Prospective study on dosimetric comparison of helical tomotherapy and 3DCRT for craniospinal irradiation - A single institution experience

Abstract

Aim: This prospective study aims to assess feasibility of helical tomotherapy (HT) for craniospinal irradiation (CSI) and perform dosimetric comparison of treatment plans for both HT and 3D conformal radiotherapy (3DCRT).

Background: CSI is a challenging procedure. Large PTV size requires field matching due to technical limitations of standard linear accelerators, which cannot irradiate such volumes as a single field. HT could help to avoid these limitations as irradiation of long fields is possible without field matching.

Materials and methods: Three adults were enrolled from 2009 to 2010. All patients received radiochemotherapy. Treatment plans in prone position for 3DCRT and in supine position for HT were generated. The superior plan was used for patients' irradiation. Plans were compared with the application of DVH, Dx parameters - where x represents a percentage of the structure volume receiving a normalized dose and homogeneity index (HI).

Results: All patients received HT irradiation. The treatment was well tolerated. The HT plans resulted in a better dose coverage and uniformity in the PTV: HI were 5.4, 7.8, 6.8 for HT vs. 10.3, 6.6, 10.4 for 3DCRT. For most organs at risk (OARs), the D(V80) was higher for HT than for 3DCRT, whereas D(V5) was lower for HT.

Conclusions: HT is feasible for CSI, and in comparison with 3DCRT it improves PTV coverage. HT reduces high dose volumes of OARs, but larger volumes of normal tissue receive low radiation dose. HT requires further study to establish correlations between dosimetrical findings and clinical outcomes, especially with regard to late sequelae of treatment.

Keywords: Craniospinal irradiation; Dosimetric comparison; Helical tomotherapy.

Fig. 1

Differential DVHs for PTV for each patient. Dashed line – 3DCRT; continuous line – HT.

Fig. 2

Cumulative DVH for OARs: eyes, lenses, parotids, thyroid glands and lungs. Grey lines represent 3DCRT; black lines – HT.

Fig. 3

Cumulative DVH for OARs: heart, kidneys, spleen, liver and intestines. Grey lines represent 3DCRT; black lines – HT.

Fig. 4

CT-transversal sections of one of the patients: HT dose distribution on the left and LINAC on the right. Sections at the level of eves, parotids and the thyroid gland. LINAC-CT-scans rotated at 180° for comparison purposes.

Fig. 5

CT-transversal sections of one of the patients: HT dose distribution on the left and LINAC on the right. Sections at the level of the heart, liver, spleen and kidneys, and intestines. LINAC-CT-scans rotated at 180° for comparison purposes.