Modulated Photon Radiotherapy Research Articles

SU‐GG‐T‐389: Mixed Electron and Photon Beams Modulated by the XMLC for Partial Breast Irradiation

Purpose: To present a modulated radiation therapy technique as a more accurate alternative to current approaches for the planning of partial breast irradiation (PBI). This technique is based on the use of modulated electron beams alone or in combination with intensity modulated photon radiation therapy (MERT+IMRT), delivered with the same collimation device (xMLC). Method and Materials: A Monte Carlo treatment planning system based on BEAMnrc/DOSXYZnrc code, named CARMEN, was developed by our group. A Linear Programming (LP) optimization procedure calculates the weight for each beamlet generated from phase space data below the jaws. An algorithm to reduce beamlets and voxels was developed to make possible the LP formulation and to solve the problem in operative times. A specific sequencer capable to consider electron and photon beams was also developed by taking into account previous full MC simulations of the xMLC. Four PBI cases were planned with CARMEN following the recommendations from the RTOG‐0413/ NSABP‐B39 trial protocol for 3D‐CRT PBI. Two cases were planned by MERT alone and the other two by MERT+IMRT as a function of PTV position in depth. Results: More than 90% of PTV volume received 90% of prescribed dose with a maximum dose ≤ 110%. A reduced dose to ipsilateral breast, lung and heart, was also achieved, especially in the low‐dose range. The addition of IMRT to MERT improved PTV coverage in depth diminishing overdosed superficial areas. MERT and MERT+IMRT solutions improved PTV homogeneity compared with the other techniques evaluated and in most of the cases reduced dose to normal tissues. Conclusions: An improved PBI plan was obtained with MERT+IMRT solution compared with 3D‐CRT and brachytherapy techniques. The accuracy of this technique by means of the xMLC opens the chance to implement the accelerated partial breast irradiation in the clinical practice.

Modulated Electron Radiotherapy for Head and Neck Cancer

Intensity modulated photon radiotherapy is employed in treating head and neck cancer even for shallow tumors that are well suited for electrons. Simple modulation of electrons using bolus and/or blocks to create segments has been used for decades, but is labor intensive. There is no commercially available treatment planning system that calculates for modulated electron fields. In this study, electron fields were modulated using photon Multi Leaf Collimators (MLC) and planned/optimized by Monte Carlo (MC) methods.

Dose painting with IMPT, helical tomotherapy and IMXT: A dosimetric comparison

Purpose A planning study is presented in order to compare the suitability of intensity modulated photon radiotherapy (IMXT), helical tomotherapy (HTT) and intensity modulated protontherapy (IMPT) for dose painting. Methods For three HNC patients, nine different treatment plans were generated. Firstly, a uniform dose escalation (uniDE) of 10% was applied to the FDG PET positive region with step-and-shoot IMXT, HTT and IMPT. Secondly, dose painting by numbers (DPBN) was performed based on dose escalation maps determined from dynamic FMISO PET data for all three treatment modalities. Thirdly, the maximum PTV dose was not constrained while maximizing TCP, whereas the same organ at risk constraints as used for conventional IMXT had to be fulfilled. The dose distributions in spinal cord and parotids were optimized with equivalent uniform dose (EUD) constraints, expressing the risk of late reactions. Results The target coverage obtained with IMPT and HTT was more conformal regarding the inhomogeneous prescriptions than with IMXT for both uniDE and DPBN. IMPT allowed significantly higher levels of sparing normal tissues. In addition, the study showed that using IMXT, HTT or IMPT theoretically allows dose escalations of up to 50% under late reaction iso-toxicity conditions. Conclusion The quality of dose painting treatment plans created for IMXT, HTT and IMPT is comparable. More accurate target coverage can be reached with HTT and IMPT, whereas IMPT allows to significantly reduce the dose to normal tissues.

