Patient Dose Analysis Using GafchromicTM EBT3 Film: A Retrospective Study with a Four Dual-Field Technique in Total Skin Electron Therapy.

OBJECTIVE: The Six dual-field is the most commonly used treatment technique in total skin electron therapy (TSET). Because of the prolonged treatment period, the patient may experience discomfort, and routine radiotherapy treatments may be affected. This reflects the idea of using a modified technique in TSET. The study aims to report our experience with the four dual-field technique and review the in-vivo dosimetry using gafchromic film. MATERIALS AND METHODS: The in-vivo dosimetry reports using gafchromic EBT-3 films of 12 patients who received TSET with the four dual-field techniques in our hospital were analysed in this study. The dosimetric parameter including percentage depth dose, dose homogeneity, flatness and symmetry were analysed in this study. RESULTS AND DISCUSSION: For all the patients, the mean dose to the skin was close to the prescription dose, and it was within 10% (99.3%-103%) of the prescription dose. The standard deviation was observed between 5.8 and 12.4 cGy. According to international standards, all of the measured dosimetric parameters were within the acceptable limit and thereby validating our technique.  The in-vivo dosimetry study using radiochromic film in TSET is relatively uncommon. So, based on our results, gafchromic films are a viable choice. The objective of our four dual-field techniques is to reduce the overall treatment time on the machine, whereas our study shows a time reduction when compared to regular techniques, which aids in the smooth operation of daily routines. CONCLUSION: The preliminary results of this novel modified technique in TSET demonstrated favourable effectiveness with minimal skin toxicity. This four dual-field technique is simple and easy to implement. Comparatively, this study shows the dose homogeneity of ±10% and better dose in the underdose areas proving the reliability and homogeneity of four-dual field technique.

Dosimetric Comparison between Single and Dual Arc-Volumetric Modulated Arc Radiotherapy and Intensity Modulated Radiotherapy for Nasopharyngeal Carcinoma Using a Simultaneous Integrated Boost Technique

Backround: Plan quality and performance of dual arc (DA) volumetric modulated arc therapy (VMAT) , single arc (SA) VMAT and nine field (9F) intensity modulated radiotherapy were compared using a simultaneous integrated boost (SIB) technique. Methods: Twelve patients treated in Elekta Synergy Platform (mlci2) by 9F-IMRT were replanned with SA/DA-VMAT using a CMS Monaco Treatment Planning System (TPS) with Monte Carlo simulation. Target delineation was conducted as per Radiation Therapy Oncology Protocols (RTOG0225 and 0615). A 70Gy dose prescribed to PTV70 and 61Gy to PTV61 in 33 fractions was applied for the SIB technique. The conformity index (CI) and homogeneity index (HI) for targets and the mean dose and maximum dose for OAR's, treatment delivery time (min), monitor units (MUs) per fraction, normal tissue integral dose and patient specific quality assurance were analysed. Results: Acceptable target coverage was achieved for PTV70 and PTV61 with all the planning techniques. No significant differences were observed except for D98 (PTV61), CI(PTV70) and HI(PTV61). Maximum dose (Dmax) to the spinal cord was lower in DA-VMAT than 9F-IMRT (p=0.002) and SA-VMAT (p=0.001). D50 (%) of parotid glands was better controlled by 9F-IMRT (p=0.001) and DA-VMAT (p=0.001) than SA-VMAT. A lower mean dose to the larynx was achieved with 9F-IMRT (P=0.001) and DA-VMAT (p=0.001) than with SA-VMAT. DA-VMAT achieved higher CI of PTV70 (P= 0.005) than SA-VMAT. For PTV61, DA-VMAT (P=0.001) and 9F-IMRT (P=0.001) achieved better HI than SA-VMAT. The average treatment delivery times were 7.67mins, 3.35 mins, 4.65 mins for 9F- IMRT, SA-VMAT and DA-VMAT, respectively. No significant difference were observed in MU/fr (p=0.9) and NTID (P=0.90) and the patient quality assurance pass rates were >95% (gamma analysis Ґ3mm, 3%). Conclusion: DA-VMAT showed better conformity over target dose and spared the OARs better or equal to IMRT. SA-VMAT could not spare the OARs well. DA-VMAT offered shorter delivery time than IMRT without compromising the plan quality.