The dosimetric impact of different photon beam energy on RapidArc radiotherapy planning for cervix carcinoma

The main purpose of this study is to know the effect of three different photon energies viz., 6, 10, and 15 mega voltage (MV) on RapidArc (RA) planning for deep-seated cervix tumor and to develop clinically acceptable RA plans with suitable photon energy. RA plans were generated for 6, 10, and 15 MV photon energies for twenty patients reported with cervix carcinoma. RA plans were evaluated in terms of planning target volume (PTV) coverage, dose to organs at risk (OARs), conformity index (CI), homogeneity index (HI), gradient measure, external volume index of dose distribution produced, total number of monitor units (MUs), nontumor integral dose (ID), and low dose volume of normal tissue. A two-sample paired t-test was performed to compare the dosimetric parameters of RA plans. Irrespective of photon energy used for RA planning, plans were dosimetrically similar in terms of PTV coverage, OARs sparing, CI and HI. The numbers of MUs were 13.4 ± 1.4% and 18.2 ± 1.5% higher and IDs were 2.7 ± 0.8% and 3.7 ± 0.9% higher in 6 MV plans in comparison to that in the 10 and 15 MV plans, respectively. V1Gy, V2Gy, V3Gy, and V4Gywere higher in 6 MV plans in comparison to that in 10 and 15 MV plans. Based on this study, 6 MV photon beam is a good choice for RA planning in case of cervix carcinoma, as it does not deliver additional exposure to patients caused by photoneutrons produced in high energy beams

Measurement and comparison of head scatter factor for 7MV unflattened (FFF) and 6MV flattened photon beam using indigenously designed columnar mini phantom

AimTo measure and compare the head scatter factor for 7[[ce:hsp sp="0.25"/]]MV unflattened and 6[[ce:hsp sp="0.25"/]]MV flattened photon beam using a home-made designed mini phantom.BackgroundThe head scatter factor (Sc) is one of the important parameters for MU calculation. There are multiple factors that influence the Sc values, like accelerator head, flattening filter, primary and secondary collimators.Materials and methodsA columnar mini phantom was designed as recommended by AAPM Task Group 74 with high and low atomic number material for measurement of head scatter factors at 10[[ce:hsp sp="0.25"/]]cm and dmax dose water equivalent thickness.ResultsThe Sc values measured with high-Z are higher than the low-Z mini phantoms observed for both 6MV-FB and 7MV-UFB photon energies. Sc values of 7MV-UFB photon beams were smaller than those of the 6MV-FB photon beams (0.6–2.2% (Primus), 0.2–1.4% (Artiste) and 0.6–3.7% (Clinac iX (2300CD))) for field sizes ranging from 10[[ce:hsp sp="0.25"/]]cm[[ce:hsp sp="0.25"/]]×[[ce:hsp sp="0.25"/]]10[[ce:hsp sp="0.25"/]]cm to 40[[ce:hsp sp="0.25"/]]cm[[ce:hsp sp="0.25"/]]×[[ce:hsp sp="0.25"/]]40[[ce:hsp sp="0.25"/]]cm. The SSD had no influence on head scatter for both flattened and unflattened beams. The presence of wedge filters influences the Sc values. The collimator exchange effects showed that the opening of the upper jaw increases Sc irrespective of FF and FFF.ConclusionsThere were significant differences in Sc values measured for 6MV-FB and unflattened 7MV-UFB photon beams over the range of field sizes from 10[[ce:hsp sp="0.25"/]]cm[[ce:hsp sp="0.25"/]]×[[ce:hsp sp="0.25"/]]10[[ce:hsp sp="0.25"/]]cm to 40[[ce:hsp sp="0.25"/]]cm[[ce:hsp sp="0.25"/]]×[[ce:hsp sp="0.25"/]]04[[ce:hsp sp="0.25"/]]cm. Different results were obtained for measurements performed with low-Z and high-Z mini phantoms

Dosimetric influence of filtered and flattening filter free photon beam on rapid arc (RA) radiotherapy planning in case of cervix carcinoma

AimTo investigate the dosimetric influence of filtered and flattening filter free (FFF) photon beam of 6 and 10[[ce:hsp sp="0.25"/]]MV energies on cervix RA radiotherapy planning and to find possibilities to develop the clinically acceptable RA plans with FFFB photon beam and explore their potential benefits to cervix cancer patients.BackgroundFFF photon beams enhances the treatment delivery by increased dose rate which results in shorter treatment time, this shorter treatment time reduces intrafraction motion and enhance comfort to the patients.Materials and methodsRA plans were generated for filtered and flattening filter free photon beams of 6 and 10[[ce:hsp sp="0.25"/]]MV energies using same dose–volumes constraints. RA plans were generated to deliver a dose of 50.4[[ce:hsp sp="0.25"/]]Gy in 28 fractions, for a cohort of eleven patients reported with cervix carcinoma. RA plans were evaluated in terms of PTV coverage, dose to OAR's, CI, HI, total no. of monitor units (MUs) and NTID and low dose volume of normal tissues.ResultsClinically acceptable and similar plans were generated for filtered and flattening filter free photon beams. FFFB delivered slightly higher mean target dose (52.28[[ce:hsp sp="0.25"/]]Gy vs. 52.0[[ce:hsp sp="0.25"/]]Gy, p[[ce:hsp sp="0.25"/]]=[[ce:hsp sp="0.25"/]]0.000 for 6[[ce:hsp sp="0.25"/]]MV and 52.42[[ce:hsp sp="0.25"/]]Gy vs. 52.0[[ce:hsp sp="0.25"/]]Gy, p[[ce:hsp sp="0.25"/]]=[[ce:hsp sp="0.25"/]]0.000 for 10[[ce:hsp sp="0.25"/]]MV) less homogeneous (1.062 vs. 1.052, p[[ce:hsp sp="0.25"/]]=[[ce:hsp sp="0.25"/]]0.000 for 6[[ce:hsp sp="0.25"/]]MV and 1.066 vs. 1.051, p[[ce:hsp sp="0.25"/]]=[[ce:hsp sp="0.25"/]]0.000 for 10[[ce:hsp sp="0.25"/]]MV) and less conformal (1.007 vs. 1.004, p[[ce:hsp sp="0.25"/]]=[[ce:hsp sp="0.25"/]]0.104 for 6[[ce:hsp sp="0.25"/]]MV and 1.012 vs. 1.003, p[[ce:hsp sp="0.25"/]]=[[ce:hsp sp="0.25"/]]0.010 for 10[[ce:hsp sp="0.25"/]]MV) RA plans compared to FB. FFFB delivered more doses to the bladder and rectum, also required more numbers of MUs in comparison to FB.ConclusionsThis study concludes that FB is more beneficial for cervix RA planning in comparison to FFFB, as FB generates more conformal and homogenous rapid arc plans and offers better OAR's sparing