Optimized therapy strategies for locally advanced adenoid cystic carcinomas using modern radiation therapy techniques

To evaluate whether modern photon techniques such as fractionated stereotactic radiation therapy (FSRT) or stereotactically guided intensity modulated photon radiation therapy (IMRT) outweigh the biologic advantages of high-LET RT such as carbon ion RT in the treatment of locally advanced adenoid cystic carcinomas. Into our study we included 63 patients with macroscopic tumor residual after surgery or inoperable adenoid cystic carcinomas treated with modern RT techniques at the University of Heidelberg. Locoregional control, disease free survival and overall survival rates achieved with modern photon techniques alone were compared to the results obtained with combined photon RT and a carbon ion boost. Since September 1998, 29 patients with locally advanced adenoid cystic carcinomas have been treated with a combination of 45 to 54 Gy of photon RT (FSRT or IMRT) and a carbon ion boost of 18 GyE. The median dose to the macroscopic tumor was 72 GyE (63 to 72 GyE) for this patient group. Since carbon ion RT at the Heavy Ion Research Center (GSI) is available within 3 beam time blocks each year only, it was our institutional policy to treat patients with carbon ions only, if presentation of the patient allowed initiation of the treatment within 6 weeks. Patients who would have had to wait for carbon ion RT longer than 6 weeks, were offered photon RT using FSRT or IMRT alone. Between June 1995 and August 2003, thirty-four patients received high dose photon RT alone using FSRT (n = 13) or IMRT (n = 21) with a median total tumor dose of 66 Gy (range 54 to 70.4 Gy) to the macroscopic tumor. Inversely planned IMRT (step-and-shoot technique) was preferred for complex shaped targets since December 1999. Dose escalation within the macroscopic tumor was realized according to the integrated boost concept. Tumor stages and age of the patients were comparable for the different patient groups. Median follow-up was 16 months for patients treated with combined photon and carbon ion RT and 24 months (30 months for FSRT and 18 months for IMRT) for patients treated with FSRT or IMRT alone. Median GTV was comparable for both groups. Actuarial locoregional control rates at 4 years were 77.5% for combined photon and carbon ion RT and 24.6% for modern photon RT alone. However, the difference was not statistically significant (p = 0.08 log rank). Disease free survival rates and overall survival rates at 4 years were comparable with 53% and 75% for combined photon and carbon ion RT and 23% and 81% for photon RT alone, respectively. Rates for late toxicity CTC grade 3 were lower than 5% for both groups. We did not observe CTC grade 4 or 5 late toxicity. Modern RT techniques such as photon FSRT, IMRT or carbon ion RT allow a safe delivery of high target doses to locally advanced adenoid cystic carcinomas. Late toxicity rates can be kept lower as compared to the historic neutron therapy data. A combination of modern photon RT and carbon ion RT seems to be advantageous showing a trend towards higher rates of locoregional control as compared to photon RT alone. However, the difference was not statistically significant and bias can not be excluded as this was not a randomized trial. A randomized clinical trial comparing photon IMRT alone with combined photon IMRT and carbon ion RT as a standard arm is warranted

Potential outcomes of modalities and techniques in radiotherapy for patients with hypopharyngeal carcinoma

Background and purpose To determine potential improvements in treatment outcome for patients with hypopharyngeal carcinoma, T4N0M0, using proton and intensity modulated photon radiotherapy (IMRT) compared to a standard 3D conformal radiotherapy treatment (3D-CRT) in terms of local tumour control probability, TCP, and normal tissue complication probability (NTCP) for the spinal cord and the parotid glands using. Patients and methods Using the three-dimensional treatment-planning system, Helax-TMS™, 5 patients were planned with protons, IMRT, and 3D-CRT plans. The prescribed dose used was 30 fractions×2.39 Gy for the protons and IMRT and 35 fractions×2.00 Gy for 3D-CRT. The treatment plans were evaluated using dose volume data and dose response models were used to calculate TCP and NTCP. The target volumes were delineated to spare the parotid glands. A dose escalation was made for protons and IMRT using NTCP constraints to the spinal cord. Results On average, protons and IMRT increase TCP by 17% compared to 3D-CRT. For the spinal cord NTCP values are zero for all methods and patients. Average NTCP values for the parotid glands were >90% for 3D-CRT and significantly lower for protons and IMRT varying from 43–65%. The average parotid gland dose was 33 Gy for the protons, 38 Gy for IMRT and 48 Gy for 3D-CRT. Conclusions Protons and IMRT gave a significant TCP increase compared to 3D-CRT while no significant difference between protons and IMRT was found. Protons generally show lower non-target tissue doses, which indicates a possibility for further dose escalation. Large individual dose differences between protons and IMRT for parotid glands indicate that some patients may benefit more from protons and others from IMRT.

