Validation of the RapidArc Delivery System Using a Volumetric Phantom as Per Task Group Report 119 of the American Association of Physicists in Medicine

Dosimetric Evaluation of the Treatment Plan on Indigenous Heterogeneous Phantoms using Analytical Anisotropic Algorithm and Acuros-XB Algorithm for Different Photon Energies

BACKGROUND

Modern radiotherapy techniques are using advanced algorithms; however, phantoms used for quality assurance have homogeneous density; accordingly, the development of heterogeneous phantom mimicking human body sites is imperative to examine variation between planned and delivered doses.

OBJECTIVE

This study aimed to analyze the accuracy of planned dose by different algorithms using indigenously developed heterogeneous thoracic phantom (HT).

MATERIAL AND METHODS

In this experimental study, computed tomography (CT) of HT was done, and the density of different parts was measured. The plan was generated on CT images of HCP with 6 and 15 Megavoltage (MV) photon beams using different treatment techniques, including three-dimensional conformal radiotherapy (3D-CRT), intensity-modulated radiation therapy (IMRT), and volumetric modulated arc therapy (VMAT). Plans were delivered by the linear accelerator, and the dose was measured using the ion chamber (IC) placed in HT; planned and measured doses were compared.

RESULTS

Density patterns for different parts of the fabricated phantom, including rib, spine, scapula, lung, chest wall, and heart were 1.849, 1.976, 1.983, 0.173, 0.855, and 0.833 g/cc, respectively. Variation between planned and IC estimated doses with the tolerance (±5%) for all photon energies using different techniques. Acuros-XB (AXB) showed a slightly higher variation between computed and IC estimated doses using HCP compared to the analytical anisotropic algorithm (AAA).

CONCLUSION

The indigenous heterogeneous phantom can accurately simulate the dosimetric scenario for different algorithms (AXB or AAA) and be also utilized for routine patient-specific QA.

Dosimetric impact of Acuros XB on cervix radiotherapy using RapidArc technique: a dosimetric study

Background

Acuros XB (AXB) may predict better rectal toxicities and treatment outcomes in cervix carcinoma. The aim of the study was to quantify the potential impact of AXB computations on the cervix radiotherapy using the RapidArc (RA ) technique as compared to anisotropic analytical algorithm (AA) computations.

Materials and methods

A cohort of 30 patients previously cared for cervix carcinoma (stages II-IIIB) was selected for the present analysis. The RA plans were computed using AA and AXB dose computation engines under identical beam setup and MLC pattern.

Results

There was no significant (p > 0.05) difference in D_95% and D_98% to the planning target volume (PTV); moreover, a significant (p < 0.05) rise was noticed for mean dose to the PTV (0.26%), D_50% (0.26%), D_2% (0.80%) and V_110% (44.24%) for AXB computation as compared to AA computations. Further, AXB estimated a significantly (p < 0.05) lower value for maximum and minimum dose to the PTV. Additionally, there was a significant (p < 0.05) reduction observed in mean dose to organs at risk (OARs) for AXB computation as compared to AA, though the reduction in mean dose was non-significant (p > 0.05) for the rectum. The maximum difference observed was 4.78% for the rectum V_50Gy, 1.72%, 1.15% in mean dose and 2.22%, 1.48% in D_2% of the left femur and right femur, respectively, between AA and AXB dose estimations.

Conclusion

For similar target coverage, there were significant differences observed between the AAA and AXB computations. AA underestimates the V_50Gy of the rectum and overestimates the mean dose and D_2% for femoral heads as compared to AXB. Therefore, the use of AXB in the case of cervix carcinoma may predict better rectal toxicities and treatment outcomes in cervix carcinoma using the RA technique.