Dosimetric influence of photon beam energy and number of arcs on volumetric modulated arc therapy in carcinoma cervix: A planning study

AimAim of the present study was to compare the dosimetric impact of different photon beam energies and number of arcs in the treatment of carcinoma cervix.BackgroundCarcinoma cervix is a common cancer in women worldwide with a high morbidity rate. Radiotherapy is used to treat such tumours. Volumetric Modulated Arc Therapy (VMAT) is considered superior to other techniques with multiple arcs and energies.Materials and methodsTwenty patients with carcinoma cervix underwent radiotherapy in a prospective observation study conducted at our institute. Volumetric modulated arc plans with 6[[ce:hsp sp="0.25"/]]MV, 10[[ce:hsp sp="0.25"/]]MV and 15[[ce:hsp sp="0.25"/]]MV photon energies using single arc (SA) and dual arc (DA) were generated. Several physical indices for planning target volume (PTV) like V95%, V100%, V110%, D98%, D50%, D2% and total number of MUs were compared. Normal Tissue Integral Dose (NTID) and dose to a shell structure PHY2.5 and PHY5.0 were analyzed.ResultsComparable dose coverage to PTV was observed for all the energies and arcs. CI for DA6MV (1.095) was better than SA6MV (1.127), SA10MV (1.116) and SA15MV (1.116). Evaluated parameters showed significant reduction in OAR doses. Mean bladder dose for DA6MV (41.90[[ce:hsp sp="0.25"/]]Gy) was better than SA6MV (42.48[[ce:hsp sp="0.25"/]]Gy), SA10MV (42.08[[ce:hsp sp="0.25"/]]Gy) and SA15MV (41.93[[ce:hsp sp="0.25"/]]Gy). Similarly, p-value for the mean rectal dose calculated was 0.001 (SA6 vs 15), 0.013 (DA6 vs 10) and 0.003 (DA6 vs 15) and subsequently favoured DA6MV. Difference in NTID was very small.ConclusionsThe study showed no greater advantage of higher energy, and DA VMAT plan with 6[[ce:hsp sp="0.25"/]]MV photon energy was a good choice of treatment for carcinoma cervix as it delivered a highly homogeneous and conformal plan with superior target coverage and better OAR sparing

Surface dose measurements and comparison of unflattened and flattened photon beams

The purpose of this study was to evaluate the central axis dose in the build-up region and the surface dose of a 6 MV and 10 MV flattened photon beam (FB) and flattening filter free (FFF) therapeutic photon beam for different square field sizes (FSs) for a Varian Truebeam linear accelerator using parallel-plate ionization chamber and Gafchromic film. Knowledge of dosimetric characteristics in the build-up region and surface dose of the FFF is essential for clinical care. The dose measurements were also obtained empirically using two different commonly used dosimeters: a p-type photon semiconductor dosimeter and a cylindrical ionization chamber. Surface dose increased linearly with FS for both FB and FFF photon beams. The surface dose values of FFF were higher than the FB FSs. The measured surface dose clearly increases with increasing FS. The FFF beams have a modestly higher surface dose in the build-up region than the FB. The dependence of source to skin distance (SSD) is less significant in FFF beams when compared to the flattened beams at extended SSDs

Impact of acuros XB algorithm in deep-inspiration breath-hold (DIBH) respiratory techniques used for the treatment of left breast cancer

AimTo investigate the impact of Acuros XB (AXB) algorithm in the deep-inspiration breath-hold (DIBH) technique used for treatment of left sided breast cancer.BackgroundAXB may estimate better lung toxicities and treatment outcome in DIBH.Materials and MethodsTreatment plans were computed using the field-in-field technique for a 6 MV beam in two respiratory phases - free breathing (FB) and DIBH. The AXB-calculations were performed under identical beam setup and the same numbers of monitor units as used for AAA-calculation.ResultsMean Hounsfield units (HU), mass density (g/cc) and relative electron density were -782.1 ± 24.8 and -883.5 ± 24.9; 0.196 ± 0.025 and 0.083 ± 0.032; 0.218 ± 0.025 and 0.117 ± 0.025 for the lung in the FB and DIBH respiratory phase, respectively. For a similar target coverage (p > 0.05) in the DIBH respiratory phase between the AXB and AAA algorithm, there was a slight increase in organ at risk (OAR) dose for AXB in comparison to AAA, except for mean dose to the ipsilateral lung. AAA predicts higher mean dose to the ipsilateral lung and lesser V20Gy for the ipsilateral and common lung in comparison to AXB. The differences in mean dose to the ipsilateral lung were 0.87 ± 2.66 % (p > 0.05) in FB, and 1.01 ± 1.07% (p