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Advances in Radiotherapy
& Nuclear Medicine Dose prescription and reporting in SRS

protocols. For instance, while some literature addresses 2.2. Patient and treatment plan selection
SBRT treatments in general, others focus on specific Inclusion criteria for treatment plans required adherence
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anatomical sites, such as lung SBRT, or prostate SBRT, to established SBRT/SRS protocols. Treatment plans were
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illustrating the challenges associated with different tumor excluded from analysis in the case of:
locations and types. 1. The dose distribution of the planning target
Moreover, the introduction of volumetric modulated volume (PTV) was significantly compromised (e.g.,
arc therapy (VMAT) has further complicated the problem re-irradiation plan, extremal proximity of PTV to
of dose prescription. VMAT enables the delivery of organs at risk [OARs], etc.)
non-uniform doses conformally to irregularly shaped 2. Cases involved single-isocenter multiple metastases,
treatment volumes. While this technique enhances tumor varied prescription doses, or SRS where the PTV was
targeting and spares the surrounding healthy tissues, it < 1 cc, as these may not provide adequate dosimetric
also magnifies the variability in dose interpretation and data.
distribution. These variations may not significantly impact This selection process ensured that the collected data
clinical outcomes, such as disease-free or overall survival. accurately reflected the clinical practices currently in use.
However, they may compromise the uniformity of clinical
trials and could introduce unwanted discrepancies in 2.3. Treatment planning
treatment delivery, both within the same institution and All treatment plans were developed using the Monaco
across national and international health-care settings. treatment planning system (TPS, Elekta AB, Sweden),
In light of these challenges, the International employing a 2 mm spatial grid for precise dose calculations.
Commission on Radiation Units and Measurements The Monte Carlo dose calculation algorithm was utilized
(ICRU) has issued guidelines in its ICRU-91 publication, to ensure high accuracy in determining dose distributions.
aiming to provide a framework for more consistent SBRT/ The treatments were delivered using an Elekta Versa
SRS practices. In addition, the European Society for HD (Elekta AB, Sweden) linear accelerator equipped with
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Therapeutic Radiation Oncology (ESTRO) has developed a 6 FFF photon beam. Each treatment plan included several
specific guidelines for lung SBRT, whereas various key dosimetric parameters:
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national study groups across Europe have released their • D : The near-maximum dose received by the most
0.1cc
own benchmarks and recommendations. These efforts irradiated 0.1 cc of the PTV
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are crucial in the promotion of a more standardized • D : The mean dose delivered to the target volume
50
approach to radiation therapy, which can improve • D : The dose received by 95% of the PTV, indicating
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patient outcomes and facilitate better inter-institutional the volume coverage
comparisons. • D : The near-minimum dose received by 99% of the
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This study was designed to evaluate the dosimetric PTV.
variability inherent in SBRT/SRS treatments, focusing on In addition, the homogeneity index (HI) and
different disease sites and individual planning strategies. conformity index (CI) were calculated for each treatment
By analyzing this variability, this study aimed to provide plan. The HI was calculated as the difference between D
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a critical view of our department’s specific radiation and D , divided by D , whereas the CI was calculated
guidelines. Furthermore, these data could serve as a 0.1cc 50
valuable resource for inter-institutional comparisons, exactly following the ICRU-91 recommendation. In all
contributing to ongoing efforts toward standardization in calculations, the 100% isodose level was defined as the
radiation therapy. Ultimately, enhancing our understanding prescription dose per fraction, as documented in the
of dosimetric variability may lead to improved protocols, Record and Verify System (MOSAIQ). This standardization
better patient care, and more reliable outcomes. allowed for consistency in comparing dosimetric outcomes
across different plans.
2. Materials and methods
2.4. Quality assurance and data analysis
2.1. Study design Each case was reviewed by a radiation medical physicist
A single-institution retrospective analysis was conducted (RMP) and an attending radiation oncologist (RO) to
to evaluate the dosimetric variability in SBRT/SRS ensure adherence to treatment protocols and quality
treatments. Clinical treatment plans utilized for patient assurance standards. This collaborative oversight was
radiotherapy were collected for this study, reflecting actual critical in validating the treatment plans and ensuring that
practice within our institution. all dosimetric calculations were accurate and reflective of

Volume 2 Issue 4 (2024) 2 doi: 10.36922/arnm.5450