Excellent treatment setup accuracy with highly conformal radiation technique will improve oral mucosal sparing by
limiting uninvolved mucosal structures from receiving high dose radiation. Therefore, a study was conducted to identify
the ideal immobilization device for interfraction treatment setup accuracy improvement. A total of twelve oral cancer
patients underwent volumetric modulated arc therapy (VMAT) was categorized into three different group depending on
immobilization device they used for treatment. HFW: headFIX® mouthpiece molded with wax, SYR: 10 cc/ml syringe and
TDW: wooden tongue depressor molded by wax. Each patient underwent image-guided radiotherapy with a total of 292
cone beam computed tomography (CBCT) data sets for position treatment setup errors measurement. The variations in
translational (lateral, longitudinal, vertical) and rotational (pitch, yaw, roll) in each CBCT image were calculated. Patient
positioning errors were analyzed for time trends over the course of radiotherapy. CTV-PTV margins were calculated from
the systematic (Σ) and random (σ) errors. Mean ± SD for absolute treatment setup error was statistically significant
(p < 0.001) lower for all translational errors and yaw direction in HFW. The interfraction 3D vector errors were 1.93 ±
0.66, 3.84 ± 1.34 and 2.79 ± 1.17 mm for the HFW, SYR and TDW respectively. There are positive increments between 3D
vector errors over the treatment fraction for all devices. The calculated CTV-PTV margins were 3.08, 2.22 and 0.81 mm,
3.76, 6.24 and 5.06 mm and 3.06, 3.45 and 4.84 mm in R-L, S-I and A-P directions, respectively. HFW shows smaller errors
in almost all comparison indicating higher accuracy and reproducibility of the immobilization device in maintaining
patient’s position. All margins calculated did not exceed hospital protocol (5 mm) except S-I and A-P directions using
SYR. However, in some special situations, such as re-irradiation or the close proximity of organs at risk and high-dose
regions or lower (i.e., 3 mm) margins could benefit from daily image guidance.
This study was carried out to investigate the suitability of using the optically stimulated luminescence dosimeter (OSLD) in measuring surface dose during radiotherapy. The water equivalent depth (WED) of the OSLD was first determined by comparing the surface dose measured using the OSLD with the percentage depth dose at the buildup region measured using a Markus ionization chamber. Surface doses were measured on a solid water phantom using the OSLD and compared against the Markus ionization chamber and Gafchromic EBT3 film measurements. The effect of incident beam angles on surface dose was also studied. The OSLD was subsequently used to measure surface dose during tangential breast radiotherapy treatments in a phantom study and in the clinical measurement of 10 patients. Surface dose to the treated breast or chest wall, and on the contralateral breast were measured. The WED of the OSLD was found to be at 0.4 mm. For surface dose measurement on a solid water phantom, the Markus ionization chamber measured 15.95% for 6 MV photon beam and 12.64% for 10 MV photon beam followed by EBT3 film (23.79% and 17.14%) and OSLD (37.77% and 25.38%). Surface dose increased with the increase of the incident beam angle. For phantom and patient breast surface dose measurement, the response of the OSLD was higher than EBT3 film. The in-vivo measurements were also compared with the treatment planning system predicted dose. The OSLD measured higher dose values compared to dose at the surface (Hp(0.0)) by a factor of 2.37 for 6 MV and 2.01 for 10 MV photon beams, respectively. The measurement of absorbed dose at the skin depth of 0.4 mm by the OSLD can still be a useful tool to assess radiation effects on the skin dermis layer. This knowledge can be used to prevent and manage potential acute skin reaction and late skin toxicity from radiotherapy treatments.