Research of effect of cavity between bolus and skin on dose deposition in shallow tissues / 中华放射肿瘤学杂志

ABSTRACT

Objective To evaluate the effect of the thickness and area of the cavity between bolus and skin upon the dose deposition in the shallow tissues.Methods The linear accelerator head model of 6 MV X ray was constructed using Geant4,which simulated the accelerator working condition of 10 cm× 10 cm field and recorded the information of emergent particles as phase space file.A water phantom of 30 × 30 × 30 cm3 was designed at the SAD level.A 30 cm × 30 cm × 1 cm water film was constructed adjacent to or with different cavities to the upper surface of the phantom.The phase space file was utilized as particle source to simulate the particle transport process.The axis depth dose distribution and lateral dose profiles in the center area of the field at a depth of 1 mm,5 mm,9 mm,15 mm and 21 mm of the phantom were obtained,respectively.The simulated data obtained from water film with different cavities were compared with those of adjacent to the water phantom.Results When the cavity was ≤ 5 mm,the cavity exerted slight effect.When the thickness was increased,the maximum dose depth (Dmax) was increased,the PDD at Dmax (PD Dmax) became less,the depth of influenced lateral dose profiles was increased and the dose in the center area was decreased.Along with the increase of cavity area,the Dmax was initially increased and then decreased,the PD Dmax was at first decreased and subsequently increased,the depth of influenced lateral dose profile was initially increased and then decreased,the dose in the center area was first decreased and subsequently increased.The lateral dose profile distant from the cavity or located at a depth ≥ 15 mm was almost not affected by the cavity.Conclusion The thickness of the cavity between bolus and skin should be less than 5 mm and the cavity area should be small as possible.