A treatment planning comparison of conventional, 3D conformal, intensity modulated photon and proton irradiation therapy in the treatment of paranasal sinus carcinoma

Purpose/Objective: To determine potential improvements in patients with paranasal sinus carcinoma by comparing proton and intensity modulated photon radiotherapy (IMRT) with conventional and conformal photon treatment techniques.

Node-positive left-sided breast cancer patients after breast-conserving surgery: potential outcomes of radiotherapy modalities and techniques

Purpose: To determine how much proton and intensity modulated photon radiotherapy (IMRT) can improve treatment results of node-positive left-sided breast cancer compared to conventional radiation qualities (X-rays and electrons) after breast-conserving surgery in terms of lower complication risks for cardiac mortality and radiation pneumonitis. Methods and material: For each of 11 patient studies, one proton plan, one IMRT, and two conventional (tangential and patched) plans were calculated using a three-dimensional treatment-planning system, Helax-TMS ™. The evaluation of the different treatment plans was made by applying the normal tissue complication probability model (NTCP) proposed by Källman (also denoted the relative seriality model) on the dose distributions in terms of dose-volume histograms. The organs at risk are the spinal cord, the left lung, the heart, and the non-critical normal tissues (including the right breast). Results: The comparison demonstrated that the proton treatment plans provide significantly lower NTCP values for the heart and lung when compared to conventional radiation qualities including IMRT for all 11 patients. At a prescribed dose of 50 Gy in the PTV, the calculated mean NTCP value for the patients decreased, on the average, from 14.7 to 0.6% for the lung (radiation pneumonitis) for the proton plans compared with the best plan using conventional radiation qualities. The corresponding figures for the heart (cardiac mortality) were from 2.1 to 0.5%. The figures for cardiac mortality for IMRT, tangential technique and the patched technique were 2.2, 6.7, and 2.1%, respectively. Conclusions: Protons appear to have major advantages in terms of lower complication risks when compared with treatments using conventional radiation qualities for treating node-positive left-sided breast cancer after breast-conserving surgery.

A treatment planning inter-comparison of proton and intensity modulated photon radiotherapy

Purpose: A comparative treatment planning study has been undertaken between standard photon delivery techniques,b intensity modulated photon methods and spot scanned protons in order to investigate the merits and limitations of each of these treatment approaches. Methods: Plans for each modality were performed using CT scans and planning information for nine patients with varying indications and lesion sites and the results have been analysed using a variety of dose and volume based parameters. Results: Over all cases, it is predicted that the use of protons could lead to a reduction of the total integral dose by a factor three compared to standard photon techniques and a factor two compared to IM photon plans. In addition, in all but one Organ at Risk (OAR) for one case, protons are predicted to reduce both mean OAR dose and the irradiated volume at the 50% mean target dose level compared to both photon methods. However, when considering the volume of an OAR irradiated to 70% or more of the target dose, little difference could be shown between proton and intensity modulated photon plans. On comparing the magnitude of dose hot spots in OARs resulting from the proton and IM photon plans, more variation was observed, and the ranking of the plans was then found to be case and OAR dependent. Conclusions: The use of protons has been found to reduce the medium to low dose load (below about 70% of the target dose) to OARs and all non-target tissues compared to both standard and inversely planned photons, but that the use of intensity modulated photons can result in similar levels of high dose conformation to that afforded by protons. However, the introduction of inverse planning methods for protons is necessary before general conclusions on the relative efficacy of photons and protons can be drawn.