R Subramani¹*, J Amalraj², P Anchineyan³, S Anchiyam⁴, B Patneedi⁵, (1) HCG ICS Cancer Center, Mumbai, MH, India, (2) Health Care Global Ent, Bangalore, KA, India

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  R Subramani

(Saturday, 3/26/2022)   [Central Time (GMT-5)]

Purpose: To evaluate the dosimetric and clinical advantages of 3D conformal Helical Tomotherapy (HT) over the 3D Direct Tomotherapy (DT) box field treatment plan. Helical Tomotherapy machines were capable of delivering helical IMRT treatments only until a decade ago. Radixact X9 was their latest unit which has the capability of delivering 3DCRT with 2 different approach say helical tomotherapy (HT) with rotational beam and Direct tomotherapy (T) with static beam.

Methods: Ten cervical cancer patients who underwent 3D helical tomotherapy treatment have been retrospectively analysed. Computed Tomography(CT) images were acquired using pelvic protocol with full bladder and 2 mm slice thickness. Planning target volume (PTV) and organs at risk (OAR) such as bladder, rectum, femoral heads and bowel were delineated. DT (Box Field) and HT plans were created using Accuray PrecisionTM TPS for Radixact X9 Tomotherapy linac having 64 binary MLC and 6 MV photons. Planning parameters such as field width, pitch and modulation factor were kept 2.5 cm, 0.287 and 2.0 respectively. For all the cases, the conventional dose regimen of 50 Gy in 25 fractions was prescribed.

Results: Both the planning techniques resulted in identical PTV coverage, the Dmean in HT and DT to bladder and rectum (mean (SD)) were 42.56 Gy (±1.997 Gy) vs. 48.08 Gy (±1.962 Gy) and 39.78 Gy (±3.035 Gy) vs 43.33 Gy (±3.667 Gy). The 3D HT plans were found to be superior to DT box field plans in terms of target conformity and homogeneity as well as producing substantial sparing of critical OARs.

Conclusion: Our result suggest that the 3D HT plans yield better dosimetric and clinical advantages over the 3D DT box fields as it producing better OARs sparing while maintaining the highly conformal target dose coverage thereby reducing the normal tissue toxicity for cervical cancer patients treatment.

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