided significantly better HI than DA VMAT and SA VMAT(p<0.05). For the OAR dose, HT had significantly lower bladder, rectum and femoral heads dose but higher penile bulb dose. DA VMAT had significantly lower bladder and bowels dose but higher penile bulb dose than SA VMAT. SA VMAT and DA VMAT had shorter beam-on time than HT.

Conclusion: All three plans achieved clinically acceptable dosimetric quality goals. HT provided better homogeneous dose distribution and lower dose to OARs. HT had the longest beam-on time.